A novel technology in microstructure design and production of environment-friendly Cu–Bi bearing alloy with guidance of CALPHAD in order to replace toxic Cu–Pb bearing alloy
Bowen Dong, Pengfei Wang, Shichao Liu, Zhenpeng Wu, Chao Ke, Qingchuan Zou, Jinchuan Jie
Abstract
In order to replace toxic Cu–Pb bearing alloy, a novel strategy to design and produce new environment-friendly Cu–Bi bearing alloy was proposed with the guidance of thermodynamic analysis and CALPHAD. It's found that alloying element Sn can slow down the nucleation of α-Cu and introduce a (α-Cu + L1 + L2) three-phase-coexistence state in Cu–Bi–Sn ternary system by weakening the separation between elements Cu and Bi. Pseudo-binary phase diagrams of the Cu–Bi–xSn (wt.%, x = 0, 2, 4, 6) systems were calculated through CALPHAD, and a (α-Cu + L1 + L2) phase region was found in Cu–Bi–6Sn phase diagram. Based on the above phase diagrams, the Cu–24Bi–xSn (wt.%, x = 0, 2, 4, 6) alloys were prepared. Bi-rich minor phase particles (MPPs) show continuously network morphology in Cu–24Bi–(0, 2, 4) alloy, and show independently rod-like morphology in Cu–24Bi–6Sn alloy. It's thus revealed that (α-Cu + L1 + L2) state introduced by alloying element Sn can effectively promote the MPPs transforming from network to rod-like morphology. Simultaneously, it's found that the friction coefficients the Cu–24Bi–xSn alloys decrease from 0.236 in Cu–24Bi to 0.182 in Cu–24Bi–6Sn. It's indicated that the self-lubricating property of the Cu–24Bi–xSn alloys will be increased with Sn content increasing from 0 wt.% to 6 wt.%. Cu–24Bi–6Sn alloy is thus identified to be the alloy with the best microstructure and self-lubricating property.