Aging Strengthening Mechanism of the Cu-1.0Zr Alloy
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TRODUCTION
COPPER alloys can be strengthened by aging, resulting in high strength and electrical conductivity, along with adequate thermal conductivity. Copper alloys are widely used in electrical switching contact bridges, as separation rings, coal-fired power plant burner nozzles, and spot welding electrodes.[1–3] According to the Cu-Zr binary phase diagram,[4] the maximum solid solubility of Zr in Cu is 0.15 pct at 1239 K (966 °C). Furthermore, the solubility of Zr in Cu decreases rapidly with decreasing temperature. In many studies the amount of Zr was between 0.05 pct and 0.3 pct, which is near or greater than the maximum solubility. Purcek et al. studied optimization of strength, ductility, and electrical conductivity of the Cu-Cr-Zr alloy by combining multi-route equal-channel angular pressing and aging, where Zr content was 0.08 pct.[5] Chatterjee et al. studied damage in thermally fatigued Cu-Cr-Zr alloy, where Zr content was 0.1 pct.[6] Deng et al. studied microstructure and physical properties of KA TIAN, BAOHONG TIAN, YI ZHANG, and YONG LIU are with the School of Materials Science and Engineering, Henan University of Science and Technology, Luoyang 471023, China, and also with the Collaborative Innovation Center of Nonferrous Metals, Luoyang, 471023, Henan Province, China. Contact e-mail: [email protected] ALEX A. VOLINSKY is with the Department of Mechanical Engineering, University of South Florida, Tampa FL 33620. Contact e-mail: [email protected] Manuscript submitted December 11, 2016. Article published online August 24, 2017 5628—VOLUME 48A, NOVEMBER 2017
powder metallurgy Cu-Zr alloys, and the Zr content was 0.1 pct.[7] Jiang et al. studied pre-deformation and aging characteristics of the Cu-Te-Zr alloy with Zr content of 0.2 pct.[8] In this study, the Zr content of the Cu-Zr alloy was selected at 1 pct, which is far higher than its maximum solid solubility. Excess Zr is supposed to form secondary phases, resulting in enhanced material properties. The Cu-Zr alloy was treated at a high temperature, developing a supersaturated solid solution. After aging, decomposition of the supersaturated solid solution produced a large number of precipitates to obtain high strength and high conductivity of copper alloys.[9] At present, there are three main mechanisms of precipitation phase strengthening: coherent strain strengthening, dislocation shear strengthening, and the Orowan dislocation bypassing strengthening mechanisms. Wang et al.[10] believe that the Cu-0.75Cr-0.13Zr alloy conforms to the Orowan dislocation bypassing strengthening mechanism. Watanabe et al.[11] also think that Cu-Cr alloy is consistent with the Orowan dislocation bypassing strengthening mechanism. However, Liu et al.[12] think that rapid solidification of the Cu-Cr alloy is in accordance with the coherent strain strengthening mechanism. Nevertheless, Holzwarth et al.[13] deemed that Cu-Cr-Zr is more suitable for the Orowan dislocation bypassing strengthening mechanism by comparing it with the coherent strain strengthening mechanism. The pr
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