Multi-phase FCC-based AlxCrFeNi2Si(1-x) medium entropy alloy coatings design for tailoring toughness and wear resistance of CSS-42L bearing steel

Abstract

Multi-phase FCC-based Al_xCrFeNi₂Si_(1-x) (x = 0, 0.2, 0.5, 0.8, 1) medium entropy alloy coatings were designed by adjusting Al/Si molar ratio and manufactured by employing laser melting deposition technology on CSS-42L aerospace bearing steel, with the comprehensive consideration on toughness and wear resistance demands of the auxiliary bearing system. Experimental results indicated that the addition of Al sets the tone of the dual-phase FCC+BCC structure of CrFeNi₂Al MEA coating, while the exclusive addition of Si promotes the formation of silicides. By adjusting the Al/Si molar ratio, a coating with a microstructure of multiphase FCC+eutectic BCC/silicide was obtained. The co-doping of Al and Si has improved the microhardness, toughness, and wear resistance of the coating to different extents. Among the studied MEA coatings, the Al_0.2CrFeNi₂Si_0.8 coating exhibited the best wear resistance while maintaining higher toughness, attributed to the synergistic effects of the FCC, and eutectic BCC/silicide phases. Second phase strengthening and solid solution strengthening caused by lattice distortion are the main mechanisms to improve the mechanical and tribological properties of the Al_xCrFeNi₂Si_(1-x) MEA coatings. The second phase mainly includes the high strength BCC phase and silicide phase, while the lattice distortion is mainly caused by the large atomic size mismatch and elastic mismatch between Al and Si atoms and other atoms.