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 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.