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Microstructural, mechanical and thermal properties of microwave sintered Cu-MWCNT nanocomposites
Journal of Alloys and Compounds 822 (2020) 153675
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Microstructural, mechanical and thermal properties of microwave sintered Cu-MWCNT nanocomposites Marjan Darabi a, Masoud Rajabi a, Noushin Nasiri b, * a b
Department of Materials Science and Engineering, Faculty of Technology and Engineering, Imam Khomeini International University (IKIU), Qazvin, Iran School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, Australia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 November 2019 Received in revised form 1 January 2020 Accepted 3 January 2020 Available online 7 January 2020
Cu nanocomposites reinforced with 0e6 vol% MWCNTs are fabricated using mixing, ball milling and microwave sintering techniques. It is found that decreasing the Cu powders size from 65 to 15 mm significantly enhances the mechanical and thermal properties of the fabricated nanocomposites. In addition, the optimal MWCNTs content in such composites is found to be 4 vol%; there exists maximum for microhardness, bending strength and thermal conductivity of Cu- MWCNT composites which rise to 82.2 HV, 155.2 MPa and 380.2 W.mk 1, respectively. However, the nanocomposites properties then fall to 75 HV, 139.5 MPa and 315.4 W.mk 1, respectively, with further increasing the MWCNT content up to 6 vol %. Furthermore, the relative density of the pellets is calculated using Archimedes method, demonstrating a lower relative density for the composites with higher MWCNTs content. These findings provide a simple and effective sintering method for the engineering of low-cost metal matrix composites. © 2020 Elsevier B.V. All rights reserved.
Keywords: Cu-MWCNT nanocomposite Microwave sintering Microhardness Thermal conductivity Relative density
1. Introduction In the past two decades, metal matrix composites (MMCs) have attracted great attentions due to their high specific modulus, strength, and thermal stability, compared to monolithic materials, to be utilized in numerous applications including automotive industries [1e3]. A wide range of matrix metals such as aluminum (Al) [4e6], copper (Cu) [7,8], titanium (Ti) [9], nickel (Ni) [10] and iron (Fe) [11] have been employed in structural application where a high strength to weight ratio, tensile strength, wear resistance and stability are the main engineering considerations [12]. Amongst them, Cu-based MMCs are commonly used in electrical applications and package materials due to copper’s excellent electrical (5.8 105 S cm 1 at 27 C) and thermal (401 W m 1 K 1 at 27 C) conductivity as well as low-cost production and availability [13,14]. However, the poor hardness, low strength and abrasion resistance are the major limitation of Cu which extensively hinders its engineering and industrial application [15,16]. To address this issue, a wide range of reinforced materials including borides, carbides, nitrides, oxides as particles, whiskers or short fibers have been introduced into Cu matrix [17,18]. Amongst them, carbon
* Corresponding author. E-mail address: [email protected] (N. Nasiri). https://doi.org/10.1016/j.jallcom.2020.153675 0925-8388/© 2020 Elsevier B.V. All rights reserved.
reinforcements such as carbon fibers, multi-walled carbon nanotubes (MWCNTs), graphene oxides and graphite nanoparticles demonstrated great attention due to their exceptional mechanical, electrical and thermal properties [19,20]. Liu et al. [21] investigated the preparation and properties of reduced graphene oxide (rGO) as well as graphene nanosheet (GNS) as reinforcement materials for aluminum matrix composites (AMCs) using power synthesis techniques. An average 40% enhancement was observed for MMCs hardness for 0.3 wt% rGO-AMCs and 0.15 wt% GNS-AMCs samples compared to unreinforced aluminum samples [21]. Tsai et al. [22] reported a minimum of 40% enhancement in the wear resistance of 1.0 wt% CNTs/Cu nanocomposites compared to that of a pure Cu sample. Despite these significant improvements upon adding CNTs into metal matrix, a homogenous dispersion of CNTs is still critical as agglomeration and inhomogeneous dispersion of CNTs could considerably restrict the mechanical and electrical performance of MMCs [23e25]. In fact, the performance of CNTs/Cu composites is strictly associated with dispersion of CNTs and density of materials [8,26]. Therefore, different methods have been used to synthesis CNT-reinforced Cu matrix composites including powder metallurgy techniques, electrochemical deposition process, melting and solidification synthesis and spray techniques [1,27,28]. However, these methods are expensive and require a few post sintering/ deformation processing steps such as rolling, hot extrusion as well
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as severe plastic deformation (SPD) [29]. In addition, excessive grain growth caused by long sintering time at high temperature could lead to a weakened interfacial strength in the fabricated MMCs [29,30]. Hence, some rapid densification methods including spark plasma sintering (SPS) and microwave sintering have been utilized due to their many inherent advantages over conventional sintering technique [31e35]. Compared to SPS technique, microwave sintering could save up to 85% of the sintering time as well as 96% of the energy [30], offering lower sintering temperature, lower porosity and lower processing cost [36e38]. Using spark plasma sintering, Guiderdoni et al. [15] fabricated homogenously dispersed double walled carbon nanotubes (DWCNT) in Cu matrix, featuring significantly microhardness (103 HV) for DWCNT/Cu composites compared to pure Cu samples. Using microwave sintering, Babu et al. [29] investigated the effect of sintering time as well as CNT diameters on the mechanical, electrical and thermal properties of the synthesized CuCNT composites. The optimal hardness of 80 HV, relative density of 91% and electrical conductivity of 47 MS m 1 were obtained at 60 min sintering time for the CNT average diameter of 20e40 nm [29]. In another research, Duan et al. [30] reported a hardness of 80 HV for the Cu-0.5 wt% CNT composite fabricated by molecular-level mixing followed by microwave sintering technique. The microhardness value decreased significantly from 80 to 55 HV by increasing the CNT content from 0.5 wt% to 1 wt% which could be attributed to the aggravated agglomeration in the composite with higher CNT content [1,30]. However, limited studies are conducted on the role Cu powder sizes, as metal matrix, play on the microstructure as well as mechanical, electrical and thermal properties of CNT-Cu composites. In our previous work [39], a simple comparison was conducted between conventional and microwave sintering methods, observing that a similar mechanical and electrical properties could be achieved in a significantly shorter synthesis time, when the samples are sintered using microwave method compared to the conventional sintering techniques. Here, the effect of matrix grain size on the microwave mechanism, scattering of microwave energy, and microwave energy absorption was investigated simultaneously. In addition, the effect of Cu powder size as well as MWCNT content on microstructural, mechanical, electrical and thermal properties of microwave sintered Cu/MWCNT composites are investigated. Mechanical properties such as physical properties of fabricated samples were then characterized by measuring relative density and thermal conductivity as well as investigating the mechanical properties, including microhardness and bending strength. Finally, the samples microhardness was compared with
other research which emphasizes the outstanding role of fine grain size of matrix and microwave energy absorption of reinforcement, leading to improved properties. Findings of this research provide a simple and effective fabrication method for the engineering of lowcost MMCs. 2. Experiment 2.1. Cu-MWCNT nanocomposites fabrication For the synthesis of Cu- MWCNT nanocomposites, six batches of copper powders with average particle size of 15, 25, 35, 45, 55 and 65 mm (supplied by Iran Powder Metallurgy Complex, with 99.9% purity) and one batch of MWCNT with a diameter of about 20 nm (supplied by US nano of America with purity level of >95%) were used. Copper powders were mixed with MWCNTs in a planetary ball mill using a stainless-steel jar (the mass ratio of ball to powder was 10:1). The powders and MWCNTs were mixed under argon (Ar) atmosphere for 10 h at 120 rpm, to prevent oxide formation. Then, the mixed powders were compacted in a uniaxial hydraulic press under the 450 MPa pressure for 60 s to obtain green pellets (Fig. 1) with two different dimensions of 40 10 3 mm3 and 10 3 mm2. 2.2. Sintering procedure The green pellets were sintered for 20 min using a microwave furnace (900 W, 2.45 GHz, LG Microwave furnace) equipped with Ar gas at a rate of 42 C.min 1 (Fig. 1). For higher overall heating rate, the samples were placed in an alumina crucible and immersed in Silicon Carbide (SiC) bed. This step provided the green pallets with a hybrid heating facility as well as reduced the thermal gradient of samples and the atmosphere around them, leading to the fabrication of crack free components. In order to minimize the heat transfer, the crucibles were covered by a layer of glass wool to eliminate the heat loss. Sintered specimens were then cooled down to room temperature (Fig. 1). 2.3. Characterization Prior to characterization, the samples were mounted and grounded using 500 to 5000 grit SiC sandpapers, and then polished with alumina based polishing slurry. The samples then were chemically etched by immersing in an etching solution of CrO3, HNO3, H2SO4 and H2O, for 10 s. The Archimedes method was used to measure the density of the sintered specimen according to ASTM B311. The thermal conductivity of the samples was measured by
Fig. 1. The preparation process for fabricating Cu-MWCNT nanocomposites using mixing, ball milling and microwave sintering techniques.
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means of a relative steady-state technique, in an experimental setup (model HT01, Deghat Azma corp), which is considered as a variation of ASTM E 1225-87 methodology. In this technique, a sample of unknown thermal conductivity is embedded vertically between two samples of known thermal conductivity with a hot plate at the top and a cold plate at the bottom. Heat is supplied by thermocouples, positioned along the length of samples. When the heat gradient reaches to zero or heat becomes constant over the entire sample, the thermal conductivity could be measured using the one-dimensional Fourier conduction equation [40]. Bending strength test was conducted using a universal testing machine (Zwick/Roaell, Z100) with the loading speed of 0.5 mm min 1, according to ASTM D790 standard. The microhardness of the samples was measured using a Vickers microhardness digital tester (HVS1000A) at a load of 50 g and a dwell time of 10 s in accordance with the ASTM standard E92. The average hardness of five different test points is the final hardness of samples. The crystal phases and surface compositions of the samples were characterized by X-Ray diffraction using (Rigaku XRD, MiniFlex 600) system equipped with Cu Ka radiation of average wavelength 1.5404 Å. Morphological examination of samples was performed using a field emission scanning electron microscope (FESEM, MIRA3 TE SCAN) at 15.0 kV. The average grain size of the nanocomposite samples was measured by analyzing FESEM micrographs with the aid of an image processing software (ImageJ). 3. Result and discussion 3.1. Microstructure Powder metallurgy is one of the most common fabrication techniques for metal-CNT nanocomposites [41,42]. As mentioned in the experimental section, the MWCNTs and Cu powders were mixed in different MWCNT volume fraction, using mechanical milling (10 h at 120 rpm). The materials defect density as well as alloying capacity increases significantly after mechanical milling due to a high level of energy generated during milling process [43,44]. Here, a microwave sintering (as densification step), followed by a post pressing process was then conducted to fabricate Cu- MWCNT nanocomposites. Fig. 2 shows the field emission scanning electron microscope (FESEM) images of Cu- MWCNT nanocomposite samples with average particle size of 15 and 65 mm, before (Fig. 2a and b) and after microwave sintering for 20 min (Fig. 2c and d). It could be seen that MWCNTs are well embedded and distributed homogeneously within the metal matrix, with no obvious crack or damage on the nanocomposite surface. This high homogeneity is expected to increase the rigidity of Cu-MWCNT nanocomposite samples compared to the pure Cu material. The fabricated nanocomposites were made of 4 vol% MWCNT added into copper powder with an average particle size of 15 mm (Fig. 2a,c) and 65 mm (Fig. 2b,d). Increasing the average size of Cu powders from 15 to 65 mm resulted in significantly coarser microstructure (Fig. 2a and b) after microwave sintering with larger voids and porosities (Fig. 2c and d). In fact, the nanocomposites fabricated by the Cu powders with smaller particle size (15 mm) demonstrated 50% reduction in grain size compared to the 65 mm Cu powders. This could be related to the important role grain size is playing in the microwave energy absorption during sintering process [45]. In addition, the CuMWCNT nanocomposite made of larger Cu powders (65 mm) demonstrated a lower level of entanglement (Fig. 2d) in comparison to that of 15 mm Cu-MWCNT nanocomposite powder (Fig. 2c), resulting in the formation of more micro-voids in the microstructure of the fabricated samples. This could be attributed to a higher level of microwave field that concentrates at the grain boundaries
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Fig. 2. FESEM micrographs of Cu-4 vol% MWCNT nanocomposites made of Cu powders with (a,c) 15 mm and (b,d) 65 mm average particles size (a,b) before and (c,d) after microwave sintering for 20 min.
in the microstructure of these nanocomposites [46,47]. In the microwave sintering process, the microwaves could propagate into the material and their energy could transfer from one point to another [34,48]. The interaction of microwaves with the material and the absorption of the energy could generate heat in the material, while the amount of energy absorbed by the material is dependent on the material’s dielectric loss factor [48]. Fig. 3 illustrates the material’s interaction with microwaves, in which the materials could be classified in three different types: transparent, opaque and absorbent. In the case of MMCs, one of the components is a high-loss material whereas the other component is a low-loss one. According to other scientific works, with decreasing of particle size of nanocomposites, the reflection loss witnesses a shift to lower frequencies and broader bandwidth where the microwave absorption reaches the maximum amount [48]. In fact, in the nanocomposite made of smaller Cu powders, higher number of powder boundaries/interfaces results in enhanced microwave field, which consequently leads to progressive necking formation at the powders interface [49]. Furthermore, the heat generated by the microwave sintering process could be transferred more slowly through a course-grained microstructure compared to a finegrained one [47] resulting in a lower density and higher level of micro-voids for the Cu-MWCNT nanocomposite made of larger Cu powders (65 mm) (Fig. 2d). This higher level of defects in the microstructure could hinder the filling pattern of matrix during the synthesize process leading to lower relative density of the fabricated nanocomposites [29,30]. Besides, higher level of defects in the microstructure might result in lower electrical and thermal conductivity in nanocomposites as they could block the electron and phonon conduction in the microstructure [29]. 3.2. X-ray diffraction The XRD patterns of Cu-4 vol% MWCNT nanocomposites made of Cu powders with different average particle size of 15 and 65 mm, before and after microwave sintering are shown in Fig. 4. The XRD patterns of both Cu-MWCNT nanocomposite powders and bulks are generally similar with no obvious change in the obtained patterns
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Fig. 3. Interaction of different types of materials with microwaves: a) Transparent, b) Opaque, c) Absorber.
Fig. 4. (a) XRD patterns of Cu-4 vol% MWCNT powders and nanocomposites and magnified view of the main XRD peaks at 2q of (b) ~ 43.3 and (c) ~ 50.4.
by increasing the average particle size of Cu powders. Although, further XRD analysis in this figure demonstrates difference among them in terms of broad peaks of fine-grained copper which can be attributed to uniform transferred heat within the structure. The peaks identified by the planes (111), (200) and (220) at 2q of about 43 , 50 and 74 respectively, were confirmed to follow JCPDS PDF 85e1326 and FCC structure with no observable peaks of other phases in the XRD patterns. The major peak corresponding to MWCNT should be observed at 26 (JCPDS PDF 26e1076) with respective lattices of (002), while no noticeable peak for MWCNT was witnessed due to low diffraction efficiency of carbon [50]. This could also be attributed to no prominent structural changes in the Cu-MWCNT nanocomposites after mechanical alloying of the powders. 3.3. Relative density The densification step in powder metallurgy technique is reported to generate macro voids and pores in the fabricated microstructure [51]. The size and density of these macro-pores in the final structure play significant role in determining the mechanical and electrical properties of the fabricated nanocomposites [22,51,52]. The relative density of the fabricated Cu-MWCNT nanocomposites could be conducted to evaluate the size and density of the generated voids and pores in the microstructure. Here, the Archimedes method [53] is used to measure the relative density of fabricated Cu-MWCNT nanocomposites made of Cu powders with average particle size of 15 up to 65 mm as a function of MWCNT vol%. As shown in Fig. 5, increasing the MWCNT content up to 6 vol%
Fig. 5. Relative density of microwave sintered Cu-MWCNT nanocomposites made of Cu powders with 15, 25, 35, 45, 55 and 65 mm particle size as a function of MWCNT content.
decreased the relative density of the fabricated Cu-MWCNT nanocomposite, regardless of Cu powder size. For nanocomposites made by 15 mm Cu powders, the relative density deceased from 97% to 95% (red circles) by increasing the MWCNT content (vol%) from 0 to 6, respectively. Increasing the average powder size from 15 to 25 resulted in decreasing the relative density from 97% and 95% (red
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circles) to 96.2% and 90.9% (blue circles), for the MWCNT content of 0 vol% and 6 vol%, respectively. Further decrease in Cu average particle size down to 65 mm led to a lower relative density of 95.6% and 90.1% (blue rectangles) for the Cu-MWCNT nanocomposites with 0 and 6 vol% MWCNT content, respectively (Fig. 5). Higher relative density was reported for the Cu composites with similar CNT content fabricated by SPS [15]. This lower density of the sample with higher MWCNT content could be attributed to the slower densification of Cu powders in the presence of extra MWCNT in the matrix [53]. Due to the higher melting point of MWCNT compared to the copper matrix [54], higher MWCNT content resulted in the formation of larger macro voids in the microstructure, and consequently decreased the relative density of the fabricated samples. In fact, increasing the size of macro voids in the microstructure could be the main reason for lower density of the composites with higher MWCNT content [30]. Similar results were reported by Babu et al. [29] for Cu-CNT nanocomposites made by 0.25e1.0 wt% CNT. The relative density of the fabricated nanocomposites decreased from 87.1% to 80.8% by increasing the CNTs content from 0.25 to 1.0 wt%. However, some materials processing techniques such as cold rolling could significantly increase the relative density of these nanocomposites via eliminating these macro voids [30]. In addition, for a wide range of MWCNT content from 1 to 6 vol%, the Cu(65 mm)-MWCNT nanocomposites featured considerably lower relative density compared to Cu(15 mm)MWCNT ones. In fact, at the MWCNT content of 6 vol% the relative density of the fabricated samples were 93.5% and 90.1% for Cu(15 mm) and Cu(65 mm)-MWCNT nanocomposites, respectively. 3.4. Microhardness Fig. 6a shows the Vickers microhardness of pure Cu and CuMWCNT nanocomposite samples with different MWCNT content from 0 to 6 vol%. Regardless of MWCNT content, the nanocomposites made of smaller Cu powder size demonstrated a higher microhardness compared to the samples fabricated by larger Cu micro-powders. This lower microhardness for nanocomposites made by larger Cu powders could be attributed to a lower level of microwave energy absorption and consequently higher level of micro-voids formed in the microstructure of these nanocomposites, compared to the ones made of smaller Cu powders [45]. In addition, the microhardness of nanocomposites made by 15 mm powder size increased rapidly from 50 HV to 74 HV by increasing the MWCNT content from 0 to 2 vol% (Fig. 6a). At 4 vol% MWCNT content, the microhardness value reached a peak of 82 HV
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for Cu(15 mm)-MWCNT nanocomposite and 66 HV for Cu(65 mm)MWCNT nanocomposites. This higher microhardness is attributed to the higher strength of MWCNT compared to pure Cu matrix. In addition, grain refinement as well as strong Cu/MWCNT interface formed during microwave synthesis could result in higher microhardness in the fabricated nanocomposites [30]. Increasing the MWCNT content in the nanocomposites could ease the load transfer from the Cu matrix to the harder MWCNT, resulting in an enhanced hardness value of the fabricated Cu-MWCNT nanocomposite. However, further increase in MWCNT content to 6 vol% led to dramatic decrease in microhardness to 75 and 54 HV for the nanocomposites made of 15 and 65 mm Cu powders, respectively (Fig. 6a). This lower microhardness could be ascribed to the formation of larger micro voids as well as a greater number of agglomerates in the nanocomposite with higher MWCNT content [29]. Fig. 6b presents a comparison of microhardness obtained by CuMWCNT nanocomposites fabricated in this research with similar nanocomposites reported in the literature [55e58]. The microhardness of 82 HV obtained by Cu-4 vol% MWCNT nanocomposites fabricated by microwave sintering technique was the highest value compared to similar reports. In contrast, the Cu-10 vol% MWCNT nanocomposite fabricated by Shukla et al. [56] demonstrated the lowest microhardness of 56 HV amongst others. Uddin et al. [55] reported a 32% increase in microhardness of Cu-0.5 vol% MWCNT nanocomposite fabricated by hot press technique, compared to the pure copper samples, which is in line with 39% increase in hardness of Cu-4 vol% MWCNT nanocomposite, obtained in this research (Fig. 6a). Moreover, Wei et al. [58] and Daoush et al. [57] succeeded in achieving hardness of about 58 and 75 HV by preparing Cu-4 vol % CNT and Cu-1 vol% CNT nanocomposite through powder metallurgy technique and electroless deposition process respectively. 3.5. Bending strength Fig. 7 shows the bending strength of microwave sintered CuMWCNT nanocomposites as a function of Cu powders size for MWCNT content of 0 vol% up to 6 vol%. Regardless of Cu powders average size, the bending strength of the fabricated nanocomposites reached a peak value of 155 MPa at 4 vol% MWCNT content, for nanocomposites made of 15 mm Cu powders size. This higher bending strength of nanocomposites with high MWCNT content could be attributed to the high elastic modulus and strength of MWCNT as well as strong interface combination between MWCNT and Cu matrix [39]. As a result, the load applied during the bending strength test could be easily transfer from the
Fig. 6. (a) Microhardness of microwave sintered Cu-MWCNT nanocomposites made of Cu powders with 15, 25, 35, 45, 55 and 65 mm particle size as a function of MWCNT content. (b) A comparison of microhardness obtained by Cu-MWCNT nanocomposites fabricated in this research (15 mm particle size) with similar nanocomposites reported in the literature.
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aggregated CNTs is weak, resulting in a significant reduction in the nanocomposite strength [30]. Moreover, morphology of the sample represents that copper has ductile fracture [30]. When MWCNT volume fraction increases to 6 vol% MWCNT, elongation declines. This sample is fractured before yielding because of significant reduction in elastic properties. It is interesting to note that the higher bending strength of nanocomposite with smaller Cu powders could be attributed to the presence of more grain boundaries in the microstructure as well as higher capacity of the nanocomposite for better incorporation of MWCNT within the matrix [57]. 3.6. Thermal conductivity
Fig. 7. Bending strength of microwave sintered Cu-MWCNT nanocomposites made of Cu powders with 15, 25, 35, 45, 55 and 65 mm particle size as a function of MWCNT content.
matrix interface, leading to a significantly higher bending strength of 25% for Cu-MWCNT nanocomposite compared to pure Cu samples. In addition, the bending strength of Cu-4 vol% MWCNT nanocomposite decreased from 155 MPa to 132 MPa by increasing the average Cu powders size from 15 to 65 mm (Fig. 7). This higher bending strength of Cu-MWCNT nanocomposites made by smaller Cu powders could be attributed to the smaller grain size in Cu(15 mm)-MWCNT compared to Cu(65 mm)-MWCNT, resulting in a higher number of grain boundaries, consequently, higher resistance to the dislocation motions, which could enhance the bending strength of the fabricated samples. Further increasing the MWCNT content up to 6 vol% resulted in decreasing down the bending strength of the fabricated CuMWCNT nanocomposites to 139 and 119, for Cu (15 mm)- and Cu (65 mm)-MWCNT (Fig. 7). This lower bonding strength could be related to weak interface bonding between CNT aggregates and clusters, in the nanocomposite with high CNT content [29,30]. The fracture surface of microwave sintered Cu-MWCNT nanocomposites with 6 vol% MWCNT content is presented in Fig. 8. As can be seen, high MWCNT content as well as large Cu powders size (65 mm) resulted in the formation of MWCNT agglomerates in the fabricated nanocomposites. The interface bonding between these
Fig. 9 shows the thermal conductivity of microwave sintered CuMWCNT nanocomposites made of Cu powders from 15 up to 65 mm particle size. Regardless of the Cu powders size, 30% rise is observed in thermal conductivity of the fabricated nanocomposites by increasing the MWCNT content from 0 to 4 vol%. This higher thermal conductivity in the fabricated nanocomposites with high MWCNT content could be attributed to remarkable effects of phonon conduction with insignificant agglomeration of MWCNT in lower volume fraction [26]. However, further increase in the
Fig. 9. Thermal conductivity of microwave sintered Cu-MWCNT nanocomposites made of Cu powders with 15, 25, 35, 45, 55 and 65 mm particle size as a function of MWCNT content.
Fig. 8. FESEM micrographs of fracture surface of Cu-6 vol% MWCNT nanocomposites made of 65 mm Cu powders.
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volume fraction of MWCNT up to 6 vol% leads to sharp reduction of thermal conductivity in the fabricated nanocomposites down to 290 W/mk. This conductivity reduction could originate from the large number of voids in the grain boundaries as well as high porosity in MWCNT clusters [30]. In addition, random orientation of MWCNT in the matrix could result in scattering of phonons through grain boundaries and consequently, restricting the thermal conductivity of the fabricated nanocomposites [59].
[4]
[5]
[6]
[7]
4. Conclusion [8]
The Cu-MWCNT composites having different Cu powders size and MWCNTs content were successfully fabricated using mixing, ball milling and microwave sintering methods. Then, the effect of Cu powder size as well as MWCNTs content on microstructural, mechanical and thermal properties of microwave sintered CuMWCNT composites are investigated. The following conclusions could be extracted based on the outcome of this research study: - Increasing the Cu powders size from 15 to 65 mm significantly decreased the mechanical and thermal properties of the fabricated nanocomposites. A 25%, 17% and 15% reduction in the microhardness, bending strength and thermal conductivity of the Cu-4vol% MWCNT composites were observed when the Cu powders size increased from 15 to 65 mm. In addition, the relative density of the fabricated nanocomposites (Cu-4vol% MWCNT) decreased slightly from 94.8% to 92.5% by increasing the Cu powders size from 15 to 65 mm. - Increasing the MWCNTs content from 0 to 6 vol% significantly impacted the mechanical and thermal properties as well as relative density of the fabricated nanocomposites. Microhardness, bending strength and thermal conductivity of fabricated Cu-MWCNTs composites with 15 mm Cu powders size increased from 50 HV, 115.4 MPa and 250 W.mk 1 to 82.2 HV, 155.2 MPa and 380.2 W.mk 1 by increasing the MWCNTs content from 0 to 4 vol%. However, further increase in the MWCNTs content up to 6 vol% resulted in lower microhardness (75 HV), bending strength (139.5 MPa) and thermal conductivity (315.4 W.mk 1).
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[9]
[10] [11]
[12]
[13]
[14]
[15]
[16]
[17] [18]
[19]
[20]
[21]
[22]
CRediT authorship contribution statement Marjan Darabi: Data curation, Formal analysis, Investigation, Methodology, Visualization, Writing - original draft. Masoud Rajabi: Conceptualization, Methodology, Supervision, Writing review & editing. Noushin Nasiri: Conceptualization, Supervision, Validation, Visualization, Writing - review & editing. Acknowledgement The authors are grateful for the research support of Iran National Science Foundation with this research work.
[23]
[24]
[25]
[26]
[27]
References [28] [1] S.R. Bakshi, D. Lahiri, A. Agarwal, Carbon nanotube reinforced metal matrix composites-a review, Int. Mater. Rev. 55 (1) (2010) 41e64. [2] R. Casati, M. Vedani, Metal matrix composites reinforced by nano-particlesda review, Metals 4 (1) (2014) 65e83. [3] P. Garg, A. Jamwal, D. Kumar, K.K. Sadasivuni, C.M. Hussain, P. Gupta, Advance
[29]
7
research progresses in aluminium matrix composites: manufacturing & applications, J. Mater. Res. Technol. 8 (5) (2019) 4924e4939. N. Nasiri, M. Emamy, A. Malekan, Microstructural evolution and tensile properties of the in situ Ale15% Mg2Si composite with extra Si contents, Mater. Des. 37 (2012) 215e222. N. Nasiri, M. Emamy, A. Malekan, M. Norouzi, Microstructure and tensile properties of cast Ale15% Mg2Si composite: effects of phosphorous addition and heat treatment, Mater. Sci. Eng. A 556 (2012) 446e453. M. Emamy, M. Khodadadi, A. Honarbakhsh Raouf, N. Nasiri, The influence of Ni addition and hot-extrusion on the microstructure and tensile properties of Ale15%Mg2Si composite, Mater. Des. 46 (2013) 381e390. K.W. Shah, Y. Lu, Morphology, large scale synthesis and building applications of copper nanomaterials, Constr. Build. Mater. 180 (2018) 544e578. K. Chu, Q. Wu, C. Jia, X. Liang, J. Nie, W. Tian, G. Gai, H. Guo, Fabrication and effective thermal conductivity of multi-walled carbon nanotubes reinforced Cu matrix composites for heat sink applications, Compos. Sci. Technol. 70 (2) (2010) 298e304. L.C. Zhang, H. Attar, Selective laser melting of titanium alloys and titanium matrix composites for biomedical applications: a review, Adv. Eng. Mater. 18 (4) (2016) 463e475. A. Lelevic, F.C. Walsh, Electrodeposition of NiP composite coatings: a review, Surf. Coat. Technol. 369 (2019) 198e220. P. Gupta, D. Kumar, O. Parkash, A. Jha, Structural and mechanical behaviour of 5% Al2O3-reinforced Fe metal matrix composites (MMCs) produced by powder metallurgy (P/M) Route, Bull. Mater. Sci. 36 (5) (2013) 859e868. C. Shoba, N. Ramanaiah, D.N. Rao, Effect of reinforcement on the cutting forces while machining metal matrix compositesean experimental approach, Eng. Sci. Technol. Int. J. 18 (4) (2015) 658e663. R.M. Sundaram, A. Sekiguchi, M. Sekiya, T. Yamada, K. Hata, Copper/carbon nanotube composites: research trends and outlook, R. Soc. Open Sci. 5 (11) (2018), 180814-180814. D. Dai, D. Gu, Thermal behavior and densification mechanism during selective laser melting of copper matrix composites: simulation and experiments, Mater. Des. 55 (2014) 482e491. s, A. Peigney, A. Weibel, V. Turq, C. Laurent, The C. Guiderdoni, C. Estourne preparation of double-walled carbon nanotube/Cu composites by spark plasma sintering, and their hardness and friction properties, Carbon 49 (13) (2011) 4535e4543. Y. Li, Q. Wang, S. Wang, A review on enhancement of mechanical and tribological properties of polymer composites reinforced by carbon nanotubes and graphene sheet: molecular dynamics simulations, Compos. B Eng. 160 (1 March 2019) 348e361. € Savas¸, R. Kayikci, Production and wear properties of metal matrix comO. posites reinforced with boride particles, Mater. Des. 51 (2013) 641e647. C. Chen, L. Guo, J. Luo, J. Hao, Z. Guo, A.A. Volinsky, Aluminum powder size and microstructure effects on properties of boron nitride reinforced aluminum matrix composites fabricated by semi-solid powder metallurgy, Mater. Sci. Eng. A 646 (2015) 306e314. H.T. Bui, B.T. Tran, D.Q. Le, X.T. Than, D.P. Doan, N.M. Phan, The effect of sintering temperature on the mechanical properties of a Cu/CNT nanocomposite prepared via a powder metallurgy method, Adv. Nat. Sci-Nanosci. 2 (1) (2011), 015006. P.-C. Tsai, Y.-R. Jeng, Experimental and numerical investigation into the effect of carbon nanotube buckling on the reinforcement of CNT/Cu composites, Compos. Sci. Technol. 79 (2013) 28e34. J. Liu, U. Khan, J. Coleman, B. Fernandez, P. Rodriguez, S. Naher, D. Brabazon, Graphene oxide and graphene nanosheet reinforced aluminium matrix composites: powder synthesis and prepared composite characteristics, Mater. Des. 94 (2016) 87e94. P.-C. Tsai, Y.-R. Jeng, J.-T. Lee, I. Stachiv, P. Sittner, Effects of carbon nanotube reinforcement and grain size refinement mechanical properties and wear behaviors of carbon nanotube/copper composites, Diam. Relat. Mater. 74 (2017) 197e204. H. Ghodrati, R. Ghomashchi, Effect of graphene dispersion and interfacial bonding on the mechanical properties of metal matrix composites: an overview, FlatChem 16 (2019) 100113. B. Chen, S. Li, H. Imai, L. Jia, J. Umeda, M. Takahashi, K. Kondoh, An approach for homogeneous carbon nanotube dispersion in Al matrix composites, Mater. Des. 72 (2015) 1e8. A. Radhamani, H.C. Lau, S. Ramakrishna, CNT-reinforced metal and steel nanocomposites: a comprehensive assessment of progress and future directions, Compos Part A Appl Sci Manuf 114 (2018) 170e187. S. Cho, K. Kikuchi, T. Miyazaki, K. Takagi, A. Kawasaki, T. Tsukada, Multiwalled carbon nanotubes as a contributing reinforcement phase for the improvement of thermal conductivity in copper matrix composites, Scr. Mater. 63 (4) (2010) 375e378. W.A.D.M. Jayathilaka, A. Chinnappan, S. Ramakrishna, A review of properties influencing the conductivity of CNT/Cu composites and their applications in wearable/flexible electronics, J. Mater. Chem. C 5 (36) (2017) 9209e9237. € m, B.P. Wilson, P.-M. Hannula, A. Peltonen, J. Aromaa, D. Janas, M. Lundstro n, Carbon nanotube-copper composites by electrodeposition K. Koziol, O. Forse on carbon nanotube fibers, Carbon 107 (2016) 281e287. R. Vignesh Babu, S. Kanagaraj, Thermal, electrical and mechanical characterization of microwave sintered Copper/carbon nanotubes (CNT) composites against sintering duration, CNT diameter and its concentration, J. Mater.
8
M. Darabi et al. / Journal of Alloys and Compounds 822 (2020) 153675
Process. Technol. 258 (2018) 296e309. [30] B. Duan, Y. Zhou, D. Wang, Y. Zhao, Effect of CNTs content on the microstructures and properties of CNTs/Cu composite by microwave sintering, J. Alloy. Comp. 771 (2019) 498e504. [31] A. Azarniya, A. Azarniya, S. Sovizi, H.R.M. Hosseini, T. Varol, A. Kawasaki, S. Ramakrishna, Physicomechanical properties of spark plasma sintered carbon nanotube-reinforced metal matrix nanocomposites, Prog. Mater. Sci. 90 (2017) 276e324. [32] H. Kwon, M. Leparoux, A. Kawasaki, Functionally graded dualnanoparticulate-reinforced aluminium matrix bulk materials fabricated by spark plasma sintering, J. Mater. Sci. Technol. 30 (8) (2014) 736e742. [33] E. Ghasali, P. Sangpour, A. Jam, H. Rajaei, K. Shirvanimoghaddam, T. Ebadzadeh, Microwave and spark plasma sintering of carbon nanotube and graphene reinforced aluminum matrix composite, Arch. Civ. Mech. Eng. 18 (4) (2018) 1042e1054. [34] F. Meng, H. Wang, F. Huang, Y. Guo, Z. Wang, D. Hui, Z. Zhou, Graphene-based microwave absorbing composites: a review and prospective, Compos. B Eng. 137 (2018) 260e277. [35] M.A. Awotunde, A.O. Adegbenjo, B.A. Obadele, M. Okoro, B.M. Shongwe, P.A. Olubambi, Influence of sintering methods on the mechanical properties of aluminium nanocomposites reinforced with carbonaceous compounds: a review, J. Mater. Res. Technol 8 (2) (2019) 2432e2449. [36] E. Ghasali, M. Alizadeh, T. Ebadzadeh, A. hossein Pakseresht, A. Rahbari, Investigation on microstructural and mechanical properties of B4Cealuminum matrix composites prepared by microwave sintering, J. Mater. Res. Technol. 4 (4) (2015) 411e415. [37] E. Ghasali, M. Alizadeh, M. Niazmand, T. Ebadzadeh, Fabrication of magnesium-boron carbide metal matrix composite by powder metallurgy route: comparison between microwave and spark plasma sintering, J. Alloy. Comp. 697 (2017) 200e207. [38] D. El Khaled, N. Novas, J. Gazquez, F. Manzano-Agugliaro, Microwave dielectric heating: applications on metals processing, Renew. Sustain. Energy Rev. 82 (2018) 2880e2892. [39] M. Darabi, M. Rajabi, Electrical and mechanical properties of Cu-CNT nanocomposites sintered by microwave technique, Metall. Mater. Eng. 23 (4) (2017) 303e317. [40] A.J. Slifka, Thermal-conductivity apparatus for steady-state, comparative measurement of ceramic coatings, J. Res. Natl. Inst. Stand. Technol. 105 (4) (2000) 591. [41] K.S. Munir, P. Kingshott, C. Wen, Carbon nanotube reinforced titanium metal matrix composites prepared by powder metallurgyda review, Crit. Rev. Solid State 40 (1) (2015) 38e55. [42] Z. Liu, B. Xiao, W. Wang, Z. Ma, Tensile strength and electrical conductivity of carbon nanotube reinforced aluminum matrix composites fabricated by powder metallurgy combined with friction stir processing, J. Mater. Sci. Technol. 30 (7) (2014) 649e655. [43] A. Canakci, T. Varol, S. Ozsahin, Prediction of effect of volume fraction, compact pressure and milling time on properties of Al-Al 2O3 MMCs using
neural networks, Met. Mater. Int. 19 (3) (2013) 519e526. [44] J. Liu, C. Suryanarayana, D. Ghosh, G. Subhash, L. An, Synthesis of MgeAl2O3 nanocomposites by mechanical alloying, J. Alloy. Comp. 563 (2013) 165e170. [45] N. Wu, X. Liu, C. Zhao, C. Cui, A. Xia, Effects of particle size on the magnetic and microwave absorption properties of carbon-coated nickel nanocapsules, J. Alloy. Comp. 656 (2016) 628e634. [46] P. Ashwath, M.A. Xavior, Effect of ceramic reinforcements on microwave sintered metal matrix composites, Mater. Manuf. Process. 33 (1) (2018) 7e12. [47] R. Menezes, R. Kiminami, Microwave sintering of aluminaezirconia nanocomposites, J. Mater. Process. Technol. 203 (1e3) (2008) 513e517. [48] P.K. Loharkar, A. Ingle, S. Jhavar, Parametric review of microwave-based materials processing and its applications, J. Mater. Res. Technol. 8 (3) (2019) 3306e3326. [49] R. Benavente, M. Salvador, F. Penaranda-Foix, E. Pallone, A. Borrell, Mechanical properties and microstructural evolution of aluminaezirconia nanocomposites by microwave sintering, Ceram. Int. 40 (7) (2014) 11291e11297. [50] Z.W. Xue, L.D. Wang, P.T. Zhao, S.C. Xu, J.L. Qi, W.D. Fei, Microstructures and tensile behavior of carbon nanotubes reinforced Cu matrix composites with molecular-level dispersion, Mater. Des. 34 (2012) 298e301. [51] K. Rajkumar, S. Aravindan, Tribological studies on microwave sintered copperecarbon nanotube composites, Wear 270 (9e10) (2011) 613e621. [52] X. Long, Y. Bai, M. Algarni, Y. Choi, Q. Chen, Study on the strengthening mechanisms of Cu/CNT nano-composites, Mater. Sci. Eng. A 645 (2015) 347e356. [53] R. Verdejo, F. Barroso-Bujans, M.A. Rodriguez-Perez, J.A. De Saja, M.A. LopezManchado, Functionalized graphene sheet filled silicone foam nanocomposites, J. Mater. Chem. 18 (19) (2008) 2221e2226. [54] R.M. Sundaram, A. Sekiguchi, M. Sekiya, T. Yamada, K. Hata, Copper/carbon nanotube composites: research trends and outlook, R. Soc. Open Sci. 5 (11) (2018) 180814. € ller, [55] S.M. Uddin, T. Mahmud, C. Wolf, C. Glanz, I. Kolaric, C. Volkmer, H. Ho U. Wienecke, S. Roth, H.-J. Fecht, Effect of size and shape of metal particles to improve hardness and electrical properties of carbon nanotube reinforced copper and copper alloy composites, Compos. Sci. Technol. 70 (16) (2010) 2253e2257. [56] A. Shukla, N. Nayan, S. Murty, S. Sharma, P. Chandran, S.R. Bakshi, K.M. George, Processing of copperecarbon nanotube composites by vacuum hot pressing technique, Mater. Sci. Eng. A 560 (2013) 365e371. [57] W.M. Daoush, B.K. Lim, C.B. Mo, D.H. Nam, S.H. Hong, Electrical and mechanical properties of carbon nanotube reinforced copper nanocomposites fabricated by electroless deposition process, Mater. Sci. Eng. A 513e514 (2009) 247e253. [58] X. Wei, H. Rui, J.-S. Li, H.-Z. Fu, Effect of electrical current on tribological property of Cu matrix composite reinforced by carbon nanotubes, Trans. Nonferrous Metals Soc. China 21 (10) (2011) 2237e2241. [59] P. Wang, R. Xiang, S. Maruyama, Chapter two - thermal conductivity of carbon nanotubes and assemblies, in: E.M. Sparrow, J.P. Abraham, J.M. Gorman (Eds.), Advances in Heat Transfer, vol. 50, Elsevier, 2018, pp. 43e122.
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Microstructural, mechanical and thermal properties of microwave sintered Cu-MWCNT nanocomposites Marjan Darabi a, Masoud Rajabi a, Noushin Nasiri b, * a b
Department of Materials Science and Engineering, Faculty of Technology and Engineering, Imam Khomeini International University (IKIU), Qazvin, Iran School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, Australia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 November 2019 Received in revised form 1 January 2020 Accepted 3 January 2020 Available online 7 January 2020
Cu nanocomposites reinforced with 0e6 vol% MWCNTs are fabricated using mixing, ball milling and microwave sintering techniques. It is found that decreasing the Cu powders size from 65 to 15 mm significantly enhances the mechanical and thermal properties of the fabricated nanocomposites. In addition, the optimal MWCNTs content in such composites is found to be 4 vol%; there exists maximum for microhardness, bending strength and thermal conductivity of Cu- MWCNT composites which rise to 82.2 HV, 155.2 MPa and 380.2 W.mk 1, respectively. However, the nanocomposites properties then fall to 75 HV, 139.5 MPa and 315.4 W.mk 1, respectively, with further increasing the MWCNT content up to 6 vol %. Furthermore, the relative density of the pellets is calculated using Archimedes method, demonstrating a lower relative density for the composites with higher MWCNTs content. These findings provide a simple and effective sintering method for the engineering of low-cost metal matrix composites. © 2020 Elsevier B.V. All rights reserved.
Keywords: Cu-MWCNT nanocomposite Microwave sintering Microhardness Thermal conductivity Relative density
1. Introduction In the past two decades, metal matrix composites (MMCs) have attracted great attentions due to their high specific modulus, strength, and thermal stability, compared to monolithic materials, to be utilized in numerous applications including automotive industries [1e3]. A wide range of matrix metals such as aluminum (Al) [4e6], copper (Cu) [7,8], titanium (Ti) [9], nickel (Ni) [10] and iron (Fe) [11] have been employed in structural application where a high strength to weight ratio, tensile strength, wear resistance and stability are the main engineering considerations [12]. Amongst them, Cu-based MMCs are commonly used in electrical applications and package materials due to copper’s excellent electrical (5.8 105 S cm 1 at 27 C) and thermal (401 W m 1 K 1 at 27 C) conductivity as well as low-cost production and availability [13,14]. However, the poor hardness, low strength and abrasion resistance are the major limitation of Cu which extensively hinders its engineering and industrial application [15,16]. To address this issue, a wide range of reinforced materials including borides, carbides, nitrides, oxides as particles, whiskers or short fibers have been introduced into Cu matrix [17,18]. Amongst them, carbon
* Corresponding author. E-mail address: [email protected] (N. Nasiri). https://doi.org/10.1016/j.jallcom.2020.153675 0925-8388/© 2020 Elsevier B.V. All rights reserved.
reinforcements such as carbon fibers, multi-walled carbon nanotubes (MWCNTs), graphene oxides and graphite nanoparticles demonstrated great attention due to their exceptional mechanical, electrical and thermal properties [19,20]. Liu et al. [21] investigated the preparation and properties of reduced graphene oxide (rGO) as well as graphene nanosheet (GNS) as reinforcement materials for aluminum matrix composites (AMCs) using power synthesis techniques. An average 40% enhancement was observed for MMCs hardness for 0.3 wt% rGO-AMCs and 0.15 wt% GNS-AMCs samples compared to unreinforced aluminum samples [21]. Tsai et al. [22] reported a minimum of 40% enhancement in the wear resistance of 1.0 wt% CNTs/Cu nanocomposites compared to that of a pure Cu sample. Despite these significant improvements upon adding CNTs into metal matrix, a homogenous dispersion of CNTs is still critical as agglomeration and inhomogeneous dispersion of CNTs could considerably restrict the mechanical and electrical performance of MMCs [23e25]. In fact, the performance of CNTs/Cu composites is strictly associated with dispersion of CNTs and density of materials [8,26]. Therefore, different methods have been used to synthesis CNT-reinforced Cu matrix composites including powder metallurgy techniques, electrochemical deposition process, melting and solidification synthesis and spray techniques [1,27,28]. However, these methods are expensive and require a few post sintering/ deformation processing steps such as rolling, hot extrusion as well
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as severe plastic deformation (SPD) [29]. In addition, excessive grain growth caused by long sintering time at high temperature could lead to a weakened interfacial strength in the fabricated MMCs [29,30]. Hence, some rapid densification methods including spark plasma sintering (SPS) and microwave sintering have been utilized due to their many inherent advantages over conventional sintering technique [31e35]. Compared to SPS technique, microwave sintering could save up to 85% of the sintering time as well as 96% of the energy [30], offering lower sintering temperature, lower porosity and lower processing cost [36e38]. Using spark plasma sintering, Guiderdoni et al. [15] fabricated homogenously dispersed double walled carbon nanotubes (DWCNT) in Cu matrix, featuring significantly microhardness (103 HV) for DWCNT/Cu composites compared to pure Cu samples. Using microwave sintering, Babu et al. [29] investigated the effect of sintering time as well as CNT diameters on the mechanical, electrical and thermal properties of the synthesized CuCNT composites. The optimal hardness of 80 HV, relative density of 91% and electrical conductivity of 47 MS m 1 were obtained at 60 min sintering time for the CNT average diameter of 20e40 nm [29]. In another research, Duan et al. [30] reported a hardness of 80 HV for the Cu-0.5 wt% CNT composite fabricated by molecular-level mixing followed by microwave sintering technique. The microhardness value decreased significantly from 80 to 55 HV by increasing the CNT content from 0.5 wt% to 1 wt% which could be attributed to the aggravated agglomeration in the composite with higher CNT content [1,30]. However, limited studies are conducted on the role Cu powder sizes, as metal matrix, play on the microstructure as well as mechanical, electrical and thermal properties of CNT-Cu composites. In our previous work [39], a simple comparison was conducted between conventional and microwave sintering methods, observing that a similar mechanical and electrical properties could be achieved in a significantly shorter synthesis time, when the samples are sintered using microwave method compared to the conventional sintering techniques. Here, the effect of matrix grain size on the microwave mechanism, scattering of microwave energy, and microwave energy absorption was investigated simultaneously. In addition, the effect of Cu powder size as well as MWCNT content on microstructural, mechanical, electrical and thermal properties of microwave sintered Cu/MWCNT composites are investigated. Mechanical properties such as physical properties of fabricated samples were then characterized by measuring relative density and thermal conductivity as well as investigating the mechanical properties, including microhardness and bending strength. Finally, the samples microhardness was compared with
other research which emphasizes the outstanding role of fine grain size of matrix and microwave energy absorption of reinforcement, leading to improved properties. Findings of this research provide a simple and effective fabrication method for the engineering of lowcost MMCs. 2. Experiment 2.1. Cu-MWCNT nanocomposites fabrication For the synthesis of Cu- MWCNT nanocomposites, six batches of copper powders with average particle size of 15, 25, 35, 45, 55 and 65 mm (supplied by Iran Powder Metallurgy Complex, with 99.9% purity) and one batch of MWCNT with a diameter of about 20 nm (supplied by US nano of America with purity level of >95%) were used. Copper powders were mixed with MWCNTs in a planetary ball mill using a stainless-steel jar (the mass ratio of ball to powder was 10:1). The powders and MWCNTs were mixed under argon (Ar) atmosphere for 10 h at 120 rpm, to prevent oxide formation. Then, the mixed powders were compacted in a uniaxial hydraulic press under the 450 MPa pressure for 60 s to obtain green pellets (Fig. 1) with two different dimensions of 40 10 3 mm3 and 10 3 mm2. 2.2. Sintering procedure The green pellets were sintered for 20 min using a microwave furnace (900 W, 2.45 GHz, LG Microwave furnace) equipped with Ar gas at a rate of 42 C.min 1 (Fig. 1). For higher overall heating rate, the samples were placed in an alumina crucible and immersed in Silicon Carbide (SiC) bed. This step provided the green pallets with a hybrid heating facility as well as reduced the thermal gradient of samples and the atmosphere around them, leading to the fabrication of crack free components. In order to minimize the heat transfer, the crucibles were covered by a layer of glass wool to eliminate the heat loss. Sintered specimens were then cooled down to room temperature (Fig. 1). 2.3. Characterization Prior to characterization, the samples were mounted and grounded using 500 to 5000 grit SiC sandpapers, and then polished with alumina based polishing slurry. The samples then were chemically etched by immersing in an etching solution of CrO3, HNO3, H2SO4 and H2O, for 10 s. The Archimedes method was used to measure the density of the sintered specimen according to ASTM B311. The thermal conductivity of the samples was measured by
Fig. 1. The preparation process for fabricating Cu-MWCNT nanocomposites using mixing, ball milling and microwave sintering techniques.
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means of a relative steady-state technique, in an experimental setup (model HT01, Deghat Azma corp), which is considered as a variation of ASTM E 1225-87 methodology. In this technique, a sample of unknown thermal conductivity is embedded vertically between two samples of known thermal conductivity with a hot plate at the top and a cold plate at the bottom. Heat is supplied by thermocouples, positioned along the length of samples. When the heat gradient reaches to zero or heat becomes constant over the entire sample, the thermal conductivity could be measured using the one-dimensional Fourier conduction equation [40]. Bending strength test was conducted using a universal testing machine (Zwick/Roaell, Z100) with the loading speed of 0.5 mm min 1, according to ASTM D790 standard. The microhardness of the samples was measured using a Vickers microhardness digital tester (HVS1000A) at a load of 50 g and a dwell time of 10 s in accordance with the ASTM standard E92. The average hardness of five different test points is the final hardness of samples. The crystal phases and surface compositions of the samples were characterized by X-Ray diffraction using (Rigaku XRD, MiniFlex 600) system equipped with Cu Ka radiation of average wavelength 1.5404 Å. Morphological examination of samples was performed using a field emission scanning electron microscope (FESEM, MIRA3 TE SCAN) at 15.0 kV. The average grain size of the nanocomposite samples was measured by analyzing FESEM micrographs with the aid of an image processing software (ImageJ). 3. Result and discussion 3.1. Microstructure Powder metallurgy is one of the most common fabrication techniques for metal-CNT nanocomposites [41,42]. As mentioned in the experimental section, the MWCNTs and Cu powders were mixed in different MWCNT volume fraction, using mechanical milling (10 h at 120 rpm). The materials defect density as well as alloying capacity increases significantly after mechanical milling due to a high level of energy generated during milling process [43,44]. Here, a microwave sintering (as densification step), followed by a post pressing process was then conducted to fabricate Cu- MWCNT nanocomposites. Fig. 2 shows the field emission scanning electron microscope (FESEM) images of Cu- MWCNT nanocomposite samples with average particle size of 15 and 65 mm, before (Fig. 2a and b) and after microwave sintering for 20 min (Fig. 2c and d). It could be seen that MWCNTs are well embedded and distributed homogeneously within the metal matrix, with no obvious crack or damage on the nanocomposite surface. This high homogeneity is expected to increase the rigidity of Cu-MWCNT nanocomposite samples compared to the pure Cu material. The fabricated nanocomposites were made of 4 vol% MWCNT added into copper powder with an average particle size of 15 mm (Fig. 2a,c) and 65 mm (Fig. 2b,d). Increasing the average size of Cu powders from 15 to 65 mm resulted in significantly coarser microstructure (Fig. 2a and b) after microwave sintering with larger voids and porosities (Fig. 2c and d). In fact, the nanocomposites fabricated by the Cu powders with smaller particle size (15 mm) demonstrated 50% reduction in grain size compared to the 65 mm Cu powders. This could be related to the important role grain size is playing in the microwave energy absorption during sintering process [45]. In addition, the CuMWCNT nanocomposite made of larger Cu powders (65 mm) demonstrated a lower level of entanglement (Fig. 2d) in comparison to that of 15 mm Cu-MWCNT nanocomposite powder (Fig. 2c), resulting in the formation of more micro-voids in the microstructure of the fabricated samples. This could be attributed to a higher level of microwave field that concentrates at the grain boundaries
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Fig. 2. FESEM micrographs of Cu-4 vol% MWCNT nanocomposites made of Cu powders with (a,c) 15 mm and (b,d) 65 mm average particles size (a,b) before and (c,d) after microwave sintering for 20 min.
in the microstructure of these nanocomposites [46,47]. In the microwave sintering process, the microwaves could propagate into the material and their energy could transfer from one point to another [34,48]. The interaction of microwaves with the material and the absorption of the energy could generate heat in the material, while the amount of energy absorbed by the material is dependent on the material’s dielectric loss factor [48]. Fig. 3 illustrates the material’s interaction with microwaves, in which the materials could be classified in three different types: transparent, opaque and absorbent. In the case of MMCs, one of the components is a high-loss material whereas the other component is a low-loss one. According to other scientific works, with decreasing of particle size of nanocomposites, the reflection loss witnesses a shift to lower frequencies and broader bandwidth where the microwave absorption reaches the maximum amount [48]. In fact, in the nanocomposite made of smaller Cu powders, higher number of powder boundaries/interfaces results in enhanced microwave field, which consequently leads to progressive necking formation at the powders interface [49]. Furthermore, the heat generated by the microwave sintering process could be transferred more slowly through a course-grained microstructure compared to a finegrained one [47] resulting in a lower density and higher level of micro-voids for the Cu-MWCNT nanocomposite made of larger Cu powders (65 mm) (Fig. 2d). This higher level of defects in the microstructure could hinder the filling pattern of matrix during the synthesize process leading to lower relative density of the fabricated nanocomposites [29,30]. Besides, higher level of defects in the microstructure might result in lower electrical and thermal conductivity in nanocomposites as they could block the electron and phonon conduction in the microstructure [29]. 3.2. X-ray diffraction The XRD patterns of Cu-4 vol% MWCNT nanocomposites made of Cu powders with different average particle size of 15 and 65 mm, before and after microwave sintering are shown in Fig. 4. The XRD patterns of both Cu-MWCNT nanocomposite powders and bulks are generally similar with no obvious change in the obtained patterns
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Fig. 3. Interaction of different types of materials with microwaves: a) Transparent, b) Opaque, c) Absorber.
Fig. 4. (a) XRD patterns of Cu-4 vol% MWCNT powders and nanocomposites and magnified view of the main XRD peaks at 2q of (b) ~ 43.3 and (c) ~ 50.4.
by increasing the average particle size of Cu powders. Although, further XRD analysis in this figure demonstrates difference among them in terms of broad peaks of fine-grained copper which can be attributed to uniform transferred heat within the structure. The peaks identified by the planes (111), (200) and (220) at 2q of about 43 , 50 and 74 respectively, were confirmed to follow JCPDS PDF 85e1326 and FCC structure with no observable peaks of other phases in the XRD patterns. The major peak corresponding to MWCNT should be observed at 26 (JCPDS PDF 26e1076) with respective lattices of (002), while no noticeable peak for MWCNT was witnessed due to low diffraction efficiency of carbon [50]. This could also be attributed to no prominent structural changes in the Cu-MWCNT nanocomposites after mechanical alloying of the powders. 3.3. Relative density The densification step in powder metallurgy technique is reported to generate macro voids and pores in the fabricated microstructure [51]. The size and density of these macro-pores in the final structure play significant role in determining the mechanical and electrical properties of the fabricated nanocomposites [22,51,52]. The relative density of the fabricated Cu-MWCNT nanocomposites could be conducted to evaluate the size and density of the generated voids and pores in the microstructure. Here, the Archimedes method [53] is used to measure the relative density of fabricated Cu-MWCNT nanocomposites made of Cu powders with average particle size of 15 up to 65 mm as a function of MWCNT vol%. As shown in Fig. 5, increasing the MWCNT content up to 6 vol%
Fig. 5. Relative density of microwave sintered Cu-MWCNT nanocomposites made of Cu powders with 15, 25, 35, 45, 55 and 65 mm particle size as a function of MWCNT content.
decreased the relative density of the fabricated Cu-MWCNT nanocomposite, regardless of Cu powder size. For nanocomposites made by 15 mm Cu powders, the relative density deceased from 97% to 95% (red circles) by increasing the MWCNT content (vol%) from 0 to 6, respectively. Increasing the average powder size from 15 to 25 resulted in decreasing the relative density from 97% and 95% (red
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circles) to 96.2% and 90.9% (blue circles), for the MWCNT content of 0 vol% and 6 vol%, respectively. Further decrease in Cu average particle size down to 65 mm led to a lower relative density of 95.6% and 90.1% (blue rectangles) for the Cu-MWCNT nanocomposites with 0 and 6 vol% MWCNT content, respectively (Fig. 5). Higher relative density was reported for the Cu composites with similar CNT content fabricated by SPS [15]. This lower density of the sample with higher MWCNT content could be attributed to the slower densification of Cu powders in the presence of extra MWCNT in the matrix [53]. Due to the higher melting point of MWCNT compared to the copper matrix [54], higher MWCNT content resulted in the formation of larger macro voids in the microstructure, and consequently decreased the relative density of the fabricated samples. In fact, increasing the size of macro voids in the microstructure could be the main reason for lower density of the composites with higher MWCNT content [30]. Similar results were reported by Babu et al. [29] for Cu-CNT nanocomposites made by 0.25e1.0 wt% CNT. The relative density of the fabricated nanocomposites decreased from 87.1% to 80.8% by increasing the CNTs content from 0.25 to 1.0 wt%. However, some materials processing techniques such as cold rolling could significantly increase the relative density of these nanocomposites via eliminating these macro voids [30]. In addition, for a wide range of MWCNT content from 1 to 6 vol%, the Cu(65 mm)-MWCNT nanocomposites featured considerably lower relative density compared to Cu(15 mm)MWCNT ones. In fact, at the MWCNT content of 6 vol% the relative density of the fabricated samples were 93.5% and 90.1% for Cu(15 mm) and Cu(65 mm)-MWCNT nanocomposites, respectively. 3.4. Microhardness Fig. 6a shows the Vickers microhardness of pure Cu and CuMWCNT nanocomposite samples with different MWCNT content from 0 to 6 vol%. Regardless of MWCNT content, the nanocomposites made of smaller Cu powder size demonstrated a higher microhardness compared to the samples fabricated by larger Cu micro-powders. This lower microhardness for nanocomposites made by larger Cu powders could be attributed to a lower level of microwave energy absorption and consequently higher level of micro-voids formed in the microstructure of these nanocomposites, compared to the ones made of smaller Cu powders [45]. In addition, the microhardness of nanocomposites made by 15 mm powder size increased rapidly from 50 HV to 74 HV by increasing the MWCNT content from 0 to 2 vol% (Fig. 6a). At 4 vol% MWCNT content, the microhardness value reached a peak of 82 HV
5
for Cu(15 mm)-MWCNT nanocomposite and 66 HV for Cu(65 mm)MWCNT nanocomposites. This higher microhardness is attributed to the higher strength of MWCNT compared to pure Cu matrix. In addition, grain refinement as well as strong Cu/MWCNT interface formed during microwave synthesis could result in higher microhardness in the fabricated nanocomposites [30]. Increasing the MWCNT content in the nanocomposites could ease the load transfer from the Cu matrix to the harder MWCNT, resulting in an enhanced hardness value of the fabricated Cu-MWCNT nanocomposite. However, further increase in MWCNT content to 6 vol% led to dramatic decrease in microhardness to 75 and 54 HV for the nanocomposites made of 15 and 65 mm Cu powders, respectively (Fig. 6a). This lower microhardness could be ascribed to the formation of larger micro voids as well as a greater number of agglomerates in the nanocomposite with higher MWCNT content [29]. Fig. 6b presents a comparison of microhardness obtained by CuMWCNT nanocomposites fabricated in this research with similar nanocomposites reported in the literature [55e58]. The microhardness of 82 HV obtained by Cu-4 vol% MWCNT nanocomposites fabricated by microwave sintering technique was the highest value compared to similar reports. In contrast, the Cu-10 vol% MWCNT nanocomposite fabricated by Shukla et al. [56] demonstrated the lowest microhardness of 56 HV amongst others. Uddin et al. [55] reported a 32% increase in microhardness of Cu-0.5 vol% MWCNT nanocomposite fabricated by hot press technique, compared to the pure copper samples, which is in line with 39% increase in hardness of Cu-4 vol% MWCNT nanocomposite, obtained in this research (Fig. 6a). Moreover, Wei et al. [58] and Daoush et al. [57] succeeded in achieving hardness of about 58 and 75 HV by preparing Cu-4 vol % CNT and Cu-1 vol% CNT nanocomposite through powder metallurgy technique and electroless deposition process respectively. 3.5. Bending strength Fig. 7 shows the bending strength of microwave sintered CuMWCNT nanocomposites as a function of Cu powders size for MWCNT content of 0 vol% up to 6 vol%. Regardless of Cu powders average size, the bending strength of the fabricated nanocomposites reached a peak value of 155 MPa at 4 vol% MWCNT content, for nanocomposites made of 15 mm Cu powders size. This higher bending strength of nanocomposites with high MWCNT content could be attributed to the high elastic modulus and strength of MWCNT as well as strong interface combination between MWCNT and Cu matrix [39]. As a result, the load applied during the bending strength test could be easily transfer from the
Fig. 6. (a) Microhardness of microwave sintered Cu-MWCNT nanocomposites made of Cu powders with 15, 25, 35, 45, 55 and 65 mm particle size as a function of MWCNT content. (b) A comparison of microhardness obtained by Cu-MWCNT nanocomposites fabricated in this research (15 mm particle size) with similar nanocomposites reported in the literature.
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aggregated CNTs is weak, resulting in a significant reduction in the nanocomposite strength [30]. Moreover, morphology of the sample represents that copper has ductile fracture [30]. When MWCNT volume fraction increases to 6 vol% MWCNT, elongation declines. This sample is fractured before yielding because of significant reduction in elastic properties. It is interesting to note that the higher bending strength of nanocomposite with smaller Cu powders could be attributed to the presence of more grain boundaries in the microstructure as well as higher capacity of the nanocomposite for better incorporation of MWCNT within the matrix [57]. 3.6. Thermal conductivity
Fig. 7. Bending strength of microwave sintered Cu-MWCNT nanocomposites made of Cu powders with 15, 25, 35, 45, 55 and 65 mm particle size as a function of MWCNT content.
matrix interface, leading to a significantly higher bending strength of 25% for Cu-MWCNT nanocomposite compared to pure Cu samples. In addition, the bending strength of Cu-4 vol% MWCNT nanocomposite decreased from 155 MPa to 132 MPa by increasing the average Cu powders size from 15 to 65 mm (Fig. 7). This higher bending strength of Cu-MWCNT nanocomposites made by smaller Cu powders could be attributed to the smaller grain size in Cu(15 mm)-MWCNT compared to Cu(65 mm)-MWCNT, resulting in a higher number of grain boundaries, consequently, higher resistance to the dislocation motions, which could enhance the bending strength of the fabricated samples. Further increasing the MWCNT content up to 6 vol% resulted in decreasing down the bending strength of the fabricated CuMWCNT nanocomposites to 139 and 119, for Cu (15 mm)- and Cu (65 mm)-MWCNT (Fig. 7). This lower bonding strength could be related to weak interface bonding between CNT aggregates and clusters, in the nanocomposite with high CNT content [29,30]. The fracture surface of microwave sintered Cu-MWCNT nanocomposites with 6 vol% MWCNT content is presented in Fig. 8. As can be seen, high MWCNT content as well as large Cu powders size (65 mm) resulted in the formation of MWCNT agglomerates in the fabricated nanocomposites. The interface bonding between these
Fig. 9 shows the thermal conductivity of microwave sintered CuMWCNT nanocomposites made of Cu powders from 15 up to 65 mm particle size. Regardless of the Cu powders size, 30% rise is observed in thermal conductivity of the fabricated nanocomposites by increasing the MWCNT content from 0 to 4 vol%. This higher thermal conductivity in the fabricated nanocomposites with high MWCNT content could be attributed to remarkable effects of phonon conduction with insignificant agglomeration of MWCNT in lower volume fraction [26]. However, further increase in the
Fig. 9. Thermal conductivity of microwave sintered Cu-MWCNT nanocomposites made of Cu powders with 15, 25, 35, 45, 55 and 65 mm particle size as a function of MWCNT content.
Fig. 8. FESEM micrographs of fracture surface of Cu-6 vol% MWCNT nanocomposites made of 65 mm Cu powders.
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volume fraction of MWCNT up to 6 vol% leads to sharp reduction of thermal conductivity in the fabricated nanocomposites down to 290 W/mk. This conductivity reduction could originate from the large number of voids in the grain boundaries as well as high porosity in MWCNT clusters [30]. In addition, random orientation of MWCNT in the matrix could result in scattering of phonons through grain boundaries and consequently, restricting the thermal conductivity of the fabricated nanocomposites [59].
[4]
[5]
[6]
[7]
4. Conclusion [8]
The Cu-MWCNT composites having different Cu powders size and MWCNTs content were successfully fabricated using mixing, ball milling and microwave sintering methods. Then, the effect of Cu powder size as well as MWCNTs content on microstructural, mechanical and thermal properties of microwave sintered CuMWCNT composites are investigated. The following conclusions could be extracted based on the outcome of this research study: - Increasing the Cu powders size from 15 to 65 mm significantly decreased the mechanical and thermal properties of the fabricated nanocomposites. A 25%, 17% and 15% reduction in the microhardness, bending strength and thermal conductivity of the Cu-4vol% MWCNT composites were observed when the Cu powders size increased from 15 to 65 mm. In addition, the relative density of the fabricated nanocomposites (Cu-4vol% MWCNT) decreased slightly from 94.8% to 92.5% by increasing the Cu powders size from 15 to 65 mm. - Increasing the MWCNTs content from 0 to 6 vol% significantly impacted the mechanical and thermal properties as well as relative density of the fabricated nanocomposites. Microhardness, bending strength and thermal conductivity of fabricated Cu-MWCNTs composites with 15 mm Cu powders size increased from 50 HV, 115.4 MPa and 250 W.mk 1 to 82.2 HV, 155.2 MPa and 380.2 W.mk 1 by increasing the MWCNTs content from 0 to 4 vol%. However, further increase in the MWCNTs content up to 6 vol% resulted in lower microhardness (75 HV), bending strength (139.5 MPa) and thermal conductivity (315.4 W.mk 1).
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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CRediT authorship contribution statement Marjan Darabi: Data curation, Formal analysis, Investigation, Methodology, Visualization, Writing - original draft. Masoud Rajabi: Conceptualization, Methodology, Supervision, Writing review & editing. Noushin Nasiri: Conceptualization, Supervision, Validation, Visualization, Writing - review & editing. Acknowledgement The authors are grateful for the research support of Iran National Science Foundation with this research work.
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References [28] [1] S.R. Bakshi, D. Lahiri, A. Agarwal, Carbon nanotube reinforced metal matrix composites-a review, Int. Mater. Rev. 55 (1) (2010) 41e64. [2] R. Casati, M. Vedani, Metal matrix composites reinforced by nano-particlesda review, Metals 4 (1) (2014) 65e83. [3] P. Garg, A. Jamwal, D. Kumar, K.K. Sadasivuni, C.M. Hussain, P. Gupta, Advance
[29]
7
research progresses in aluminium matrix composites: manufacturing & applications, J. Mater. Res. Technol. 8 (5) (2019) 4924e4939. N. Nasiri, M. Emamy, A. Malekan, Microstructural evolution and tensile properties of the in situ Ale15% Mg2Si composite with extra Si contents, Mater. Des. 37 (2012) 215e222. N. Nasiri, M. Emamy, A. Malekan, M. Norouzi, Microstructure and tensile properties of cast Ale15% Mg2Si composite: effects of phosphorous addition and heat treatment, Mater. Sci. Eng. A 556 (2012) 446e453. M. Emamy, M. Khodadadi, A. Honarbakhsh Raouf, N. Nasiri, The influence of Ni addition and hot-extrusion on the microstructure and tensile properties of Ale15%Mg2Si composite, Mater. Des. 46 (2013) 381e390. K.W. Shah, Y. Lu, Morphology, large scale synthesis and building applications of copper nanomaterials, Constr. Build. Mater. 180 (2018) 544e578. K. Chu, Q. Wu, C. Jia, X. Liang, J. Nie, W. Tian, G. Gai, H. Guo, Fabrication and effective thermal conductivity of multi-walled carbon nanotubes reinforced Cu matrix composites for heat sink applications, Compos. Sci. Technol. 70 (2) (2010) 298e304. L.C. Zhang, H. Attar, Selective laser melting of titanium alloys and titanium matrix composites for biomedical applications: a review, Adv. Eng. Mater. 18 (4) (2016) 463e475. A. Lelevic, F.C. Walsh, Electrodeposition of NiP composite coatings: a review, Surf. Coat. Technol. 369 (2019) 198e220. P. Gupta, D. Kumar, O. Parkash, A. Jha, Structural and mechanical behaviour of 5% Al2O3-reinforced Fe metal matrix composites (MMCs) produced by powder metallurgy (P/M) Route, Bull. Mater. Sci. 36 (5) (2013) 859e868. C. Shoba, N. Ramanaiah, D.N. Rao, Effect of reinforcement on the cutting forces while machining metal matrix compositesean experimental approach, Eng. Sci. Technol. Int. J. 18 (4) (2015) 658e663. R.M. Sundaram, A. Sekiguchi, M. Sekiya, T. Yamada, K. Hata, Copper/carbon nanotube composites: research trends and outlook, R. Soc. Open Sci. 5 (11) (2018), 180814-180814. D. Dai, D. Gu, Thermal behavior and densification mechanism during selective laser melting of copper matrix composites: simulation and experiments, Mater. Des. 55 (2014) 482e491. s, A. Peigney, A. Weibel, V. Turq, C. Laurent, The C. Guiderdoni, C. Estourne preparation of double-walled carbon nanotube/Cu composites by spark plasma sintering, and their hardness and friction properties, Carbon 49 (13) (2011) 4535e4543. Y. Li, Q. Wang, S. Wang, A review on enhancement of mechanical and tribological properties of polymer composites reinforced by carbon nanotubes and graphene sheet: molecular dynamics simulations, Compos. B Eng. 160 (1 March 2019) 348e361. € Savas¸, R. Kayikci, Production and wear properties of metal matrix comO. posites reinforced with boride particles, Mater. Des. 51 (2013) 641e647. C. Chen, L. Guo, J. Luo, J. Hao, Z. Guo, A.A. Volinsky, Aluminum powder size and microstructure effects on properties of boron nitride reinforced aluminum matrix composites fabricated by semi-solid powder metallurgy, Mater. Sci. Eng. A 646 (2015) 306e314. H.T. Bui, B.T. Tran, D.Q. Le, X.T. Than, D.P. Doan, N.M. Phan, The effect of sintering temperature on the mechanical properties of a Cu/CNT nanocomposite prepared via a powder metallurgy method, Adv. Nat. Sci-Nanosci. 2 (1) (2011), 015006. P.-C. Tsai, Y.-R. Jeng, Experimental and numerical investigation into the effect of carbon nanotube buckling on the reinforcement of CNT/Cu composites, Compos. Sci. Technol. 79 (2013) 28e34. J. Liu, U. Khan, J. Coleman, B. Fernandez, P. Rodriguez, S. Naher, D. Brabazon, Graphene oxide and graphene nanosheet reinforced aluminium matrix composites: powder synthesis and prepared composite characteristics, Mater. Des. 94 (2016) 87e94. P.-C. Tsai, Y.-R. Jeng, J.-T. Lee, I. Stachiv, P. Sittner, Effects of carbon nanotube reinforcement and grain size refinement mechanical properties and wear behaviors of carbon nanotube/copper composites, Diam. Relat. Mater. 74 (2017) 197e204. H. Ghodrati, R. Ghomashchi, Effect of graphene dispersion and interfacial bonding on the mechanical properties of metal matrix composites: an overview, FlatChem 16 (2019) 100113. B. Chen, S. Li, H. Imai, L. Jia, J. Umeda, M. Takahashi, K. Kondoh, An approach for homogeneous carbon nanotube dispersion in Al matrix composites, Mater. Des. 72 (2015) 1e8. A. Radhamani, H.C. Lau, S. Ramakrishna, CNT-reinforced metal and steel nanocomposites: a comprehensive assessment of progress and future directions, Compos Part A Appl Sci Manuf 114 (2018) 170e187. S. Cho, K. Kikuchi, T. Miyazaki, K. Takagi, A. Kawasaki, T. Tsukada, Multiwalled carbon nanotubes as a contributing reinforcement phase for the improvement of thermal conductivity in copper matrix composites, Scr. Mater. 63 (4) (2010) 375e378. W.A.D.M. Jayathilaka, A. Chinnappan, S. Ramakrishna, A review of properties influencing the conductivity of CNT/Cu composites and their applications in wearable/flexible electronics, J. Mater. Chem. C 5 (36) (2017) 9209e9237. € m, B.P. Wilson, P.-M. Hannula, A. Peltonen, J. Aromaa, D. Janas, M. Lundstro n, Carbon nanotube-copper composites by electrodeposition K. Koziol, O. Forse on carbon nanotube fibers, Carbon 107 (2016) 281e287. R. Vignesh Babu, S. Kanagaraj, Thermal, electrical and mechanical characterization of microwave sintered Copper/carbon nanotubes (CNT) composites against sintering duration, CNT diameter and its concentration, J. Mater.
8
M. Darabi et al. / Journal of Alloys and Compounds 822 (2020) 153675
Process. Technol. 258 (2018) 296e309. [30] B. Duan, Y. Zhou, D. Wang, Y. Zhao, Effect of CNTs content on the microstructures and properties of CNTs/Cu composite by microwave sintering, J. Alloy. Comp. 771 (2019) 498e504. [31] A. Azarniya, A. Azarniya, S. Sovizi, H.R.M. Hosseini, T. Varol, A. Kawasaki, S. Ramakrishna, Physicomechanical properties of spark plasma sintered carbon nanotube-reinforced metal matrix nanocomposites, Prog. Mater. Sci. 90 (2017) 276e324. [32] H. Kwon, M. Leparoux, A. Kawasaki, Functionally graded dualnanoparticulate-reinforced aluminium matrix bulk materials fabricated by spark plasma sintering, J. Mater. Sci. Technol. 30 (8) (2014) 736e742. [33] E. Ghasali, P. Sangpour, A. Jam, H. Rajaei, K. Shirvanimoghaddam, T. Ebadzadeh, Microwave and spark plasma sintering of carbon nanotube and graphene reinforced aluminum matrix composite, Arch. Civ. Mech. Eng. 18 (4) (2018) 1042e1054. [34] F. Meng, H. Wang, F. Huang, Y. Guo, Z. Wang, D. Hui, Z. Zhou, Graphene-based microwave absorbing composites: a review and prospective, Compos. B Eng. 137 (2018) 260e277. [35] M.A. Awotunde, A.O. Adegbenjo, B.A. Obadele, M. Okoro, B.M. Shongwe, P.A. Olubambi, Influence of sintering methods on the mechanical properties of aluminium nanocomposites reinforced with carbonaceous compounds: a review, J. Mater. Res. Technol 8 (2) (2019) 2432e2449. [36] E. Ghasali, M. Alizadeh, T. Ebadzadeh, A. hossein Pakseresht, A. Rahbari, Investigation on microstructural and mechanical properties of B4Cealuminum matrix composites prepared by microwave sintering, J. Mater. Res. Technol. 4 (4) (2015) 411e415. [37] E. Ghasali, M. Alizadeh, M. Niazmand, T. Ebadzadeh, Fabrication of magnesium-boron carbide metal matrix composite by powder metallurgy route: comparison between microwave and spark plasma sintering, J. Alloy. Comp. 697 (2017) 200e207. [38] D. El Khaled, N. Novas, J. Gazquez, F. Manzano-Agugliaro, Microwave dielectric heating: applications on metals processing, Renew. Sustain. Energy Rev. 82 (2018) 2880e2892. [39] M. Darabi, M. Rajabi, Electrical and mechanical properties of Cu-CNT nanocomposites sintered by microwave technique, Metall. Mater. Eng. 23 (4) (2017) 303e317. [40] A.J. Slifka, Thermal-conductivity apparatus for steady-state, comparative measurement of ceramic coatings, J. Res. Natl. Inst. Stand. Technol. 105 (4) (2000) 591. [41] K.S. Munir, P. Kingshott, C. Wen, Carbon nanotube reinforced titanium metal matrix composites prepared by powder metallurgyda review, Crit. Rev. Solid State 40 (1) (2015) 38e55. [42] Z. Liu, B. Xiao, W. Wang, Z. Ma, Tensile strength and electrical conductivity of carbon nanotube reinforced aluminum matrix composites fabricated by powder metallurgy combined with friction stir processing, J. Mater. Sci. Technol. 30 (7) (2014) 649e655. [43] A. Canakci, T. Varol, S. Ozsahin, Prediction of effect of volume fraction, compact pressure and milling time on properties of Al-Al 2O3 MMCs using
neural networks, Met. Mater. Int. 19 (3) (2013) 519e526. [44] J. Liu, C. Suryanarayana, D. Ghosh, G. Subhash, L. An, Synthesis of MgeAl2O3 nanocomposites by mechanical alloying, J. Alloy. Comp. 563 (2013) 165e170. [45] N. Wu, X. Liu, C. Zhao, C. Cui, A. Xia, Effects of particle size on the magnetic and microwave absorption properties of carbon-coated nickel nanocapsules, J. Alloy. Comp. 656 (2016) 628e634. [46] P. Ashwath, M.A. Xavior, Effect of ceramic reinforcements on microwave sintered metal matrix composites, Mater. Manuf. Process. 33 (1) (2018) 7e12. [47] R. Menezes, R. Kiminami, Microwave sintering of aluminaezirconia nanocomposites, J. Mater. Process. Technol. 203 (1e3) (2008) 513e517. [48] P.K. Loharkar, A. Ingle, S. Jhavar, Parametric review of microwave-based materials processing and its applications, J. Mater. Res. Technol. 8 (3) (2019) 3306e3326. [49] R. Benavente, M. Salvador, F. Penaranda-Foix, E. Pallone, A. Borrell, Mechanical properties and microstructural evolution of aluminaezirconia nanocomposites by microwave sintering, Ceram. Int. 40 (7) (2014) 11291e11297. [50] Z.W. Xue, L.D. Wang, P.T. Zhao, S.C. Xu, J.L. Qi, W.D. Fei, Microstructures and tensile behavior of carbon nanotubes reinforced Cu matrix composites with molecular-level dispersion, Mater. Des. 34 (2012) 298e301. [51] K. Rajkumar, S. Aravindan, Tribological studies on microwave sintered copperecarbon nanotube composites, Wear 270 (9e10) (2011) 613e621. [52] X. Long, Y. Bai, M. Algarni, Y. Choi, Q. Chen, Study on the strengthening mechanisms of Cu/CNT nano-composites, Mater. Sci. Eng. A 645 (2015) 347e356. [53] R. Verdejo, F. Barroso-Bujans, M.A. Rodriguez-Perez, J.A. De Saja, M.A. LopezManchado, Functionalized graphene sheet filled silicone foam nanocomposites, J. Mater. Chem. 18 (19) (2008) 2221e2226. [54] R.M. Sundaram, A. Sekiguchi, M. Sekiya, T. Yamada, K. Hata, Copper/carbon nanotube composites: research trends and outlook, R. Soc. Open Sci. 5 (11) (2018) 180814. € ller, [55] S.M. Uddin, T. Mahmud, C. Wolf, C. Glanz, I. Kolaric, C. Volkmer, H. Ho U. Wienecke, S. Roth, H.-J. Fecht, Effect of size and shape of metal particles to improve hardness and electrical properties of carbon nanotube reinforced copper and copper alloy composites, Compos. Sci. Technol. 70 (16) (2010) 2253e2257. [56] A. Shukla, N. Nayan, S. Murty, S. Sharma, P. Chandran, S.R. Bakshi, K.M. George, Processing of copperecarbon nanotube composites by vacuum hot pressing technique, Mater. Sci. Eng. A 560 (2013) 365e371. [57] W.M. Daoush, B.K. Lim, C.B. Mo, D.H. Nam, S.H. Hong, Electrical and mechanical properties of carbon nanotube reinforced copper nanocomposites fabricated by electroless deposition process, Mater. Sci. Eng. A 513e514 (2009) 247e253. [58] X. Wei, H. Rui, J.-S. Li, H.-Z. Fu, Effect of electrical current on tribological property of Cu matrix composite reinforced by carbon nanotubes, Trans. Nonferrous Metals Soc. China 21 (10) (2011) 2237e2241. [59] P. Wang, R. Xiang, S. Maruyama, Chapter two - thermal conductivity of carbon nanotubes and assemblies, in: E.M. Sparrow, J.P. Abraham, J.M. Gorman (Eds.), Advances in Heat Transfer, vol. 50, Elsevier, 2018, pp. 43e122.