- Email: [email protected]
Excellent mechanical properties of copper-graphite composites with the addition of tantalum alloying element
Vacuum 169 (2019) 108913
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
Short communication
Excellent mechanical properties of copper-graphite composites with the addition of tantalum alloying element
T
Faisal Nazeera,b, Zhuang Maa,b, Lihong Gaoa,b,∗, Abdul Malika,b, Muhammad Abubaker Khana,b, Fuchi Wanga,b, Hezhang Lia,b a b
School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, 100081, China National Key Laboratory of Science and Technology on Materials Under Shock and Impact, Beijing, 100081, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Hybrid composites Strength-ductility Bending strength Hardness Thermal conductivity
In this study, the effect of novel metal tantalum was investigated on the properties of copper-graphite composites. The complete mechanical behavior of copper-tantalum-graphite hybrid composites was examined. The addition of tantalum increased the compressive, tensile and bending strength of composites as well as the hardness and thermal conductivity. The compression, tensile, bending and hardness values for Cu–Ta-GF (0.5) composites are 20.7%, 138%, 69% and 93% higher than pure Cu and these are also far better than Cu-GF composites. The excellent mechanical and thermal properties with good relation of strength-ductility ratio open up a new window to use these materials as heat sinks in thermal packaging system.
Metal matrix composites have been extensively used in many fields such as aerospace, vehicles and thermal packaging industries [1]. Copper is the best choice as a metal matrix due to its excellent properties such as higher thermal and electrical conductivity, cost-effective but has poor mechanical properties [2,3]. To improve the properties of Cu matrix different kinds of filler are used such as CNTs [4], graphite [5,6] and graphene oxide [7–9]. These fillers have the potential to increase the mechanical properties of the Cu matrix but there are several problems such as interface bonding and strengthening behavior of Cu. To improve further the properties of these metal-carbon composites the third element introduces to enhance their properties. The typical elements are used to improve the interface bonding and improve the mechanical properties are Titanium (Ti) [10], Zirconium (Zr) [11], Chromium (Cr) [12] and Nickel (Ni) [13]. These elements can increase the strength of composites but the ductility is reduced. To maintain the strength, ductility and interface bonding is still a challenge. Tantalum as third phase in the Cu-GF composites is a good choice due to its extra ordinary mechanical properties such as high young modulus (186 GPa), excellent Vickers hardness (870–1200 Mpa) and highly ductile material. Most of the traditional hard materials like Titanium and Silicon they have high young modulus values but their ductility is not very good. The aim of this work to increase the overall mechanical properties of Cu-GF composites so we choose this rare metal to use as a third phase instead of traditional element. In this work, we introduced new rare metal tantalum (Ta) to
∗
enhance the mechanical properties and interface bonding of Cu-GF composites prepared via ball milling and molecular level mixing followed by hot press sintering. The introduction of new rare metal has a great influence on the microstructural and mechanical properties of CuGF composites. The copper and tantalum powder is mixed by keeping the constant ratio of 1 wt% of tantalum powder. The powders are mixed through wet ball milling with the help of ethanol solvent for 4 h by using zirconium ball and ball to powder ratio was set 15:1. After that powder was dried through vacuum filtration machine and put in an oven for 24 h for further dryness. The GF was ultra-sonicated in the ratio of ethanol to water 9:1 for 30 min in an ultra-sonication machine. After that, the ultra-sonicated GF solution was mixed with copper and tantalum dried powder by mechanical mixing for 4 h to not destroy the structure of powders. The hybrid composite powders were dried and put in an oven for 48 h. The composites powder was annealed before sintering at 400C for 2 h in the presence of argon and nitrogen gas to remove the oxygen functional group from the composites. These oxygen functional cause voids during the sintering process and as the results the overall properties of composites deteriorate. The dried hybrid composite powder was loaded into a graphite die having inner diameter 25 mm and length 10 mm for hot press sintering. The temperature and pressure were set 980C° and 30 MPa for 4 h during the hot press sintering process. The temperature was raised at the constant rate of 10C°/min during the sintering process and the pressure was applied when the temperature
Corresponding author. School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, 100081, China. E-mail address: [email protected] (L. Gao).
https://doi.org/10.1016/j.vacuum.2019.108913 Received 23 July 2019; Received in revised form 24 August 2019; Accepted 28 August 2019 Available online 29 August 2019 0042-207X/ © 2019 Published by Elsevier Ltd.
Vacuum 169 (2019) 108913
F. Nazeer, et al.
Fig. 1. Powders SEM analysis (a) Cu (b) GF (c) Ta (d) Cu-GF (0.5) (e) EDX (f) Cu–Ta-GF (0.5).
that with the addition of GF and Ta the yield strength (YS) and ultimate compressive strength (UCS) of Cu-GF and Cu–Ta-GF are increased significantly. The YS and UCS of Cu–Ta-GF (0.5) composites are 147 MPa and 780 MPa which are 105% and 20.7% higher than pure Cu which have YS (71 MPa) and UCS (646 MPa), respectively. Only with the addition of GF in the Cu matrix also enhance the YS and UCS values of CuGF composites. The similar kind of phenomenon is also observed during the tensile testing of pure Cu and the composites. The yield strength (YS) and ultimate tensile strength (UTS) are increased significantly by the addition of GF and by further adding the Ta in the Cu-GF composites. The YS and UTS for Cu–Ta-GF (0.5) composites are 148 MPa and 276 MPa which are 138% and 53% higher than pure Cu as well higher than Cu-GF composites. The addition of GF and Ta enhanced the YS and UTS greatly due to the following strengthening mechanism. There are mainly six mechanisms involved in the strengthening of materials such as load transfer, thermal mismatch, Orowan looping system, solid solution strengthening, precipitation strengthening and grain refinement. In the present work, there are mainly first mechanism load transfer is involved to improve the YS and UTS of the composites. It is also worth noting in the tensile behavior of Cu-GF (1) and Cu–Ta-GF (0.5) double yield strength phenomenon is observed at the strain rate 1 and 3%. While this phenomenon is absent in the pure Cu and other two composites materials. One of the reasons behind this is that the first yielding point is due to matrix yielding while the second point is due to reinforcement yielding. As we know the GF and Ta have high values of UTS while the toughness values of Ta is better than GF. The GF has the low ability to resist again the crack propagation while the alloying element Ta supports the Cu-GF composites resist again the tensile loading due to this we achieve high strength-ductility values for Cu–TaGF (0.5) composites. However, the double yielding points are also needed to be further investigated in future. The relationship between UTS and elongation of Cu and different composites can be seen in Fig. 3c. The addition of GF increases the values of UTS but with the sacrifice of elongation while the addition of alloying element maintains both the UTS and elongation of Cu–Ta-GF composites to a higher extent value. The bending strength of Cu-GF and Cu–Ta-GF (0.5) composites are also increased significantly as can be revealed in Fig. 3d. The value of bending strength for pure Cu is 280 MPa while for Cu-GF (1) and Cu–Ta-GF (0.5) the values are 334 and 474 MPa, which are 19% and 69% higher than pure Cu, respectively. Due to the high ductility property of the composites, none of the samples is broken during the testing and bending into the rectangular shape. The Vickers hardness values of pure Cu and different composites are demonstrated in Fig. 3e. Like all the other mechanical properties the hardness values of Cu-GF
reached at 600 °C under the Ar gas atmosphere. The microstructure analysis of powders and bulk composites was carried out with the help of scanning electron microscopy (SEM, Hitachi S-4800, Japan) equipped with energy dispersive spectroscopy (EDS). Compressive strength of composites was measured with the help of (INSTRON-5566, Norwood, America) having sample dimensions diameter 3 mm and height 4 mm. For each composite three sample were carried out to measure the compression test and then take the average result. The tensile test was performed with an (Instron universal material machine) with the crosshead speed of 0.5 mm/min. The sample was machined in the dog-bone shaped with the gauge length 12 mm, gauge width 3 mm and thickness 2 mm. Vickers hardness was calculated with the help of (AHVD-1000, China) by applying 100 gF and dwelling time was set 15 s and seven indentations were observed for each sample. The bending strength of Cu, Cu-GF and Cu–Ta/GF composites of dimensions 20 mm × 4 mm × 3 mm was measured by threepoint bending method with a crosshead speed of 0.5 mm/min and span of 30 mm at room temperature according to electro-mechanical universal testing machine (INSTRON-5566, Norwood, America). Fig. 1 shows the microstructure analysis of as received powders as well as Cu–Ta-GF hybrid composites powders. The SEM image of Cu is after ball milled which shows the typical flake-like the structure of Cu powder which changes during the ball milling process. The Fig. 1 (b, c) are as received the graphite and tantalum powders. Fig. 1d is the Cu-GF composites after the molecular level mixing and EDX analysis clearly represent the presence of GF in the composite powder while in Fig. 1f the presence of Ta powder can also be seen in the GF/Cu–Ta hybrid composites powders. At 0.5 and 1 wt%, GF the interface between Cu and GF is really strong which can be seen in the inset of Fig. 2a, b. As we can see at very high resolution 500 nm the interface is really strong and no void is present at the interface of Cu and GF. The GF particles are aligned well in the Cu matrix during the sintering process perpendicular to the applied force direction. With the addition of Ta at a low percentage of GF (0.5 wt%), the mixing is really good which can be seen in the area marked with the circle in Fig. 2c and still no obvious voids were seen in this figure. By increasing the GF wt% and the addition of Ta cause to a mismatch between the Ta and GF which creates the significant voids between them are seen in the inset of Fig. 2d. The EDX analysis of Cu–Ta-GF clearly shows the presence of each element in the bulk composites. The agglomeration of Ta particles is obvious at a higher percentage of GF while it can't be seen with a lower percentage of GF. The complete mechanical behavior of Cu-GF and Cu–Ta-GF composites are shown in Fig. 3. Compression test curve clearly indicates 2
Vacuum 169 (2019) 108913
F. Nazeer, et al.
Fig. 2. Cross-sectional microstructure analysis of Cu-GF and Cu–Ta-GF composites. (a) Cu-GF (0.5) (b) Cu-GF (1) (c) Cu–Ta-GF (0.5) (d) Cu–Ta-GF (1).
addition of Ta element the density of Cu-0.5 GF-1Ta is really good while the density of Cu-1GF-Ta is very low due to the presence of many voids in the composites. The SEM fractographs of Cu, Cu-GF and Cu–Ta-GF are shown in Fig. 4. In Fig. 4a the Cu shows the ductile fracture which is a common structure of Cu fracture. By the addition of GF in the Cu matrix, the dimples are reduced and some cracks are produced in the fracture which means the ductility of the composites reduced and the strength is increased which is in good agreement with our tensile testing curves. Moreover, the addition of Ta in the Cu-GF composites produced the small and larger dimples in the fracture surface of composites. The presence of large dimples indicates that the materials absorb more
and Cu–Ta-GF have a similar trend and increased significantly compared with pure Cu. The hardness values for Cu-GF (1) and Cu–Ta-GF (0.5) are observed 60 HV and 83 HV which are 39% and 93% higher than pure Cu (43 HV). The addition of Ta particles in the Cu-GF composites strengthen the materials and counteracts to pushing the force on the boundaries of Cu-GF composites which leads to increase the hardness of materials according to Zener pinning effect. The mixing of Cu–Ta-GF (0.5) is excellent which reveals in Fig. 2c also help to improve the hardness values of this composites. The density of the composites was measured with the help of Archimedes principle are shown in Fig. 3f. Firstly with the addition of GF 0.5 and 1 wt% the relative density of Cu-GF composites are 92.4 and 97.8%. Furthermore, with the
Fig. 3. Mechanical properties of pure Cu, Cu-GF and Cu–Ta-GF composites (a) compressive strength (b) Tensile property (c) UTS vs Elongation (d) Bending strength (e) Vickers hardness (f) Relative density. 3
Vacuum 169 (2019) 108913
F. Nazeer, et al.
Fig. 4. Fracture morphology (a) Cu (b) Cu-GF (0.5) (c) Cu-GF (1) (d,e) Cu–Ta-GF (0.5) (f) Cu–Ta-GF (1).
energy during the fracture which leads to demonstrate the better plastic toughness of composites. Another phenomenon is also observed in Fig. 4d the Ta particles makes a bridging and this bridge mechanism is one of the main cause to enhance the ductility of the composites. Due to these reasons, the Cu–Ta-GF (0.5) have excellent UTS and elongation values. With the addition of more GF in the Cu–Ta composites the values of UTS and elongation decrease significantly. At a higher ratio of GF and Ta, the obvious agglomeration can be seen in the fracture mechanism and can also reveal in the SEM figures of composites which cause to reduce the strength due to poor mixing. The Cu-GF and Cu–Ta-GF composites were successfully fabricated through flake powder metallurgy routes and check the effect of Ta alloying element on the mechanical properties of Cu-GF composites. With the addition of Ta, the interface interaction of Cu-GF (0.5) composites significantly improves which is favorable for the better mechanical properties of the composites. Compressive, tensile and bending strength of Cu increased with the addition of GF and further enhanced by the addition of Ta rare metal. The compression, tensile, bending and hardness values for Cu–Ta-GF (0.5) composites are 20.7%, 138%, 69% and 93% higher than pure Cu and these are also far better than Cu-GF composites. Therefore, this work focus on the improved the interfacial bonding of Cu-GF composites and a remarkable increase in the mechanical properties of Cu and Cu-GF composites with the addition of a very low percentage of new alloying element.
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
Acknowledgement
[12]
The authors acknowledge the financial support of the National Natural Science Foundation of China (51772027).
[13]
References [1] S.F. Bartolucci, J. Paras, M.A. Rafiee, J. Rafiee, S. Lee, D. Kapoor, N. Koratkar,
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Graphene–aluminum nanocomposites, Mater. Sci. Eng., A 528 (27) (2011) 7933–7937. S.B. Chandrasekhar, S. Sudhakara Sarma, M. Ramakrishna, P. Suresh Babu, T.N. Rao, B.P. Kashyap, Microstructure and properties of hot extruded Cu–1wt% Al2O3 nano-composites synthesized by various techniques, Mater. Sci. Eng., A 591 (2014) 46–53. F. Nazeer, Z. Ma, L. Gao, A. Malik, M. Abubaker Khan, F. Wang, H. Li, Effect of processing routes on mechanical and thermal properties of copper–graphene composites, Mater. Sci. Technol. 35 (14) (2019) 1770–1774. P. Yang, X. You, J. Yi, D. Fang, R. Bao, T. Shen, Y. Liu, J. Tao, C. Li, Influence of dispersion state of carbon nanotubes on electrical conductivity of copper matrix composites, J. Alloy. Comp. 752 (2018) 376–380. F. Nazeer, Z. Ma, L. Gao, F. Wang, M.A. Khan, A. Malik, Thermal and mechanical properties of copper-graphite and copper-reduced graphene oxide composites, Compos. B Eng. 163 (2019) 77–85. D.-S. Wang, S.-Y. Chang, T.-S. Chen, T.-H. Chou, Y.-C. Huang, J.-B. Wu, M.-S. Leu, H.-J. Lai, Stress writing textured graphite conducting wires/patterns in insulating amorphous carbon matrix as interconnects, Sci. Rep. 7 (1) (2017) 9727. F. Nazeer, Z. Ma, Y. Xie, L. Gao, A. Malik, M.A. Khan, F. Wang, H. Li, A novel fabrication method of copper–reduced graphene oxide composites with highly aligned reduced graphene oxide and highly anisotropic thermal conductivity, RSC Adv. 9 (31) (2019) 17967–17974. F. Nazeer, Z. Ma, L. Gao, M. Abubaker Khan, A. Malik, F. Wang, H. Li, Effect of particle size on mechanical and anisotropic thermal conductivity of copper-reduced graphene oxide composites, Results Phys. 14 (2019) 102432. H. Yue, L. Yao, X. Gao, S. Zhang, E. Guo, H. Zhang, X. Lin, B. Wang, Effect of ballmilling and graphene contents on the mechanical properties and fracture mechanisms of graphene nanosheets reinforced copper matrix composites, J. Alloy. Comp. 691 (2017) 755–762. Y. Jiang, D. Wang, S. Liang, F. Cao, J. Zou, P. Xiao, Effect of local alloying on interfacial bonding in laminated copper matrix composites reinforced by carbon nanotubes, Mater. Sci. Eng., A 748 (2019) 173–179. K. Chu, C. Jia, H. Guo, W. Li, On the thermal conductivity of Cu–Zr/diamond composites, Mater. Des. 45 (2013) 36–42. K. Chu, F. Wang, Y.-b. Li, X.-h. Wang, D.-j. Huang, H. Zhang, Interface structure and strengthening behavior of graphene/CuCr composites, Carbon 133 (2018) 127–139. Y.J. Mai, F.X. Chen, W.Q. Lian, L.Y. Zhang, C.S. Liu, X.H. Jie, Preparation and tribological behavior of copper matrix composites reinforced with nickel nanoparticles anchored graphene nanosheets, J. Alloy. Comp. 756 (2018) 1–7.
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
Short communication
Excellent mechanical properties of copper-graphite composites with the addition of tantalum alloying element
T
Faisal Nazeera,b, Zhuang Maa,b, Lihong Gaoa,b,∗, Abdul Malika,b, Muhammad Abubaker Khana,b, Fuchi Wanga,b, Hezhang Lia,b a b
School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, 100081, China National Key Laboratory of Science and Technology on Materials Under Shock and Impact, Beijing, 100081, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Hybrid composites Strength-ductility Bending strength Hardness Thermal conductivity
In this study, the effect of novel metal tantalum was investigated on the properties of copper-graphite composites. The complete mechanical behavior of copper-tantalum-graphite hybrid composites was examined. The addition of tantalum increased the compressive, tensile and bending strength of composites as well as the hardness and thermal conductivity. The compression, tensile, bending and hardness values for Cu–Ta-GF (0.5) composites are 20.7%, 138%, 69% and 93% higher than pure Cu and these are also far better than Cu-GF composites. The excellent mechanical and thermal properties with good relation of strength-ductility ratio open up a new window to use these materials as heat sinks in thermal packaging system.
Metal matrix composites have been extensively used in many fields such as aerospace, vehicles and thermal packaging industries [1]. Copper is the best choice as a metal matrix due to its excellent properties such as higher thermal and electrical conductivity, cost-effective but has poor mechanical properties [2,3]. To improve the properties of Cu matrix different kinds of filler are used such as CNTs [4], graphite [5,6] and graphene oxide [7–9]. These fillers have the potential to increase the mechanical properties of the Cu matrix but there are several problems such as interface bonding and strengthening behavior of Cu. To improve further the properties of these metal-carbon composites the third element introduces to enhance their properties. The typical elements are used to improve the interface bonding and improve the mechanical properties are Titanium (Ti) [10], Zirconium (Zr) [11], Chromium (Cr) [12] and Nickel (Ni) [13]. These elements can increase the strength of composites but the ductility is reduced. To maintain the strength, ductility and interface bonding is still a challenge. Tantalum as third phase in the Cu-GF composites is a good choice due to its extra ordinary mechanical properties such as high young modulus (186 GPa), excellent Vickers hardness (870–1200 Mpa) and highly ductile material. Most of the traditional hard materials like Titanium and Silicon they have high young modulus values but their ductility is not very good. The aim of this work to increase the overall mechanical properties of Cu-GF composites so we choose this rare metal to use as a third phase instead of traditional element. In this work, we introduced new rare metal tantalum (Ta) to
∗
enhance the mechanical properties and interface bonding of Cu-GF composites prepared via ball milling and molecular level mixing followed by hot press sintering. The introduction of new rare metal has a great influence on the microstructural and mechanical properties of CuGF composites. The copper and tantalum powder is mixed by keeping the constant ratio of 1 wt% of tantalum powder. The powders are mixed through wet ball milling with the help of ethanol solvent for 4 h by using zirconium ball and ball to powder ratio was set 15:1. After that powder was dried through vacuum filtration machine and put in an oven for 24 h for further dryness. The GF was ultra-sonicated in the ratio of ethanol to water 9:1 for 30 min in an ultra-sonication machine. After that, the ultra-sonicated GF solution was mixed with copper and tantalum dried powder by mechanical mixing for 4 h to not destroy the structure of powders. The hybrid composite powders were dried and put in an oven for 48 h. The composites powder was annealed before sintering at 400C for 2 h in the presence of argon and nitrogen gas to remove the oxygen functional group from the composites. These oxygen functional cause voids during the sintering process and as the results the overall properties of composites deteriorate. The dried hybrid composite powder was loaded into a graphite die having inner diameter 25 mm and length 10 mm for hot press sintering. The temperature and pressure were set 980C° and 30 MPa for 4 h during the hot press sintering process. The temperature was raised at the constant rate of 10C°/min during the sintering process and the pressure was applied when the temperature
Corresponding author. School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, 100081, China. E-mail address: [email protected] (L. Gao).
https://doi.org/10.1016/j.vacuum.2019.108913 Received 23 July 2019; Received in revised form 24 August 2019; Accepted 28 August 2019 Available online 29 August 2019 0042-207X/ © 2019 Published by Elsevier Ltd.
Vacuum 169 (2019) 108913
F. Nazeer, et al.
Fig. 1. Powders SEM analysis (a) Cu (b) GF (c) Ta (d) Cu-GF (0.5) (e) EDX (f) Cu–Ta-GF (0.5).
that with the addition of GF and Ta the yield strength (YS) and ultimate compressive strength (UCS) of Cu-GF and Cu–Ta-GF are increased significantly. The YS and UCS of Cu–Ta-GF (0.5) composites are 147 MPa and 780 MPa which are 105% and 20.7% higher than pure Cu which have YS (71 MPa) and UCS (646 MPa), respectively. Only with the addition of GF in the Cu matrix also enhance the YS and UCS values of CuGF composites. The similar kind of phenomenon is also observed during the tensile testing of pure Cu and the composites. The yield strength (YS) and ultimate tensile strength (UTS) are increased significantly by the addition of GF and by further adding the Ta in the Cu-GF composites. The YS and UTS for Cu–Ta-GF (0.5) composites are 148 MPa and 276 MPa which are 138% and 53% higher than pure Cu as well higher than Cu-GF composites. The addition of GF and Ta enhanced the YS and UTS greatly due to the following strengthening mechanism. There are mainly six mechanisms involved in the strengthening of materials such as load transfer, thermal mismatch, Orowan looping system, solid solution strengthening, precipitation strengthening and grain refinement. In the present work, there are mainly first mechanism load transfer is involved to improve the YS and UTS of the composites. It is also worth noting in the tensile behavior of Cu-GF (1) and Cu–Ta-GF (0.5) double yield strength phenomenon is observed at the strain rate 1 and 3%. While this phenomenon is absent in the pure Cu and other two composites materials. One of the reasons behind this is that the first yielding point is due to matrix yielding while the second point is due to reinforcement yielding. As we know the GF and Ta have high values of UTS while the toughness values of Ta is better than GF. The GF has the low ability to resist again the crack propagation while the alloying element Ta supports the Cu-GF composites resist again the tensile loading due to this we achieve high strength-ductility values for Cu–TaGF (0.5) composites. However, the double yielding points are also needed to be further investigated in future. The relationship between UTS and elongation of Cu and different composites can be seen in Fig. 3c. The addition of GF increases the values of UTS but with the sacrifice of elongation while the addition of alloying element maintains both the UTS and elongation of Cu–Ta-GF composites to a higher extent value. The bending strength of Cu-GF and Cu–Ta-GF (0.5) composites are also increased significantly as can be revealed in Fig. 3d. The value of bending strength for pure Cu is 280 MPa while for Cu-GF (1) and Cu–Ta-GF (0.5) the values are 334 and 474 MPa, which are 19% and 69% higher than pure Cu, respectively. Due to the high ductility property of the composites, none of the samples is broken during the testing and bending into the rectangular shape. The Vickers hardness values of pure Cu and different composites are demonstrated in Fig. 3e. Like all the other mechanical properties the hardness values of Cu-GF
reached at 600 °C under the Ar gas atmosphere. The microstructure analysis of powders and bulk composites was carried out with the help of scanning electron microscopy (SEM, Hitachi S-4800, Japan) equipped with energy dispersive spectroscopy (EDS). Compressive strength of composites was measured with the help of (INSTRON-5566, Norwood, America) having sample dimensions diameter 3 mm and height 4 mm. For each composite three sample were carried out to measure the compression test and then take the average result. The tensile test was performed with an (Instron universal material machine) with the crosshead speed of 0.5 mm/min. The sample was machined in the dog-bone shaped with the gauge length 12 mm, gauge width 3 mm and thickness 2 mm. Vickers hardness was calculated with the help of (AHVD-1000, China) by applying 100 gF and dwelling time was set 15 s and seven indentations were observed for each sample. The bending strength of Cu, Cu-GF and Cu–Ta/GF composites of dimensions 20 mm × 4 mm × 3 mm was measured by threepoint bending method with a crosshead speed of 0.5 mm/min and span of 30 mm at room temperature according to electro-mechanical universal testing machine (INSTRON-5566, Norwood, America). Fig. 1 shows the microstructure analysis of as received powders as well as Cu–Ta-GF hybrid composites powders. The SEM image of Cu is after ball milled which shows the typical flake-like the structure of Cu powder which changes during the ball milling process. The Fig. 1 (b, c) are as received the graphite and tantalum powders. Fig. 1d is the Cu-GF composites after the molecular level mixing and EDX analysis clearly represent the presence of GF in the composite powder while in Fig. 1f the presence of Ta powder can also be seen in the GF/Cu–Ta hybrid composites powders. At 0.5 and 1 wt%, GF the interface between Cu and GF is really strong which can be seen in the inset of Fig. 2a, b. As we can see at very high resolution 500 nm the interface is really strong and no void is present at the interface of Cu and GF. The GF particles are aligned well in the Cu matrix during the sintering process perpendicular to the applied force direction. With the addition of Ta at a low percentage of GF (0.5 wt%), the mixing is really good which can be seen in the area marked with the circle in Fig. 2c and still no obvious voids were seen in this figure. By increasing the GF wt% and the addition of Ta cause to a mismatch between the Ta and GF which creates the significant voids between them are seen in the inset of Fig. 2d. The EDX analysis of Cu–Ta-GF clearly shows the presence of each element in the bulk composites. The agglomeration of Ta particles is obvious at a higher percentage of GF while it can't be seen with a lower percentage of GF. The complete mechanical behavior of Cu-GF and Cu–Ta-GF composites are shown in Fig. 3. Compression test curve clearly indicates 2
Vacuum 169 (2019) 108913
F. Nazeer, et al.
Fig. 2. Cross-sectional microstructure analysis of Cu-GF and Cu–Ta-GF composites. (a) Cu-GF (0.5) (b) Cu-GF (1) (c) Cu–Ta-GF (0.5) (d) Cu–Ta-GF (1).
addition of Ta element the density of Cu-0.5 GF-1Ta is really good while the density of Cu-1GF-Ta is very low due to the presence of many voids in the composites. The SEM fractographs of Cu, Cu-GF and Cu–Ta-GF are shown in Fig. 4. In Fig. 4a the Cu shows the ductile fracture which is a common structure of Cu fracture. By the addition of GF in the Cu matrix, the dimples are reduced and some cracks are produced in the fracture which means the ductility of the composites reduced and the strength is increased which is in good agreement with our tensile testing curves. Moreover, the addition of Ta in the Cu-GF composites produced the small and larger dimples in the fracture surface of composites. The presence of large dimples indicates that the materials absorb more
and Cu–Ta-GF have a similar trend and increased significantly compared with pure Cu. The hardness values for Cu-GF (1) and Cu–Ta-GF (0.5) are observed 60 HV and 83 HV which are 39% and 93% higher than pure Cu (43 HV). The addition of Ta particles in the Cu-GF composites strengthen the materials and counteracts to pushing the force on the boundaries of Cu-GF composites which leads to increase the hardness of materials according to Zener pinning effect. The mixing of Cu–Ta-GF (0.5) is excellent which reveals in Fig. 2c also help to improve the hardness values of this composites. The density of the composites was measured with the help of Archimedes principle are shown in Fig. 3f. Firstly with the addition of GF 0.5 and 1 wt% the relative density of Cu-GF composites are 92.4 and 97.8%. Furthermore, with the
Fig. 3. Mechanical properties of pure Cu, Cu-GF and Cu–Ta-GF composites (a) compressive strength (b) Tensile property (c) UTS vs Elongation (d) Bending strength (e) Vickers hardness (f) Relative density. 3
Vacuum 169 (2019) 108913
F. Nazeer, et al.
Fig. 4. Fracture morphology (a) Cu (b) Cu-GF (0.5) (c) Cu-GF (1) (d,e) Cu–Ta-GF (0.5) (f) Cu–Ta-GF (1).
energy during the fracture which leads to demonstrate the better plastic toughness of composites. Another phenomenon is also observed in Fig. 4d the Ta particles makes a bridging and this bridge mechanism is one of the main cause to enhance the ductility of the composites. Due to these reasons, the Cu–Ta-GF (0.5) have excellent UTS and elongation values. With the addition of more GF in the Cu–Ta composites the values of UTS and elongation decrease significantly. At a higher ratio of GF and Ta, the obvious agglomeration can be seen in the fracture mechanism and can also reveal in the SEM figures of composites which cause to reduce the strength due to poor mixing. The Cu-GF and Cu–Ta-GF composites were successfully fabricated through flake powder metallurgy routes and check the effect of Ta alloying element on the mechanical properties of Cu-GF composites. With the addition of Ta, the interface interaction of Cu-GF (0.5) composites significantly improves which is favorable for the better mechanical properties of the composites. Compressive, tensile and bending strength of Cu increased with the addition of GF and further enhanced by the addition of Ta rare metal. The compression, tensile, bending and hardness values for Cu–Ta-GF (0.5) composites are 20.7%, 138%, 69% and 93% higher than pure Cu and these are also far better than Cu-GF composites. Therefore, this work focus on the improved the interfacial bonding of Cu-GF composites and a remarkable increase in the mechanical properties of Cu and Cu-GF composites with the addition of a very low percentage of new alloying element.
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
Acknowledgement
[12]
The authors acknowledge the financial support of the National Natural Science Foundation of China (51772027).
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