Effects of Pre-Deformation and Heat Treatment on the Microstructure and Mechanical Properties of Cu-2.5Be Sheets

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JMEPEG https://doi.org/10.1007/s11665-020-05064-6

Effects of Pre-Deformation and Heat Treatment on the Microstructure and Mechanical Properties of Cu-2.5Be Sheets Yang Liu, Deshan Chen, Daibo Zhu, Xiaojin Liu, Tan Han, and Peng Zhang (Submitted July 14, 2020; in revised form August 8, 2020) This study investigated the effects of pre-deformation reduction and subsequent heat treatment on the microstructure and mechanical properties of Cu-2.5Be alloy. Twin formation mechanism and the strengthening contribution of boundaries and b particles were analyzed and discussed, and the results indicate that the following relative oriented relationship existed between the b and the surrounding a(Cu): (111)ai(110)b and [011]ai[001]b. Meanwhile, the main formation mechanism of annealing twins in Cu-2.5Be alloy is ‘‘growth accidents.’’ Pre-deformation can significantly increase the yield strength of Cu-2.5Be alloy while maintaining good plasticity. The analysis of strengthening contributions indicated that the presence of twins and grain boundaries significantly improved the strength and ductility of the Cu-2.5Be alloy. Keywords

Cu-2.5Be sheets, EBSD, heat treatment, mechanical properties, pre-deformation

1. Introduction Due to their excellent mechanical properties and electrical conductivity, Cu-Be sheets are widely used in the electronics industries. The attractive properties of these alloys are caused by the precipitation sequence that exists during their aging process (Ref 1-3). In particular, due to the immense secondary electron emission (SEE) performance of BeO, copper beryllium sheets can be used as electrodes for photomultiplier tubes. Recent findings suggest that the SEE properties of the copper beryllium alloy enhance with the Beryllium content (Ref 4). However, with an increase in Be content, especially over 2.3 wt.%, hard and brittle particles could form in copper beryllium alloys, which may cause processing and formability problems. To overcome these problems, our former work focused on the effects of annealing on the cold-rolled Cu-2.7Be sheets, which still obtained relatively higher strength and lower ductility (Ref 5, 6). Therefore, Cu-Be sheets with lower Be content (Cu2.5Be) are studied and pre-deformation and subsequent heat treatment are used to get better processing and formability properties than previous Cu-2.7Be sheets.

Yang Liu, School of Mechanical Engineering, Xiangtan University, Xiangtan 411105, China; and School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore; Deshan Chen and Xiaojin Liu, School of Mechanical Engineering, Xiangtan University, Xiangtan 411105, China; Daibo Zhu, School of Mechanical Engineering, Xiangtan University, Xiangtan 411105, China; and Kinkou Suzhou Co., Ltd., Taicang 215400, China; Tan Han, Kinkou Suzhou Co., Ltd., Taicang 215400, China; and Peng Zhang, School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai 264209, China. Contact e-mails: [email protected] and [email protected].

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