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Graphene nanoflakes reinforced Al-20Si matrix composites prepared by pressure infiltration method
Author’s Accepted Manuscript Graphene nanoflakes reinforced Al-20Si matrix composites prepared by pressure infiltration method Wenshu Yang, Guoqin Chen, Jing Qiao, Shufeng Liu, Rui Xiao, Ronghua Dong, Murid Hussain, Gaohui Wu www.elsevier.com/locate/msea
PII: DOI: Reference:
S0921-5093(17)30790-6 http://dx.doi.org/10.1016/j.msea.2017.06.027 MSA35165
To appear in: Materials Science & Engineering A Received date: 28 December 2016 Revised date: 5 June 2017 Accepted date: 7 June 2017 Cite this article as: Wenshu Yang, Guoqin Chen, Jing Qiao, Shufeng Liu, Rui Xiao, Ronghua Dong, Murid Hussain and Gaohui Wu, Graphene nanoflakes reinforced Al-20Si matrix composites prepared by pressure infiltration method, Materials Science & Engineering A, http://dx.doi.org/10.1016/j.msea.2017.06.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Graphene nanoflakes reinforced Al-20Si matrix composites prepared by pressure infiltration method
Wenshu Yanga*, Guoqin Chena, Jing Qiaoa, Shufeng Liub, Rui Xiaoc, Ronghua Dongd, Murid Hussaine, Gaohui Wua* a. Department of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, China. b. Beijing Institute of Electronic System Engineering, Beijing, 100854, China c. The 14th Research Institute of China Electronic Technology Group Corporation, Nanjing 210000, China; d. Beijing Institute of Aerospace Control Devices, Beijing 100039, China e. Department of Chemical Engineering, COMSATS Institute of Information Technology, M.A. Jinnah Building, Defence Road, Off Raiwind Road, Lahore-54000, Pakistan.
*Corresponding author: Dr. Wenshu Yang and Prof. Gaohui Wu P. O. 3023, Science park, No. 2 Yikuang street, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150080, P. R. China Tel: +86-451-86402373-5051; Fax: +86 451 86412164 E-mail: [email protected] and [email protected] 1 / 28
Abstract:
It has not been reported in the existed literatures that whether it is possible
to prepare GNFs/Al composites by pressure infiltration method due to the poor wettability and severe reaction behavior between carbon and molten Al. In the present study, microstructure and mechanical behavior of graphene nanoflakes (GNFs) reinforced Al-20Si (GNFs/Al-20Si) composites prepared by the pressure infiltration method have been thoroughly investigated. The Al-20Si matrix was chosen to inhibit the formation of Al4C3. It has found that the GNFs and Al alloy matrix has been well bonded without formation of Al4C3, which authenticated the effectiveness of the alloying treatment. Moreover, the hardness and the elastic modulus of the composites were increased linearly with the increase in the GNFs content. After addition of 1.5 wt.% GNFs, the ultimate tensile strength and bending strength attained the peak values, which increased 130% and 230% to that of Al matrix, respectively. To the best of our knowledge, it is the highest strengthening ratio in Al matrix composites reinforced with graphene reinforcements. Furthermore, based on the modified shear-lag model and combined with the literatures’ data, the strengthening behavior of GNFs/Al composites has been extensively discussed. It is concluded that the pressure infiltration method is the most feasible and successful way to prepare GNFs/Al composites without formation of Al4C3 and with high strengthening ratio. Keywords: Al matrix composites; Graphene; Pressure infiltration method; Si element; Strengthening mechanism;
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1. Introduction Graphene demonstrates high elastic modulus (higher than 1000 GPa [1]), high fracture strength (more than 130 GPa [1]), and extremely high thermal conductivity (about 5300 W/(m·K) [2]), which is much higher than the other reported materials such as SiC ceramic phase [3, 4], C fibres [5] and carbon nanotubes [6]. Therefore, graphene has been considered as an ideal reinforcement for composites. It has been generally found that the addition of graphene nanoflakes (GNFs), which possesses similar properties of single-layer graphene but easier to be produced and handled, could significantly improve the mechanical properties of polymers [7, 8] and ceramics [9, 10]. The effect of graphene or GNFs on the microstructure and performance of Al matrix composites have not been fully understood yet, while the present investigation of the graphene/Al composites is mainly focused on the optimization of the preparation method and parameters. Bartolucci et al. [11] found that the formation of aluminum carbide (Al4C3) was detrimental for the mechanical properties of graphene/pure Al composite prepared by hot isostatic pressing and extrusion technique. Wang et al. [12] and Rashad et al. [13] found that the mechanical properties of Al matrix composites could be significantly improved by the addition of GNFs. Bastwros et al. [14] revealed that the agglomeration of graphene is detrimental to the mechanical performance of the GNFs/Al composite. Yan et al. [15] also observed that the tensile strength and elongation of the GNFs/Al composites could be improved by the GNFs incorporation. S. E. Shin et al. [16, 17] firstly revealed that the higher strengthening efficiency of few-layer graphene than multi-walled carbon nanotube could be mainly attributed to their larger specific surface. Furthermore, S. E. Shin et al. [17] also found that the 3 / 28
mechanical properties of graphene and multi-walled carbon nanotube reinforced Al or Ti composites were agreed well with the modified Rule of Mixture after introducing the geometry factor, interfacial bonding factor, and alignment factor. Latief et al. [18] found that the high amount GNFs (up to 5wt. %) could also been introduced into the composites with improved hardness and compressive strength. Gao et al. [19] found that graphene oxide (GO) sheets could also been used as reinforcement. Zhang et al. [20] revealed that the presence of Al4C3 could act as a strengthening phase in the GNFs/5083Al composite material. The investigation of graphene/Al composites is still at the embryonic stage, and most of the researches are mainly focusing on the optimization of the preparation methods and corresponding parameters. The key techniques reported in the literatures to prepare graphene/Al composites are solid methods such as hot pressing [11, 12, 15, 18-20], semi-powder method [13, 14], and hot-rolling method [16, 17]. However, pressure infiltration method, which has been widely used for the preparation of Al matrix composites, has not been reported yet for the preparation of graphene/Al composites. It has not been responded that whether it is possible to prepare GNFs/Al composites by pressure infiltration method due to the poor wettability and severe reaction behavior between carbon and molten Al. The microstructure and mechanical behavior of the GNFs/Al composites prepared by the pressure infiltration method has not been explored yet. In the present study, the microstructure and mechanical behavior of graphene nanoflakes (GNFs) reinforced Al-20Si (GNFs/Al-20Si) composites prepared by the pressure infiltration method have been investigated. The Al-20Si matrix was used with the aim to inhibit the formation of Al4C3, which would be discussed in 4 / 28
detail in the following paragraph. The effect of the GNFs on the microstructure and the mechanical properties of the GNFs/Al-20Si composites have also been investigated. Moreover, comparing with the data from literatures, the strengthening behavior of the GNFs/Al-20Si composites has been discussed as well. 2. Material and methods Graphene oxides were firstly synthesized by Hummer's method and then chemically reduced to GNFs, as shown in Fig.1a and b. The Al-20Si powders with average diameter of 10 μm (as shown in Fig.1c) and the alloy were supplied by Northeast Light Alloy Co., Ltd. China. The flow chart of the present work is given in Fig.2. The GNFs were firstly mixed with Al-20Si powders using a planetary mill at a rotation speed of 300 rpm for 3 h. The mixture was subsequently pre-densified to prepare a preform in a steel mold. The mold with the preform was then heated at 500 ºC, while the Al-20Si alloy was melted at 770 ºC. Afterwards, the molten Al was poured into the mold and then infiltrated into the preform under pressure of 5 MPa for 10 min. After the solidification of the composites in air, the GNFs/Al-20Si composites with GNFs content of 0.5, 1.5, 2.5 and 3.5 wt.% were obtained. For comparison, the Al-20Si specimens were also prepared by the same process. After that, all the samples were annealed at 400 ºC for 2 h. Microstructure of the GNFs/Al-20Si composites specimens were observed by FEI Sirion Quanta 200 scanning electron microscope (SEM) and JEM-2010F transmission electron microscopy (TEM). X-ray diffraction (XRD) analysis was carried out on Rigaku D/max-rB diffractometer to identify the main phases and to reveal the potential reaction in the GNFs/Al-20Si composites. The specimens were subjected to Cu-Kα 5 / 28
radiation (0.15418 nm) with a scanning speed of 2◦/min between the scan range of 15◦ and 90◦. Elastic modulus, tensile and bending tests were performed to characterize the strengthening effect of the GNFs. Samples with dimensions of 3×4×36 mm were machined for elastic modulus and bending tests. The dimensions of tensile tests have been reported in our recently work [21]. Elastic modulus was evaluated by an impulse excitation technique according to ASTM E1876-09 on EMT-01 instrument (Zhuosheng Instrument Co., Ltd. China). Three-point bending tests with 30 mm span and tensile tests were performed on Instron 5569 universal electrical tensile testing machine with a cross-head speed of 0.5 mm/min, and five samples were tested to improve the statistical significance of the results. In order to characterize the effect of GNFs on the fracture behavior, the fracture surface of GNFs/Al-20Si composites was observed by FEI Sirion Quanta 200 SEM. 3. Results and discussion Morphology of the GNFs/Al-20Si composites has been shown in Fig.3. It is clear that the dimension of the primary Si in Al matrix were significantly refined after the addition of GNFs (Fig.3). Moreover, few pores were found in the Al-20Si matrix (as pointed out by arrows in Fig.3a) and the composites (as pointed bout by arrows in Fig.3b to e), which could be mainly due to the shrinkage behavior of Al-Si matrix during solidification [22]. The presence of the pores is detrimental to their mechanical properties. The size of primary Si was measured by Nano Measure 1.2 software. The size of primary Si (acicular sharp) in Al-20Si alloy was about 46 μm in length. However, after the addition of 0.5, 1.5, and 3.5 wt.% GNFs, the size of the primary Si was reduced to about 8.1 μm, 7.6 μm and 18.6 μm, respectively. It indicated that the size of the 6 / 28
primary Si was firstly decreased with the addition of low content GNFs and then was increased after addition of high content GNF. It has been widely found that the grain size of primary Si in Al-20Si matrix composites could be greatly refined by the introduction of the reinforcements [23, 24]. After addition of 35, 40 and 45 vol.% SiC particles, Ma et al. [24] found that the grain size of the primary Si was decreased from 72.5 μm to about 25.4, 12.4 and 11.2 μm, respectively, which could be mainly attributed to the heterogeneous nucleation of silicon. During solidification, the surface of uniformly distributed GNFs could provide more nucleation sites for the primary Si and inhibit the growth of the primary Si, Therefore, the grain size of primary Si has been greatly refined in the present work with the low content GNFs. However, the grains of primary Si in 3.5 wt.% GNFs/Al-20Si composites (Fig.3e) were coarsen than that of 1.5 wt.% composite (Fig.3c), implying the agglomeration of GNFs. The amount of the primary Si in the composites was constant. Therefore, more nucleation and slow growth of the primary Si leads to the refined size and vice versa. The uniformly distributed GNFs provide the nucleation sites for the primary Si. However, the agglomeration of GNFs at high content (3.5wt.%) leads to the less nucleation sites for the primary Si, which shows the way to the larger size of the primary Si. It has been found by Bastwros et al. [14] that agglomeration of graphene is detrimental to the mechanical performance of composite. XRD analysis (Fig.4) indicated that the main phases found in the composites were Al and Si [23, 24] in low content GNFs/Al-20Si composites, while weak peaks of C [13] were detected in 3.5 wt.% GNFs/Al-20Si composites, also indicating the agglomeration of GNFs at higher amount. However, no peak of Al4C3 was detected. TEM observation 7 / 28
of 3.5 wt.% GNFs/Al-20Si composites has been shown in Fig.5a, and only Si, Al, and wrinkled GNFs were found in the composites, and no trace of Al4C3 has been observed. Further, HRTEM observation (Fig.5b) has indicated that the GNFs and Al alloy matrix has been well bonded, which is beneficial for the strengthening effect of GNFs since transferring the stress by the interface is an important strengthening mechanism of graphene. Yolshina et al. [25] proposed a very simple and effective method (corrosion test) to detect the presence of Al4C3. After immersing the samples in NaCl solution for 6 h, the samples would be covered with white phase if there is Al4C3 in the composites, and our immersing tests further verified that no significant Al4C3 was formed in the composites (Fig.6). One of the main challenges using liquid infiltration methods to fabricate carbonaceous Al matrix composites is the formation of brittle Al4C3. Although it has been reported that Al4C3 could act as the dispersed precipitate to improve the mechanical strength of the GNFs/5083Al composites [20], it has been considered as the unfavorable phase in graphene/Al composites due to its brittle character [11, 15]. Moreover, Al4C3 would also deteriorate the corrosion resistance of the composites since it could be easily decomposed in moist environment [26]. The main challenge using liquid infiltration methods to fabricate carbonaceous Al matrix composites is the inhibitation of the formation of Al4C3 since the reaction of Al and C to form is usually very severe at temperature above the melting point of the Al alloy [27]. Our previous work regarding carbon fibre reinforced Al matrix composites indicates that the addition of alloying elements is a reliable method to inhibit the formation of Al4C3 [27, 28], while Si and Mg have been found to be the most effective inhibiting elements [29]. In 8 / 28
the present work, Al alloy with high Si content was chosen with the aim to inhibit the formation of Al4C3, and the microstructure observation verified the effectiveness of the alloying treatment, indicating that it is possible to prepare the GNFs/Al composite with controlled interfacial reaction by pressure infiltration method. The relationship of the amount of the GNFs and the relative density, hardness, and elastic modulus of the composites has been shown in Fig.7. Despite the relative density was decreased, the hardness and the elastic modulus were increased linearly with the increase of GNFs content. As shown in Fig.8, the tensile and bending strength of GNFs/Al-20Si composites attained the peak values after the addition of 1.5 wt.% GNFs, and were decreased with further addition of GNFs. Moreover, the elongation of composites was also higher than that of Al-20Si matrix alloy. It has been widely found that the mechanical strength of GNFs/Al composites is increased with the amount of GNFs, regardless of the preparation methods [15-20]. Yan et al. [15], Shin et al. [16, 17], and Li et al. [30] attributed the significant strengthening effect of GNFs to the large aspect ratio characteristic. Meanwhile, fine-precipitates strengthening has also been considered as the main strengthening mechanism of GNFs [15, 20]. Anyway, both strengthening effects are strongly dependent to the amount of GNFs, which agrees well with the experimental results that the strength of the composites was increased with the GNFs’ concentration. However, the mechanical properties of the composites could also be decreased with the addition of GNFs. Bartolucci et al. [11] found that the hardness and ultimate tensile strength of the graphene/Al composite were decreased after addition of 0.1wt.% graphene, which was attributed to the severe formation of brittle Al4C3. However, no significant formation of Al4C3 was found in the present work. Bastwros et 9 / 28
al. [14] found that the agglomeration of the GNFs could also lead towards the decreased compressive strength. In the present work, 3.5 wt.% GNFs/Al-20Si composites with severe agglomeration also demonstrated decreased tensile properties, which agrees well with the experimental results of Bastwros et al. [14]. Compared with the Al-20Si samples, the tensile and bending strength have been increased 130% and 230%, respectively, which are the highest increments reported in Al matrix composites reinforced with graphene reinforcements [10-20]. The representative fracture surface of Al-20Si alloy and GNFs/Al-20Si composites have been shown in Fig.9. The fracture surface of Al-20Si (Fig.9a) was rather flat and was mainly characterized by the fracture of primary Si while no significant dimples and tear ridges were found. In 0.5 wt.% GNFs/Al-20Si composite (Fig.9b), very small pull-out of GNFs was observed, as pointed out by arrows in Fig.9b. Fracture surface 1.5 wt.% GNFs/Al-20Si composite has been shown in Fig.9c and d. Few dimples and tear ridges could be observed, while the significant pull-out of GNFs (pointed out by arrows in Fig.9c and d), indicating the good interfacial binding between GNFs and Al matrix. In the fracture surface of 2.5 and 3.5 wt.% GNFs/Al-20Si composites, spherical phases, which have been marked out by blue boxes in Fig.9e and f, were found. EDS analysis revealed that these phases were composed by about 13 at.% C, 62 at.% O and 25 at.% Al, which might be related to the agglomeration of GNFs and Al2O3. Variation of stress that a material begins to deform plastically (such as yield strength) is usually used for the discussion of the strengthening behavior during the plastic deformation period. However, residual strain of 0.2%, which is used to determine the tradition yield strength (σ0.2), has not been obtained in the present work 10 / 28
due to the brittle character of the composites. Therefore, the stress of 0.1% residual strain (also named as yield strength) was used in the present work for the discussion. Fig.10a shows the relationship between the GNFs content and the yield strength of GNFs/Al composites summarized from existed literatures [12, 13, 15, 16, 20, 25, 31-33]. Regardless of the properties of the matrix alloys, it is clear that the yield strength of composites is almost increased linearly with the graphene content. Strengthening ratio f, which is defined as (σc‒σm)/σm (σc and σm are the yield strengths of the composite and matrix,
respectively),
represents
comprehensive
strengthening
effect
of
the
reinforcement, and the strengthening ratio of the composites are strongly related to the amount of the reinforcement. The relationship between f and the GNFs content is shown in Fig.10b, while most of the reported data are in the yellow area. It is clear that the trend of strengthening ratio is increased with the content of GNFs. Based on the modified shear-lag model, Yan et al. [15], Shin et al. [16, 17], and Li et al. [30] have discussed the strengthening mechanism of graphene, which is expressed as:
c mVm
m S
( )Vr 2 A
(1)
where the Vm and Vr are the volume content of matrix and graphene, τm is the shear stress of matrix (about 0.5σm) [30], S and A are the interfacial areas and cross-section areas of graphene, respectively. Since the volume amounts of graphene reinforcement introduced in the composites are very low (usually less than 2wt.%), the relationship between σc and the amount of graphene reinforcement could be further simplified as Eq. 2, while the f could be calculated as Eq.3, respectively:
c m
m S 4
( )Vr A
(2) 11 / 28
S V f ( ) r A 4
(3)
It is clear that the strengthening ratio f of graphene/Al composites is mainly affected by the characters (specific surface area, thickness or the corresponding cross-section area) and amount of the graphene. Based on Eq.3, the strengthening ratio and corresponding yield strength of graphene/Al composites are increased with amount (Vr) of graphene, which agrees well with the experimental results (Fig.10a). Moreover, at a given amount of graphene, the strengthening ratio and the yield strength are mainly affected by the specific area (S) and the cross-section area (A) of graphene (i.e the thickness or the layer numbers). As an important strengthening mechanism in composites, the effect of the interface shear stress transferring strengthening is strongly related to the amount of interfacial atoms that participate into the load-transferring process [34, 35]. For composites reinforced with the certain amount of graphene with larger specific area and less layers, more C atoms at the surface could contact with Al matrix to form interfacial bonding. Subsequently, more C and Al atoms could participate the load-transferring behavior, leading to higher yield strength and strengthening ratio. According to Eq.2, in order to design high strength graphene/Al composites, it is suggested that graphene with larger specific area, thinner layers and high strength Al matrix (rather than Al-20Si with low strength) should be adopted. Moreover, the present work indicates that the pressure infiltration method could also be used to prepared graphene/Al composite with high strengthening ratio and without formation of Al4C3. 4. Conclusions The main techniques reported to prepare graphene/Al composites are solid methods such as powder metallurgy technique. However, the investigation of the 12 / 28
graphene/Al composites prepared by pressure infiltration method, which has been widely used to prepare Al matrix composite in industry, has not been reported in the existed literatures. It has not been responded that whether it is possible to prepare GNFs/Al composites by pressure infiltration method due to the poor wettability and severe reaction behavior between carbon and molten Al. Therefore, in the present study, graphene nanoflakes (GNFs) reinforced Al-20Si (GNFs/Al-20Si) composites were prepared by pressure infiltration method, and the Al-20Si matrix was chosen to inhibit the formation of Al4C3. XRD analysis, TEM observation, and immersing test indicated that the formation of Al4C3 was hindered. After addition of 1.5 wt.% GNFs, the ultimate tensile strength and bending strength have been increased 130 and 230% compared to that of Al matrix, respectively. Based on the modified shear-lag model, and combined with the literatures’ data, the strengthening behavior of GNFs/Al composites has been discussed. It is concluded that pressure infiltration method is the most feasible and successful way to prepare GNFs/Al composites with high strengthening ratio and without formation of Al4C3. Acknowledgments This work was supported by the National Natural Science Foundation of China (grant numbers 51501047 and 51571069), China Postdoctoral Science Foundation (grant number 2016M590280), Heilongjiang Postdoctoral Foundation (grant number LBH-Z16075) and the Fundamental Research Funds for the Central Universities (grant numbers HIT.NSRIF.20161 and HIT. MKSTISP. 201615). References [1] C. Lee, X. We, J.W. Kysar, J. Hone, Measurement of the elastic properties and 13 / 28
intrinsic strength of monolayer graphene, Science. 2008, 321: 385–388. [2] A.A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, C.N. Lau, Superior thermal conductivity of single-layer graphene, Nano Lett. 2008, 8: 902–907. [3] G. Cheng, T.H. Chang, Q. Qin, H. Huang, Y. Zhu, Mechanical properties of silicon carbide nanowires: effect of size-dependent defect density, Nano Lett. 2014, 14: 754–758 [4] R. Dong, W. Yang, P. Wu, M. Hussain, Z. Xiu, G. Wu, P. Wang, Microstructure characterization of SiC nanowires as reinforcements in composites, Mater Charact. 2015, 103: 37–41. [5] T. Naganuma, K. Naito, J.M. Yang, J. Kyono, D. Sasakura, Y. Kagawa, The effect of a compliant polyimide nanocoating on the tensile properties of a high strength PAN-based carbon fiber, Compos Sci Technol. 2009, 69: 1319–1322. [6] S. Xie, W. Li, Z. Pan, B. Chang, L. Sun, Mechanical and physical properties on carbon nanotube, J Phys Chem Solids. 2000, 61: 1153–1158. [7] L. Shao, J. Li, Y. Guang, Y. Zhang, H. Zhang, X. Che, Y. Wang, PVA/polyethyleneimine-functionalized
graphene
composites
with
optimized
properties, Mater. Des. 2016, 99: 235–242. [8] F. Wang, L. T. Drzal, Y. Qin, Z.g Huang, Enhancement of fracture toughness, mechanical and thermal properties of rubber/epoxy composites by incorporation of graphene nanoplatelets, Compos Part A-Appl S. 2016, 87: 10–22. [9] K. P. D.S Tonello, E. Padovano, C. Badini, S. Biamino, M. Pavese, P. Fino, Fabrication and characterization of laminated SiC composites reinforced with 14 / 28
graphene nanoplatelets, Mater. Sci. Eng. A. 2016, 659: 158–164. [10] Y. Cheng, Y. Zhang, T. Wan, Z. Yin, J. Wang, Mechanical properties and toughening mechanisms of graphene platelets reinforced Al2O3/TiC composite ceramic tool materials by microwave sintering, Mater. Sci. Eng. A. 2017, 680: 190–196. [11] S.F. Bartolucci, J. Paras, M.A. Rafiee, J. Rafiee, S. Lee, D. Kapoor, N. Koratkar, Graphene–aluminum nanocomposites, Mater. Sci. Eng. A. 2011, 528: 7933–7937. [12] J. Wang, Z. Li, G. Fan, H. Pan, Z. Chen, D. Zhang, Reinforcement with graphene nanosheets in aluminum matrix composites, Scripta Mater. 2012, 65: 594–597. [13] M. Rashad, F. Pan, A. Tang, M. Asif. Effect of Graphene Nanoplatelets addition on mechanical properties of pure aluminum using a semi-powder method. Prog Nat Sci. 2014, 24: 101–108. [14] M. Bastwros, G.Y. Kim, C. Zhu, K. Zhang, S. Wang, X. Tang, X. Wang, Effect of ball milling on graphene reinforced Al6061 composite fabricated by semi-solid sintering, Compos Part B-Eng. 2014, 60: 111–118. [15] S.J. Yan, S.L. Dai, X.Y. Zhang, C. Yang, Q.H. Hong, J.Z. Chen, Z.M. Lin, Investigating aluminum alloy reinforced by graphene nanoflakes, Mater. Sci. Eng. A. 2014, 612: 440–444. [16] S.E. Shin, H.J. Choi, J.H. Shin, D.H. Bae, Strengthening behavior of few-layered graphene/aluminum composites, Carbon. 2015, 82: 143–151. [17] S.E. Shin, H.J. Choi, J.Y. Hwang, D.H. Bae, Strengthening behavior of carbon/metal nanocomposites, Sci Rep-UK. 2015, 5: 16114. [18] F.H. Latief, E.S.M. Sherif, Effects of sintering temperature and graphite addition on the mechanical properties of aluminum, J Ind Eng Chem. 2012, 18: 2129–2134. 15 / 28
[19] X. Gao, H. Yue, E. Guo, H. Zhang, X. Lin, L. Yao, B. Wang, Preparation and tensile properties of homogeneously dispersed graphene reinforced aluminum matrix composites, Mater Des. 2016, 94: 54–60. [20] H. Zhang, C. Xu, W. Xiao, K. Ameyama, C. Ma, Enhanced mechanical properties of Al5083 alloy with graphene nanoplates prepared by ball milling and hot extrusion, Mater. Sci. Eng. A. 2016, 658: 8–15. [21] 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. 2017, 682: 38–44. [22] G. Nicoletto, R. Konečná, S. Fintova, Characterization of microshrinkage casting defects of Al–Si alloys by X-ray computed tomography and metallography, Int J Fatigue. 2012, 41: 39–46. [23] P. Ma, C. Zou, H. Wang, J. Jie, Y. Jia, B. Fu, Z. Wei, Microstructure evolution and precipitation of SiC particle reinforced Al–20Si composite solidified under high pressures, Mater Lett. 2012, 79: 232–234. [24] P. Ma, C.M. Zou, H.W. Wang, S. Scudino, B.G. Fu, Z.J. Wei, U. Kühn, J. Eckert, Effects of high pressure and SiC content on microstructure and precipitation kinetics of Al–20Si alloy, J. Alloy. Compd. 2014, 586: 639–644. [25] L.A. Yolshina, R.V. Muradymov, I.V. Korsun, G.A. Yakovlev, S.V. Smirnov, Novel aluminum-graphene and aluminum-graphite metallic composite materials: Synthesis and properties, J. Alloy. Compd. 2016, 663: 449–459. [26] I.E. Monje, E. Louis, J.M. Molina, Role of Al4C3 on the stability of the thermal conductivity of Al/diamond composites subjected to constant or oscillating 16 / 28
temperature in a humid environment, J Mater Sci. 2016, 51: 8027–8036. [27] C. Wang, G. Chen, X. Wang, Y. Zhang, W. Yangu, G. Wu, Effect of Mg Content on the Thermodynamics of Interface Reaction in C/Al Composite, Metall Mater Trans A. 2012, 43: 2514–2519. [28] X. Wang, D. Jiang, G. Wu, B. Li, P. Li, Effect of Mg content on the mechanical properties and microstructure of Gr f /Al composite, Mater. Sci. Eng. A. 2008, 497: 31–36. [29] J. Pelleg, D. Ashkenazi, M. Ganor, The influence of a third element on the interface reactions in metal–matrix composites (MMC): Al–graphite system, Mater. Sci. Eng. A. 2000, 281: 239–247. [30] Z. Li, G. Fan, Q. Guo, Z. Li, Y. Su, D. Zhang, Synergistic strengthening effect of graphene-carbon nanotube hybrid structure in aluminum matrix composites, Carbon, 2015, 95: 419–427. [31] M. Fattahi, A.R. Gholami, A. Eynalvandpour, E. Ahmadi, Y. Fattahi, S. Akhavan, Improved microstructure and mechanical properties in gas tungsten arc welded aluminum joints by using graphene nanosheets/aluminum composite filler wires. Micron. 2014, 64: 20–27. [32] L. Zhao, H. Lu, Z. Gao, Microstructure and mechanical properties of Al/graphene composite produced by high-pressure torsion, Adv Eng Mater. 17 (2016) 976–981. [33] J.L. Li, Y.C. Xiong, X.D. Wang, S.J. Yan, C. Yang, W.W. He, J.Z. Chen, S.Q. Wang, X.Y. Zhang, S.L. Dai, Microstructure and tensile properties of bulk nanostructured aluminum-graphene composites prepared via cryomilling, Mater. Sci. Eng. A. 2015, 626: 400–405. 17 / 28
[34] 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. 2015, 648: 41–46. [35] L. Xin, W. Yang, Q. Zhao, R. Dong, P. Wu, Z. Xiu, M. Hussain, G. Wu, Strengthening behavior in SiC nanowires reinforced pure Al composite, J. Alloy. Compd. 2017, 695: 2406–2412.
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Fig.1 Microstructure of graphene nanoflakes and Al-20Si powders used in the present work; (a) TEM observation of graphene nanoflakes with low magnification; (b) TEM observation of graphene nanoflakes with high magnification; (c) SEM observation of Al-20Si powders.
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Fig.2 The flow chart of the preparation process of GNFs/Al-20Si composites.
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Fig.3 Representative morphology of Al-20Si alloy and GNFs/Al-20Si composites; (a) Al-20Si alloy, (b) 0.5wt.% GNFs/Al-20Si composite, (c) 1.5wt.% GNFs/Al-20Si composite, (d) 2.5wt.% GNFs/Al-20Si composite, (e) 3.5wt.% GNFs/Al-20Si composite.
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Fig.4 XRD analysis of Al-20Si alloy and GNFs/Al-20Si composites.
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Fig.5 TEM observation of 3.5 wt.% GNFs/Al-20Si composites; (a) Low magnification, (b) HRTEM image.
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Fig.6 The 3.5 wt.% GNFs/Al-20Si composite samples for immersing test; (a) before test, (b) after test.
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Fig.7 Relationship of the amount of GNFs and the relative density, hardness and elastic modulus of the GNFs/Al-20Si composites.
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Fig.8 Tensile and bending properties of GNFs/Al-20Si composites; (a) Tensile curves, (b) Relationship between ultimate tensile stress and GNFs content, (c) Bending curves, (d) Relationship between ultimate bending stress and GNFs content.
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Fig.9 The representative fracture surface of Al-20Si alloy and GNFs/Al-20Si composites; (a) Al-20Si, (b) 0.5 wt.% GNFs/Al-20Si, (c)(d) 1.5 wt.% GNFs/Al-20Si, (e) 2.5 wt.% GNFs/Al-20Si (f) 3.5 wt.% GNFs/Al-20Si. (d) is the high magnification of (c).
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Fig.10 The relationship between GNFs content and (a) the yield strength and (b) strengthening ratio of GNFs/Al composites. The data are obtained from the existed literatures.
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PII: DOI: Reference:
S0921-5093(17)30790-6 http://dx.doi.org/10.1016/j.msea.2017.06.027 MSA35165
To appear in: Materials Science & Engineering A Received date: 28 December 2016 Revised date: 5 June 2017 Accepted date: 7 June 2017 Cite this article as: Wenshu Yang, Guoqin Chen, Jing Qiao, Shufeng Liu, Rui Xiao, Ronghua Dong, Murid Hussain and Gaohui Wu, Graphene nanoflakes reinforced Al-20Si matrix composites prepared by pressure infiltration method, Materials Science & Engineering A, http://dx.doi.org/10.1016/j.msea.2017.06.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Graphene nanoflakes reinforced Al-20Si matrix composites prepared by pressure infiltration method
Wenshu Yanga*, Guoqin Chena, Jing Qiaoa, Shufeng Liub, Rui Xiaoc, Ronghua Dongd, Murid Hussaine, Gaohui Wua* a. Department of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, China. b. Beijing Institute of Electronic System Engineering, Beijing, 100854, China c. The 14th Research Institute of China Electronic Technology Group Corporation, Nanjing 210000, China; d. Beijing Institute of Aerospace Control Devices, Beijing 100039, China e. Department of Chemical Engineering, COMSATS Institute of Information Technology, M.A. Jinnah Building, Defence Road, Off Raiwind Road, Lahore-54000, Pakistan.
*Corresponding author: Dr. Wenshu Yang and Prof. Gaohui Wu P. O. 3023, Science park, No. 2 Yikuang street, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150080, P. R. China Tel: +86-451-86402373-5051; Fax: +86 451 86412164 E-mail: [email protected] and [email protected] 1 / 28
Abstract:
It has not been reported in the existed literatures that whether it is possible
to prepare GNFs/Al composites by pressure infiltration method due to the poor wettability and severe reaction behavior between carbon and molten Al. In the present study, microstructure and mechanical behavior of graphene nanoflakes (GNFs) reinforced Al-20Si (GNFs/Al-20Si) composites prepared by the pressure infiltration method have been thoroughly investigated. The Al-20Si matrix was chosen to inhibit the formation of Al4C3. It has found that the GNFs and Al alloy matrix has been well bonded without formation of Al4C3, which authenticated the effectiveness of the alloying treatment. Moreover, the hardness and the elastic modulus of the composites were increased linearly with the increase in the GNFs content. After addition of 1.5 wt.% GNFs, the ultimate tensile strength and bending strength attained the peak values, which increased 130% and 230% to that of Al matrix, respectively. To the best of our knowledge, it is the highest strengthening ratio in Al matrix composites reinforced with graphene reinforcements. Furthermore, based on the modified shear-lag model and combined with the literatures’ data, the strengthening behavior of GNFs/Al composites has been extensively discussed. It is concluded that the pressure infiltration method is the most feasible and successful way to prepare GNFs/Al composites without formation of Al4C3 and with high strengthening ratio. Keywords: Al matrix composites; Graphene; Pressure infiltration method; Si element; Strengthening mechanism;
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1. Introduction Graphene demonstrates high elastic modulus (higher than 1000 GPa [1]), high fracture strength (more than 130 GPa [1]), and extremely high thermal conductivity (about 5300 W/(m·K) [2]), which is much higher than the other reported materials such as SiC ceramic phase [3, 4], C fibres [5] and carbon nanotubes [6]. Therefore, graphene has been considered as an ideal reinforcement for composites. It has been generally found that the addition of graphene nanoflakes (GNFs), which possesses similar properties of single-layer graphene but easier to be produced and handled, could significantly improve the mechanical properties of polymers [7, 8] and ceramics [9, 10]. The effect of graphene or GNFs on the microstructure and performance of Al matrix composites have not been fully understood yet, while the present investigation of the graphene/Al composites is mainly focused on the optimization of the preparation method and parameters. Bartolucci et al. [11] found that the formation of aluminum carbide (Al4C3) was detrimental for the mechanical properties of graphene/pure Al composite prepared by hot isostatic pressing and extrusion technique. Wang et al. [12] and Rashad et al. [13] found that the mechanical properties of Al matrix composites could be significantly improved by the addition of GNFs. Bastwros et al. [14] revealed that the agglomeration of graphene is detrimental to the mechanical performance of the GNFs/Al composite. Yan et al. [15] also observed that the tensile strength and elongation of the GNFs/Al composites could be improved by the GNFs incorporation. S. E. Shin et al. [16, 17] firstly revealed that the higher strengthening efficiency of few-layer graphene than multi-walled carbon nanotube could be mainly attributed to their larger specific surface. Furthermore, S. E. Shin et al. [17] also found that the 3 / 28
mechanical properties of graphene and multi-walled carbon nanotube reinforced Al or Ti composites were agreed well with the modified Rule of Mixture after introducing the geometry factor, interfacial bonding factor, and alignment factor. Latief et al. [18] found that the high amount GNFs (up to 5wt. %) could also been introduced into the composites with improved hardness and compressive strength. Gao et al. [19] found that graphene oxide (GO) sheets could also been used as reinforcement. Zhang et al. [20] revealed that the presence of Al4C3 could act as a strengthening phase in the GNFs/5083Al composite material. The investigation of graphene/Al composites is still at the embryonic stage, and most of the researches are mainly focusing on the optimization of the preparation methods and corresponding parameters. The key techniques reported in the literatures to prepare graphene/Al composites are solid methods such as hot pressing [11, 12, 15, 18-20], semi-powder method [13, 14], and hot-rolling method [16, 17]. However, pressure infiltration method, which has been widely used for the preparation of Al matrix composites, has not been reported yet for the preparation of graphene/Al composites. It has not been responded that whether it is possible to prepare GNFs/Al composites by pressure infiltration method due to the poor wettability and severe reaction behavior between carbon and molten Al. The microstructure and mechanical behavior of the GNFs/Al composites prepared by the pressure infiltration method has not been explored yet. In the present study, the microstructure and mechanical behavior of graphene nanoflakes (GNFs) reinforced Al-20Si (GNFs/Al-20Si) composites prepared by the pressure infiltration method have been investigated. The Al-20Si matrix was used with the aim to inhibit the formation of Al4C3, which would be discussed in 4 / 28
detail in the following paragraph. The effect of the GNFs on the microstructure and the mechanical properties of the GNFs/Al-20Si composites have also been investigated. Moreover, comparing with the data from literatures, the strengthening behavior of the GNFs/Al-20Si composites has been discussed as well. 2. Material and methods Graphene oxides were firstly synthesized by Hummer's method and then chemically reduced to GNFs, as shown in Fig.1a and b. The Al-20Si powders with average diameter of 10 μm (as shown in Fig.1c) and the alloy were supplied by Northeast Light Alloy Co., Ltd. China. The flow chart of the present work is given in Fig.2. The GNFs were firstly mixed with Al-20Si powders using a planetary mill at a rotation speed of 300 rpm for 3 h. The mixture was subsequently pre-densified to prepare a preform in a steel mold. The mold with the preform was then heated at 500 ºC, while the Al-20Si alloy was melted at 770 ºC. Afterwards, the molten Al was poured into the mold and then infiltrated into the preform under pressure of 5 MPa for 10 min. After the solidification of the composites in air, the GNFs/Al-20Si composites with GNFs content of 0.5, 1.5, 2.5 and 3.5 wt.% were obtained. For comparison, the Al-20Si specimens were also prepared by the same process. After that, all the samples were annealed at 400 ºC for 2 h. Microstructure of the GNFs/Al-20Si composites specimens were observed by FEI Sirion Quanta 200 scanning electron microscope (SEM) and JEM-2010F transmission electron microscopy (TEM). X-ray diffraction (XRD) analysis was carried out on Rigaku D/max-rB diffractometer to identify the main phases and to reveal the potential reaction in the GNFs/Al-20Si composites. The specimens were subjected to Cu-Kα 5 / 28
radiation (0.15418 nm) with a scanning speed of 2◦/min between the scan range of 15◦ and 90◦. Elastic modulus, tensile and bending tests were performed to characterize the strengthening effect of the GNFs. Samples with dimensions of 3×4×36 mm were machined for elastic modulus and bending tests. The dimensions of tensile tests have been reported in our recently work [21]. Elastic modulus was evaluated by an impulse excitation technique according to ASTM E1876-09 on EMT-01 instrument (Zhuosheng Instrument Co., Ltd. China). Three-point bending tests with 30 mm span and tensile tests were performed on Instron 5569 universal electrical tensile testing machine with a cross-head speed of 0.5 mm/min, and five samples were tested to improve the statistical significance of the results. In order to characterize the effect of GNFs on the fracture behavior, the fracture surface of GNFs/Al-20Si composites was observed by FEI Sirion Quanta 200 SEM. 3. Results and discussion Morphology of the GNFs/Al-20Si composites has been shown in Fig.3. It is clear that the dimension of the primary Si in Al matrix were significantly refined after the addition of GNFs (Fig.3). Moreover, few pores were found in the Al-20Si matrix (as pointed out by arrows in Fig.3a) and the composites (as pointed bout by arrows in Fig.3b to e), which could be mainly due to the shrinkage behavior of Al-Si matrix during solidification [22]. The presence of the pores is detrimental to their mechanical properties. The size of primary Si was measured by Nano Measure 1.2 software. The size of primary Si (acicular sharp) in Al-20Si alloy was about 46 μm in length. However, after the addition of 0.5, 1.5, and 3.5 wt.% GNFs, the size of the primary Si was reduced to about 8.1 μm, 7.6 μm and 18.6 μm, respectively. It indicated that the size of the 6 / 28
primary Si was firstly decreased with the addition of low content GNFs and then was increased after addition of high content GNF. It has been widely found that the grain size of primary Si in Al-20Si matrix composites could be greatly refined by the introduction of the reinforcements [23, 24]. After addition of 35, 40 and 45 vol.% SiC particles, Ma et al. [24] found that the grain size of the primary Si was decreased from 72.5 μm to about 25.4, 12.4 and 11.2 μm, respectively, which could be mainly attributed to the heterogeneous nucleation of silicon. During solidification, the surface of uniformly distributed GNFs could provide more nucleation sites for the primary Si and inhibit the growth of the primary Si, Therefore, the grain size of primary Si has been greatly refined in the present work with the low content GNFs. However, the grains of primary Si in 3.5 wt.% GNFs/Al-20Si composites (Fig.3e) were coarsen than that of 1.5 wt.% composite (Fig.3c), implying the agglomeration of GNFs. The amount of the primary Si in the composites was constant. Therefore, more nucleation and slow growth of the primary Si leads to the refined size and vice versa. The uniformly distributed GNFs provide the nucleation sites for the primary Si. However, the agglomeration of GNFs at high content (3.5wt.%) leads to the less nucleation sites for the primary Si, which shows the way to the larger size of the primary Si. It has been found by Bastwros et al. [14] that agglomeration of graphene is detrimental to the mechanical performance of composite. XRD analysis (Fig.4) indicated that the main phases found in the composites were Al and Si [23, 24] in low content GNFs/Al-20Si composites, while weak peaks of C [13] were detected in 3.5 wt.% GNFs/Al-20Si composites, also indicating the agglomeration of GNFs at higher amount. However, no peak of Al4C3 was detected. TEM observation 7 / 28
of 3.5 wt.% GNFs/Al-20Si composites has been shown in Fig.5a, and only Si, Al, and wrinkled GNFs were found in the composites, and no trace of Al4C3 has been observed. Further, HRTEM observation (Fig.5b) has indicated that the GNFs and Al alloy matrix has been well bonded, which is beneficial for the strengthening effect of GNFs since transferring the stress by the interface is an important strengthening mechanism of graphene. Yolshina et al. [25] proposed a very simple and effective method (corrosion test) to detect the presence of Al4C3. After immersing the samples in NaCl solution for 6 h, the samples would be covered with white phase if there is Al4C3 in the composites, and our immersing tests further verified that no significant Al4C3 was formed in the composites (Fig.6). One of the main challenges using liquid infiltration methods to fabricate carbonaceous Al matrix composites is the formation of brittle Al4C3. Although it has been reported that Al4C3 could act as the dispersed precipitate to improve the mechanical strength of the GNFs/5083Al composites [20], it has been considered as the unfavorable phase in graphene/Al composites due to its brittle character [11, 15]. Moreover, Al4C3 would also deteriorate the corrosion resistance of the composites since it could be easily decomposed in moist environment [26]. The main challenge using liquid infiltration methods to fabricate carbonaceous Al matrix composites is the inhibitation of the formation of Al4C3 since the reaction of Al and C to form is usually very severe at temperature above the melting point of the Al alloy [27]. Our previous work regarding carbon fibre reinforced Al matrix composites indicates that the addition of alloying elements is a reliable method to inhibit the formation of Al4C3 [27, 28], while Si and Mg have been found to be the most effective inhibiting elements [29]. In 8 / 28
the present work, Al alloy with high Si content was chosen with the aim to inhibit the formation of Al4C3, and the microstructure observation verified the effectiveness of the alloying treatment, indicating that it is possible to prepare the GNFs/Al composite with controlled interfacial reaction by pressure infiltration method. The relationship of the amount of the GNFs and the relative density, hardness, and elastic modulus of the composites has been shown in Fig.7. Despite the relative density was decreased, the hardness and the elastic modulus were increased linearly with the increase of GNFs content. As shown in Fig.8, the tensile and bending strength of GNFs/Al-20Si composites attained the peak values after the addition of 1.5 wt.% GNFs, and were decreased with further addition of GNFs. Moreover, the elongation of composites was also higher than that of Al-20Si matrix alloy. It has been widely found that the mechanical strength of GNFs/Al composites is increased with the amount of GNFs, regardless of the preparation methods [15-20]. Yan et al. [15], Shin et al. [16, 17], and Li et al. [30] attributed the significant strengthening effect of GNFs to the large aspect ratio characteristic. Meanwhile, fine-precipitates strengthening has also been considered as the main strengthening mechanism of GNFs [15, 20]. Anyway, both strengthening effects are strongly dependent to the amount of GNFs, which agrees well with the experimental results that the strength of the composites was increased with the GNFs’ concentration. However, the mechanical properties of the composites could also be decreased with the addition of GNFs. Bartolucci et al. [11] found that the hardness and ultimate tensile strength of the graphene/Al composite were decreased after addition of 0.1wt.% graphene, which was attributed to the severe formation of brittle Al4C3. However, no significant formation of Al4C3 was found in the present work. Bastwros et 9 / 28
al. [14] found that the agglomeration of the GNFs could also lead towards the decreased compressive strength. In the present work, 3.5 wt.% GNFs/Al-20Si composites with severe agglomeration also demonstrated decreased tensile properties, which agrees well with the experimental results of Bastwros et al. [14]. Compared with the Al-20Si samples, the tensile and bending strength have been increased 130% and 230%, respectively, which are the highest increments reported in Al matrix composites reinforced with graphene reinforcements [10-20]. The representative fracture surface of Al-20Si alloy and GNFs/Al-20Si composites have been shown in Fig.9. The fracture surface of Al-20Si (Fig.9a) was rather flat and was mainly characterized by the fracture of primary Si while no significant dimples and tear ridges were found. In 0.5 wt.% GNFs/Al-20Si composite (Fig.9b), very small pull-out of GNFs was observed, as pointed out by arrows in Fig.9b. Fracture surface 1.5 wt.% GNFs/Al-20Si composite has been shown in Fig.9c and d. Few dimples and tear ridges could be observed, while the significant pull-out of GNFs (pointed out by arrows in Fig.9c and d), indicating the good interfacial binding between GNFs and Al matrix. In the fracture surface of 2.5 and 3.5 wt.% GNFs/Al-20Si composites, spherical phases, which have been marked out by blue boxes in Fig.9e and f, were found. EDS analysis revealed that these phases were composed by about 13 at.% C, 62 at.% O and 25 at.% Al, which might be related to the agglomeration of GNFs and Al2O3. Variation of stress that a material begins to deform plastically (such as yield strength) is usually used for the discussion of the strengthening behavior during the plastic deformation period. However, residual strain of 0.2%, which is used to determine the tradition yield strength (σ0.2), has not been obtained in the present work 10 / 28
due to the brittle character of the composites. Therefore, the stress of 0.1% residual strain (also named as yield strength) was used in the present work for the discussion. Fig.10a shows the relationship between the GNFs content and the yield strength of GNFs/Al composites summarized from existed literatures [12, 13, 15, 16, 20, 25, 31-33]. Regardless of the properties of the matrix alloys, it is clear that the yield strength of composites is almost increased linearly with the graphene content. Strengthening ratio f, which is defined as (σc‒σm)/σm (σc and σm are the yield strengths of the composite and matrix,
respectively),
represents
comprehensive
strengthening
effect
of
the
reinforcement, and the strengthening ratio of the composites are strongly related to the amount of the reinforcement. The relationship between f and the GNFs content is shown in Fig.10b, while most of the reported data are in the yellow area. It is clear that the trend of strengthening ratio is increased with the content of GNFs. Based on the modified shear-lag model, Yan et al. [15], Shin et al. [16, 17], and Li et al. [30] have discussed the strengthening mechanism of graphene, which is expressed as:
c mVm
m S
( )Vr 2 A
(1)
where the Vm and Vr are the volume content of matrix and graphene, τm is the shear stress of matrix (about 0.5σm) [30], S and A are the interfacial areas and cross-section areas of graphene, respectively. Since the volume amounts of graphene reinforcement introduced in the composites are very low (usually less than 2wt.%), the relationship between σc and the amount of graphene reinforcement could be further simplified as Eq. 2, while the f could be calculated as Eq.3, respectively:
c m
m S 4
( )Vr A
(2) 11 / 28
S V f ( ) r A 4
(3)
It is clear that the strengthening ratio f of graphene/Al composites is mainly affected by the characters (specific surface area, thickness or the corresponding cross-section area) and amount of the graphene. Based on Eq.3, the strengthening ratio and corresponding yield strength of graphene/Al composites are increased with amount (Vr) of graphene, which agrees well with the experimental results (Fig.10a). Moreover, at a given amount of graphene, the strengthening ratio and the yield strength are mainly affected by the specific area (S) and the cross-section area (A) of graphene (i.e the thickness or the layer numbers). As an important strengthening mechanism in composites, the effect of the interface shear stress transferring strengthening is strongly related to the amount of interfacial atoms that participate into the load-transferring process [34, 35]. For composites reinforced with the certain amount of graphene with larger specific area and less layers, more C atoms at the surface could contact with Al matrix to form interfacial bonding. Subsequently, more C and Al atoms could participate the load-transferring behavior, leading to higher yield strength and strengthening ratio. According to Eq.2, in order to design high strength graphene/Al composites, it is suggested that graphene with larger specific area, thinner layers and high strength Al matrix (rather than Al-20Si with low strength) should be adopted. Moreover, the present work indicates that the pressure infiltration method could also be used to prepared graphene/Al composite with high strengthening ratio and without formation of Al4C3. 4. Conclusions The main techniques reported to prepare graphene/Al composites are solid methods such as powder metallurgy technique. However, the investigation of the 12 / 28
graphene/Al composites prepared by pressure infiltration method, which has been widely used to prepare Al matrix composite in industry, has not been reported in the existed literatures. It has not been responded that whether it is possible to prepare GNFs/Al composites by pressure infiltration method due to the poor wettability and severe reaction behavior between carbon and molten Al. Therefore, in the present study, graphene nanoflakes (GNFs) reinforced Al-20Si (GNFs/Al-20Si) composites were prepared by pressure infiltration method, and the Al-20Si matrix was chosen to inhibit the formation of Al4C3. XRD analysis, TEM observation, and immersing test indicated that the formation of Al4C3 was hindered. After addition of 1.5 wt.% GNFs, the ultimate tensile strength and bending strength have been increased 130 and 230% compared to that of Al matrix, respectively. Based on the modified shear-lag model, and combined with the literatures’ data, the strengthening behavior of GNFs/Al composites has been discussed. It is concluded that pressure infiltration method is the most feasible and successful way to prepare GNFs/Al composites with high strengthening ratio and without formation of Al4C3. Acknowledgments This work was supported by the National Natural Science Foundation of China (grant numbers 51501047 and 51571069), China Postdoctoral Science Foundation (grant number 2016M590280), Heilongjiang Postdoctoral Foundation (grant number LBH-Z16075) and the Fundamental Research Funds for the Central Universities (grant numbers HIT.NSRIF.20161 and HIT. MKSTISP. 201615). References [1] C. Lee, X. We, J.W. Kysar, J. Hone, Measurement of the elastic properties and 13 / 28
intrinsic strength of monolayer graphene, Science. 2008, 321: 385–388. [2] A.A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, C.N. Lau, Superior thermal conductivity of single-layer graphene, Nano Lett. 2008, 8: 902–907. [3] G. Cheng, T.H. Chang, Q. Qin, H. Huang, Y. Zhu, Mechanical properties of silicon carbide nanowires: effect of size-dependent defect density, Nano Lett. 2014, 14: 754–758 [4] R. Dong, W. Yang, P. Wu, M. Hussain, Z. Xiu, G. Wu, P. Wang, Microstructure characterization of SiC nanowires as reinforcements in composites, Mater Charact. 2015, 103: 37–41. [5] T. Naganuma, K. Naito, J.M. Yang, J. Kyono, D. Sasakura, Y. Kagawa, The effect of a compliant polyimide nanocoating on the tensile properties of a high strength PAN-based carbon fiber, Compos Sci Technol. 2009, 69: 1319–1322. [6] S. Xie, W. Li, Z. Pan, B. Chang, L. Sun, Mechanical and physical properties on carbon nanotube, J Phys Chem Solids. 2000, 61: 1153–1158. [7] L. Shao, J. Li, Y. Guang, Y. Zhang, H. Zhang, X. Che, Y. Wang, PVA/polyethyleneimine-functionalized
graphene
composites
with
optimized
properties, Mater. Des. 2016, 99: 235–242. [8] F. Wang, L. T. Drzal, Y. Qin, Z.g Huang, Enhancement of fracture toughness, mechanical and thermal properties of rubber/epoxy composites by incorporation of graphene nanoplatelets, Compos Part A-Appl S. 2016, 87: 10–22. [9] K. P. D.S Tonello, E. Padovano, C. Badini, S. Biamino, M. Pavese, P. Fino, Fabrication and characterization of laminated SiC composites reinforced with 14 / 28
graphene nanoplatelets, Mater. Sci. Eng. A. 2016, 659: 158–164. [10] Y. Cheng, Y. Zhang, T. Wan, Z. Yin, J. Wang, Mechanical properties and toughening mechanisms of graphene platelets reinforced Al2O3/TiC composite ceramic tool materials by microwave sintering, Mater. Sci. Eng. A. 2017, 680: 190–196. [11] S.F. Bartolucci, J. Paras, M.A. Rafiee, J. Rafiee, S. Lee, D. Kapoor, N. Koratkar, Graphene–aluminum nanocomposites, Mater. Sci. Eng. A. 2011, 528: 7933–7937. [12] J. Wang, Z. Li, G. Fan, H. Pan, Z. Chen, D. Zhang, Reinforcement with graphene nanosheets in aluminum matrix composites, Scripta Mater. 2012, 65: 594–597. [13] M. Rashad, F. Pan, A. Tang, M. Asif. Effect of Graphene Nanoplatelets addition on mechanical properties of pure aluminum using a semi-powder method. Prog Nat Sci. 2014, 24: 101–108. [14] M. Bastwros, G.Y. Kim, C. Zhu, K. Zhang, S. Wang, X. Tang, X. Wang, Effect of ball milling on graphene reinforced Al6061 composite fabricated by semi-solid sintering, Compos Part B-Eng. 2014, 60: 111–118. [15] S.J. Yan, S.L. Dai, X.Y. Zhang, C. Yang, Q.H. Hong, J.Z. Chen, Z.M. Lin, Investigating aluminum alloy reinforced by graphene nanoflakes, Mater. Sci. Eng. A. 2014, 612: 440–444. [16] S.E. Shin, H.J. Choi, J.H. Shin, D.H. Bae, Strengthening behavior of few-layered graphene/aluminum composites, Carbon. 2015, 82: 143–151. [17] S.E. Shin, H.J. Choi, J.Y. Hwang, D.H. Bae, Strengthening behavior of carbon/metal nanocomposites, Sci Rep-UK. 2015, 5: 16114. [18] F.H. Latief, E.S.M. Sherif, Effects of sintering temperature and graphite addition on the mechanical properties of aluminum, J Ind Eng Chem. 2012, 18: 2129–2134. 15 / 28
[19] X. Gao, H. Yue, E. Guo, H. Zhang, X. Lin, L. Yao, B. Wang, Preparation and tensile properties of homogeneously dispersed graphene reinforced aluminum matrix composites, Mater Des. 2016, 94: 54–60. [20] H. Zhang, C. Xu, W. Xiao, K. Ameyama, C. Ma, Enhanced mechanical properties of Al5083 alloy with graphene nanoplates prepared by ball milling and hot extrusion, Mater. Sci. Eng. A. 2016, 658: 8–15. [21] 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. 2017, 682: 38–44. [22] G. Nicoletto, R. Konečná, S. Fintova, Characterization of microshrinkage casting defects of Al–Si alloys by X-ray computed tomography and metallography, Int J Fatigue. 2012, 41: 39–46. [23] P. Ma, C. Zou, H. Wang, J. Jie, Y. Jia, B. Fu, Z. Wei, Microstructure evolution and precipitation of SiC particle reinforced Al–20Si composite solidified under high pressures, Mater Lett. 2012, 79: 232–234. [24] P. Ma, C.M. Zou, H.W. Wang, S. Scudino, B.G. Fu, Z.J. Wei, U. Kühn, J. Eckert, Effects of high pressure and SiC content on microstructure and precipitation kinetics of Al–20Si alloy, J. Alloy. Compd. 2014, 586: 639–644. [25] L.A. Yolshina, R.V. Muradymov, I.V. Korsun, G.A. Yakovlev, S.V. Smirnov, Novel aluminum-graphene and aluminum-graphite metallic composite materials: Synthesis and properties, J. Alloy. Compd. 2016, 663: 449–459. [26] I.E. Monje, E. Louis, J.M. Molina, Role of Al4C3 on the stability of the thermal conductivity of Al/diamond composites subjected to constant or oscillating 16 / 28
temperature in a humid environment, J Mater Sci. 2016, 51: 8027–8036. [27] C. Wang, G. Chen, X. Wang, Y. Zhang, W. Yangu, G. Wu, Effect of Mg Content on the Thermodynamics of Interface Reaction in C/Al Composite, Metall Mater Trans A. 2012, 43: 2514–2519. [28] X. Wang, D. Jiang, G. Wu, B. Li, P. Li, Effect of Mg content on the mechanical properties and microstructure of Gr f /Al composite, Mater. Sci. Eng. A. 2008, 497: 31–36. [29] J. Pelleg, D. Ashkenazi, M. Ganor, The influence of a third element on the interface reactions in metal–matrix composites (MMC): Al–graphite system, Mater. Sci. Eng. A. 2000, 281: 239–247. [30] Z. Li, G. Fan, Q. Guo, Z. Li, Y. Su, D. Zhang, Synergistic strengthening effect of graphene-carbon nanotube hybrid structure in aluminum matrix composites, Carbon, 2015, 95: 419–427. [31] M. Fattahi, A.R. Gholami, A. Eynalvandpour, E. Ahmadi, Y. Fattahi, S. Akhavan, Improved microstructure and mechanical properties in gas tungsten arc welded aluminum joints by using graphene nanosheets/aluminum composite filler wires. Micron. 2014, 64: 20–27. [32] L. Zhao, H. Lu, Z. Gao, Microstructure and mechanical properties of Al/graphene composite produced by high-pressure torsion, Adv Eng Mater. 17 (2016) 976–981. [33] J.L. Li, Y.C. Xiong, X.D. Wang, S.J. Yan, C. Yang, W.W. He, J.Z. Chen, S.Q. Wang, X.Y. Zhang, S.L. Dai, Microstructure and tensile properties of bulk nanostructured aluminum-graphene composites prepared via cryomilling, Mater. Sci. Eng. A. 2015, 626: 400–405. 17 / 28
[34] 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. 2015, 648: 41–46. [35] L. Xin, W. Yang, Q. Zhao, R. Dong, P. Wu, Z. Xiu, M. Hussain, G. Wu, Strengthening behavior in SiC nanowires reinforced pure Al composite, J. Alloy. Compd. 2017, 695: 2406–2412.
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Fig.1 Microstructure of graphene nanoflakes and Al-20Si powders used in the present work; (a) TEM observation of graphene nanoflakes with low magnification; (b) TEM observation of graphene nanoflakes with high magnification; (c) SEM observation of Al-20Si powders.
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Fig.2 The flow chart of the preparation process of GNFs/Al-20Si composites.
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Fig.3 Representative morphology of Al-20Si alloy and GNFs/Al-20Si composites; (a) Al-20Si alloy, (b) 0.5wt.% GNFs/Al-20Si composite, (c) 1.5wt.% GNFs/Al-20Si composite, (d) 2.5wt.% GNFs/Al-20Si composite, (e) 3.5wt.% GNFs/Al-20Si composite.
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Fig.4 XRD analysis of Al-20Si alloy and GNFs/Al-20Si composites.
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Fig.5 TEM observation of 3.5 wt.% GNFs/Al-20Si composites; (a) Low magnification, (b) HRTEM image.
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Fig.6 The 3.5 wt.% GNFs/Al-20Si composite samples for immersing test; (a) before test, (b) after test.
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Fig.7 Relationship of the amount of GNFs and the relative density, hardness and elastic modulus of the GNFs/Al-20Si composites.
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Fig.8 Tensile and bending properties of GNFs/Al-20Si composites; (a) Tensile curves, (b) Relationship between ultimate tensile stress and GNFs content, (c) Bending curves, (d) Relationship between ultimate bending stress and GNFs content.
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Fig.9 The representative fracture surface of Al-20Si alloy and GNFs/Al-20Si composites; (a) Al-20Si, (b) 0.5 wt.% GNFs/Al-20Si, (c)(d) 1.5 wt.% GNFs/Al-20Si, (e) 2.5 wt.% GNFs/Al-20Si (f) 3.5 wt.% GNFs/Al-20Si. (d) is the high magnification of (c).
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Fig.10 The relationship between GNFs content and (a) the yield strength and (b) strengthening ratio of GNFs/Al composites. The data are obtained from the existed literatures.
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