Achieving excellent mechanical and robust lubrication behavior in the CoCrNi medium-entropy alloy via in-situ graphite

The unsatisfactory wear resistance and lubrication performance of CoCrNi multi-principal elements alloys (MPEAs) have emerged as critical challenges, impeding their extensive utilization as advanced engineering materials, despite their desirable mechanical and physical properties. Incorporating graphite to obtain MPEAs-based self-lubricating composites is believed to improve the wear resistance. However, it is challenging to prepare composites with high strength, large plasticity, and excellent anti-friction performance simultaneously. The present study reports the fabrication of novel CoCrNi MPEA-based self-lubricating composites, consisting of in-situ graphite and high-hardness silicides/carbides as reinforcement, prepared by powder metallurgy and reactive sintering. The 20.6 vol% Gr@CoCrNi–SiC composite exhibits an optimal trade-off between strength and ductility, along with anti-friction and wear resistance which is superior to the reported composites with different solid lubricants. The wear mechanism is attributed to the coordinated deformation mechanism between the CoCrNi FCC matrix and silicides/carbides, and the stabile lubrication effect supported by the structural transformation from the original polycrystalline lattice structure to core-shell nanocomposite structure (similar to diamond-like carbon) of the in-situ graphite. This simple, economical and practical strategy contributes to the development of MPEA self-lubricating composites with excellent comprehensive properties.