Microstructure and mechanical properties of SiC nanowires reinforced titanium matrix composites

Journal of Alloys and Compounds xxx (xxxx) xxx

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Microstructure and mechanical properties of SiC nanowires reinforced titanium matrix composites Yue Liu a, Longlong Dong a, Jinwen Lu a, Wangtu Huo a, Yan Du a, Wei Zhang a, Yusheng Zhang b, * a b

Advanced Materials Research Central, Northwest Institute for Non-ferrous Metal Research, Xi’an, Shaanxi, 710016, PR China Xi’an Rare Metal Materials Institute Co., Ltd, Xi’an, Shaanxi, 710016, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 28 August 2019 Received in revised form 22 October 2019 Accepted 7 November 2019 Available online xxx

In order to improve the mechanical properties of Ti materials, SiC nanowires (SiCNWs) as reinforcement phase were added into Ti matrix. The SiCNWs reinforced Ti matrix (SiCNWs/Ti) composites were prepared by spark plasma sintering method. The effect of SiCNWs content on the microstructure and mechanical properties of the composites was investigated. The average grain size of Ti matrix in the composites decreased significantly compared with that of pure Ti after introducing SiCNWs due to grain refinment strengthening effect. XRD and TEM analysis results reveal that SiCNWs were closely bound to Ti matrix, and no reaction production was formed between them in the composites, indicating that the structural integrity of SiCNWs in the composites was preserved after sintering. The ultimate tensile strength of SiCNWs/Ti composites increases at first and then decreases with an increase of weight fraction of SiCNWs. Compared with the pure Ti, the tensile strength of the SiCNWs/Ti composites containing 0.50 wt% SiCNWs increased by 52%. The excellent tensile strength of the SiCNWs/Ti composites was mainly attributed to the grain refinement of Ti matrix, bridging, pullout and breaking of the SiCNWs. © 2019 Elsevier B.V. All rights reserved.

Keywords: Ti matrix composites SiC nanowires Tensile strength Reinforcing mechanism

1. Introduction Ti and its alloy are widely used in airplane and automotive industries due to their high specific strength, excellent corrosion resistance and cryogenic properties. With the increasing demand for high specific strength of engineering materials, Ti and its alloy with high strength have received a lot of attention lately. In order to improve their mechanical properties, Ti matrix composites (TiMCs) containing reinforced phases with different size and shape, such as carbon nanotube [1e4], graphene [5e7], TiC [8], TiB2 [9,10] and SiC particles [11,12], were fabricated using different preparation methods. Recently, a large amount of studies have focused on the SiC particles reinforced TiMCs, especially on the microstructure evolution of interface between SiC particle and Ti matrix [13e16]. Nevertheless, there are some challenge in SiC particles reinforced TiMCs, including: (1) Mismatch in the coefficient of thermal expansion. The crack was generated firstly and then propagated at

* Corresponding author. E-mail addresses: [email protected], [email protected] (Y. Zhang).

the SiC/Ti interface due to the great difference of coefficient of thermal expansion (CTE) between SiC particles (CTE6 1 K ) and Ti matrix (CTETi ¼ 8.5  106 K1) [17], SiC ¼ 4.3  10 leading to the exfoliation of SiC particles; (2) Serious interfacial reaction between SiC and Ti matrix. The structure of SiC particle could be destroyed attributed to high chemical activity of Ti matrix during high sintering temperature process, limiting the enhancement of mechanical properties of the composites. However, as reported that this issues can be effectively assuage via reducing sintering temperature. SiCNWs have high aspect ratio, which were used as an ideal reinforced phase in ceramic matrix composites, polymer matrix composites and metal matrix composites due to their excellent elastic modulus (610e660 GPa) [18e20] and ultimate flexural strength (53.4e55 GPa) [21e23]. Recently, SiCNWs reinforced metal matrix composites prepared using hot-pressed method has been extensively investigated. For examples, Yang et al. [24] fabricated SiCNWs reinforced 6061Al matrix composites using pressure infiltration method, and found that the tensile strength and yield strength of SiCNWs/6061 Al matrix composites were increased by 15% and 8.2%, respectively. Zhang et al. [25] prepared SiCNWs reinforced AZ91D Mg matrix composites by liquid-solid extrusion

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following vacuum infiltration process. The results showed that the tensile strength of the SiCNWs/AZ91D Mg matrix composites was improved by 33% after introducing SiCNWs. These experimental results show that the mechanical properties of SiCNWs reinforced Al and Mg matrix composites were substantially improved compared with that of Al and Mg alloy [24,26e29]. However, there is rarely reported Ti matrix composites reinforced with SiCNWs attributed to severe interface reaction between SiCNWs and Ti matrix in the preparation process, leading to the loss of structural integrity of SiCNWs. Aiming at further improve the mechanical properties of Ti materials, SiCNWs prepared by sol-gel carbothermal reduction were introduced into Ti matrix in this work. The SiCNWs reinforced Ti matrix (SiCNWs/Ti) composites was fabricated using spark plasma sintering (SPS) technique. The mechanical properties of SiCNWs/Ti composites were investigated, and the mechanism of SiCNWs on the mechanical properties of the composites was discussed. Fig. 1. The schematic diagram of preparation process of SiCNWs/Ti composites.

2. Experimental 2.1. Materials preparation The SiCNWs with a diameter of 100e200 nm and a length of 5e30 mm were prepared by sol-gel carbothermic reduction method. SiCNWs were removed from the surface of carbon materials by mechanical exfoliation and ultrasonic oscillation. The detailed fabrication process of SiCNWs was described in our previous study [30]. Spherical Ti powders (Sino-Euro Materials Technologies of Xi’an Co., Ltd.) with diameters of 15e60 mm were used as raw materials. Table 1 displays the characteristics of Ti powders. Fig. 1 shows the preparation process of SiCNWs/Ti composites. Firstly, SiCNWs were added to an ethanol solution, and subsequently sonicated by an ultrasonic homogenizer for 2 h. Then titanium powders were added into the SiCNWs suspension. The powders were mixed using mechanical stirrer with a rotation rate of 200 rpm for 12 h. So the SiCNWs can be retained completely in the preparation process. The dried mixtures were pour into molybdenum alloy die with internal diameter of 50 mm and sintered using SPS system (Sojitz Machinery Corporation, Tokyo, Japan) at 700  C for 5 min. The applied holding compressive pressure and vacuum are adjusted to 120 MPa and 5.0  102 Pa, respectively. The mass fraction of SiCNWs in composites were about 0.25 wt%, 0.50 wt%, 0.75 wt%, 1.00 wt%. Hereafter, they were marked as Ti0.25SiCNWs, Ti-0.50SiCNWs, Ti-0.75SiCNWs, Ti-1.00SiCNWs. For comparison, pure titanium without SiCNWs were fabricated at the same process. 2.2. Characterizations The tensile properties of the composites were investigated using Intron 5848 Microtester at room temperature with stretching rate of 1 mm/min. The tensile specimens with 4 mm in width and 2 mm in thickness were cut from the composites using electric discharge machining according to the GB/T228-2002. At least three samples were performed for each composites, and the final mechanical properties were obtained by the average values. The phase structure and compositions of as-sintered composites

were conducted using X-ray diffraction (XRD, X’Pert Pro MPD). The microstructure and fracture surface of the composites were characterized using field emission scanning electron microscopy (FESEM, ZEISS Supra 55) and high-resolution transmission electron microscopy (HRTEM, FEI Tecnai F30 G2) combined with energy dispersive spectroscopy (EDS). 3. Results and discussion 3.1. Microstructure observation Fig. 2 shows the SEM image and XRD pattern of SiCNWs. From Fig. 2(a), it can be seen that SiCNWs with long and straight shape were randomly oriented. Their diameter and length were about 100e300 nm and several tens of micrometers (inset of Fig. 2(a)). The white product in Fig. 2(a) was defined as 3C-SiC crystal (JCPDS Card no. 29e1129) based on XRD analysis results, as shown in Fig. 2(b). Furthermor, four major characteristic peaks located at 35.59 , 41.38 , 59.97, and 71.77 were observed, corresponding to the diffraction of (111), (200), (220) and (311) planes of 3C-SiC [21], respectively. The morphology of mixed powders is shown in Fig. 2(c). It displays that the regular spherical Ti powder with diameter of 15e60 mm have no aggregation. An carefully observation in Fig. 2(d) shows that the SiCNWs physically adsorbs on the surface of Ti powders. Fig. 3 presents the microstructure of the SiCNWs/Ti composites prepared by SPS process. Form Fig. 3(aee), it can be seen that the Ti matrix with strip-shaped alpha Ti grains has a homogeneous microstructure. Few pores and black spots (white arrow) located at grain boundary are observed on the surface of SiCNWs/Ti composites. Using SEM technique to further analysis these black spots, it found that they were SiCNWs at the grain boundary of Ti matrix (inset of Fig. 3(e)). After adding SiCNWs into Ti matrix, the grain size of the Ti matrix decreases with the increasing of SiCNWs content in the composites. The grain size of Ti matrix was estimated using quantitative metallography method. The average grain size of pure

Table 1 Characteristics of the Ti powders. Materials

Impurity element (wt%)

Pure Ti

Fe 0.09

C 0.005

N 0.005

O 0.071

H 0.0026

Ti Bal.

Density (g/cm3)

Diameter (mm)

4.50

15e60

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Fig. 2. (a) SEM image of SiCNWs; (b) XRD pattern of SiCNWs; (c) SEM image of mixed powders; (d) an enlarged view regions marked in Fig. 2(c).

Ti is approximately 160 mm. The average grain size of Ti0.25SiCNWs, Ti-0.50SiCNWs, Ti-0.75SiCNWs and Ti-1.00SiCNWs composites is about 65 mm, 51 mm, 43 mm and 39 mm, respectively. This suggests that the grain growth of Ti matrix could be effectively prevented due to the Zener pinning effect induced by SiCNWs. Fig. 3(f) shows the XRD spectra of the SiCNWs/Ti composites with 0.25 wt%, 0.50 wt%, 0.75 wt%, 1.00 wt% and without SiCNWs. It displays that only the diffraction peaks of SiC and Ti were detected in the Ti-1.00SiCNWs composites. But, no diffraction peaks of SiC were detected in the Ti-0.25SiCNWs and Ti-0.50SiCNWs composites owing to low content. No new diffraction peak of carbides and silicides was found, confirming that no reaction product was produced. Warren et al. have reported that carbides and silicides were easily formed through chemical reaction between Ti and SiC (Eq. (1)) when the sintering temperature exceeds 1000  C [31]. Although in-situ formed TiC with the state of dispersion distribution have an excellent strengthening effect on the Ti matrix [32], the chemical reaction will inevitably break the structural integrity of the SiC and thereby reduce their mechanical properties. The same conclusion was obtained in the SiC nanoparticle reinforced Ti matrix composites [33]. SiC þ Ti/TixSiy þ TiC

(1)

DG ¼ 218.89 þ 2.23  104T-2.47  106T2þ2.63  109T3 (500  C < T < 2000  C)

3.2. Interface analysis of SiCNWs/Ti composites TEM and HRTEM images of Ti-1.00SiCNWs composites prepared by SPS process are displayed in Fig. 4. From Fig. 4(a), it can be seen that the SiCNWs was located between two matrix grains. No defect was observed in the high magnification bright-field TEM image of SiCNWs/Ti interface (Fig. 4(b)). Fig. 4(c) shows the HRTEM image of SiCNWs/Ti interface corresponding to the local area of Fig. 4(b). It can be seen that no carbides and silicides was generated at the interface between SiCNWs and Ti matrix. And no pores and defects

was found at the SiCNW/Ti interface (Fig. 4(d)), which indicates that good interfacial bonding was obtained for SiCNWs/Ti composites prepared by SPS process. The embedded SiCNWs within Ti matrix were clearly visible in the HRTEM image. The crystal lattice fringe spacing is approximately 0.25 nm, which is consistent with the ideal crystal structure of SiC (111) plane. The structural characteristics of the SiCNWs/Ti composites corresponding to the selected area in Fig. 4(c) were clarified by their selected area electron diffraction (SAED) pattern in the nano-beam electron diffraction mode. Fig. 4(e) and (f) show the selected area electron diffraction (SAED) pattern corresponding to the local region of Fig. 4(a). The area “A” and “B” were Ti matrix and SiCNW confirmed by the corresponding SAED pattern, respectively. 3.3. Mechanical properties To evaluate the mechanical properties of SiCNWs/Ti composites, quasi-static tensile tests have been conducted. Fig. 5 shows the relationship among SiCNWs content, ultimate tensile strength (UTS) and yield strength (YS) of composites. Fig. 5(a) shows the engineering stress-strain curves of the composites with and without SiCNWs. The plots suggest that the weight fraction of SiCNWs has a significant influence on the tensile strength of the composites. The elongation of SiCNWs/Ti composites decreases with the increasing of weight fraction of SiCNWs. Their YS and UTS curve can be divided into two stages, as shown in Fig. 5(b). (1) Ascent stage. The YS and UTS of SiCNWs/Ti composites was continuously improved with the increasement of SiCNWs content. Compared with pure Ti, the YS and UTS of Ti-0.25SiCNWs composites was increased by 21% and 32%, respectively. When the SiCNWs content increased to 0.50 wt%, the YS and UTS of Ti0.50SiCNWs composites reached peak values of 665 ± 10 MPa and 726 ± 10 MPa, which is raised by 45% and 44%, respectively. (2) Descent stage. When the content of SiCNWs further increased to 0.75 wt%, the YS and UTS of the composites is 604 ± 10 MPa and 658 ± 15 MPa, respectively. Compared with Ti-0.50SiCNWs composites, the YS and UTS of the Ti-0.75SiCNWs composites is decreased by 9% and 10%, respectively. The same trend goes for the composites with the SiCNWs content of 1.00 wt% and the detailed

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Fig. 3. Microstructure and XRD pattern of SiCNWs/Ti composites with different SiCNWs content prepared by SPS process: (a) pure Ti; (b) 0.25 wt% SiCNWs; (c) 0.50 wt% SiCNWs; (d) 0.75 wt% SiCNWs; (e) 1.00 wt% SiCNWs; (f) XRD pattern.

data were concluded in Table 2. In order to investigate the mechanical properties of Ti matrix composites reinforced with different reinforcements, they were prepared by a variety of methods, such as hot pressing (HP), spark plasma sintering (SPS), powder metallurgy (PM) and casting. The interface between Ti matrix and reinforcement was strong due to interface reaction in high temperature sinterining process, leading to an improvement of mechanical properties. However, the addition of excess reinforcements resulted in a significant decrease in the tensile ductility. Fig. 5(c) compares the tensile properties reported for Ti matrix composites reinforced with different reinforcements. It can be seen obviously that the Ti-0.50SiCNWs composites with UTS of 726 ± 10 MPa is comparable to the reported values of Ti-X composites (X refer to reinforced phase) [34e36], and even highter than some results, while most of their elongations were insufficient (<10%). The superior ductility and tensile strength of the SiCNWs/Ti composites are attributed to characteristics and distribution of SiCNs in the Ti matrix composites. 3.4. Fracture morphology The fracture surfaces of the Ti matrix composites with different SiCNWs contents are shown in Fig. 6. The fracture surface of pure Ti

in Fig. 6(a) displays typical ductile fracture characteristics with a lot of dimples and tearing ridges. After introducing SiCNWs into pure Ti matrix, the SiCNWs/Ti composites exhibit a typical quasicleavage fracture surface. Compared with pure Ti, there is significant difference in the fracture surface of the SiCNWs/Ti composites. Fig. 6(b) shows the fracture morphology of Ti-0.25SiCNWs composites. The dimples and tearing ridges were observed in the SiCNWs/Ti composites. Their amount is highest among the SiCNWs/Ti composites, implying better plastic behavior and high bearing capacity. With increment of SiCNWs content, the facture surface of the SiCNWs/Ti composites were mainly characterized by fold structure decorated with lots of dimples and tearing ridges (as shown in Fig. 6(cee)). From Fig. 6(c) and (d), it can be seen that the pull-out SiCNWs with intact structure were distributed in Ti matrix. Some micro-voids and cracks were generated around the SiCNWs on the fracture surface, and the cracks grow along tension direction. A bridge fabricated by SiCNW was formed between two grain boundary, which is beneficial to prevent crack propagation, resulting in improvement of mechanical properties of SiCNWs/Ti composites. The fractured SiCNWs was observed in the dimple (inset of Fig. 6(e)), indicating excellent interface bonding between SiCNW and Ti matrix. When the SiCNWs content in the composites increased to 1.00 wt%, large SiCNWs-rich areas and cracks were

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Fig. 4. TEM and HRTEM images of Ti-1.00SiCNWs composites: (a) TEM image of SiCNWs/Ti composites; (b) a magnified image of the area inside Fig. 4 (a); (c) HRTEM image of SiCNWs located between two matrix grains; (d) the interface between SiCNW and Ti grain; (e) SAED pattern of area “A” in Fig. 4 (a); (f) SAED pattern of area “B” in Fig. 4 (b).

found in the fractrue surface (Fig. 6(f)). In SiCNWs-rich area, the aggregation of SiCNWs would bring about weak-bonding between SiCNWs and Ti matrix. The cracks were easily formed around SiCNWs due to the large difference in CTE between SiCNWs and Ti matrix, leading to the substantial reduction of elongation of the SiCNWs/Ti composites. 3.5. Strengthening mechanism From the viewpoint of the reinforcing mechanism of the short

fibers or whisker reinforced metal matrix composites, the microstructure and mechanical properties of the composites have a close relationship with the geometry, distribution characteristic and physical performance of the reinforcement in metal matrix. For SiCNWs/Ti composites, the grain growth of Ti matrix was resisted by the uniform distribution of SiCNWs during sintering process. The grain size of the Ti matrix in the SiCNWs/Ti composites is smaller than that of pure Ti. Thus, the grain refinment strengthening mechanism of Ti matrix by Zener pinning effect should be considerated. During the mechanics test, when the SiCNWs/Ti

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Fig. 5. (a) The engineering stress-strain curves and (b) corresponding mechanical properties of the SiCNWs/Ti composites; (c) tensile strength of Ti matrix composites reinfroced with different ceramics.

Table 2 Tensile properties of SiCNWs/Ti composites.

sc ¼ ðsm þ DsGS Þ½Vs ðg þ 4Þ = 4 þ ð1  Vs Þ

Content (%)

YS (MPa)

UTS (MPa)

Elongation (%)

Average grain size (mm)

0 0.25 0.50 0.75 1.00

459 ± 12 556 ± 10 665 ± 15 604 ± 10 552 ± 9

504 ± 18 668 ± 12 726 ± 10 658 ± 15 609 ± 16

20 ± 3 12 ± 2 7.5 ± 2 5±2 3±1

160 65 51 43 39



DsGS ¼ k d0:5  d0:5 S 0



where sm is the yield strength of Ti matrix, DsGS is the grain refinment strengthening effect, Vs is the volume fraction of SiCNW, g is the aspect ratio of the SiCNW.

sm ¼ s0 þ kd0:5 s

composites was loaded, the load was transferred from Ti matrix to SiCNWs. So the load-bearing transfer is another strengthening mechansim for SiCNWs/Ti composites. The strength improved by grain refinment strengthening effect (DsGS ) can be calculated accroding to Hall-Petch relationship [37,38]:

(2)

where k is the Hall-Petch coefficient (k ¼ 0.68 MPa m1/2 [39]), dS and d0 are the average grain sizes of SiCNWs/Ti composites and pure Ti, respectively. The grain refinment strengthening effect (DsGS ) were calculated using Eq. (2), Fig. 7(a) displays the relationship between grain refinment strengthening effect (DsGS ) and the weight fraction of SiCNWs. In order to evaluate the contribution of these two strengthening mechansim for the mechanical properties of the SiCNWs/Ti composites, the mixture model developed by Prewo and Nardone was used to explain the strengthering mechanism [40,41]. Thus, the yield strength (sc ) of the SiCNWs/Ti composites can be estimated by the modified model:

(3)

(4)

here, s0 is the friction stress (defined as 450 MPa [42]), k is HallPetch coefficient, ds is the average grain size of the Ti matrix. The combination of Eqs. (3) and (4) gives the yield strength (sc ) of the SiCNWs/Ti composites:





sc ¼ s0 þ kd0:5 þ DsGS ½Vs ðg þ 4Þ = 4 þ ð1  Vs Þ s

(5)

Eq. (5) reveals that the yield strength (sc ) has a close relationship with dS, VS and g. The yield strength (sc ) of the SiCNWs/Ti composites increases with the decresement of the average grain size. The aspect ratio of the SiCNW (g) was also change with the increasement of volume fraction of SiCNW (VS) duet to the aggregation effect. In order to facilitate the calculation of the yield strength (sc ) of the SiCNWs/Ti composites, we assume that the aspect ratio of the SiCNW (g) was not change with the increasement of weight fraction of SiCNWs. According to the average radius and length of SiCNWs used in this experiment, the ideal aspect ratio of the SiCNWs with a sequential arrangement in space is approximately 300. In fact, the SiCNWs were randomly oriented in the SiCNWs/Ti composites and got together in a local area (Fig. 6(f)). By using the Hong’s method [43], the calculated aspect ratio (g) of SiCNW was obtained, which is about 150. So the calculated yield strength (sc ) of the SiCNWs/Ti composites can be obtained accroding to Eq. (5). Fig. 7(b) shows the calculated and experimental yield strength (sc ) of the SiCNWs/Ti composites. It clearly

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Fig. 6. Representative fracture surface of SiCNWs/Ti composite with different content: (a) pure Ti; (b) 0.25%; (c) 0.50%; (d) 0.75%; (e) 1.00%, (f) aggregation of SiCNWs (enlarged view regions marked in Fig. 6(e)).

reveals that the theoretical yield strength of the SiCNWs/Ti composites increases in pretty much a straight line with an increase in the weight fraction of SiCNWs. By comparison, the experimental yield strength (sc ) of the SiCNWs/Ti composites presents a different trend, which first rises up to 665 MPa at 0.50 wt% SiCNWs and then drops with the further increase of the weight fraction of SiCNWs. It is the result from the aggregation effect of SiCNWs in the composites containing high weight fraction of SiCNWs. Moreover, the aggregation effect of SiCNWs will result in the decrement of effective aspect ratio of SiCNWs. Consequently, the yield strength of the SiCNWs/Ti composite increases firstly and then decrease with increasing of SiCNWs content. The real aspect ratio of SiCNWs in the composites could be calculated by using Eq. (5). The calculation results are shown in Fig. 7(c). The calculated aspect ratio of Ti-0.25SiCNWs and Ti0.50SiCNWs composites is close to the initial effective aspect ratio of SiCNWs (150). But the real aspect ratio of SiCNWs decreases significantly when the SiCNWs content exceed 0.50 wt% in the SiCNWs/Ti composites, revealing that severe aggregation of SiCNWs was generated in the Ti-0.75SiCNWs and Ti-1.00SiCNWs composites, lead to the decrement of the 0.2%YS of the SiCNWs/Ti composite. Hence, the yield strength of the SiCNWs/Ti composite

increases firstly and then decrease with increasing of SiCNWs content under the interaction effects of average grain size of Ti matrix, weight fraction and aspect ratio of SiCNWs. To investigate the strengthening mechanism of SiCNWs/Ti matrix composites, the fracture surface of the composites after tensile tests were analysed using HRSEM. The microcracks were found on the fracture surface of the SiCNWs/Ti composites. Clearly observation in Fig. 8(a) shows that the microcrack was bridged by SiCNWs between two grain boundary. The SiCNWs bridging behavior could prevent the broadening of the crack, which are contributed to the improvement of 0.2%YS of the SiCNWs/Ti composites. The direction of crack propagation was changed from the initial orientation to another orientation when it encountered SiCNWs in the composites (Fig. 8(b)), which would consume considerable energy by increasing the path of crack propagation. As a result, the propagating path of the microcracks with zigzag pattern was gengered in the composites. Further analysis found that the inflection point of the microcrack is near the SiCNWs bridging, leading to the enhancement of mechanical properties of the SiCNWs/Ti composites. The pull-out or debongding SiCNWs can be observed in fracture surface of the SiCNWs/Ti composites, as shown in Fig. 8(c). The other end of the SiCNW was deeply

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Fig. 7. (a) Grain refinment strengthening effect; (b) The experimental and calculation YS of the SiCNWs/Ti composites; (c) The aspect ratio of SiCNWs in the SiCNWs/Ti composites.

Fig. 8. SEM images of SiCNWs/Ti composites after tensile test: (a) Microcrack bridging by the SiCNWs between two grain boundary; (b) Microcrack deflection near the SiCNWs on the fracture surface; (c) SiCNWs pull-out feature; (d) Fractured SiCNWs.

embedded in the Ti matrix. Elemental analysis of the SiCNWs by EDS (inset of Fig. 8(c)) reveals that the SiCNW was covered by a layer Ti alloy, which was pulled out from Ti matrix during tensile test, indicating excellent interface bonding between SiCNW and Ti matrix. When both ends of SiCNWs were deeply inserted in Ti matrix, the SiCNWs/Ti interfacial bond strength is high, they could

not pulled out from Ti matrix, resulting in fracture of SiCNWs during tensile test, as shown in Fig. 8(d). Thus, it can be inferred that the SiCNWs could hinder the microcrak propagation and change the path of the microcrack growth in the composites, leading to the improvement of the mechanical properties of the composites. The strengthening mechanism of SiCNWs/Ti

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composites can be attributed to the combination of the grain refinement of Ti matrix, bridging effect, pullout and breaking of the SiCNWs. For short fibers or whiskers reinforced metal matrix composites, when they were loaded, the applied force can be transferred from metal matrix to the fibers or whiskers by interface shear stress, which developed along the interface between metal matrix and fibers or whiskers. So, the length of the fibers or whiskers is a critical parameter for interface stress transfer. The critical length (lc ) of SiCNW can be defined as [42]:

lc ¼ ss ,ds =sm

(6)

where ss is UTS of the SiCNW, ds is the average diameter of the SiCNW, sm is the strength of Ti matrix. In this work, the ss , ds and sm of the 0.5 wt% SiCNWs/Ti composite are set as 50 GPa [44,45], 100 nm and 592 MPa, respectively. So, the critical length (lc ) of SiCNW is approximately 8.5 mm, which is in the range of the length of SiCNW (5e20 mm). If the length of SiCNW (lSiCNW) is less than the critical length (lc ) of SiCNW, i. e. lSiCNW
4. Conclusions SiCNWs/Ti composites with uniform distribution of SiCNWs was successfully prepared by SPS process. The effect of SiCNWs contents on the microstructure and mechanical properties of the composites was investigated. The grain size of Ti matrix was effectively refined owing to the introduction of the SiCNWs. The tensile strength of SiCNWs/Ti composites increases at first and then decreases with an increase of weight fraction of SiCNWs, which is closely related with effective aspect ratio of SiCNWs. The optimal concentration of SiCNWs reinforcements in Ti matrix is 0.5 wt%, in which exhibit excellent tensile strength (726 ± 10 MPa), increased by 52% compared with pure Ti. SiCNWs/Ti interfaces indicated that no obvious reaction product was formed between SiCNWs and Ti matrix after sintering, and the structure of SiCNWs was retained in the composites. The strengthening mechanism of SiCNWs/Ti composites can be attributed to the combination of the grain refinement of Ti matrix, bridging effect, pullout and breaking of the SiCNWs.

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.

Acknowledgements This work was supported by the National Security Major Basic Research Plan of China and the funded by Northwest Institute for Nonferrous Metal Research (K1652-1, K1652-12, K1740), National Natural Science Foundation of China (Grant No. U1737108), the Natural Science Basic Research Plan in ShaanXi Province of China (2017ZDJC-19), Innovation Team in Key Areas of Shaanxi Province (2016KCT-30), Key Research and Development Projects of Shaanxi Province (No. 2019GY-164), and Science and Technology Project of Weiyang District of Xi’an City (2018057).

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References [1] K.S. Munir, Y. Li, D. Liang, M. Qian, W. Xu, C. Wen, Effect of dispersion method on the deterioration, interfacial interactions and re-agglomeration of carbon nanotubes in titanium metal matrix composites, Mater. Des. 88 (2015) 138e148. [2] A.O. Adegbenjo, P.A. Olubambi, J.H. Potgieter, M.B. Shongwe, M. Ramakokovhu, Spark plasma sintering of graphitized multi-walled carbon nanotube reinforced Ti6Al4V, Mater. Des. 128 (2017) 119e129. [3] G. Fan, Y. Jiang, Z. Tan, Q. Guo, D.-b. Xiong, Y. Su, R. Lin, L. Hu, Z. Li, D. Zhang, Enhanced interfacial bonding and mechanical properties in CNT/Al composites fabricated by flake powder metallurgy, Carbon 130 (2018) 333e339. [4] B. Chen, J. Shen, X. Ye, H. Imai, J. Umeda, M. Takahashi, K. Kondoh, Solid-state interfacial reaction and load transfer efficiency in carbon nanotubes (CNTs)reinforced aluminum matrix composites, Carbon 114 (2017) 198e208. [5] X. Mu, H. Cai, H. Zhang, Q. Fan, Z. Zhang, Y. Wu, Y. Ge, D. Wang, Interface evolution and superior tensile properties of multi-layer graphene reinforced pure Ti matrix composite, Mater. Des. 140 (2018) 431e441. [6] Y. Jiang, X. Fan, X. Xiao, T. Qin, L. Zhang, F. Jiang, M. Li, S. Li, H. Ge, L. Chen, Novel AgPd hollow spheres anchored on graphene as an efficient catalyst for dehydrogenation of formic acid at room temperature, J. Mater. Chem. 4 (2016) 657e666. [7] M. Li, X. Xiao, Y. Liu, W. Zhang, Y. Zhang, L. Chen, Ternary perovskite cobalt titanate/graphene composite material as long-term cyclic anode for lithiumion battery, J. Alloy. Comp. 700 (2017) 54e60. [8] M.D. Hayat, H. Singh, Z. He, P. Cao, Titanium metal matrix composites: an overview, Compos. Appl. Sci. Manuf. 121 (2019) 418e438. [9] L. Huang, L. Geng, H. Peng, Microstructurally inhomogeneous composites: is a homogeneous reinforcement distribution optimal? Prog. Mater. Sci. 71 (2015) 93e168. [10] L.J. Huang, L. Geng, H. Peng, J. Zhang, Room temperature tensile fracture characteristics of in situ TiBw/Ti6Al4V composites with a quasi-continuous network architecture, Scr. Mater. 64 (2011) 844e847. [11] G. Sivakumar, V. Ananthi, S. Ramanathan, Production and mechanical properties of nano SiC particle reinforced Tie6Ale4V matrix composite, Trans. Nonferrous Metals Soc. China 27 (2017) 82e90. [12] E. Lacoste, C. Arvieu, J.-M. Quenisset, Correlation between microstructures of SiC-reinforced titanium matrix composite and liquid route processing parameters, J. Mater. Sci. 50 (2015) 5583e5592. [13] T. Ye, Y. Xu, J. Ren, Effects of SiC particle size on mechanical properties of SiC particle reinforced aluminum metal matrix composite, Mater. Sci. Eng. A 753 (2019) 146e155. [14] J. Shang, L. Ke, F. Liu, F. Lv, L. Xing, Aging behavior of nano SiC particles reinforced AZ91D composite fabricated via friction stir processing, J. Alloy. Comp. 797 (2019) 1240e1248. [15] X. Tang, L. Meng, J. Zhan, W. Jian, W. Li, X. Yao, Y. Han, Strengthening effects of encapsulating graphene in SiC particle-reinforced Al-matrix composites, Comput. Mater. Sci. 153 (2018) 275e281. [16] G. Tosun, M. Kurt, The Porosity, Microstructure, and Hardness of Al-Mg Composites Reinforced with Micro Particle SiC/Al2O3 Produced Using Powder Metallurgy, Composites Part B: Engineering, 2019, p. 106965. [17] L. Yue, Q. Fu, B. Wang, T. Liu, S. Jia, The ablation behavior and mechanical property of C/C-SiC-ZrB 2 composites fabricated by reactive melt infiltration, Ceram. Int. 43 (2017) 6138e6147. [18] Z.L. Wang, Z. Dai, R.P. Gao, Z. Bai, J.L. Gole, Side-by-side silicon carbideesilica biaxial nanowires: synthesis, structure, and mechanical properties, Appl. Phys. Lett. 77 (2000) 3349e3351. [19] C. Tang, S. Fan, H. Dang, J. Zhao, C. Zhang, P. Li, Q. Gu, Growth of SiC nanorods prepared by carbon nanotubes-confined reaction, J. Cryst. Growth 210 (2000) 595e599. [20] H. Lin, H. Li, T. Wang, Q. Shen, X. Shi, T. Feng, Influence of temperature and oxygen on the growth of large-scale SiC nanowires, CrystEngComm (2019) 21. [21] J. Huang, Z. Lei, L. Cao, H. Ouyang, H. Wei, C. Li, F. Jie, Effect of the incorporation of SiC nanowire on mullite/SiC protective coating for carbon/carbon composites, Corros. Sci. 107 (2016) 85e95. [22] Y. Zhang, B. Yang, P. Zhang, J. Zhang, J. Ren, Z. Hu, SiC nanowire toughened ZrB2-SiC ablative coating for SiC coated C/C composites, Ceram. Int. 41 (2015). S027288421501487X. [23] L. Su, H. Wang, M. Niu, X. Fan, M. Ma, Z. Shi, S.-W. Guo, Ultralight, recoverable, and high-temperature-resistant SiC nanowire aerogel, ACS Nano 68 (2018) acsnano.7b08577. [24] W. Yang, G. Chen, J. Qiao, Q. Zhang, R. Dong, G. Wu, Effect of Mg addition on the microstructure and mechanical properties of SiC nanowires reinforced 6061Al matrix composite, Mater. Sci. Eng. A 689 (2017) 189e194. [25] T. Zhang, L. Qi, J. Fu, J. Zhou, X. Chao, Effect of SiC nanowires addition on the interfacial microstructure and mechanical properties of the Cf-SiCNWs/AZ91D composite, J. Alloy. Comp. 776 (2019) 746e756. [26] R. Dong, W. Yang, P. Wu, M. Hussain, G. Wu, L. Jiang, High content SiC nanowires reinforced Al composite with high strength and plasticity, Mater. Sci. Eng. A 630 (2015) 8e12. [27] W. Yang, R. Dong, Z. Yu, P. Wu, M. Hussain, G. Wu, Strengthening behavior in high content SiC nanowires reinforced Al composite, Mater. Sci. Eng. A 648 (2015) 41e46. [28] R. Dong, W. Yang, Z. Yu, P. Wu, M. Hussain, L. Jiang, G. Wu, Aging behavior of

Please cite this article as: Y. Liu et al., Microstructure and mechanical properties of SiC nanowires reinforced titanium matrix composites, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152953

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[29]

[30]

[31] [32]

[33]

[34]

[35] [36]

[37]

Y. Liu et al. / Journal of Alloys and Compounds xxx (xxxx) xxx 6061Al matrix composite reinforced with high content SiC nanowires, J. Alloy. Comp. 649 (2015) 1037e1042. L. Xin, W. Yang, Q. Zhao, R. Dong, X. Liang, Z. Xiu, M. Hussain, G. Wu, Effect of extrusion treatment on the microstructure and mechanical behavior of SiC nanowires reinforced Al matrix composites, Mater. Sci. Eng. A 682 (2017) 38e44. L. Yue, Q. Fu, H. Lin, B. Wang, L. Lu, Synthesis and characterisation of selfassembled SiC nanowires and nanoribbons by using solegel carbothermal reduction, Adv. Appl. Ceram. (2017) 1e7. R. Warren, C.-H. Andersson, Silicon carbide fibres and their potential for use in composite materials. Part II, Composites 15 (1984) 101e111. X. Zhang, F. Song, Z. Wei, W. Yang, Z. Dai, Microstructural and mechanical characterization of in-situ TiC/Ti titanium matrix composites fabricated by graphene/Ti sintering reaction, Mater. Sci. Eng. A 705 (2017) 153e159. W. Yu, S. Sing, C. Chua, C. Kuo, X. Tian, Particle-reinforced metal matrix nanocomposites fabricated by selective laser melting: a state of the art review, Prog. Mater. Sci. 104 (2019) 330e379. Y. Zhang, Z. Wei, L. Shi, X.I. Mingzhe, Characterization of laser powder deposited Ti-TiC composites and functional gradient materials, J. Mater. Process. Technol. 206 (2008) 438e444. Y. Jiao, L. Huang, L. Geng, Progress on discontinuously reinforced titanium matrix composites, J. Alloy. Comp. 767 (2018) 1196e1215. I. Akin, O. Kaya, Microstructures and properties of silicon carbide- and graphene nanoplatelet-reinforced titanium diboride composites, J. Alloy. Comp. 729 (2017) 949e959. X.N. Mu, H.N. Cai, H.M. Zhang, Q.B. Fan, F.C. Wang, Z.H. Zhang, Y.X. Ge, R. Shi, Y. Wu, Z. Wang, D.D. Wang, S. Chang, Uniform dispersion and interface analysis of nickel coated graphene nanoflakes/pure titanium matrix composites, Carbon 137 (2018) 146e155.

[38] 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. [39] X.N. Mu, H.M. Zhang, H.N. Cai, Q.B. Fan, Z.H. Zhang, Y. Wu, Z.J. Fu, D.H. Yu, Microstructure evolution and superior tensile properties of low content graphene nanoplatelets reinforced pure Ti matrix composites, Mater. Sci. Eng. A 687 (2017) 164e174. [40] V.C. Nardone, K.M. Prewo, On the strength of discontinuous silicon carbide reinforced aluminum composites, Scr. Metall. 20 (1986) 43e48. [41] W.J. Kim, S.H. Lee, High-temperature deformation behavior of carbon nanotube (CNT)-reinforced aluminum composites and prediction of their hightemperature strength, Composites Part A Applied Science & Manufacturing 67 (2014) 308e315. [42] F.C. Wang, Z.H. Zhang, Y.J. Sun, Y. Liu, Z.-Y. Hu, H. Wang, A.V. Korznikov, E. Korznikova, Z.-F. Liu, S. Osamu, Rapid and low temperature spark plasma sintering synthesis of novel carbon nanotube reinforced titanium matrix composites, Carbon 95 (2015) 396e407. [43] S.H. Hong, K.H. Chung, C.H. Lee, Effects of hot extrusion parameters on the tensile properties and microstructures of SiCw-2124Al composites, Mater. Sci. Eng. A 206 (1996) 225e232. [44] J. Prakash, R. Venugopalan, B.M. Tripathi, S.K. Ghosh, J.K. Chakravartty, A.K. Tyagi, Chemistry of one dimensional silicon carbide materials: principle, production, application and future prospects, Prog. Solid State Chem. 43 (2015) 98e122. [45] E.W. Wong, P.E. Sheehan, C.M. Lieber, Nanobeam mechanics: elasticity, strength, and toughness of nanorods and nanotubes, Science 277 (1997) 1971e1975.

Please cite this article as: Y. Liu et al., Microstructure and mechanical properties of SiC nanowires reinforced titanium matrix composites, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152953