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In situ formation of Cu–ZrO2 composites by chemical routes
Journal of Alloys and Compounds 425 (2006) 390–394
In situ formation of Cu–ZrO2 composites by chemical routes Jian Ding, Naiqin Zhao ∗ , Chunsheng Shi, Xiwen Du, Jiajun Li School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China Received 19 October 2005; received in revised form 30 November 2005; accepted 20 January 2006 Available online 2 March 2006
Abstract Composite of copper and 3 mol% yttria-stabilized 5 wt.% zirconia (3-YSZ) have been prepared by hydrogen (PH2 = 0.1 atm) reduction of a homogeneous mixture of equably dispersed CuO and ZrO2 formed by three chemical processes. In these processes, the 5%ZrO2 /Cu nano-composite has been formed in situ by (1) addition of NaOH solution to certain amount of dispersed Cu(NO3 )2 , ZrOCl2 and Y(NO3 )3 alcohol solution, following filtration; or (2) by adding ammonia to ZrOCl2 , Y(NO3 )3 solution, then adding Cu(NO3 )2 solution to the deposition; (3) the mixture of Zr(OH)4 and Cu(NO3 )2 ·3H2 O, mixing and heating the final composition in the three cases to acquire the blending. And calcined them at 500 ◦ C for 1 h. The 5%ZrO2 /Cu composites were fabricated by quenching and final sintering at 900 ◦ C for 90 min in vacuum atmosphere. The three process were named process A, process B, and process C. The characterization of the composite samples has been done by XRD, SEM, TEM and metallography techniques. Results from XRD and TEM indicated that different crystal structure zirconia was formed in the three processes. In comparison, the composite microstructure of process B was more homogenous. The comparative conductivity and Vickers hardness were 64% IACS and 120, which were much higher than the other two processes. © 2006 Elsevier B.V. All rights reserved. Keywords: Cu matrix composites; Nano-sized material; Mechanochemical synthesis; Powder metallurgy
1. Introduction In situ metal matrix composites(MMCs) is multiphase material whose reinforcing phases are synthesis by chemical reaction during fabrication, while a conventional ex situ MMCs is fabricated by directly adding reinforcements into its matrix [1]. The in situ chemical process has several advantages over ex situ chemical process, such as more homogenous reinforcement, excellent surface bonding, pure interphase, and appears to be a suitable method for preparing metal–ceramic nano-composite. Therefore, research along this route has potential applications in prepare metal–ceramic composite [2]. The Cu-based MMCS, being the most commonly used MMCs, are widely adopted in automobile and wiring industries. But it requires high-strength and electrical conductivity with the development of industry [3,4]. The main requirement for structure of dispersion-strengthened materials is a homogenous distribution and small size of reinforcement [5].
∗
Corresponding author. Tel.: +86 22 87401601; fax: +86 22 27405874. E-mail address: [email protected] (N. Zhao).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.01.058
Nanometer-sized (nm-sized) materials are increasingly receiving recognition as practical structural and functional materials with good prospects, and have been developed extensively in recent years [6]. Jena selected nano-alumina as the reinforcement in in situ chemical process and acquired comparing performance to internal oxidation process [7,8]. Zirconia as a ceramic material finds many applications as piezoelectric devices, ceramic condensers and oxygen sensors due to some of its unique properties such as high hardness, low coefficient of friction, high elastic modulus, chemical inertness and high melting point [9]. The present work aims at producing homogeneous ZrO2 /Cu composites from chemically prepared CuO–ZrO2 mixtures, and different chemical processes have been investigated.
2. Experimental 2.1. Materials The chemicals of Cu(NO3 )2 ·3H2 O, Y(NO3 )3 ·6H2 O, ZrOCl2 ·8H2 O and Zr(OH)4 used in this experiment, were analytically grade (99.0%). And the chemicals like NaOH and NH3 ·H2 O used, were of reagent grade.
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2.2. Composites fabrication 5%ZrO2 /Cu nano-composite powders were prepared in the following three different ways: Process A: known amount of ZrOCl2 ·8H2 O and Y(NO3 )3 ·6H2 O was dissolved in the required amount of alcohol to receive 0.1 mol/L ZrOCl2 and added Cu(NO3 )2 ·3H2 O. Then 0.5 mol/L sodium hydroxide was titrated to the mixture till solution pH was up to 9.0, and the colloid depositions were formed. The mixing depositions were filtrated, then calcined at 500 ◦ C to obtain the composite powder of the Cu and Zr oxides. Then the composite oxide powder was deoxidized in a H2 atmosphere at 650 ◦ C for 45 min to obtain the final ZrO2 –Cu nano-composite powder. Process B: ZrOCl2 ·8H2 O, Y(NO3 )3 ·6H2 O and Cu(NO3 )2 ·3H2 O were taken in the required proportion. ZrOCl2 ·8H2 O and Y(NO3 )3 ·6H2 O was dissolved in accounted alcohol solution to get 0.1 mol/L ZrOCl2 solution. Then 15% ammonia was titrated to the mixing solution till the colloid formed and the solution pH was up to 9.0, then deposited for about 12 h, and the required amount of copper nitrate was added to it. The same fabricating conditions of calcination and reduction is the same as process A. Process C: known amount of Cu(NO3 )2 ·3H2 O, Y(NO3 )3 ·6H2 O and zirconium hydroxide were fully mixed in the desired proportion, and then calcined and deoxidized in the same condition with processes A and B. The composite powder with the ZrO2 content of 5 wt.% obtained by the above three processes, were named as sample A, sample B, sample C, respectively. Then the composite powders made by differential in situ chemical processes were compressed at 500 MPa, sintered at 900 ◦ C for 1.5 h and a heating rate of 10 ◦ C/min in vacuum atmosphere to acquire cylindrical specimens of 12 mm in diameter and 3 mm in height. Phase identification was carried out by a Rigaku X-ray diffract meter with Cu K␣ radiation, λ = 0.15418 and at 36 kV and 26 mA. The X-ray data were collected in step of 0.02◦ (2θ) with the scanning scope of 20–90◦ . Composite powder was observed using scanning electron microscopy(SEM; Model PHILIPS XL-30 ESEM). And the zirconia extracted from the ZrO2 /Cu composite powder were characterized using transmission electron microscopy (TEM; Model JEOL JEM-2010). The ZrO2 /Cu nano-composite microhardness was tested in Vickers hardness tester (model: MH-6) with 50 g load. The comparative conductivity was tested in whirlpool conductivity (Model: FQR7501).
3. Results and discussion
Fig. 1. X-ray diffraction patterns of non-reductive and reductive composite powder by different processes.
3.2. Characteristic of the composite powder and ZrO2 Fig. 3(a,c,e) shows SEM images of CuO, ZrO2 nanocomposite with 5%ZrO2 in the processes A–C. Different morphologys of the precursor powder have been acquired in the three processes. Fig. 3(b,d,f) shows SEM images of Cu, ZrO2 nano-composite powder with 5%ZrO2 in the processes A–C. The reductive ZrO2 /Cu composite powder made by the three processes were all the same round. The granularity of composite powder was uniform in the processes A and B. But the uneven and conglomerated composite powder could be seen in the process C. To identify the character of zirconia of the composite powder, zirconia was extracted from the ZrO2 /Cu composite powder by nitric acid. From Fig. 4(a), it can be seen that zirconia powders
3.1. XRD analysis The XRD pattern of composite powder fabricated from the three processes are shown in Fig. 1. The sharp XRD peaks on the pattern correspond to Cu phase and low intensity could be attributed to ZrO2 phase. The three strongest XRD peaks of copper are the same. The weak peaks are zirconia. Through analysis from Figs. 1 and 2, the weak XRD peak presenting at 30.27 was corresponding tetragonal zirconia, but other two weak peaks presenting at 28.18 and 31.469 were corresponding monoclinic ZrO2 in the process A. The XRD peak presenting at 30.11 was tetragonal zirconia in the process B. But monoclinic ZrO2 also existed in the process B, it is so weak that could not be seen in Fig. 1. The XRD presenting at 28.172 was monoclinic ZrO2 in the process C. Fig. 2 shows the X-ray diffraction(XRD) spectra of nanozirconia extracted from the three processes. It could be seen that the same ZrO2 crystal types of monoclinic and tetragonal exist in the processes A and B. But only monoclinic ZrO2 exist in the process C. The morphologys of the three processes are shown in Fig. 4.
Fig. 2. X-ray diffraction patterns of nano-ZrO2 extracted from Cu–ZrO2 composite powder by different processes.
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Fig. 3. Morphologys of ZrO2 /Cu composite powder by different processes (a) sample A (non-reductive); (b) sample A (reductive); (c) sample B (non-reductive); (d) sample B (reductive); (e) sample C (non-reductive); (f) sample C (reductive).
have round and elliptic appearance, and particle size is in the range of 15–50 nm. According to analysis from Figs. 1 and 2, it is clear that tetragonal and monoclinic ZrO2 exist in the process A. From Fig. 4(b), it can be seen that the morphologys of nanozirconia powder are round and quadrate, and particle size is most about 30 nm,which are tetragonal and monoclinic ZrO2 . And from Fig. 4(c), the monoclinic ZrO2 morphology and size of zirconia are irregular.
3.3. Microstructure analysis In this experiment, the composite samples were sintered in vacuum atmosphere. It should be further mentioned here that, the sintering studies carried out in the vacuum had been made to avoid any possible contamination of oxygen that might be present in the composite. And to nano-composite, it is very important to obtain small and homogenous reinforcement in the matrix in order to enhance mechanical, electrical proper-
Fig. 4. TEM images of ZrO2 extracted from the ZrO2 /Cu composite of different processes powder by nitric acid.
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Fig. 5. Optical images of the composite metallographical structure by means of (a) sample A; (b) sample B; (c) sample C; (d) part of sample C magnified 50 times.
ties. Fig. 5 shows the microstructure of the three preparing routes. And the Cu–5%ZrO2 composite of sample A, sample B and sample C had been examined by optical microscope. In Fig. 5(a) and (b), small and compact grain could be observed. The distribution of ZrO2 particles in the copper matrix, had been found to be uniform. The sample had also been examined in EDS, where two distinct phases, were namely Cu and ZrO2 phase as Fig. 6. However, comparing the sample A, sample B to sample C, it could be seen that the composite made by the former, were better homogeneous structure than the latter and less holes were examined. The composites metallographs of samples A and B, were found to have uniform dispersion of ZrO2 particles with grain refinement compared to that in sample C. However, neither the size nor the distribution of ZrO2 particles in the copper matrix has been found to be uniform in sample C.
Fig. 6. Energy dispersive spectrum (a) of ZrO2 /Cu nano-composite fabricated by process C (b).
Table 1 Vickers microhardness and electric conductivity 5.0 wt.% ZrO2 –Cu composite Sample A Densification (%) Microhardness (HV) Comparative conductivity (% IACS)
70.4 114.7 58.8
Sample B 72.1 120 64
Sample C 69.5 98.12 56.2
3.4. Comparisons of the composite performances Table 1 and Fig. 7 are the properties comparison of the 5%ZrO2 –Cu composite by the three processes. It implies that the zirconia as dispersoid has great effect on dispersion hardening. Since the preparing techniques and sintering were combined in the process, the compact green density directly influenced the properties of composite [10].
Fig. 7. Comparative of microhardness and electrical conductivity of 5.0 wt.% ZrO2 –Cu composite in the three processes.
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The developed samples of process C had lower hardness and electric conductivity than the other two processing samples. It implied that the worse effect of zirconia as dispersoid on dispersion hardening in process C. From Fig. 6(c), it could be concluded that sample C had more cavity and surface defects than samples A and B. On the other hand, the electric conductivity of the composite in process B was higher than processes A and B. Such good electric conductivities of developed samples were due to the effect of high purity of copper matrix as well as the good uniformity and narrow size distribution of synthesized zirconia particles described as in Figs. 3–5. 4. Conclusion Cu–ZrO2 (3YZ) composites have been prepared by three chemical routes. Different morphology of the reductive and non-reductive composite powder were acquired in the three processes. The crystal structures of zirconia in the three processes were differ from each other. Experimental results showed that the process A and B generated very fine and well dispersed zirconia particles in the copper matrix. And the sample B seemed to be the best with respect to the microstructure. The comparative conductivity and Vickers hardness of process B were 64%
IACS and 120, which were much higher than the other two processes. Acknowledgements The authors acknowledge the financial support by Tianjin Municipal Science and Technology Commission (No. 05YFJZJC01900) and Doctor Fund from the Educational Ministry of China (No. 20050056062). References [1] [2] [3] [4] [5] [6] [7]
P. Yu, Ch.J. Deng, N.G. Ma, M.Y. Yau, Acta Mater. 51 (2003) 3445. H.X. Lu, J. Hu, Ch.P. Chen, H. Wei, Ceram. Int. 31 (2005) 481. M.A. Morris, D.G. Morris, Acta Mater. 35 (1987) 2511. D.G. Morris, M.A. Morris, Mater. Sci. Eng. A 104 (1988) 201. D.W. Lee, G.H. Ha, B.K. Kim, Scripta Mater. 44 (2001) 2137. D.L. Zhao, H.Sh. Zhao, W.Ch. Zhou, Physica E 9 (2001) 679. M.S. Motta, P.K. Jena, E.A. Brocchi, I.G. Sol´orzano, Mater. Sci. Eng. C 15 (2001) 175. [8] P.K. Jena, E.A. Brocchi, I.G. Sol´orzano, M.S. Motta, Mater. Sci. Eng. A 371 (2004) 72. [9] V. Ramaswamy, M. Bhagwat, D. Srinivas, A.V. Ramaswamy, Catal. Today 97 (2004) 63. [10] S.H. Liang, Zh.K. Fan, L. Xu, L. Fang, Composite, Part A 35 (2004) 1446.
In situ formation of Cu–ZrO2 composites by chemical routes Jian Ding, Naiqin Zhao ∗ , Chunsheng Shi, Xiwen Du, Jiajun Li School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China Received 19 October 2005; received in revised form 30 November 2005; accepted 20 January 2006 Available online 2 March 2006
Abstract Composite of copper and 3 mol% yttria-stabilized 5 wt.% zirconia (3-YSZ) have been prepared by hydrogen (PH2 = 0.1 atm) reduction of a homogeneous mixture of equably dispersed CuO and ZrO2 formed by three chemical processes. In these processes, the 5%ZrO2 /Cu nano-composite has been formed in situ by (1) addition of NaOH solution to certain amount of dispersed Cu(NO3 )2 , ZrOCl2 and Y(NO3 )3 alcohol solution, following filtration; or (2) by adding ammonia to ZrOCl2 , Y(NO3 )3 solution, then adding Cu(NO3 )2 solution to the deposition; (3) the mixture of Zr(OH)4 and Cu(NO3 )2 ·3H2 O, mixing and heating the final composition in the three cases to acquire the blending. And calcined them at 500 ◦ C for 1 h. The 5%ZrO2 /Cu composites were fabricated by quenching and final sintering at 900 ◦ C for 90 min in vacuum atmosphere. The three process were named process A, process B, and process C. The characterization of the composite samples has been done by XRD, SEM, TEM and metallography techniques. Results from XRD and TEM indicated that different crystal structure zirconia was formed in the three processes. In comparison, the composite microstructure of process B was more homogenous. The comparative conductivity and Vickers hardness were 64% IACS and 120, which were much higher than the other two processes. © 2006 Elsevier B.V. All rights reserved. Keywords: Cu matrix composites; Nano-sized material; Mechanochemical synthesis; Powder metallurgy
1. Introduction In situ metal matrix composites(MMCs) is multiphase material whose reinforcing phases are synthesis by chemical reaction during fabrication, while a conventional ex situ MMCs is fabricated by directly adding reinforcements into its matrix [1]. The in situ chemical process has several advantages over ex situ chemical process, such as more homogenous reinforcement, excellent surface bonding, pure interphase, and appears to be a suitable method for preparing metal–ceramic nano-composite. Therefore, research along this route has potential applications in prepare metal–ceramic composite [2]. The Cu-based MMCS, being the most commonly used MMCs, are widely adopted in automobile and wiring industries. But it requires high-strength and electrical conductivity with the development of industry [3,4]. The main requirement for structure of dispersion-strengthened materials is a homogenous distribution and small size of reinforcement [5].
∗
Corresponding author. Tel.: +86 22 87401601; fax: +86 22 27405874. E-mail address: [email protected] (N. Zhao).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.01.058
Nanometer-sized (nm-sized) materials are increasingly receiving recognition as practical structural and functional materials with good prospects, and have been developed extensively in recent years [6]. Jena selected nano-alumina as the reinforcement in in situ chemical process and acquired comparing performance to internal oxidation process [7,8]. Zirconia as a ceramic material finds many applications as piezoelectric devices, ceramic condensers and oxygen sensors due to some of its unique properties such as high hardness, low coefficient of friction, high elastic modulus, chemical inertness and high melting point [9]. The present work aims at producing homogeneous ZrO2 /Cu composites from chemically prepared CuO–ZrO2 mixtures, and different chemical processes have been investigated.
2. Experimental 2.1. Materials The chemicals of Cu(NO3 )2 ·3H2 O, Y(NO3 )3 ·6H2 O, ZrOCl2 ·8H2 O and Zr(OH)4 used in this experiment, were analytically grade (99.0%). And the chemicals like NaOH and NH3 ·H2 O used, were of reagent grade.
J. Ding et al. / Journal of Alloys and Compounds 425 (2006) 390–394
391
2.2. Composites fabrication 5%ZrO2 /Cu nano-composite powders were prepared in the following three different ways: Process A: known amount of ZrOCl2 ·8H2 O and Y(NO3 )3 ·6H2 O was dissolved in the required amount of alcohol to receive 0.1 mol/L ZrOCl2 and added Cu(NO3 )2 ·3H2 O. Then 0.5 mol/L sodium hydroxide was titrated to the mixture till solution pH was up to 9.0, and the colloid depositions were formed. The mixing depositions were filtrated, then calcined at 500 ◦ C to obtain the composite powder of the Cu and Zr oxides. Then the composite oxide powder was deoxidized in a H2 atmosphere at 650 ◦ C for 45 min to obtain the final ZrO2 –Cu nano-composite powder. Process B: ZrOCl2 ·8H2 O, Y(NO3 )3 ·6H2 O and Cu(NO3 )2 ·3H2 O were taken in the required proportion. ZrOCl2 ·8H2 O and Y(NO3 )3 ·6H2 O was dissolved in accounted alcohol solution to get 0.1 mol/L ZrOCl2 solution. Then 15% ammonia was titrated to the mixing solution till the colloid formed and the solution pH was up to 9.0, then deposited for about 12 h, and the required amount of copper nitrate was added to it. The same fabricating conditions of calcination and reduction is the same as process A. Process C: known amount of Cu(NO3 )2 ·3H2 O, Y(NO3 )3 ·6H2 O and zirconium hydroxide were fully mixed in the desired proportion, and then calcined and deoxidized in the same condition with processes A and B. The composite powder with the ZrO2 content of 5 wt.% obtained by the above three processes, were named as sample A, sample B, sample C, respectively. Then the composite powders made by differential in situ chemical processes were compressed at 500 MPa, sintered at 900 ◦ C for 1.5 h and a heating rate of 10 ◦ C/min in vacuum atmosphere to acquire cylindrical specimens of 12 mm in diameter and 3 mm in height. Phase identification was carried out by a Rigaku X-ray diffract meter with Cu K␣ radiation, λ = 0.15418 and at 36 kV and 26 mA. The X-ray data were collected in step of 0.02◦ (2θ) with the scanning scope of 20–90◦ . Composite powder was observed using scanning electron microscopy(SEM; Model PHILIPS XL-30 ESEM). And the zirconia extracted from the ZrO2 /Cu composite powder were characterized using transmission electron microscopy (TEM; Model JEOL JEM-2010). The ZrO2 /Cu nano-composite microhardness was tested in Vickers hardness tester (model: MH-6) with 50 g load. The comparative conductivity was tested in whirlpool conductivity (Model: FQR7501).
3. Results and discussion
Fig. 1. X-ray diffraction patterns of non-reductive and reductive composite powder by different processes.
3.2. Characteristic of the composite powder and ZrO2 Fig. 3(a,c,e) shows SEM images of CuO, ZrO2 nanocomposite with 5%ZrO2 in the processes A–C. Different morphologys of the precursor powder have been acquired in the three processes. Fig. 3(b,d,f) shows SEM images of Cu, ZrO2 nano-composite powder with 5%ZrO2 in the processes A–C. The reductive ZrO2 /Cu composite powder made by the three processes were all the same round. The granularity of composite powder was uniform in the processes A and B. But the uneven and conglomerated composite powder could be seen in the process C. To identify the character of zirconia of the composite powder, zirconia was extracted from the ZrO2 /Cu composite powder by nitric acid. From Fig. 4(a), it can be seen that zirconia powders
3.1. XRD analysis The XRD pattern of composite powder fabricated from the three processes are shown in Fig. 1. The sharp XRD peaks on the pattern correspond to Cu phase and low intensity could be attributed to ZrO2 phase. The three strongest XRD peaks of copper are the same. The weak peaks are zirconia. Through analysis from Figs. 1 and 2, the weak XRD peak presenting at 30.27 was corresponding tetragonal zirconia, but other two weak peaks presenting at 28.18 and 31.469 were corresponding monoclinic ZrO2 in the process A. The XRD peak presenting at 30.11 was tetragonal zirconia in the process B. But monoclinic ZrO2 also existed in the process B, it is so weak that could not be seen in Fig. 1. The XRD presenting at 28.172 was monoclinic ZrO2 in the process C. Fig. 2 shows the X-ray diffraction(XRD) spectra of nanozirconia extracted from the three processes. It could be seen that the same ZrO2 crystal types of monoclinic and tetragonal exist in the processes A and B. But only monoclinic ZrO2 exist in the process C. The morphologys of the three processes are shown in Fig. 4.
Fig. 2. X-ray diffraction patterns of nano-ZrO2 extracted from Cu–ZrO2 composite powder by different processes.
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Fig. 3. Morphologys of ZrO2 /Cu composite powder by different processes (a) sample A (non-reductive); (b) sample A (reductive); (c) sample B (non-reductive); (d) sample B (reductive); (e) sample C (non-reductive); (f) sample C (reductive).
have round and elliptic appearance, and particle size is in the range of 15–50 nm. According to analysis from Figs. 1 and 2, it is clear that tetragonal and monoclinic ZrO2 exist in the process A. From Fig. 4(b), it can be seen that the morphologys of nanozirconia powder are round and quadrate, and particle size is most about 30 nm,which are tetragonal and monoclinic ZrO2 . And from Fig. 4(c), the monoclinic ZrO2 morphology and size of zirconia are irregular.
3.3. Microstructure analysis In this experiment, the composite samples were sintered in vacuum atmosphere. It should be further mentioned here that, the sintering studies carried out in the vacuum had been made to avoid any possible contamination of oxygen that might be present in the composite. And to nano-composite, it is very important to obtain small and homogenous reinforcement in the matrix in order to enhance mechanical, electrical proper-
Fig. 4. TEM images of ZrO2 extracted from the ZrO2 /Cu composite of different processes powder by nitric acid.
J. Ding et al. / Journal of Alloys and Compounds 425 (2006) 390–394
393
Fig. 5. Optical images of the composite metallographical structure by means of (a) sample A; (b) sample B; (c) sample C; (d) part of sample C magnified 50 times.
ties. Fig. 5 shows the microstructure of the three preparing routes. And the Cu–5%ZrO2 composite of sample A, sample B and sample C had been examined by optical microscope. In Fig. 5(a) and (b), small and compact grain could be observed. The distribution of ZrO2 particles in the copper matrix, had been found to be uniform. The sample had also been examined in EDS, where two distinct phases, were namely Cu and ZrO2 phase as Fig. 6. However, comparing the sample A, sample B to sample C, it could be seen that the composite made by the former, were better homogeneous structure than the latter and less holes were examined. The composites metallographs of samples A and B, were found to have uniform dispersion of ZrO2 particles with grain refinement compared to that in sample C. However, neither the size nor the distribution of ZrO2 particles in the copper matrix has been found to be uniform in sample C.
Fig. 6. Energy dispersive spectrum (a) of ZrO2 /Cu nano-composite fabricated by process C (b).
Table 1 Vickers microhardness and electric conductivity 5.0 wt.% ZrO2 –Cu composite Sample A Densification (%) Microhardness (HV) Comparative conductivity (% IACS)
70.4 114.7 58.8
Sample B 72.1 120 64
Sample C 69.5 98.12 56.2
3.4. Comparisons of the composite performances Table 1 and Fig. 7 are the properties comparison of the 5%ZrO2 –Cu composite by the three processes. It implies that the zirconia as dispersoid has great effect on dispersion hardening. Since the preparing techniques and sintering were combined in the process, the compact green density directly influenced the properties of composite [10].
Fig. 7. Comparative of microhardness and electrical conductivity of 5.0 wt.% ZrO2 –Cu composite in the three processes.
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The developed samples of process C had lower hardness and electric conductivity than the other two processing samples. It implied that the worse effect of zirconia as dispersoid on dispersion hardening in process C. From Fig. 6(c), it could be concluded that sample C had more cavity and surface defects than samples A and B. On the other hand, the electric conductivity of the composite in process B was higher than processes A and B. Such good electric conductivities of developed samples were due to the effect of high purity of copper matrix as well as the good uniformity and narrow size distribution of synthesized zirconia particles described as in Figs. 3–5. 4. Conclusion Cu–ZrO2 (3YZ) composites have been prepared by three chemical routes. Different morphology of the reductive and non-reductive composite powder were acquired in the three processes. The crystal structures of zirconia in the three processes were differ from each other. Experimental results showed that the process A and B generated very fine and well dispersed zirconia particles in the copper matrix. And the sample B seemed to be the best with respect to the microstructure. The comparative conductivity and Vickers hardness of process B were 64%
IACS and 120, which were much higher than the other two processes. Acknowledgements The authors acknowledge the financial support by Tianjin Municipal Science and Technology Commission (No. 05YFJZJC01900) and Doctor Fund from the Educational Ministry of China (No. 20050056062). References [1] [2] [3] [4] [5] [6] [7]
P. Yu, Ch.J. Deng, N.G. Ma, M.Y. Yau, Acta Mater. 51 (2003) 3445. H.X. Lu, J. Hu, Ch.P. Chen, H. Wei, Ceram. Int. 31 (2005) 481. M.A. Morris, D.G. Morris, Acta Mater. 35 (1987) 2511. D.G. Morris, M.A. Morris, Mater. Sci. Eng. A 104 (1988) 201. D.W. Lee, G.H. Ha, B.K. Kim, Scripta Mater. 44 (2001) 2137. D.L. Zhao, H.Sh. Zhao, W.Ch. Zhou, Physica E 9 (2001) 679. M.S. Motta, P.K. Jena, E.A. Brocchi, I.G. Sol´orzano, Mater. Sci. Eng. C 15 (2001) 175. [8] P.K. Jena, E.A. Brocchi, I.G. Sol´orzano, M.S. Motta, Mater. Sci. Eng. A 371 (2004) 72. [9] V. Ramaswamy, M. Bhagwat, D. Srinivas, A.V. Ramaswamy, Catal. Today 97 (2004) 63. [10] S.H. Liang, Zh.K. Fan, L. Xu, L. Fang, Composite, Part A 35 (2004) 1446.