- Email: [email protected]
The effect of SiC particle size on the properties of Cu–SiC composites
Materials and Design 36 (2012) 633–639
Contents lists available at SciVerse ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Short Communication
The effect of SiC particle size on the properties of Cu–SiC composites G. Celebi Efe, 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 12 September 2011 Accepted 9 November 2011 Available online 25 November 2011
a b s t r a c t SiC particulate-reinforced copper composites were prepared by powder metallurgy (PM) method and conventional atmospheric sintering. Scanning electron microscope (SEM), X-ray diffraction (XRD) techniques were used to characterize the sintered composites. The effect of SiC content and particle size on the relative density, hardness and electrical conductivity of composites were investigated. The relative densities of Cu–SiC composites sintered at 700 °C for 2 h are ranged from 97.3% to 91.8% for SiC with 1 lm particle size and from 97.5% to 95.2% for SiC with 5 lm particle size. Microhardness of composites ranged from 143 to 167 HV for SiC having 1 lm particle size and from 156 to 182 HV for SiC having 5 lm particle size. The electrical conductivity of composites changed between 85.9% IACS and 55.7% IACS for SiC with 1 lm particle size, between 87.9% IACS and 65.2% IACS for SiC with 5 lm particle size. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Copper with atomic number 29 and atomic weight 63.54, occupies the first position of subgroup IB in the periodic chart of the elements. Subgroup IB also includes silver and gold, and in fact, copper shares many characteristics with these other noble metals as a result of its atomic and electron structure [1]. Among these materials, silver has the highest electrical conductivity. But, silver is used in small amounts as electrical conductor due to its high cost. As bulk materials, the most used conductors are copper and aluminum. The main reason for preferring copper is its high conductivity compared to aluminum as well as high strength [2]. 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. The electrical conductivity scale established in 1913 was based on a copper standard defined as 100%, and the electrical conductivity of any material is still expressed as percent IACS (International Annealed Copper Standard), equal to 100 times the ratio of the volume resistivity of the annealed copper standard (0.017241 lX m) at 20 °C (68 °F) to the value measured for the material concerned [3,4]. The mechanical strength of copper can be increased dramatically either by age hardening or by introducing dispersoid particles in its ⇑ Corresponding author. Tel.: +90 264 295 57 59; fax: +90 264 295 56 01. E-mail address: [email protected] (C. Bindal). 0261-3069/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2011.11.019
matrix. The age-hardenable copper alloys are prone to precipitate coarsening at high temperatures, thereby reducing their strength drastically. In this respect, dispersion-strengthened copper has the ability to retain most of its properties on exposure to high temperatures. Dispersoid particles such as oxides, carbides, borides are insoluble in the copper matrix, and are thermally stable at high temperatures. The dispersion-strengthened copper alloys generally can be classified as the copper-based matrix composites [5]. Their distinctive properties of high stiffness, high strength, good resistance and low coefficient of thermal expansion that could not be found in monolithic materials have promoted a number of applications for them. The incorporation of ceramic particulate reinforcement can improve the high temperature mechanical property and wear resistance significantly, without severe deterioration of thermal and electrical conductivity of the matrix. In other words particulate-reinforced copper matrix composites may have many prominent advantages that the single copper alloys do not possess. Therefore, these kinds of materials are considered to be promising candidates for applications where high conductivity, high mechanical property and good wear resistance are required [6]. Literatures have pointed out that copper matrix composites reinforced with SiC fiber are candidate materials for heat sinks in future fusion reactors as they combine high thermal conductivity and sufficient mechanical strength for working temperatures up to 550 °C under neutron irradiation. Metal matrix composites, reinforced with particulate or discontinuous fibers of SiC or Al2O3, are potential candidate materials for a variety applications. The importance of these composites could be attributed to their high stiffness, superior room and elevated temperature strengths, improved wear resistance and low coefficient of thermal expansion [7]. The particle reinforced metal matrix composites can be synthesized by such
634
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
2. Experimental details
uniaxial pressure
Punch
die powder 15 mm 3-4 mm
(b)
(a)
(c)
Fig. 1. Schematic presentation of die used (a) die, (b) die section and (c) pressed sample.
methods as standard ingot metallurgy (IM), powder metallurgy (PM), disintegrated melt deposition (DMD) technique, spray atomization and co-deposition approach. Different method results in different properties. The PM processing route is generally preferred since it shows a number of product advantages. Powder metallurgy process (PM) lends itself well for economical mass production components. Different metal matrix composites are manufactured by this PM route. The uniform distribution of ceramic particle reinforcements is readily realized. On the other hand, the solid-state process minimizes the reactions between the metal matrix and the ceramic reinforcement, and thus enhances the bonding between the reinforcement and the matrix. However, the coefficient of thermal expansion (CTE) mismatch between the reinforcement and the matrix will give rise to high residual stress, which leads to the low tensile ductility of the composite [7–9]. In the present study SiC was selected as reinforcement for its superior mechanical properties of high hardness, high anti-wear stiffness during grinding operation, high electric conductivity to comply with the IACS’s electrode standard, and high thermal conductivity to obtain higher thermal shock resistance [9]. In this investigation, the effect of SiC particle size on the mechanical and physical properties of silicon carbide particle reinforced copper matrix composites were studied.
Element
wt. %
O
2.776
Cu
97.224
(a)
The metal matrix composites studied in this work were based on pure copper reinforced with 1, 2, 3 and 5 wt.% SiC particles. Copper powder (99.9% purity; 10 lm in diameter) and SiC particle (99.5% purity; 1 lm and 5 lm in diameter) were purchased from Alfa-Aesar. SiC particles were mixed mechanically with the calculated amount of copper powder and were pressed in a steel mold of 15 mm in diameter with an axial pressure of 280 MPa. After that, they were embedded in graphite and sintered at 700 °C in an open atmospheric furnace for 2 h. The sintering compacts were pressed with a load of 850 MPa in order to increase the relative density and electrical conductivity of test samples with 3–4 mm in thickness and diameter of 15 mm. Fig. 1 shows schematic presentation of die used and test material produced. The relative densities of composites were measured by a method based on Archimedes’ law. Microstructure analysis of composites was performed with a JEOL JSM5600 model scanning electron microscope (SEM). The presence of phases formed within the sintered samples was determined by Xray diffraction using Cu Ka radiation with a wavelength of 1.5418 A over a 2h range of 10–80°. 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 a Leica WMHT-Mod model Vickers hardness instrument under an applied load of 50 g. Electrical conductivity of Cu– SiC composites was determined by GE model electric resistivity measurement instrument. 3. Results and discussion 3.1. Microstructure SEM micrographs and EDS analysis of Cu and reinforcement agent SiC powders used in experimental studies were given in Fig. 2. It is seen from Fig. 1a that copper powder is in spherical shape with particle size of 10 lm. A slight amount of oxygen detected in the EDS analysis of Cu powder, probably results from the reaction of copper powder with atmosphere. As it is known well that copper oxides are not protective oxides. The shape of SiC particles with a diameter of 1 and 5 lm were angular and irregular (Fig. 2b and c). It was determined that amount of oxygen decreased with increasing the particle size of SiC due to the decreasing surface area of SiC. Previous study done by Kang and Kang [10] reported that most common methods for fabricating Cu/SiC composites is PM with
Element
wt. %
Element
wt. %
C
57.537
C
64.151
O
5.899
O
4.995
Si
29.950
Si
37.468
(b) Fig. 2. SEM micrographs and EDS analysis of (a) copper powder and (b and c) SiC particles.
(c)
635
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
SiC, wt.%
1
Cu-1µmSiC
Cu-5µmSiC
SiC
SiC Cu
2
3
5
Fig. 3. SEM micrographs of Cu–SiC composites reinforced with SiC particles in 1 lm particle size (left side) and in 5 lm particle size (right side).
sintering or hot-pressing. Also, study done by Guabin et al. [11] revealed that the Al2O3/Cu composite is plastically deformed for increasing the density and electrical conductivity of composite concerning. Similarly, in the present study following sintering, the test samples were immediately pressed with a load of 850 MPa in order to increase the relative density and electrical conductivity of test samples. Fig. 3 shows the micrographs of Cu–SiC composites with different SiC content and particle size. It can be observed that SiC particles were dispersed uniformly in the copper matrix. It is seen that SiC particles with 1 lm particle size are uniformly distributed around copper particles and they are predominantly at the joining points of copper grains, when the SiC content exceeds 2 wt.%, the interfaces become weaker and the continuity of the well-bonded interfaces is destroyed for composites reinforced with SiC particles
of 5 lm. Small amount of SiC particles located in copper grains due to ductile nature of copper as shown in Fig. 3 (right side). EDS analysis showed that dark gray and cornered particles reflect the SiC particles, and white regions (Fig. 4, mark 5) indicate the Al2O3 probably resulted from polishing and the gray areas show the copper matrix (Figs. 4 and 5). Oxygen was not detected in the EDS analysis of Cu–SiC composite having 1 lm and 5 lm particle size of SiC. The oxygen detected in EDS analysis (Fig. 4) is coming from alumina as cited above. 3.2. XRD Fig. 6 shows XRD patterns of the Cu–SiC composites sintered at 700 °C for 2 h, having 1 and 5 lm particle size SiC. Cu and SiC peaks
636
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
Cu
Mark 1 Si
Cu
Cu
C Si
Si
Mark 2
Mark 3
Cu Cu C
Cu
O
Si
Cu
Cu Cu
C Cu
Mark 4
Mark 5
Cu
Cu O C
Cu C
Al
Cu
Cu
Fig. 4. SEM–EDS analyses of Cu–SiC composite containing 5 wt.% SiC in 1 lm particle size.
Si
Cu
Cu Cu
C Cu
Si
Mark
Si
2
Mark 1
Mark 3
Cu Cu Cu Cu
C
Si
Mark 4
C
Cu
Cu
Mark 5
Cu Cu Cu C
Cu
Cu
Fig. 5. SEM–EDS analyses of Cu–SiC composite containing 3 wt.% SiC in 5 lm particle size.
637
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
(a) Intensity (Counts)
10000 Cu : 8000 6000 4000 2000 0 0
20
40
60
80
100
2θ
Cu 12000
Cu :
Intensity (Counts)
Intensity (Counts)
10000 8000 6000 4000 2000 0
Cu :
10000 8000 6000 4000 2000 0
0
20
40
60
80
100
0
20
40
2θ
100
80
100
10000
Cu :
Cu :
10000 SiC: 8000
Intensity (Counts)
Intensiry (Counts)
80
Cu-2wt.%SiC
Cu-1wt.%SiC 12000
60
2θ
6000 4000 2000 0
8000 SiC: 6000 4000 2000 0
0
20
40
60
80
100
2θ
Cu-3wt.%SiC
0
20
40
60
2θ
Cu-5wt.%SiC
Fig. 6. XRD patterns of Cu–SiC composites (a) having 1 lm particle size of SiC and (b) having 5 lm particle size of SiC including pure Cu.
were detected and oxygen was not determined in the XRD analysis of composites. It can be said that graphite used as oxygen eliminator completed its mission successfully. SiC peaks become clear with increasing the weight percentage of SiC. 3.3. Relative density The relative densities of copper and Cu–SiC composites were determined according to Archimedes’ method. The relative densities of Cu–SiC composites were reduced from 97.3% to 91.8% for SiC with 1 lm particle size and from 97.5% to 95.2% for SiC with 5 lm particle size with increasing amount of SiC. Fig. 7 reveals that the relative densities of composites tend to decrease with increasing SiC content. This is due to the fact that the density of SiC particles is much smaller than that of copper. In composite with low SiC volume fraction, less Cu–SiC interface means less copper atom diffusion barrier. Therefore, copper atoms can diffuse easily and fill the interstices between the SiC particles, thus leading to a higher densification of the composite [12,13]. Moreover, relative densities of composites increased with increasing the particle size of SiC. Probably, increasing the particle size of SiC leads to contact of more Cu–Cu grains together and so more intensive form appears [14]. 3.4. Hardness Fig. 8 shows the effects of the amount and size of reinforcement particle on the hardness of sintered composites. For hardness
measurements, a load of 50 g was utilized. Five measurements for each composite specimen were carried out in the hardness test for reproducibility. The hardness of Cu–SiC composites ranged from 143 to 167 HVN for SiC having 1 lm particle size and 156– 182 HVN for SiC having 5 lm particle size. Hardness was found to increase with increasing SiC addition and particle size. Increasing the SiC content, more strongly impeded plastic flow, causing the hardness of Cu–SiC composite to increase with the amount of reinforcing particles. This result was consistent with the other researches [14]. The average hardness of Cu–SiC composite specimen with 5 lm particle size SiC is higher than that of the with 1 lm particle sized SiC particles. Depending on particle size of SiC, the reason of increasing in hardness can be attributed to contact area of indenter to SiC. 3.5. Electrical conductivity Electrical conductivity is a very useful property which is affected by chemical composition and the stress state of crystalline structures. At present study, relative densities of samples were considerably increased by hot pressing after sintering immediately and a density of 8.72 g/cm3 was obtained for pure copper which is in good agreement with literature (8.9 g/cm3). It was known that the higher the relative density the higher the electrical conductivity. The electrical conductivity of the samples ranged from 86% IACS to 56% IACS for SiC with 1 lm particle size and from 88% IACS to 66% IACS for SiC with 5 lm particle size as a function of SiC content. As it can be seen
638
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
Intensity (Counts)
(b)
Cu :
10000 8000 6000 4000 2000 0 0
20
40
60
80
100
2θ
Cu 12000
Cu :
10000
Intensity (Counts)
Intensity (Counts)
12000
8000 6000 4000 2000
Cu : SiC:
10000 8000 6000 4000 2000
0
0 0
20
40
60
80
100
0
20
40
60
2θ
Cu-1wt.%SiC
80
100
10000
Cu : SiC:
Intensity (Counts)
Intensity (Counts)
100
Cu-2wt.%SiC
12000 10000
80
2θ
8000 6000 4000 2000
Cu : SiC:
8000 6000 4000 2000
0
0 0
20
40
60
80
100
0
20
40
60
2θ
2θ
Cu-3wt.%SiC
Cu-5wt.%SiC Fig. 6 (continued)
99
195 190
98
1µm SiC 5µm SiC
97
180
Hardness, HVN
Relative Density, %
185
96 95 94
175 170 165 160 155
93
150
1µm SiC 5µm SiC
92 91
1
2
145 140 3
4
5
SiC, wt.%
135
1
2
3
4
5
SiC, wt.%
Fig. 7. Relative density of the Cu–SiC composites vs. SiC content and particle size.
Fig. 8. Microhardness of the Cu–SiC composites vs. SiC content and particle size.
from Fig. 9 that electrical conductivity of composites was decreased with increment in SiC content, because ceramic based SiC forms a barrier to motion of copper electrons, providing electrical conductivity. Electrical conductivity of a metal depends mainly on the mobility of electrons in the structure. SiC particles added into the pure copper redouble the electrical resistivity via distorting
the structure and so electrical conductivity of composites decreases with increasing the volume ratio of SiC [15–17]. On the other hand, particle size of SiC also affects the electrical conductivity of composite and it increase as particle size increases. Electrical conductivity of composites increased with increasing particle size of SiC. Because with increasing particle size of SiC, added into the pure copper, less
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
Acknowledgment
95 90
Electrical Conductivity, %IACS
639
The authors thank to experts Fuat Kayis for performing XRD and SEM–EDS studies and special appreciation are extended to technician Ersan Demir of Sakarya University for assisting with experimental studies. Also, the appreciations are extended to Prof. Metin Usta of GYTE for his notable support. This work was conducted a project supported by TUBITAK with Contract number of 106M118.
85 80 75 70 65
References
60
1µm SiC 5µm SiC
55 50
1
2
3
4
5
SiC, wt.% Fig. 9. Electrical conductivity of the Cu–SiC composites vs. SiC content and particle size.
electrons are scattered and thus mobility and electrical conductivity increase [17]. 4. Conclusions The effects of particle size and amount of reinforcement component on the some properties of sintered Cu–SiC composites were investigated. Copper–SiC composites were manufactured successfully by conventional powder metallurgy method embedding in graphite powders without using any inert medium (gas or vacuum). The presence of Cu and SiC were verified by XRD analysis technique and EDS analysis. The all of composites manufactured have remarkable high relative density. Hardness of the composites was increased with increasing amount and particle size of added SiC. It was observed that the electrical conductivity of all Cu–SiC composites are in good agreement with literature. As a result, the relative densities, the hardness and the electrical conductivity of all Cu–SiC composites with 5 lm particle size of SiC are higher than that of 1 lm particle size of SiC.
[1] Kundig K, Günter J. Copper. ASM International; 2001. [2] Celebi Efe G, Altinsoy I, Yener T, Ipek M, Zeytin S, Bindal C. Characterization of cemented Cu–SiC composites. Vacuum 2010;85:643–7. [3] Joseph R. Davis. Copper and copper alloys. ASM International Handbook. [4] Zhu J, Liu L, Zhao H, Shen B, Hu W. Microstructure and performance of electroformed Cu/nano-SiC composite. Mater Des 2007;28:1958–62. [5] Tjong SC, Lau KC. Tribological behaviour of SiC particle-reinforced copper matrix composites. Mater Lett 2000;43:274–80. [6] Zhan Y, Zhang G. The effect of interfacial modifying on the mechanical and wear properties of SiCp/Cu composites. Mater Lett 2003;57:4459–583. [7] Moustafa SF, Hamıd ZA, Elhay AM. Copper matrix SiC and Al2O3 particulate composites by powder metallurgy technique. Mater Lett 2002;53:224–49. [8] Wanga H, Zhanga R, Hua X, Wangb CA, Huangb Y. Characterization of a powder metallurgy SiC/Cu–Al composite. Mater Process Technol 2008;197:43–8. [9] Shu KM, Tu GC. Study of electrical discharge grinding using metal matrix composite electrodes. Mach Tools Manuf 2003;43:845–54. [10] 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. [11] Guabin L, Jibing S, Quanmei G, Ru W. Fabrication of the nanometer Al2O3/Cu composite by internal oxidation. Mater Process Technol 2005;170:336–40. [12] Celebi Efe GF, Altinsoy I, Ipek M, Zeytin S, Bindal C. Some properties of Cu–SiC composites produced by powder metallurgy method. Kovove Mater Metall Mater 2011;49:131–6. [13] Çelebi Efe GF. Development of conductive copper composites reinforced with SiC. PhD Thesis. Sakarya University, Institute of Science and Technology; 2010. [14] 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. _ Yener T, Ipek _ [15] 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. [16] Smiht W. Principles of materials science and engineering. 2nd ed. McGrawHill; 1990. [17] Richerson DW. Modern ceramic engineering. Taylor & Francis CRC Press; 2006.
Contents lists available at SciVerse ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Short Communication
The effect of SiC particle size on the properties of Cu–SiC composites G. Celebi Efe, 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 12 September 2011 Accepted 9 November 2011 Available online 25 November 2011
a b s t r a c t SiC particulate-reinforced copper composites were prepared by powder metallurgy (PM) method and conventional atmospheric sintering. Scanning electron microscope (SEM), X-ray diffraction (XRD) techniques were used to characterize the sintered composites. The effect of SiC content and particle size on the relative density, hardness and electrical conductivity of composites were investigated. The relative densities of Cu–SiC composites sintered at 700 °C for 2 h are ranged from 97.3% to 91.8% for SiC with 1 lm particle size and from 97.5% to 95.2% for SiC with 5 lm particle size. Microhardness of composites ranged from 143 to 167 HV for SiC having 1 lm particle size and from 156 to 182 HV for SiC having 5 lm particle size. The electrical conductivity of composites changed between 85.9% IACS and 55.7% IACS for SiC with 1 lm particle size, between 87.9% IACS and 65.2% IACS for SiC with 5 lm particle size. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Copper with atomic number 29 and atomic weight 63.54, occupies the first position of subgroup IB in the periodic chart of the elements. Subgroup IB also includes silver and gold, and in fact, copper shares many characteristics with these other noble metals as a result of its atomic and electron structure [1]. Among these materials, silver has the highest electrical conductivity. But, silver is used in small amounts as electrical conductor due to its high cost. As bulk materials, the most used conductors are copper and aluminum. The main reason for preferring copper is its high conductivity compared to aluminum as well as high strength [2]. 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. The electrical conductivity scale established in 1913 was based on a copper standard defined as 100%, and the electrical conductivity of any material is still expressed as percent IACS (International Annealed Copper Standard), equal to 100 times the ratio of the volume resistivity of the annealed copper standard (0.017241 lX m) at 20 °C (68 °F) to the value measured for the material concerned [3,4]. The mechanical strength of copper can be increased dramatically either by age hardening or by introducing dispersoid particles in its ⇑ Corresponding author. Tel.: +90 264 295 57 59; fax: +90 264 295 56 01. E-mail address: [email protected] (C. Bindal). 0261-3069/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2011.11.019
matrix. The age-hardenable copper alloys are prone to precipitate coarsening at high temperatures, thereby reducing their strength drastically. In this respect, dispersion-strengthened copper has the ability to retain most of its properties on exposure to high temperatures. Dispersoid particles such as oxides, carbides, borides are insoluble in the copper matrix, and are thermally stable at high temperatures. The dispersion-strengthened copper alloys generally can be classified as the copper-based matrix composites [5]. Their distinctive properties of high stiffness, high strength, good resistance and low coefficient of thermal expansion that could not be found in monolithic materials have promoted a number of applications for them. The incorporation of ceramic particulate reinforcement can improve the high temperature mechanical property and wear resistance significantly, without severe deterioration of thermal and electrical conductivity of the matrix. In other words particulate-reinforced copper matrix composites may have many prominent advantages that the single copper alloys do not possess. Therefore, these kinds of materials are considered to be promising candidates for applications where high conductivity, high mechanical property and good wear resistance are required [6]. Literatures have pointed out that copper matrix composites reinforced with SiC fiber are candidate materials for heat sinks in future fusion reactors as they combine high thermal conductivity and sufficient mechanical strength for working temperatures up to 550 °C under neutron irradiation. Metal matrix composites, reinforced with particulate or discontinuous fibers of SiC or Al2O3, are potential candidate materials for a variety applications. The importance of these composites could be attributed to their high stiffness, superior room and elevated temperature strengths, improved wear resistance and low coefficient of thermal expansion [7]. The particle reinforced metal matrix composites can be synthesized by such
634
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
2. Experimental details
uniaxial pressure
Punch
die powder 15 mm 3-4 mm
(b)
(a)
(c)
Fig. 1. Schematic presentation of die used (a) die, (b) die section and (c) pressed sample.
methods as standard ingot metallurgy (IM), powder metallurgy (PM), disintegrated melt deposition (DMD) technique, spray atomization and co-deposition approach. Different method results in different properties. The PM processing route is generally preferred since it shows a number of product advantages. Powder metallurgy process (PM) lends itself well for economical mass production components. Different metal matrix composites are manufactured by this PM route. The uniform distribution of ceramic particle reinforcements is readily realized. On the other hand, the solid-state process minimizes the reactions between the metal matrix and the ceramic reinforcement, and thus enhances the bonding between the reinforcement and the matrix. However, the coefficient of thermal expansion (CTE) mismatch between the reinforcement and the matrix will give rise to high residual stress, which leads to the low tensile ductility of the composite [7–9]. In the present study SiC was selected as reinforcement for its superior mechanical properties of high hardness, high anti-wear stiffness during grinding operation, high electric conductivity to comply with the IACS’s electrode standard, and high thermal conductivity to obtain higher thermal shock resistance [9]. In this investigation, the effect of SiC particle size on the mechanical and physical properties of silicon carbide particle reinforced copper matrix composites were studied.
Element
wt. %
O
2.776
Cu
97.224
(a)
The metal matrix composites studied in this work were based on pure copper reinforced with 1, 2, 3 and 5 wt.% SiC particles. Copper powder (99.9% purity; 10 lm in diameter) and SiC particle (99.5% purity; 1 lm and 5 lm in diameter) were purchased from Alfa-Aesar. SiC particles were mixed mechanically with the calculated amount of copper powder and were pressed in a steel mold of 15 mm in diameter with an axial pressure of 280 MPa. After that, they were embedded in graphite and sintered at 700 °C in an open atmospheric furnace for 2 h. The sintering compacts were pressed with a load of 850 MPa in order to increase the relative density and electrical conductivity of test samples with 3–4 mm in thickness and diameter of 15 mm. Fig. 1 shows schematic presentation of die used and test material produced. The relative densities of composites were measured by a method based on Archimedes’ law. Microstructure analysis of composites was performed with a JEOL JSM5600 model scanning electron microscope (SEM). The presence of phases formed within the sintered samples was determined by Xray diffraction using Cu Ka radiation with a wavelength of 1.5418 A over a 2h range of 10–80°. 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 a Leica WMHT-Mod model Vickers hardness instrument under an applied load of 50 g. Electrical conductivity of Cu– SiC composites was determined by GE model electric resistivity measurement instrument. 3. Results and discussion 3.1. Microstructure SEM micrographs and EDS analysis of Cu and reinforcement agent SiC powders used in experimental studies were given in Fig. 2. It is seen from Fig. 1a that copper powder is in spherical shape with particle size of 10 lm. A slight amount of oxygen detected in the EDS analysis of Cu powder, probably results from the reaction of copper powder with atmosphere. As it is known well that copper oxides are not protective oxides. The shape of SiC particles with a diameter of 1 and 5 lm were angular and irregular (Fig. 2b and c). It was determined that amount of oxygen decreased with increasing the particle size of SiC due to the decreasing surface area of SiC. Previous study done by Kang and Kang [10] reported that most common methods for fabricating Cu/SiC composites is PM with
Element
wt. %
Element
wt. %
C
57.537
C
64.151
O
5.899
O
4.995
Si
29.950
Si
37.468
(b) Fig. 2. SEM micrographs and EDS analysis of (a) copper powder and (b and c) SiC particles.
(c)
635
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
SiC, wt.%
1
Cu-1µmSiC
Cu-5µmSiC
SiC
SiC Cu
2
3
5
Fig. 3. SEM micrographs of Cu–SiC composites reinforced with SiC particles in 1 lm particle size (left side) and in 5 lm particle size (right side).
sintering or hot-pressing. Also, study done by Guabin et al. [11] revealed that the Al2O3/Cu composite is plastically deformed for increasing the density and electrical conductivity of composite concerning. Similarly, in the present study following sintering, the test samples were immediately pressed with a load of 850 MPa in order to increase the relative density and electrical conductivity of test samples. Fig. 3 shows the micrographs of Cu–SiC composites with different SiC content and particle size. It can be observed that SiC particles were dispersed uniformly in the copper matrix. It is seen that SiC particles with 1 lm particle size are uniformly distributed around copper particles and they are predominantly at the joining points of copper grains, when the SiC content exceeds 2 wt.%, the interfaces become weaker and the continuity of the well-bonded interfaces is destroyed for composites reinforced with SiC particles
of 5 lm. Small amount of SiC particles located in copper grains due to ductile nature of copper as shown in Fig. 3 (right side). EDS analysis showed that dark gray and cornered particles reflect the SiC particles, and white regions (Fig. 4, mark 5) indicate the Al2O3 probably resulted from polishing and the gray areas show the copper matrix (Figs. 4 and 5). Oxygen was not detected in the EDS analysis of Cu–SiC composite having 1 lm and 5 lm particle size of SiC. The oxygen detected in EDS analysis (Fig. 4) is coming from alumina as cited above. 3.2. XRD Fig. 6 shows XRD patterns of the Cu–SiC composites sintered at 700 °C for 2 h, having 1 and 5 lm particle size SiC. Cu and SiC peaks
636
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
Cu
Mark 1 Si
Cu
Cu
C Si
Si
Mark 2
Mark 3
Cu Cu C
Cu
O
Si
Cu
Cu Cu
C Cu
Mark 4
Mark 5
Cu
Cu O C
Cu C
Al
Cu
Cu
Fig. 4. SEM–EDS analyses of Cu–SiC composite containing 5 wt.% SiC in 1 lm particle size.
Si
Cu
Cu Cu
C Cu
Si
Mark
Si
2
Mark 1
Mark 3
Cu Cu Cu Cu
C
Si
Mark 4
C
Cu
Cu
Mark 5
Cu Cu Cu C
Cu
Cu
Fig. 5. SEM–EDS analyses of Cu–SiC composite containing 3 wt.% SiC in 5 lm particle size.
637
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
(a) Intensity (Counts)
10000 Cu : 8000 6000 4000 2000 0 0
20
40
60
80
100
2θ
Cu 12000
Cu :
Intensity (Counts)
Intensity (Counts)
10000 8000 6000 4000 2000 0
Cu :
10000 8000 6000 4000 2000 0
0
20
40
60
80
100
0
20
40
2θ
100
80
100
10000
Cu :
Cu :
10000 SiC: 8000
Intensity (Counts)
Intensiry (Counts)
80
Cu-2wt.%SiC
Cu-1wt.%SiC 12000
60
2θ
6000 4000 2000 0
8000 SiC: 6000 4000 2000 0
0
20
40
60
80
100
2θ
Cu-3wt.%SiC
0
20
40
60
2θ
Cu-5wt.%SiC
Fig. 6. XRD patterns of Cu–SiC composites (a) having 1 lm particle size of SiC and (b) having 5 lm particle size of SiC including pure Cu.
were detected and oxygen was not determined in the XRD analysis of composites. It can be said that graphite used as oxygen eliminator completed its mission successfully. SiC peaks become clear with increasing the weight percentage of SiC. 3.3. Relative density The relative densities of copper and Cu–SiC composites were determined according to Archimedes’ method. The relative densities of Cu–SiC composites were reduced from 97.3% to 91.8% for SiC with 1 lm particle size and from 97.5% to 95.2% for SiC with 5 lm particle size with increasing amount of SiC. Fig. 7 reveals that the relative densities of composites tend to decrease with increasing SiC content. This is due to the fact that the density of SiC particles is much smaller than that of copper. In composite with low SiC volume fraction, less Cu–SiC interface means less copper atom diffusion barrier. Therefore, copper atoms can diffuse easily and fill the interstices between the SiC particles, thus leading to a higher densification of the composite [12,13]. Moreover, relative densities of composites increased with increasing the particle size of SiC. Probably, increasing the particle size of SiC leads to contact of more Cu–Cu grains together and so more intensive form appears [14]. 3.4. Hardness Fig. 8 shows the effects of the amount and size of reinforcement particle on the hardness of sintered composites. For hardness
measurements, a load of 50 g was utilized. Five measurements for each composite specimen were carried out in the hardness test for reproducibility. The hardness of Cu–SiC composites ranged from 143 to 167 HVN for SiC having 1 lm particle size and 156– 182 HVN for SiC having 5 lm particle size. Hardness was found to increase with increasing SiC addition and particle size. Increasing the SiC content, more strongly impeded plastic flow, causing the hardness of Cu–SiC composite to increase with the amount of reinforcing particles. This result was consistent with the other researches [14]. The average hardness of Cu–SiC composite specimen with 5 lm particle size SiC is higher than that of the with 1 lm particle sized SiC particles. Depending on particle size of SiC, the reason of increasing in hardness can be attributed to contact area of indenter to SiC. 3.5. Electrical conductivity Electrical conductivity is a very useful property which is affected by chemical composition and the stress state of crystalline structures. At present study, relative densities of samples were considerably increased by hot pressing after sintering immediately and a density of 8.72 g/cm3 was obtained for pure copper which is in good agreement with literature (8.9 g/cm3). It was known that the higher the relative density the higher the electrical conductivity. The electrical conductivity of the samples ranged from 86% IACS to 56% IACS for SiC with 1 lm particle size and from 88% IACS to 66% IACS for SiC with 5 lm particle size as a function of SiC content. As it can be seen
638
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
Intensity (Counts)
(b)
Cu :
10000 8000 6000 4000 2000 0 0
20
40
60
80
100
2θ
Cu 12000
Cu :
10000
Intensity (Counts)
Intensity (Counts)
12000
8000 6000 4000 2000
Cu : SiC:
10000 8000 6000 4000 2000
0
0 0
20
40
60
80
100
0
20
40
60
2θ
Cu-1wt.%SiC
80
100
10000
Cu : SiC:
Intensity (Counts)
Intensity (Counts)
100
Cu-2wt.%SiC
12000 10000
80
2θ
8000 6000 4000 2000
Cu : SiC:
8000 6000 4000 2000
0
0 0
20
40
60
80
100
0
20
40
60
2θ
2θ
Cu-3wt.%SiC
Cu-5wt.%SiC Fig. 6 (continued)
99
195 190
98
1µm SiC 5µm SiC
97
180
Hardness, HVN
Relative Density, %
185
96 95 94
175 170 165 160 155
93
150
1µm SiC 5µm SiC
92 91
1
2
145 140 3
4
5
SiC, wt.%
135
1
2
3
4
5
SiC, wt.%
Fig. 7. Relative density of the Cu–SiC composites vs. SiC content and particle size.
Fig. 8. Microhardness of the Cu–SiC composites vs. SiC content and particle size.
from Fig. 9 that electrical conductivity of composites was decreased with increment in SiC content, because ceramic based SiC forms a barrier to motion of copper electrons, providing electrical conductivity. Electrical conductivity of a metal depends mainly on the mobility of electrons in the structure. SiC particles added into the pure copper redouble the electrical resistivity via distorting
the structure and so electrical conductivity of composites decreases with increasing the volume ratio of SiC [15–17]. On the other hand, particle size of SiC also affects the electrical conductivity of composite and it increase as particle size increases. Electrical conductivity of composites increased with increasing particle size of SiC. Because with increasing particle size of SiC, added into the pure copper, less
G. Celebi Efe et al. / Materials and Design 36 (2012) 633–639
Acknowledgment
95 90
Electrical Conductivity, %IACS
639
The authors thank to experts Fuat Kayis for performing XRD and SEM–EDS studies and special appreciation are extended to technician Ersan Demir of Sakarya University for assisting with experimental studies. Also, the appreciations are extended to Prof. Metin Usta of GYTE for his notable support. This work was conducted a project supported by TUBITAK with Contract number of 106M118.
85 80 75 70 65
References
60
1µm SiC 5µm SiC
55 50
1
2
3
4
5
SiC, wt.% Fig. 9. Electrical conductivity of the Cu–SiC composites vs. SiC content and particle size.
electrons are scattered and thus mobility and electrical conductivity increase [17]. 4. Conclusions The effects of particle size and amount of reinforcement component on the some properties of sintered Cu–SiC composites were investigated. Copper–SiC composites were manufactured successfully by conventional powder metallurgy method embedding in graphite powders without using any inert medium (gas or vacuum). The presence of Cu and SiC were verified by XRD analysis technique and EDS analysis. The all of composites manufactured have remarkable high relative density. Hardness of the composites was increased with increasing amount and particle size of added SiC. It was observed that the electrical conductivity of all Cu–SiC composites are in good agreement with literature. As a result, the relative densities, the hardness and the electrical conductivity of all Cu–SiC composites with 5 lm particle size of SiC are higher than that of 1 lm particle size of SiC.
[1] Kundig K, Günter J. Copper. ASM International; 2001. [2] Celebi Efe G, Altinsoy I, Yener T, Ipek M, Zeytin S, Bindal C. Characterization of cemented Cu–SiC composites. Vacuum 2010;85:643–7. [3] Joseph R. Davis. Copper and copper alloys. ASM International Handbook. [4] Zhu J, Liu L, Zhao H, Shen B, Hu W. Microstructure and performance of electroformed Cu/nano-SiC composite. Mater Des 2007;28:1958–62. [5] Tjong SC, Lau KC. Tribological behaviour of SiC particle-reinforced copper matrix composites. Mater Lett 2000;43:274–80. [6] Zhan Y, Zhang G. The effect of interfacial modifying on the mechanical and wear properties of SiCp/Cu composites. Mater Lett 2003;57:4459–583. [7] Moustafa SF, Hamıd ZA, Elhay AM. Copper matrix SiC and Al2O3 particulate composites by powder metallurgy technique. Mater Lett 2002;53:224–49. [8] Wanga H, Zhanga R, Hua X, Wangb CA, Huangb Y. Characterization of a powder metallurgy SiC/Cu–Al composite. Mater Process Technol 2008;197:43–8. [9] Shu KM, Tu GC. Study of electrical discharge grinding using metal matrix composite electrodes. Mach Tools Manuf 2003;43:845–54. [10] 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. [11] Guabin L, Jibing S, Quanmei G, Ru W. Fabrication of the nanometer Al2O3/Cu composite by internal oxidation. Mater Process Technol 2005;170:336–40. [12] Celebi Efe GF, Altinsoy I, Ipek M, Zeytin S, Bindal C. Some properties of Cu–SiC composites produced by powder metallurgy method. Kovove Mater Metall Mater 2011;49:131–6. [13] Çelebi Efe GF. Development of conductive copper composites reinforced with SiC. PhD Thesis. Sakarya University, Institute of Science and Technology; 2010. [14] 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. _ Yener T, Ipek _ [15] 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. [16] Smiht W. Principles of materials science and engineering. 2nd ed. McGrawHill; 1990. [17] Richerson DW. Modern ceramic engineering. Taylor & Francis CRC Press; 2006.