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An investigation of the effect of SiC particle size on Cu–SiC composites
Composites: Part B 43 (2012) 1813–1822
Contents lists available at SciVerse ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
An investigation of the effect of SiC particle size on Cu–SiC composites G. Celebi Efe, M. Ipek, S. Zeytin, C. Bindal ⇑ Sakarya University, Engineering Faculty, Department of Metallurgy and Materials Engineering, Esentepe Campus, 54187 Sakarya, Turkey
a r t i c l e
i n f o
Article history: Received 28 July 2011 Received in revised form 1 December 2011 Accepted 2 January 2012 Available online 12 January 2012 Keywords: E. Sintering A. Particle-reinforcement B. Electrical properties B. Hardness
a b s t r a c t In this study mechanical properties of copper were enhanced by adding 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles into the matrix. SiC particles of having 1 lm, 5 lm and 30 lm sizes were used as reinforcement. Composite samples were produced by powder metallurgy method and sintering was performed in an open atmospheric furnace at 700 °C for 2 h. Optical and SEM studies showed that the distribution of the reinforced particle was uniform. XRD analysis indicated that the dominant components in the sintered composites were Cu and SiC. Relative density and electrical conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Hardness of the composites increased with both amount and the particle size of SiC particles. A maximum relative density of 98% and electrical conductivity of 96% IACS were obtained for Cu–1 wt.% SiC with 30 lm particle size. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Today, copper and copper alloys remain one of the major groups of commercial metals, ranking third behind only iron/steel and aluminum in production and consumption. They are widely used because of their excellent electrical and thermal conductivities, outstanding resistance to corrosion, ease of fabrication, and good strength and fatigue resistance. Pure copper is used extensively for cables and wires, electrical contacts, and a wide variety of other parts that are required to pass electrical current [1]. But its application at high temperature is limited due to poor mechanical properties [2,3]. Adding hard particles into copper matrix, not only enhances the mechanical performance and wear resistance but also keeps its desirable electrical and thermal conductivity, thus the application scope of copper is extended [4,5]. Among copperbased composites, high strength, high conductivity, resistance to high temperatures, and wear, are very important and necessary qualities for electric contact materials, resistant electrodes, and many other industrial applications as compared to pure copper and copper alloys [6–10]. Copper-base metal matrix composites with reinforcing ceramic particles such as oxides, borides and carbides were developed to utilize as electrode materials because the ceramic particles are stable at high temperatures [11]. SiC particles could be used as reinforcement material to enhance the strength of copper matrix [12]. The mechanical and physical characteristics, especially the high specific strength and modulus of the SiC-fibers, make them an interesting choice for reinforcing metal and ceramic ⇑ Corresponding author. Tel.: +90 264 295 57 59; fax: +90 264 295 56 01. E-mail address: [email protected] (C. Bindal). 1359-8368/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesb.2012.01.006
matrix composites. Temperatures up to 800 °C have no significant effect on these properties [13], thus SiC is a key candidate for hightemperature applications [14]. Cu–SiC composites have attracted strong interest as they combine high thermal and electrical conductivity with mechanical strength, mouldability and low production cost [12,15,16]. They could be used as electrical contact materials in relays, contactors, switches, circuit breaks, electronic packaging where good electrical and thermal conductivity as well as welding or brazing properties are required [12,16]. In the present work SiC particle reinforced copper matrix composites were produced by powder metallurgy technique. Influence of the particle size and concentration of SiC on mechanical and electrical properties of copper were studied. The morphology, microstructure, microhardness, and electrical property of Cu/SiC composite have been investigated. 2. Experimental details 2.1. Production of test materials In order to manufacture Cu–SiC composites copper powder with 99.9 percent (pct) purity and 10 lm particle size and SiC powder with 99.5 percent (pct) purity and 1, 5 and 30 lm particle size were used as starting materials. The powders including 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC reinforcement were mixed mechanically. Prior to sintering, the mixture was cold pressed into a cylindrical compact in a metal die of 15 mm in diameter under a axial pressure of 280 MPa (Fig. 1). The sintering of Cu and Cu–SiC composites were performed at 700 °C for 2 h in an open atmospheric furnace. Within the furnace compacted samples were embedded
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(a)
(b)
(c)
Fig. 1. Schematic presentation of die used: (a) die, (b) cross-section of die, and (c) pressed compact sample.
radiation with a wavelength of 1.5418 A over a 2h range of 10– 90°. The relative densities of the samples were measured using the Archimedes’ principle. Microstructural analyses were performed by scanning electron microscopy and optical microscopy. In order to detect the Cu, SiC and any oxide of Cu and SiC particles, EDS analyses were performed. Microhardness of both pure copper and composites were determined using Vickers indentation technique with a load of 50 g for Cu–SiC composites with 1 lm SiC particle, and of 100 g for the composites with 5–30 lm SiC particle. The samples were first surface finished and then five measurements were performed on each sample and averaged to obtain the accurate hardness of the specimen. Microhardness measurements were performed by taking care of the indentation mark to include the Cu grains and SiC particles homogenously. Electrical conductivities of polished samples were determined by GE model electric resistivity measurement instrument. 3. Results and discussion 3.1. Microstructure
into the graphite powder. As soon as the samples were removed from the furnace at 700 °C they were immediately pressed with a load of 850 MPa in order to increase the relative density and electrical conductivity. 2.2. Characterization Phase analyses of starting powders and sintered samples were performed via Rigaku X-ray diffractometer by using Cu Ka
Fig. 2 illustrates the SEM microstructures of Cu powder and SiC reinforcement agent of different particle size. As can be seen copper powder is in spherical shape and 10 lm size and SiC particles are in irregular and angular shape and 1, 5, 30 lm size. Microstructural morphologies of polished surfaces of the sintered composites reinforced with SiC particles of different sizes were shown in Fig. 3. Grey regions imply Cu matrix and dark grey and cornered particles imply the reinforcement component of SiC.
Fig. 2. SEM micrographs of starting powders of: (a) Cu powder with 10 lm particle size, (b) SiC powder with 1 lm particle size, (c) SiC powder with 5 lm particle size, and (d) SiC powder with 30 lm particle size.
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Fig. 3. Optical micrographs of Cu–SiC composites reinforced with different content and particle size of SiC sintered at 700 °C for 2 h.
It is seen from Fig. 3 that SiC particles homogeneously dispersed in Cu matrix and were generally surrounded by Cu grains for the Cu–SiC composites reinforced with 1 lm SiC particles. For the composite materials, it is very important to obtain homogeneous reinforcement in the matrix in order to enhance mechanical, electrical and thermal properties [17]. Etched micrograph of sintered pure copper sample was given in the Fig. 4 and it can be seen that the morphology of Cu grains are approximately spherical and at about 10 lm size. SEM images of sintered composites including 1 and 5 wt.% SiC were given in Fig. 5. It is seen from Fig. 5 that SiC particles of 1 lm were located at the grain boundaries of copper grains. So as to confirm this, SEM X-ray dot mapping analysis was performed on Cu–3 wt.% SiC with 1 lm particle size (Fig. 6). Black regions in SEM micrograph (Fig. 6) illustrates SiC particles whereas white points in Fig. 5 probably indicate the Al2O3 which might come from polishing media used during metallographing preparation of the sample. It is clear from the Fig. 6 that oxygen and aluminum exist together in the matrix suggesting presence of Al2O3. While no oxygen was found in the EDS analysis of Cu–SiC composite having 5 and 30 lm SiC particle (Fig. 7b and c), slight oxygen was detected at Cu–SiC interface of the sample with 1 lm SiC particle (Fig. 7a, Mark3). This is due to the increasing surface area of SiC particles (Fig. 7). Kang and Kang [18] reported that SiC in con-
Fig. 4. SEM micrograph of pure copper etched with 40% HNO3 + H2O solution sintered at 700 °C for 2 h.
tact with Cu was decomposed into Si and fine carbon at high temperatures. The presence of oxygen in the Cu–SiC interface can be attributed to this fact. But it is obvious that there is a good bonding between Cu matrix and SiC reinforcement agent and no other
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Fig. 5. SEM micrographs of Cu–SiC composites reinforced with different content and particle size of SiC sintered at 700 °C for 2 h.
phase formation was seen. Similarly SEM-Map analyse of Cu– 3 wt.% SiC with 30 lm particle size indicates that black and cornered particles show SiC, oxygen and aluminum exist together (Fig. 8).
tured by powder metallurgy method. This result is very important as far as the electrical conductivity point of view is concerned for related materials. 3.3. Relative density
3.2. XRD In Fig. 9, the XRD patterns of initial copper and SiC powders are shown. It is seen from Fig. 9 that there is no other component except Cu and SiC in the powders. XRD patterns of the composites with SiC particles of different sizes are similar to each other and consist of copper and SiC peaks dominantly (Figs. 10–12). SiC peaks become clear with increasing weight percentage and particle size of SiC. No oxide peak was observed in the XRD analyses of Cu–SiC composites after sintering at 700 °C for 2 h. XRD and EDS analysis showed that there is not any formation of copper oxide and silicon dioxide in the Cu–SiC composites which were manufac-
Relative densities were calculated using Archimedes’ principle. The evolution of density as a function of SiC content and particle size is reported by using the contour diagram in Fig. 13. In order to predict the variation of relative density, hardness and electrical conductivity of test materials, a contour diagram was established for industrial applications. By means of these diagrams it is possible to estimate results for the conditions that we did not perform experimentally. The density increases with the size of SiC but decreases with weight percentage of SiC. Maximum density was reached for a SiC size of 30 lm (between 97.7 ± 0.6 and 96.2 ± 0.8% for the whole composition). In composite with low
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Fig. 6. SEM map analysis of Cu–3 wt.% SiC having 1 lm size SiC composite sintered at 700 °C for 2 h.
SiC volume fraction, less Cu–SiC interface means less copper atom diffusion barrier, copper atoms can diffuse easily and fill the interstices between the SiC particles, thus leading to a higher densification of the composite [3,19]. This is also due to the density of SiC particles being much lower than that of copper [20] Similarly with increasing particle size of SiC, diffusion barriers of composite decreases and hence relative density increases. That is to say in Cu–SiC composites reinforced with 1 lm SiC particles, defective regions and mostly Cu–SiC interfaces are in majority.
search [22]. It is thought that higher amount of ceramic particles in the matrix would result in more dislocations that increases the hardness of the composite [19,23,24]. Hardness of composites increased also with increasing particle size of SiC. However, the average hardness of Cu–SiC composite specimen with 5 and 30 lm SiC particles is higher than that of the Cu–SiC composite specimen with 1 lm SiC particles. This may be due to the improved bond between the matrix and the reinforcement [21].
3.5. Electrical conductivity 3.4. Hardness The measured hardness values for Cu and Cu–SiC composites versus SiC particle size and content were shown in Fig. 14 by using contour diagram. A contour diagram was established for predicting hardness of Cu–SiC composite as a function of particle size and the amount of reinforcing SiC constituent. Apparently, the hardness of copper improves considerably with the additions of SiC particles at the expense of its ductility [20] that can be attributed to higher hardness of SiC [21]. This result was consistent with another re-
Electrical conductivity values of Cu and Cu–SiC composites, depends on the particle size and rate of reinforcement which were given in the Fig. 15 by using the contour diagram. Electrical conductivity of composites decreases with increasing weight percentage of SiC. Electrical conductivity of a metal mainly depends on the motion of electrons in the structure. Ceramic based SiC particles distort the structure and forms barrier for copper electrons providing electrical conductivity. Therefore electrical conductivity of composites decreases with increasing the amount of SiC
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Fig. 7. SEM-EDS analysis of: (a) Cu–2 wt.% SiC (1 lm), (b) Cu–5 wt.% SiC (5 lm), and (c) Cu–5 wt.% SiC (30 lm) composite sintered at 700 °C for 2 h.
[25–27]. When coarse SiC particles were used, the conductivity increased remarkably. This result is in very good agreement with study of Hussain et al. [28]. With the addition of coarse SiC particles into the copper matrix, electrons can scatter easily and hence electrical conductivity increases [27]. The electrical conductivity of two-phase composites is determined by many factors, such as: (i) the electrical conductivities of the constituent phases; (ii) the volume fractions and distributions of the constituent
phases; (iii) the size, shape, orientation and spacing of the phases; (iv) interaction between phases; and (v) the preparation method. Usually, the existence of a continuous copper network strongly affects the electrical conductivity of a particulate-reinforced Cu matrix composite. Once a highly conducting network is present across the whole composite, the reinforced particles lose their connectivity and act as isolated clusters in a highly conductive phase; hence the electrical conductivity of the composite ap-
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Fig. 8. SEM map analysis of Cu–3 wt.% SiC having 30 lm size SiC composite sintered at 700 °C for 2 h.
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proaches that of pure copper [29]. In the present work, the uniform distribution of SiC particles in the copper matrix and the relatively clean interface between them promote the formation of conducting network, leading to good electrical conductivity of the composite.
4. Conclusions In conclusion, a new Cu–SiC composite has been successfully fabricated by the PM method at 700 °C under a pressure of 280 MPa in the present work. The presence of copper and SiC
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Fig. 14. Hardness contour diagram of Cu–SiC composites sintered at 700 °C for 2 h as a function of SiC content and particle size.
was verified by XRD and EDS analysis. As a result of hot pressing just after the sintering process, conductive Cu–SiC composite with high density has been produced through PM method at lower sintering temperatures. The properties of Cu–SiC composites such as relative density, hardness and electrical conductivity have been improved with increasing particle size of SiC. With the addition of SiC particulates, hardness of copper is effectively improved without much loss of the electrical conductivity. Thus SiC is proven
to be a promising reinforcement for copper, especially in the field of electrical components.
Acknowledgements The authors thank to experts Fuat Kayis for performing XRD and SEM-EDS studies and special appreciation are extended to techni-
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: Experimental
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cian Ersan Demir of Sakarya University for assisting with experimental studies. This work was conducted under a project supported by TUBITAK with the contract number of 106M118. The special appreciations are extended to Assoc. Prof. Dr. Sakıp Koksal of Sakarya University for his notable supports. References [1] Joseph RD, Copper and copper alloys. ASM international handbook. ASM; 2001. [2] Zhang R, Gao L, Guo J. Effect of Cu2O on the fabrication of SiCp/Cu nanocomposites using coated particles and conventional sintering. Composites: Part A 2004;35:1301–5. [3] Celebi Efe GF, Altinsoy I, Ipek M, Zeytin S, Bindal C. Some properties of Cu–SiC composites produced by powder metallurgy method. Kovove Mater 2011;49:131–6. [4] Zhu J, Liu L, Zhao H, Shen B. Microstructure and performance of electroformed Cu/nano-SiC composite. Mater Des 2007;28:1958–62. [5] Celebi Efe G, Yener T, Altinsoy I, Ipek M, Zeytin S, Bindal C. The fabrication and properties of SiC particulate reinforced copper matrix composites. In: 13th international materials symposium, Denizli, Turkey, 13–15th October 2010.
[6] Dhokey NB, Paretkar RK. Study of wear mechanisms in copper-based SiCp (20% by volume) reinforced composite. Wear 2008;265:117–33. [7] Tjong SC, Lau KC. Abrasive wear behavior of TiB2 particle-reinforced copper matrix composites. Mater Sci Eng A 2000;82:183–6. [8] Hea J, Zhaoa N, Shi C, Dua X, Li J, Nashc P. Reinforcing copper matrix composites through molecular-level mixing of functionalized nanodiamond by co-deposition route. Mater Sci Eng A 2008;490:293–9. [9] Zhan Y, Zhang G. The effect of interfacial modifying on the mechanical and wear properties of SiCp/Cu composites. Mater Lett 2003;57:4583–91. [10] Efe GC, Altınsoy I, Yener T, Ipek M, Zeytin S, Bindal C. Investigation of some properties of SiC particle reinforced copper composites, 5th IPMC, AnkaraTurkey; 2008. [11] Kwon DH, Nguyen TD, Huynh KX, Choi PP, Chang MG, Yuma YS, et al. Mechanical, electrical and wear properties of Cu–TiB2 nanocomposites fabricated by MA-SHS and SPS. J Ceram Process Res 2006;7(3):275–9. [12] Zhang R, Gao L, Guo J. Temperature-sensitivity of coating copper on submicron silicon carbide particles by electroless deposition in a rotation flask. Surf Coat Technol 2003;166:67–71. [13] http://www.copper.org/education/production.html. [14] Celebi Efe GF. Development of conductive copper composites reinforced with SiC. Ph.D. Thesis, Sakarya University, Institute of Science and Technology; June 2010. [15] Barmouz M, Asadi P, BesharatiGivi MK, Taherishargh M. Investigation of mechanical properties of Cu/SiC Composite fabricated by FSP: effect of SiC particles’ Size and volume fraction. Mater Sci Eng A 2011;528:1740–9. [16] Treichler R, Weissgaerber T, Kiendl T. Tofsims analysis of Cu–SiC composites for thermal management applications, vol. 252. Elsevier; 2004. p. 7086–88. [17] Kang HK. Microstructure and electrical conductivity of high volume Al2 O3reinforced copper matrix composites produced by plasma spray. Surf Coat Technol 2005;190:448–52. [18] Kang HK, Kang SB. Thermal decomposition of silicon carbide in a plasma sprayed Cu/SiC composite deposit. Mater Sci Eng A 2006;428:336–45. [19] Shu K-M, Tu GC. The microstructure and the thermal expansion characteristics of Cu/SiCp composites. Mater Sci Eng 2003;349:236–47. [20] Tjong SC, Lau KC. Tribological behavior of SiC particle-reinforced copper matrix composites. Mater Lett 2000;43:274–80. [21] Ramesh CS, Ahmed RN, Mujeebu MA, Abdullah MZ. Fabrication and study on tribological characteristics of cast copper-TiO2-boric acid hybrid composites. Mater Des 2009;30:1632–7. [22] Lin YC, Li HC, Liou SS, Shie MT. Mechanism of plastic deformation of powder metallurgy metal matrix composites of Cu–Sn/SiC and 6061/SiC under compressive stress. Mater Sci Eng A 2004;373:363–9. [23] Celebi Efe G, Altinsoy I, Yener T, Ipek M, Zeytin S, Bindal C. Characterization of cemented Cu–SiC composites. Vacuum 2010;85:643–7. [24] Zhu J, Liu L, Hu G, Shen B, Hu W, Ding W. Study on composite electroforming of Cu/SiC composites. Mater Lett 2004;58:1634–7. _ Yener T, Ipek _ [25] Celebi Efe G, Altinsoy I, M, Zeytin S, Bindal C. An investigation on cemented cu reinforced by SiC particles. In: Proceedings of ICAMMM 2010, Sultan Qaboos University, Oman, 13–15 December 2010. [26] Smith W. Principles of materials science and engineering. 2nd ed. McGrawHill; 1990. [27] Richerson DW. Modern ceramic engineering. Taylor & Francis CRC Press; 2006. [28] Hussain S, Barbariol I, Roitti S, Sbaizero O. Electrical conductivity of an insulator matrix (alumina) and conductor particle (molybdenum) composites. J Eur Ceram Soc 2003;23:315–21. [29] Zhang J, He L, Zhou Y. Highly conductive and strengthened copper matrix composite reinforced by Zr2Al3C4 particulates. Scripta Mater 2009;60:976–9.
Contents lists available at SciVerse ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
An investigation of the effect of SiC particle size on Cu–SiC composites G. Celebi Efe, M. Ipek, S. Zeytin, C. Bindal ⇑ Sakarya University, Engineering Faculty, Department of Metallurgy and Materials Engineering, Esentepe Campus, 54187 Sakarya, Turkey
a r t i c l e
i n f o
Article history: Received 28 July 2011 Received in revised form 1 December 2011 Accepted 2 January 2012 Available online 12 January 2012 Keywords: E. Sintering A. Particle-reinforcement B. Electrical properties B. Hardness
a b s t r a c t In this study mechanical properties of copper were enhanced by adding 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles into the matrix. SiC particles of having 1 lm, 5 lm and 30 lm sizes were used as reinforcement. Composite samples were produced by powder metallurgy method and sintering was performed in an open atmospheric furnace at 700 °C for 2 h. Optical and SEM studies showed that the distribution of the reinforced particle was uniform. XRD analysis indicated that the dominant components in the sintered composites were Cu and SiC. Relative density and electrical conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Hardness of the composites increased with both amount and the particle size of SiC particles. A maximum relative density of 98% and electrical conductivity of 96% IACS were obtained for Cu–1 wt.% SiC with 30 lm particle size. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Today, copper and copper alloys remain one of the major groups of commercial metals, ranking third behind only iron/steel and aluminum in production and consumption. They are widely used because of their excellent electrical and thermal conductivities, outstanding resistance to corrosion, ease of fabrication, and good strength and fatigue resistance. Pure copper is used extensively for cables and wires, electrical contacts, and a wide variety of other parts that are required to pass electrical current [1]. But its application at high temperature is limited due to poor mechanical properties [2,3]. Adding hard particles into copper matrix, not only enhances the mechanical performance and wear resistance but also keeps its desirable electrical and thermal conductivity, thus the application scope of copper is extended [4,5]. Among copperbased composites, high strength, high conductivity, resistance to high temperatures, and wear, are very important and necessary qualities for electric contact materials, resistant electrodes, and many other industrial applications as compared to pure copper and copper alloys [6–10]. Copper-base metal matrix composites with reinforcing ceramic particles such as oxides, borides and carbides were developed to utilize as electrode materials because the ceramic particles are stable at high temperatures [11]. SiC particles could be used as reinforcement material to enhance the strength of copper matrix [12]. The mechanical and physical characteristics, especially the high specific strength and modulus of the SiC-fibers, make them an interesting choice for reinforcing metal and ceramic ⇑ Corresponding author. Tel.: +90 264 295 57 59; fax: +90 264 295 56 01. E-mail address: [email protected] (C. Bindal). 1359-8368/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesb.2012.01.006
matrix composites. Temperatures up to 800 °C have no significant effect on these properties [13], thus SiC is a key candidate for hightemperature applications [14]. Cu–SiC composites have attracted strong interest as they combine high thermal and electrical conductivity with mechanical strength, mouldability and low production cost [12,15,16]. They could be used as electrical contact materials in relays, contactors, switches, circuit breaks, electronic packaging where good electrical and thermal conductivity as well as welding or brazing properties are required [12,16]. In the present work SiC particle reinforced copper matrix composites were produced by powder metallurgy technique. Influence of the particle size and concentration of SiC on mechanical and electrical properties of copper were studied. The morphology, microstructure, microhardness, and electrical property of Cu/SiC composite have been investigated. 2. Experimental details 2.1. Production of test materials In order to manufacture Cu–SiC composites copper powder with 99.9 percent (pct) purity and 10 lm particle size and SiC powder with 99.5 percent (pct) purity and 1, 5 and 30 lm particle size were used as starting materials. The powders including 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC reinforcement were mixed mechanically. Prior to sintering, the mixture was cold pressed into a cylindrical compact in a metal die of 15 mm in diameter under a axial pressure of 280 MPa (Fig. 1). The sintering of Cu and Cu–SiC composites were performed at 700 °C for 2 h in an open atmospheric furnace. Within the furnace compacted samples were embedded
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(a)
(b)
(c)
Fig. 1. Schematic presentation of die used: (a) die, (b) cross-section of die, and (c) pressed compact sample.
radiation with a wavelength of 1.5418 A over a 2h range of 10– 90°. The relative densities of the samples were measured using the Archimedes’ principle. Microstructural analyses were performed by scanning electron microscopy and optical microscopy. In order to detect the Cu, SiC and any oxide of Cu and SiC particles, EDS analyses were performed. Microhardness of both pure copper and composites were determined using Vickers indentation technique with a load of 50 g for Cu–SiC composites with 1 lm SiC particle, and of 100 g for the composites with 5–30 lm SiC particle. The samples were first surface finished and then five measurements were performed on each sample and averaged to obtain the accurate hardness of the specimen. Microhardness measurements were performed by taking care of the indentation mark to include the Cu grains and SiC particles homogenously. Electrical conductivities of polished samples were determined by GE model electric resistivity measurement instrument. 3. Results and discussion 3.1. Microstructure
into the graphite powder. As soon as the samples were removed from the furnace at 700 °C they were immediately pressed with a load of 850 MPa in order to increase the relative density and electrical conductivity. 2.2. Characterization Phase analyses of starting powders and sintered samples were performed via Rigaku X-ray diffractometer by using Cu Ka
Fig. 2 illustrates the SEM microstructures of Cu powder and SiC reinforcement agent of different particle size. As can be seen copper powder is in spherical shape and 10 lm size and SiC particles are in irregular and angular shape and 1, 5, 30 lm size. Microstructural morphologies of polished surfaces of the sintered composites reinforced with SiC particles of different sizes were shown in Fig. 3. Grey regions imply Cu matrix and dark grey and cornered particles imply the reinforcement component of SiC.
Fig. 2. SEM micrographs of starting powders of: (a) Cu powder with 10 lm particle size, (b) SiC powder with 1 lm particle size, (c) SiC powder with 5 lm particle size, and (d) SiC powder with 30 lm particle size.
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Fig. 3. Optical micrographs of Cu–SiC composites reinforced with different content and particle size of SiC sintered at 700 °C for 2 h.
It is seen from Fig. 3 that SiC particles homogeneously dispersed in Cu matrix and were generally surrounded by Cu grains for the Cu–SiC composites reinforced with 1 lm SiC particles. For the composite materials, it is very important to obtain homogeneous reinforcement in the matrix in order to enhance mechanical, electrical and thermal properties [17]. Etched micrograph of sintered pure copper sample was given in the Fig. 4 and it can be seen that the morphology of Cu grains are approximately spherical and at about 10 lm size. SEM images of sintered composites including 1 and 5 wt.% SiC were given in Fig. 5. It is seen from Fig. 5 that SiC particles of 1 lm were located at the grain boundaries of copper grains. So as to confirm this, SEM X-ray dot mapping analysis was performed on Cu–3 wt.% SiC with 1 lm particle size (Fig. 6). Black regions in SEM micrograph (Fig. 6) illustrates SiC particles whereas white points in Fig. 5 probably indicate the Al2O3 which might come from polishing media used during metallographing preparation of the sample. It is clear from the Fig. 6 that oxygen and aluminum exist together in the matrix suggesting presence of Al2O3. While no oxygen was found in the EDS analysis of Cu–SiC composite having 5 and 30 lm SiC particle (Fig. 7b and c), slight oxygen was detected at Cu–SiC interface of the sample with 1 lm SiC particle (Fig. 7a, Mark3). This is due to the increasing surface area of SiC particles (Fig. 7). Kang and Kang [18] reported that SiC in con-
Fig. 4. SEM micrograph of pure copper etched with 40% HNO3 + H2O solution sintered at 700 °C for 2 h.
tact with Cu was decomposed into Si and fine carbon at high temperatures. The presence of oxygen in the Cu–SiC interface can be attributed to this fact. But it is obvious that there is a good bonding between Cu matrix and SiC reinforcement agent and no other
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Fig. 5. SEM micrographs of Cu–SiC composites reinforced with different content and particle size of SiC sintered at 700 °C for 2 h.
phase formation was seen. Similarly SEM-Map analyse of Cu– 3 wt.% SiC with 30 lm particle size indicates that black and cornered particles show SiC, oxygen and aluminum exist together (Fig. 8).
tured by powder metallurgy method. This result is very important as far as the electrical conductivity point of view is concerned for related materials. 3.3. Relative density
3.2. XRD In Fig. 9, the XRD patterns of initial copper and SiC powders are shown. It is seen from Fig. 9 that there is no other component except Cu and SiC in the powders. XRD patterns of the composites with SiC particles of different sizes are similar to each other and consist of copper and SiC peaks dominantly (Figs. 10–12). SiC peaks become clear with increasing weight percentage and particle size of SiC. No oxide peak was observed in the XRD analyses of Cu–SiC composites after sintering at 700 °C for 2 h. XRD and EDS analysis showed that there is not any formation of copper oxide and silicon dioxide in the Cu–SiC composites which were manufac-
Relative densities were calculated using Archimedes’ principle. The evolution of density as a function of SiC content and particle size is reported by using the contour diagram in Fig. 13. In order to predict the variation of relative density, hardness and electrical conductivity of test materials, a contour diagram was established for industrial applications. By means of these diagrams it is possible to estimate results for the conditions that we did not perform experimentally. The density increases with the size of SiC but decreases with weight percentage of SiC. Maximum density was reached for a SiC size of 30 lm (between 97.7 ± 0.6 and 96.2 ± 0.8% for the whole composition). In composite with low
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Fig. 6. SEM map analysis of Cu–3 wt.% SiC having 1 lm size SiC composite sintered at 700 °C for 2 h.
SiC volume fraction, less Cu–SiC interface means less copper atom diffusion barrier, copper atoms can diffuse easily and fill the interstices between the SiC particles, thus leading to a higher densification of the composite [3,19]. This is also due to the density of SiC particles being much lower than that of copper [20] Similarly with increasing particle size of SiC, diffusion barriers of composite decreases and hence relative density increases. That is to say in Cu–SiC composites reinforced with 1 lm SiC particles, defective regions and mostly Cu–SiC interfaces are in majority.
search [22]. It is thought that higher amount of ceramic particles in the matrix would result in more dislocations that increases the hardness of the composite [19,23,24]. Hardness of composites increased also with increasing particle size of SiC. However, the average hardness of Cu–SiC composite specimen with 5 and 30 lm SiC particles is higher than that of the Cu–SiC composite specimen with 1 lm SiC particles. This may be due to the improved bond between the matrix and the reinforcement [21].
3.5. Electrical conductivity 3.4. Hardness The measured hardness values for Cu and Cu–SiC composites versus SiC particle size and content were shown in Fig. 14 by using contour diagram. A contour diagram was established for predicting hardness of Cu–SiC composite as a function of particle size and the amount of reinforcing SiC constituent. Apparently, the hardness of copper improves considerably with the additions of SiC particles at the expense of its ductility [20] that can be attributed to higher hardness of SiC [21]. This result was consistent with another re-
Electrical conductivity values of Cu and Cu–SiC composites, depends on the particle size and rate of reinforcement which were given in the Fig. 15 by using the contour diagram. Electrical conductivity of composites decreases with increasing weight percentage of SiC. Electrical conductivity of a metal mainly depends on the motion of electrons in the structure. Ceramic based SiC particles distort the structure and forms barrier for copper electrons providing electrical conductivity. Therefore electrical conductivity of composites decreases with increasing the amount of SiC
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Fig. 7. SEM-EDS analysis of: (a) Cu–2 wt.% SiC (1 lm), (b) Cu–5 wt.% SiC (5 lm), and (c) Cu–5 wt.% SiC (30 lm) composite sintered at 700 °C for 2 h.
[25–27]. When coarse SiC particles were used, the conductivity increased remarkably. This result is in very good agreement with study of Hussain et al. [28]. With the addition of coarse SiC particles into the copper matrix, electrons can scatter easily and hence electrical conductivity increases [27]. The electrical conductivity of two-phase composites is determined by many factors, such as: (i) the electrical conductivities of the constituent phases; (ii) the volume fractions and distributions of the constituent
phases; (iii) the size, shape, orientation and spacing of the phases; (iv) interaction between phases; and (v) the preparation method. Usually, the existence of a continuous copper network strongly affects the electrical conductivity of a particulate-reinforced Cu matrix composite. Once a highly conducting network is present across the whole composite, the reinforced particles lose their connectivity and act as isolated clusters in a highly conductive phase; hence the electrical conductivity of the composite ap-
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Fig. 8. SEM map analysis of Cu–3 wt.% SiC having 30 lm size SiC composite sintered at 700 °C for 2 h.
20000 18000
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Fig. 10. XRD patterns of Cu and Cu–SiC composites with 1 lm SiC particle size sintered at 700 °C.
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Fig. 11. XRD patterns of Cu and Cu–SiC composites with 5 lm SiC particle size sintered at 700 °C.
proaches that of pure copper [29]. In the present work, the uniform distribution of SiC particles in the copper matrix and the relatively clean interface between them promote the formation of conducting network, leading to good electrical conductivity of the composite.
4. Conclusions In conclusion, a new Cu–SiC composite has been successfully fabricated by the PM method at 700 °C under a pressure of 280 MPa in the present work. The presence of copper and SiC
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: Experimental
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Fig. 13. Relative density contour diagram of Cu–SiC composites sintered at 700 °C for 2 h as a function of SiC content and particle size.
Fig. 14. Hardness contour diagram of Cu–SiC composites sintered at 700 °C for 2 h as a function of SiC content and particle size.
was verified by XRD and EDS analysis. As a result of hot pressing just after the sintering process, conductive Cu–SiC composite with high density has been produced through PM method at lower sintering temperatures. The properties of Cu–SiC composites such as relative density, hardness and electrical conductivity have been improved with increasing particle size of SiC. With the addition of SiC particulates, hardness of copper is effectively improved without much loss of the electrical conductivity. Thus SiC is proven
to be a promising reinforcement for copper, especially in the field of electrical components.
Acknowledgements The authors thank to experts Fuat Kayis for performing XRD and SEM-EDS studies and special appreciation are extended to techni-
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: Experimental
30
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wt. %SiC Fig. 15. Electrical conductivity contour diagram of Cu–SiC composites sintered at 700 °C for 2 h as a function of SiC particle size and content.
cian Ersan Demir of Sakarya University for assisting with experimental studies. This work was conducted under a project supported by TUBITAK with the contract number of 106M118. The special appreciations are extended to Assoc. Prof. Dr. Sakıp Koksal of Sakarya University for his notable supports. References [1] Joseph RD, Copper and copper alloys. ASM international handbook. ASM; 2001. [2] Zhang R, Gao L, Guo J. Effect of Cu2O on the fabrication of SiCp/Cu nanocomposites using coated particles and conventional sintering. Composites: Part A 2004;35:1301–5. [3] Celebi Efe GF, Altinsoy I, Ipek M, Zeytin S, Bindal C. Some properties of Cu–SiC composites produced by powder metallurgy method. Kovove Mater 2011;49:131–6. [4] Zhu J, Liu L, Zhao H, Shen B. Microstructure and performance of electroformed Cu/nano-SiC composite. Mater Des 2007;28:1958–62. [5] Celebi Efe G, Yener T, Altinsoy I, Ipek M, Zeytin S, Bindal C. The fabrication and properties of SiC particulate reinforced copper matrix composites. In: 13th international materials symposium, Denizli, Turkey, 13–15th October 2010.
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