- Email: [email protected]
The influence of TiB2 content on microstructure and properties of W–30Cu composites prepared by electroless plating and powder metallurgy
Advanced Powder Technology 26 (2015) 1058–1063
Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Original Research Paper
The influence of TiB2 content on microstructure and properties of W–30Cu composites prepared by electroless plating and powder metallurgy Li-Mei Huang a, Lai-Ma Luo a,b,⇑, Ji-Gui Cheng a,b, Xiao-Yong Zhu a,b, Yu-Cheng Wu a,b,⇑ a b
School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China Engineering Research Center of Powder Metallurgy of Anhui Province, Hefei 230009, China
a r t i c l e
i n f o
Article history: Received 20 June 2014 Received in revised form 19 April 2015 Accepted 23 April 2015 Available online 4 May 2015 Keywords: W–Cu composite materials TiB2 nanoparticles Electroless plating Powder metallurgy Properties
a b s t r a c t W–30Cu composite materials with different concentrations of TiB2 particles ranging from 0 to 2 wt.% were prepared by electroless plating with simplified pretreatment and powder metallurgy. The morphologies of W–30Cu composite powders, original TiB2 powders, W–30Cu/TiB2 composite powders were characterized using field emission scanning electron microscopy. X-ray diffraction analysis was used to characterize the phase of W–30Cu/TiB2 composite powders. Relative density, electrical conductivity, and hardness of the W–30Cu/TiB2 composites were examined. Results showed that uniform Cu-coated W composite powders were successfully synthesized by electroless plating with simplified pretreatment. The addition of TiB2 nanoparticles significantly affected the microstructure and properties of W–Cu composite materials. A good combination of the relative density, electrical conductivity, and hardness of the W–30Cu composite materials can be obtained with the incorporation of TiB2 additive at 0.25 wt.%. Ó 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1. Introduction W–Cu composite materials are widely used in the electrical and electronic fields due to their combining the natural properties of W, for example the high melting temperature, high sputtering threshold, low activation under neutron irradiation, low tritium retention, low coefficient of thermal expansion and good thermal stability, with those unique properties of Cu, such as high electrical conductivity and thermal conductivity [1–4]. However, with the increasing need of higher capability of electric powder systems and extended grids of electric power transmission, it is required that the contact materials as switchers can bear ultrahigh voltage and larger capability. It should optimize and control the compositions and microstructures of W–Cu composite materials, except for high mechanical properties, high electrical and thermal conductivity at room temperatures, and excellent chemical stability at the elevated temperatures [5]. Ultra-fine second phase strengthening is considered to be effective in mitigating these problems in ⇑ Corresponding authors at: School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China. Tel./fax: +86 551 62901012. E-mail addresses: [email protected] (L.-M. Luo), [email protected] (Y.-C. Wu).
W–Cu composite materials. These well-dispersed ultra-fine particles could inhibit the grain growth during sintering, hinder the grain boundary sliding and stabilize the microstructure [6]. TiB2 is a refractory compound that exhibits outstanding features such as high melting point (2980 °C), high hardness (HV 34–39.6 GPa) and high modulus (530–569 GPa) characteristics. The combination of its excellent properties has made TiB2 increasingly important for a wide range of applications in erosive, abrasive, corrosive or high-temperature environments [7–10]. Fabricating high-quality W–Cu composite materials is difficult because the crystal structure of tungsten and copper are different, poor wettability between tungsten and copper. Studies have reported the fabrication of W–Cu composite materials using infiltration method [11], and activated sintering [12]. The infiltration method is including the preparation of the W skeleton and filling the W skeleton with melted Cu, it is a time consuming and complex process, and require high energy. Super/nano-powders have higher activation energy, therefore the sintering temperature and sintering time are lower [13]. Methods for preparing superfine/nano-composite powders include mechanical alloying [14], thermo-chemistry method [15], mechano-chemical processing [16], and spray drying [17]. However, these methods can be
http://dx.doi.org/10.1016/j.apt.2015.04.015 0921-8831/Ó 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1059
L.-M. Huang et al. / Advanced Powder Technology 26 (2015) 1058–1063
problematic. The mechanical alloying process is liable to introduce the contamination of iron and cobalt by the use of stainless steel and tungsten carbide balls or jars, such contaminations significantly affect the properties of the resulting materials [18]. Electroless plating is an autocatalytic method in which the reduction of the metallic ions in the solution and the film deposition can be performed by the oxidation of chemical compound present in the solution itself. The method does not need a current supply and sets no limits on the shape and type of substrate. This method produces composite powders with even phase dispersing and high purity [19–20]. In this paper, W–30Cu composite powders were prepared by electroless plating with simplified pretreatment, then TiB2 at different concentrations was added to W–30Cu composite powders by blending. W–30Cu/(0, 0.25, 0.5, 1, 2)TiB2 composite materials were fabricated by powder metallurgy. The effects of different TiB2 concentrations on the microstructure, relative density, hardness, and compressive strength of W–30Cu composite material were investigated.
2. Experimental The components used in the electroless copper plating solution are listed in Table 1. W powder with an average size of 1.0 lm– 1.3 lm was used. The electroless copper plating solution was maintained at pH 11–13 by adjusting the amount of sodium hydroxide during the plating process. The electroless plating was performed using ultrasonic bath (frequency: 40 KHz; power: 400 W). The ultrasonic wave resulted in uniformly dispersed particles in the bath to reduce agglomeration. Temperature was maintained at 60 °C, and supply reaction energy was regulated to speed up the electroless plating reaction. To produce a surface with catalytic activity, the W powder was pretreated before electroless plating, the solution and operation for the simplified pretreatment were adopted from the optimum process described previously [21]. The electroless copper plating bath was prepared following Table 1. The pretreated W powders were added into the electroless plating according to a stoichiometric ratio of W to Cu (Cu
Table 1 Composition of the electroless copper plating solution. Role
Chemicals name
Chemical formula
Concentration
Main salt Reduction agent Complexing agent Stabilizing agent Regulator
Copper sulfate Formaldehyde Sodium EDTA 2,20 -Dipyridyl Sodium hydroxide
CuSO45H2O HCHO C10H14N2Na2O82H2O C10H8N2 NaOH
16.8 g/L 26 ml/L 50 g/L 0.030–0.040 g/L pH: 11–13
Fig. 1. FE-SEM micrographs of the powders (a) W–30Cu composite powders; (b) original TiB2 powder; (c) W–30Cu/1TiB2 composite powders.
1060
L.-M. Huang et al. / Advanced Powder Technology 26 (2015) 1058–1063
wt.% = 30%). After the electroless plating procedure, the W–30Cu Composite powders were washed using deionized water many times to remove the remaining liquid after electroless plating, and then were dried in a vacuum oven at 50 °C for 2 h. Addition of different TiB2 concentration (0, 0.25, 0.5, 1, and 2 wt.%) into the W–Cu composite powders was conducted by blending, and then reduced at 500 °C under hydrogen for 60 min. The reduced W–30Cu/(0, 0.25, 0.5, 1, 2) TiB2 composite powders were compacted into 40 mm 8 mm dimension under pressure of 400 MPa. The obtained green samples were sintered at a temperature of 1300 °C under protective hydrogen for 60 min. The phase structure of the W–30Cu/TiB2 composite powders after blending was characterized by X-ray diffraction (XRD) (operating voltage: 40 KV; operating current: 40 mA; step size: 0.026°). Field emission scanning electron microscopy (FE-SEM) (operating voltage: 5.0–15.0 KV; operating current: 10 lA) was used to characterize the morphology of the W–Cu composite powders after electroless plating, the W–30Cu/TiB2 composite powders after blending, the sintered samples, and the fractured sintered samples. The relative density of the sintered alloys was measured based on Archimedes’ principle. Vickers hardness was measured on polished sections at an average of 10 readings by using the HV1-10A hardness tester along the cross-sectional surface of the specimen, with a load of 10 N for 15 s. The electrical resistivity measured using four-point method.
3. Results and discussion 3.1. Powder characteristics Fig. 1(a) shows the FE-SEM image of W–30Cu composite powders after electroless plating. As shown in Fig. 1(a), Cu is uniformly and densely coated on the surface of W powders after electroless plating, almost no Cu uncoated-W particles were developed. Fig. 1(b) presents the FE-SEM image of original TiB2 powders. As shown in Fig. 1(b), the powders were mostly polygon particles, the average grain size of the original powder was about 800 nm, and the powder consists of a small number of big particles of 5–6 lm, which were consisted of small agglomerated particles. Fig. 1(c) presents the FE-SEM image of W–30Cu/1TiB2 composite powders after blending. As can be seen in Fig. 1(c), the TiB2 powders and W–30Cu composite powders were evenly distributed.
Fig. 2. XRD pattern of the W–30Cu/1TiB2 composite powders.
XRD analysis results of W–30Cu/1TiB2 composite powders after blending is presented in Fig. 2. As presented in figure, only W, Cu, and TiB2 phases were identified in the composite powders. Therefore, electroless plating did not introduce impurities into the W–30Cu composite powders, blending did not introduce impurities into the W–30Cu/TiB2 composite powders. 3.2. Sintered samples characteristics 3.2.1. Density of sintered samples Fig. 3 shows the relative density of the sintered samples with different TiB2 content. With the increase of the TiB2 content, the relative density of the sintered samples decreased. The density of TiB2 (4.52 g/cm3) is less than that of W (19.35 g/cm3) and Cu (8.92 g/cm3), and the wettability between TiB2 and Cu is less than that between W and Cu at high temperature, the addition of TiB2 inhibited the rearrangement of the W particles to a certain extent in the liquid phase sintering, affecting the densification of the composite materials. 3.2.2. Microstructure of sintered samples Fig. 4 presents the microstructures of W–30Cu composite materials with different TiB2 content. As can be seen in the figures, the Cu matrix has formed a network structure, the W particles are distributed homogeneously in the Cu matrix, and pores were nearly absent in sintered samples. The dispersal of the additional particles in the composite materials reduced the probability of contact among W particles. TiB2 supplementation prevented the agglomeration of W particles and inhibited the growth of W grains during the process of sintering. Comparing Fig. 4(a) and Fig. 4(c), the addition of TiB2 refined the W grain size in the sample. However, the agglomerated TiB2 particles (as shown by the arrows in Fig. 4(e) and (f)), formation of Cu pools, and pores existed in the samples due to the poor wettability between TiB2 and Cu during sintering. The FE-SEM morphologies of the fractured W–30Cu/0.25TiB2 and W–30Cu/2TiB2 composites are presented in Fig. 5. As shown in Fig. 5, the sintered samples reveal transgranular failure of the W grain (as shown by the arrows in Fig. 5(a)) and ductile failure of the Cu matrix, network of Cu that formed throughout the composites (as shown by the arrows in Fig. 5(b)). The ductile fracture surfaces of Cu fully cover the surfaces of the W particles. The W particles showed nearly the same size as the initial ones. These properties may be due to electroless plating and dispersed TiB2
Fig. 3. Relative density of the W–30Cu/(0, 0.25, 0.5, 1, 2) TiB2 composite materials.
L.-M. Huang et al. / Advanced Powder Technology 26 (2015) 1058–1063
1061
Fig. 4. FE-SEM micrographs of the W–Cu/TiB2 composite materials (a) low magnification image of W–30Cu/0TiB2 composite material; (b) high magnification image of (a); (c) low magnification image of W–30Cu/0.25TiB2 composite material; (d) high magnification image of (c); (e) low magnification image of W–30Cu/2TiB2 composite material; (f) high magnification image of (e).
particles. Cu is continuously and uniformly plated over all the surfaces in the form of atoms, regardless of the size and shape of the W powder. The addition of TiB2 particles reduced the probability of contact between W particles and the agglomeration phenomenon of W particles, and inhibited W grains growth. TiB2 improved the compressive strength of composite material. However, the addition of TiB2 at higher than 0.25 wt.% concentration resulted in the formation of Cu pools and pores (as shown in Fig. 4(e) and (f)), which lead to the fracture involves transgranular failure of W grains along with a number of W-matrix interface failure (as shown by arrows in Fig. 5(c) and (d)). 3.2.3. Electrical conductivity of sintered samples The imaginary line denotes that electrical conductivity of GB IACS was 42.0%. The electrical conductivity (as percent of the
International Annealed Copper Standard: %IACS; %IACS = 0.017241/q ⁄ 100%, q is the resistivity) of sintered samples is presented in Fig. 6. As the TiB2 content increases, resistivity increased and electrical conductivity decreased. The electric conductivity of TiB2 is much lower than that of Cu and W, and TiB2 addition can inevitably increase additional interfaces and electron scattering, W–30Cu/TiB2 composites with have lower electrical conductivity than W–30Cu composites. 3.2.4. Hardness of sintered samples The measured Vickers hardness of the sintered samples is presented in Fig. 7. As can be seen, the Vickers hardness values of the sintered samples increase with the increase of TiB2 content and reach to the highest values of 209.53 at 0.5% TiB2 concentration. TiB2 addition increases the hardness of W–30Cu composite
1062
L.-M. Huang et al. / Advanced Powder Technology 26 (2015) 1058–1063
Fig. 5. FE-SEM morphologies of the fractured W–Cu/TiB2 composite materials (a) low magnification image of W–30Cu/0.25TiB2 composite material; (b) high magnification image of (a); (c) low magnification image of W–30Cu/2TiB2 composite material; (d) high magnification image of (c).
Fig. 6. Electrical conductivity of the W–30Cu/(0, 0.25, 0.5, 1, 2) TiB2 composite materials. Fig. 7. Vickers hardness of the W–30Cu/(0, 0.25, 0.5, 1, 2) TiB2 composite materials.
materials because the hardness of TiB2 is much higher than that of Cu and W. Relative density and mechanical behavior were directly related, that is, hardness increased with increasing density. The microstructural homogeneity can also be characterized by quantitative analysis of the hardness values for composites. Excessive TiB2 addition resulted in non-homogeneity of the microstructure of composite materials with the agglomeration of TiB2, Cu, and pores. The combined effects resulted in a dramatic decrease of Vickers hardness of the W–30Cu composite materials at TiB2 concentrations higher than 0.5% (Fig. 7).
4. Conclusions W–30Cu/(0, 0.25, 0.5, 1, 2) wt.% TiB2 composites were prepared by electroless plating with simplified pretreatment and powder metallurgy. The copper matrix has formed a network structure and the addition of TiB2 refined the W grain size in the sintered samples. A good combination of the relative density (93.38%), electrical conductivity (45.90%), and hardness (HV: 196.90) of the W– Cu composite materials can be obtained with the incorporation of TiB2 additive at 0.25 wt.%.
L.-M. Huang et al. / Advanced Powder Technology 26 (2015) 1058–1063
Acknowledgments This paper was supported by National Magnetic Confinement Fusion Program with Grant No. 2014GB121001, The Fundamental Research Funds for the Central Universities No. 2012HGQC0032.
References [1] Z.J. Zhou, Y.S. Kwon, Fabrication of W–Cu composite by resistance sintering under ultra-high pressure, J. Mater. Process. Tech. 168 (2005) 107–111. [2] M. Ardestani, H. Arabi, H.R. Rezaie, H. Razavizadeh, Synthesis and densification of W–30 wt.%Cu composite powders using ammonium meta tungstate and copper nitrate as precursors, Int. J. Refract. Met. Hard Mater. 27 (2009) 796– 800. [3] B.B. Liu, J.H. Chen, J.X. Xie, Fabrication of W/Cu20 composite materials with nearly full density by particle size distribution method, Rare Met. Mater. Eng. 39 (2010) 0017–0021. [4] W.G. Chen, Z.Y. Kang, H.F. Shen, B.J. Ding, Arc erosion behavior of a nanocomposite W–Cu electrical contact material, Rare Met. 25 (2006) 37–42. [5] X.H. Yang, S.H. Liang, X.H. Wang, P.H. Xiao, Z.K. Fan, Effect of WC and CeO2 on microstructure and properties of W–Cu electrical contact material, Int. J. Refract. Met. Hard. Mater. 28 (2010) 305–311. [6] X.H. Yang, K. Fan, S.H. Liang, P. Xiao, Effects of Y2O3 on properties of Cu–W electrical contact materials, Chin. J. Mater. Res. 21 (2007) 414–420. [7] A.G. Nazari, M. Mozafari, Simulation of structural features on mechanochemical synthesis of AlO3–TiB2 nanocomposite by optimized artificial neural network, Adv. Powder Technol. 23 (2012) 220–227. [8] M.S. Wong, Y.C. Lee, Deposition and characterization of Ti–B–N monolithic and multilayer coatings, Surf. Coat. Technol. 120–121 (1999) 194–199. [9] H.Y. Wang, Q.C. Jiang, Y. Wang, B.X. Ma, F. Zhao, Fabrication of TiB2 particulate reinforced magnesium matrix composites by powder metallurgy, Mater. Lett. 58 (2004) 3509–3513.
1063
[10] Z.L. Li, W.M. Wang, J.L. Wang, Effects of TiB2 on microstructure of nano-grained Cu–Cr–TiB2 composite powders prepared by mechanical alloying, Adv. Powder Technol. 25 (2014) 415–422. [11] H. Ibrahim, A. Aziz, A. Rahmat, Enhanced liquid-phase sintering of W–Cu composites by liquid infiltration, Int. J. Refract. Met. Hard Mater. 43 (2014) 222–226. [12] P.G. Chen, Q. Shen, G.Q. Luo, M.J. Li, L.M. Zhang, The mechanical properties of W–Cu composite by activated sintering, Int. J. Refract. Met. Hard Mater. 36 (2013) 220–224. [13] L.H. Zhu, X.M. Ma, J.X. Lei, Properties and microstructure of a newly developed AgC electrical contact material, Rare Met. Mater. Eng. 33 (2004) 349–353. [14] M.H. Maneshian, A. Simchi, Z.R. Hesabi, Structural changes during synthesizing of nanostructured W–20 wt.%Cu composite powder by mechanical alloying, Mater. Sci. Eng. A 445–446 (2007) 86–93. [15] J.Q. Li, W.G. Chen, W.J. Tao, F. Shao, B.J. Ding, Nano-composite powder of tungsten coated copper produced by thermo-chemistry co-reduction, Rare Met. Mater. Eng. 41 (2012) 2091–2094. [16] A. Dolatmoradi, S. Raygan, H. Abdizadeh, Mechanochemical synthesis of W–Cu nanocomposites via in-situ co-reduction of the oxides, Powder Technol. 233 (2013) 208–214. [17] X.L. Shi, H. Yang, S. Wang, G.Q. Shao, X.L. Duan, Z. Xiong, T.G. Wang, Characterization of W–20Cu ultrafine composite powder prepared by spray drying and calcining-continuous reduction technology, Mater. Chem. Phys. 104 (2007) 235–239. [18] S.H. Hong, B.K. Kim, Fabrication of W–20 wt.%Cu composite nanopowder and sintered alloy with high thermal conductivity, Mater. Lett. 57 (2003) 2761– 2767. [19] J. Sudagar, J.S. Lian, W. Sha, Electroless nickel, alloy, composite and nano coatings – a critical review, J. Alloys Compd. 571 (2013) 183–204. [20] Y. Zhao, T. Zhang, R. Zhang, J.P. Chen, Y.X. Duan, Hollow ceramic microsphere coated with co by electroless plating and its electromagnetic properties, Rare Met. Mater. Eng. 39 (2010) 0587–0592. [21] L.M. Huang, L.M. Luo, X.Y. Ding, G.N. Luo, X. Zan, J.G. Cheng, Y.C. Wu, Effects of simplified pretreatment process on the morphology of W–Cu composite powder prepared by electroless plating and its sintering characterization, Powder Technol. 258 (2014) 216–221.
Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Original Research Paper
The influence of TiB2 content on microstructure and properties of W–30Cu composites prepared by electroless plating and powder metallurgy Li-Mei Huang a, Lai-Ma Luo a,b,⇑, Ji-Gui Cheng a,b, Xiao-Yong Zhu a,b, Yu-Cheng Wu a,b,⇑ a b
School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China Engineering Research Center of Powder Metallurgy of Anhui Province, Hefei 230009, China
a r t i c l e
i n f o
Article history: Received 20 June 2014 Received in revised form 19 April 2015 Accepted 23 April 2015 Available online 4 May 2015 Keywords: W–Cu composite materials TiB2 nanoparticles Electroless plating Powder metallurgy Properties
a b s t r a c t W–30Cu composite materials with different concentrations of TiB2 particles ranging from 0 to 2 wt.% were prepared by electroless plating with simplified pretreatment and powder metallurgy. The morphologies of W–30Cu composite powders, original TiB2 powders, W–30Cu/TiB2 composite powders were characterized using field emission scanning electron microscopy. X-ray diffraction analysis was used to characterize the phase of W–30Cu/TiB2 composite powders. Relative density, electrical conductivity, and hardness of the W–30Cu/TiB2 composites were examined. Results showed that uniform Cu-coated W composite powders were successfully synthesized by electroless plating with simplified pretreatment. The addition of TiB2 nanoparticles significantly affected the microstructure and properties of W–Cu composite materials. A good combination of the relative density, electrical conductivity, and hardness of the W–30Cu composite materials can be obtained with the incorporation of TiB2 additive at 0.25 wt.%. Ó 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1. Introduction W–Cu composite materials are widely used in the electrical and electronic fields due to their combining the natural properties of W, for example the high melting temperature, high sputtering threshold, low activation under neutron irradiation, low tritium retention, low coefficient of thermal expansion and good thermal stability, with those unique properties of Cu, such as high electrical conductivity and thermal conductivity [1–4]. However, with the increasing need of higher capability of electric powder systems and extended grids of electric power transmission, it is required that the contact materials as switchers can bear ultrahigh voltage and larger capability. It should optimize and control the compositions and microstructures of W–Cu composite materials, except for high mechanical properties, high electrical and thermal conductivity at room temperatures, and excellent chemical stability at the elevated temperatures [5]. Ultra-fine second phase strengthening is considered to be effective in mitigating these problems in ⇑ Corresponding authors at: School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China. Tel./fax: +86 551 62901012. E-mail addresses: [email protected] (L.-M. Luo), [email protected] (Y.-C. Wu).
W–Cu composite materials. These well-dispersed ultra-fine particles could inhibit the grain growth during sintering, hinder the grain boundary sliding and stabilize the microstructure [6]. TiB2 is a refractory compound that exhibits outstanding features such as high melting point (2980 °C), high hardness (HV 34–39.6 GPa) and high modulus (530–569 GPa) characteristics. The combination of its excellent properties has made TiB2 increasingly important for a wide range of applications in erosive, abrasive, corrosive or high-temperature environments [7–10]. Fabricating high-quality W–Cu composite materials is difficult because the crystal structure of tungsten and copper are different, poor wettability between tungsten and copper. Studies have reported the fabrication of W–Cu composite materials using infiltration method [11], and activated sintering [12]. The infiltration method is including the preparation of the W skeleton and filling the W skeleton with melted Cu, it is a time consuming and complex process, and require high energy. Super/nano-powders have higher activation energy, therefore the sintering temperature and sintering time are lower [13]. Methods for preparing superfine/nano-composite powders include mechanical alloying [14], thermo-chemistry method [15], mechano-chemical processing [16], and spray drying [17]. However, these methods can be
http://dx.doi.org/10.1016/j.apt.2015.04.015 0921-8831/Ó 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1059
L.-M. Huang et al. / Advanced Powder Technology 26 (2015) 1058–1063
problematic. The mechanical alloying process is liable to introduce the contamination of iron and cobalt by the use of stainless steel and tungsten carbide balls or jars, such contaminations significantly affect the properties of the resulting materials [18]. Electroless plating is an autocatalytic method in which the reduction of the metallic ions in the solution and the film deposition can be performed by the oxidation of chemical compound present in the solution itself. The method does not need a current supply and sets no limits on the shape and type of substrate. This method produces composite powders with even phase dispersing and high purity [19–20]. In this paper, W–30Cu composite powders were prepared by electroless plating with simplified pretreatment, then TiB2 at different concentrations was added to W–30Cu composite powders by blending. W–30Cu/(0, 0.25, 0.5, 1, 2)TiB2 composite materials were fabricated by powder metallurgy. The effects of different TiB2 concentrations on the microstructure, relative density, hardness, and compressive strength of W–30Cu composite material were investigated.
2. Experimental The components used in the electroless copper plating solution are listed in Table 1. W powder with an average size of 1.0 lm– 1.3 lm was used. The electroless copper plating solution was maintained at pH 11–13 by adjusting the amount of sodium hydroxide during the plating process. The electroless plating was performed using ultrasonic bath (frequency: 40 KHz; power: 400 W). The ultrasonic wave resulted in uniformly dispersed particles in the bath to reduce agglomeration. Temperature was maintained at 60 °C, and supply reaction energy was regulated to speed up the electroless plating reaction. To produce a surface with catalytic activity, the W powder was pretreated before electroless plating, the solution and operation for the simplified pretreatment were adopted from the optimum process described previously [21]. The electroless copper plating bath was prepared following Table 1. The pretreated W powders were added into the electroless plating according to a stoichiometric ratio of W to Cu (Cu
Table 1 Composition of the electroless copper plating solution. Role
Chemicals name
Chemical formula
Concentration
Main salt Reduction agent Complexing agent Stabilizing agent Regulator
Copper sulfate Formaldehyde Sodium EDTA 2,20 -Dipyridyl Sodium hydroxide
CuSO45H2O HCHO C10H14N2Na2O82H2O C10H8N2 NaOH
16.8 g/L 26 ml/L 50 g/L 0.030–0.040 g/L pH: 11–13
Fig. 1. FE-SEM micrographs of the powders (a) W–30Cu composite powders; (b) original TiB2 powder; (c) W–30Cu/1TiB2 composite powders.
1060
L.-M. Huang et al. / Advanced Powder Technology 26 (2015) 1058–1063
wt.% = 30%). After the electroless plating procedure, the W–30Cu Composite powders were washed using deionized water many times to remove the remaining liquid after electroless plating, and then were dried in a vacuum oven at 50 °C for 2 h. Addition of different TiB2 concentration (0, 0.25, 0.5, 1, and 2 wt.%) into the W–Cu composite powders was conducted by blending, and then reduced at 500 °C under hydrogen for 60 min. The reduced W–30Cu/(0, 0.25, 0.5, 1, 2) TiB2 composite powders were compacted into 40 mm 8 mm dimension under pressure of 400 MPa. The obtained green samples were sintered at a temperature of 1300 °C under protective hydrogen for 60 min. The phase structure of the W–30Cu/TiB2 composite powders after blending was characterized by X-ray diffraction (XRD) (operating voltage: 40 KV; operating current: 40 mA; step size: 0.026°). Field emission scanning electron microscopy (FE-SEM) (operating voltage: 5.0–15.0 KV; operating current: 10 lA) was used to characterize the morphology of the W–Cu composite powders after electroless plating, the W–30Cu/TiB2 composite powders after blending, the sintered samples, and the fractured sintered samples. The relative density of the sintered alloys was measured based on Archimedes’ principle. Vickers hardness was measured on polished sections at an average of 10 readings by using the HV1-10A hardness tester along the cross-sectional surface of the specimen, with a load of 10 N for 15 s. The electrical resistivity measured using four-point method.
3. Results and discussion 3.1. Powder characteristics Fig. 1(a) shows the FE-SEM image of W–30Cu composite powders after electroless plating. As shown in Fig. 1(a), Cu is uniformly and densely coated on the surface of W powders after electroless plating, almost no Cu uncoated-W particles were developed. Fig. 1(b) presents the FE-SEM image of original TiB2 powders. As shown in Fig. 1(b), the powders were mostly polygon particles, the average grain size of the original powder was about 800 nm, and the powder consists of a small number of big particles of 5–6 lm, which were consisted of small agglomerated particles. Fig. 1(c) presents the FE-SEM image of W–30Cu/1TiB2 composite powders after blending. As can be seen in Fig. 1(c), the TiB2 powders and W–30Cu composite powders were evenly distributed.
Fig. 2. XRD pattern of the W–30Cu/1TiB2 composite powders.
XRD analysis results of W–30Cu/1TiB2 composite powders after blending is presented in Fig. 2. As presented in figure, only W, Cu, and TiB2 phases were identified in the composite powders. Therefore, electroless plating did not introduce impurities into the W–30Cu composite powders, blending did not introduce impurities into the W–30Cu/TiB2 composite powders. 3.2. Sintered samples characteristics 3.2.1. Density of sintered samples Fig. 3 shows the relative density of the sintered samples with different TiB2 content. With the increase of the TiB2 content, the relative density of the sintered samples decreased. The density of TiB2 (4.52 g/cm3) is less than that of W (19.35 g/cm3) and Cu (8.92 g/cm3), and the wettability between TiB2 and Cu is less than that between W and Cu at high temperature, the addition of TiB2 inhibited the rearrangement of the W particles to a certain extent in the liquid phase sintering, affecting the densification of the composite materials. 3.2.2. Microstructure of sintered samples Fig. 4 presents the microstructures of W–30Cu composite materials with different TiB2 content. As can be seen in the figures, the Cu matrix has formed a network structure, the W particles are distributed homogeneously in the Cu matrix, and pores were nearly absent in sintered samples. The dispersal of the additional particles in the composite materials reduced the probability of contact among W particles. TiB2 supplementation prevented the agglomeration of W particles and inhibited the growth of W grains during the process of sintering. Comparing Fig. 4(a) and Fig. 4(c), the addition of TiB2 refined the W grain size in the sample. However, the agglomerated TiB2 particles (as shown by the arrows in Fig. 4(e) and (f)), formation of Cu pools, and pores existed in the samples due to the poor wettability between TiB2 and Cu during sintering. The FE-SEM morphologies of the fractured W–30Cu/0.25TiB2 and W–30Cu/2TiB2 composites are presented in Fig. 5. As shown in Fig. 5, the sintered samples reveal transgranular failure of the W grain (as shown by the arrows in Fig. 5(a)) and ductile failure of the Cu matrix, network of Cu that formed throughout the composites (as shown by the arrows in Fig. 5(b)). The ductile fracture surfaces of Cu fully cover the surfaces of the W particles. The W particles showed nearly the same size as the initial ones. These properties may be due to electroless plating and dispersed TiB2
Fig. 3. Relative density of the W–30Cu/(0, 0.25, 0.5, 1, 2) TiB2 composite materials.
L.-M. Huang et al. / Advanced Powder Technology 26 (2015) 1058–1063
1061
Fig. 4. FE-SEM micrographs of the W–Cu/TiB2 composite materials (a) low magnification image of W–30Cu/0TiB2 composite material; (b) high magnification image of (a); (c) low magnification image of W–30Cu/0.25TiB2 composite material; (d) high magnification image of (c); (e) low magnification image of W–30Cu/2TiB2 composite material; (f) high magnification image of (e).
particles. Cu is continuously and uniformly plated over all the surfaces in the form of atoms, regardless of the size and shape of the W powder. The addition of TiB2 particles reduced the probability of contact between W particles and the agglomeration phenomenon of W particles, and inhibited W grains growth. TiB2 improved the compressive strength of composite material. However, the addition of TiB2 at higher than 0.25 wt.% concentration resulted in the formation of Cu pools and pores (as shown in Fig. 4(e) and (f)), which lead to the fracture involves transgranular failure of W grains along with a number of W-matrix interface failure (as shown by arrows in Fig. 5(c) and (d)). 3.2.3. Electrical conductivity of sintered samples The imaginary line denotes that electrical conductivity of GB IACS was 42.0%. The electrical conductivity (as percent of the
International Annealed Copper Standard: %IACS; %IACS = 0.017241/q ⁄ 100%, q is the resistivity) of sintered samples is presented in Fig. 6. As the TiB2 content increases, resistivity increased and electrical conductivity decreased. The electric conductivity of TiB2 is much lower than that of Cu and W, and TiB2 addition can inevitably increase additional interfaces and electron scattering, W–30Cu/TiB2 composites with have lower electrical conductivity than W–30Cu composites. 3.2.4. Hardness of sintered samples The measured Vickers hardness of the sintered samples is presented in Fig. 7. As can be seen, the Vickers hardness values of the sintered samples increase with the increase of TiB2 content and reach to the highest values of 209.53 at 0.5% TiB2 concentration. TiB2 addition increases the hardness of W–30Cu composite
1062
L.-M. Huang et al. / Advanced Powder Technology 26 (2015) 1058–1063
Fig. 5. FE-SEM morphologies of the fractured W–Cu/TiB2 composite materials (a) low magnification image of W–30Cu/0.25TiB2 composite material; (b) high magnification image of (a); (c) low magnification image of W–30Cu/2TiB2 composite material; (d) high magnification image of (c).
Fig. 6. Electrical conductivity of the W–30Cu/(0, 0.25, 0.5, 1, 2) TiB2 composite materials. Fig. 7. Vickers hardness of the W–30Cu/(0, 0.25, 0.5, 1, 2) TiB2 composite materials.
materials because the hardness of TiB2 is much higher than that of Cu and W. Relative density and mechanical behavior were directly related, that is, hardness increased with increasing density. The microstructural homogeneity can also be characterized by quantitative analysis of the hardness values for composites. Excessive TiB2 addition resulted in non-homogeneity of the microstructure of composite materials with the agglomeration of TiB2, Cu, and pores. The combined effects resulted in a dramatic decrease of Vickers hardness of the W–30Cu composite materials at TiB2 concentrations higher than 0.5% (Fig. 7).
4. Conclusions W–30Cu/(0, 0.25, 0.5, 1, 2) wt.% TiB2 composites were prepared by electroless plating with simplified pretreatment and powder metallurgy. The copper matrix has formed a network structure and the addition of TiB2 refined the W grain size in the sintered samples. A good combination of the relative density (93.38%), electrical conductivity (45.90%), and hardness (HV: 196.90) of the W– Cu composite materials can be obtained with the incorporation of TiB2 additive at 0.25 wt.%.
L.-M. Huang et al. / Advanced Powder Technology 26 (2015) 1058–1063
Acknowledgments This paper was supported by National Magnetic Confinement Fusion Program with Grant No. 2014GB121001, The Fundamental Research Funds for the Central Universities No. 2012HGQC0032.
References [1] Z.J. Zhou, Y.S. Kwon, Fabrication of W–Cu composite by resistance sintering under ultra-high pressure, J. Mater. Process. Tech. 168 (2005) 107–111. [2] M. Ardestani, H. Arabi, H.R. Rezaie, H. Razavizadeh, Synthesis and densification of W–30 wt.%Cu composite powders using ammonium meta tungstate and copper nitrate as precursors, Int. J. Refract. Met. Hard Mater. 27 (2009) 796– 800. [3] B.B. Liu, J.H. Chen, J.X. Xie, Fabrication of W/Cu20 composite materials with nearly full density by particle size distribution method, Rare Met. Mater. Eng. 39 (2010) 0017–0021. [4] W.G. Chen, Z.Y. Kang, H.F. Shen, B.J. Ding, Arc erosion behavior of a nanocomposite W–Cu electrical contact material, Rare Met. 25 (2006) 37–42. [5] X.H. Yang, S.H. Liang, X.H. Wang, P.H. Xiao, Z.K. Fan, Effect of WC and CeO2 on microstructure and properties of W–Cu electrical contact material, Int. J. Refract. Met. Hard. Mater. 28 (2010) 305–311. [6] X.H. Yang, K. Fan, S.H. Liang, P. Xiao, Effects of Y2O3 on properties of Cu–W electrical contact materials, Chin. J. Mater. Res. 21 (2007) 414–420. [7] A.G. Nazari, M. Mozafari, Simulation of structural features on mechanochemical synthesis of AlO3–TiB2 nanocomposite by optimized artificial neural network, Adv. Powder Technol. 23 (2012) 220–227. [8] M.S. Wong, Y.C. Lee, Deposition and characterization of Ti–B–N monolithic and multilayer coatings, Surf. Coat. Technol. 120–121 (1999) 194–199. [9] H.Y. Wang, Q.C. Jiang, Y. Wang, B.X. Ma, F. Zhao, Fabrication of TiB2 particulate reinforced magnesium matrix composites by powder metallurgy, Mater. Lett. 58 (2004) 3509–3513.
1063
[10] Z.L. Li, W.M. Wang, J.L. Wang, Effects of TiB2 on microstructure of nano-grained Cu–Cr–TiB2 composite powders prepared by mechanical alloying, Adv. Powder Technol. 25 (2014) 415–422. [11] H. Ibrahim, A. Aziz, A. Rahmat, Enhanced liquid-phase sintering of W–Cu composites by liquid infiltration, Int. J. Refract. Met. Hard Mater. 43 (2014) 222–226. [12] P.G. Chen, Q. Shen, G.Q. Luo, M.J. Li, L.M. Zhang, The mechanical properties of W–Cu composite by activated sintering, Int. J. Refract. Met. Hard Mater. 36 (2013) 220–224. [13] L.H. Zhu, X.M. Ma, J.X. Lei, Properties and microstructure of a newly developed AgC electrical contact material, Rare Met. Mater. Eng. 33 (2004) 349–353. [14] M.H. Maneshian, A. Simchi, Z.R. Hesabi, Structural changes during synthesizing of nanostructured W–20 wt.%Cu composite powder by mechanical alloying, Mater. Sci. Eng. A 445–446 (2007) 86–93. [15] J.Q. Li, W.G. Chen, W.J. Tao, F. Shao, B.J. Ding, Nano-composite powder of tungsten coated copper produced by thermo-chemistry co-reduction, Rare Met. Mater. Eng. 41 (2012) 2091–2094. [16] A. Dolatmoradi, S. Raygan, H. Abdizadeh, Mechanochemical synthesis of W–Cu nanocomposites via in-situ co-reduction of the oxides, Powder Technol. 233 (2013) 208–214. [17] X.L. Shi, H. Yang, S. Wang, G.Q. Shao, X.L. Duan, Z. Xiong, T.G. Wang, Characterization of W–20Cu ultrafine composite powder prepared by spray drying and calcining-continuous reduction technology, Mater. Chem. Phys. 104 (2007) 235–239. [18] S.H. Hong, B.K. Kim, Fabrication of W–20 wt.%Cu composite nanopowder and sintered alloy with high thermal conductivity, Mater. Lett. 57 (2003) 2761– 2767. [19] J. Sudagar, J.S. Lian, W. Sha, Electroless nickel, alloy, composite and nano coatings – a critical review, J. Alloys Compd. 571 (2013) 183–204. [20] Y. Zhao, T. Zhang, R. Zhang, J.P. Chen, Y.X. Duan, Hollow ceramic microsphere coated with co by electroless plating and its electromagnetic properties, Rare Met. Mater. Eng. 39 (2010) 0587–0592. [21] L.M. Huang, L.M. Luo, X.Y. Ding, G.N. Luo, X. Zan, J.G. Cheng, Y.C. Wu, Effects of simplified pretreatment process on the morphology of W–Cu composite powder prepared by electroless plating and its sintering characterization, Powder Technol. 258 (2014) 216–221.