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

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 alpha-Cu and introduce a (alpha-Cu + L-1 + L-2) three-phase-coexistence state in Cu-Bi -Sn ternary system by weakening the separation between elements Cu and Bi. Pseudobinary phase diagrams of the Cu-Bi-xSn (wt.%, x = 0, 2, 4, 6) systems were calculated through CALPHAD, and a (alpha-Cu + L-1 + L-2) 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 (alpha-Cu + L-1 + L-2) 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. (C) 2021 The Author(s). Published by Elsevier B.V.