Fabrication and performance assessment of CoCrNi-based medium entropy alloy with silver-coated graphene

Graphene and its derivatives are widely used to improve the friction performance of metal composite materials. Unfortunately, challenges like uniform graphene dispersion and severe interfacial reactions hinder the development of graphene-reinforced medium entropy composite (MEC). In this work, silver-decorated reduced graphene oxide (rGO) as a reinforcement for CoCrNi MEA was prepared through a one-step chemical reduction method, achieving uniform graphene dispersion and alleviating the severe interfacial reaction. During spark plasma sintering (SPS), minimal graphene decomposition occurred, forming hard Cr₂₃C₆ carbides. The friction testing showed that thermal and mechanical stresses facilitated the formation of a self-lubricating layer enriched with rGO and silver on the worn surface, leading to a synergistic effect among various solid lubricants and significantly improving the tribological performance. Under a load of 5 N, the average friction coefficient (COF) of the Ag@rGO/CoCrNi composite was 0.41, a 36.9 % reduction compared to the CoCrNi matrix, while the wear rate decreased by 6.5 %. At 15 N, the COF further reduced to 0.37, a 25.1 % decrease. Microscopic investigation elucidated sub-surface nano twins and FCC-HCP phase transition under high-stress conditions. This work provides a new strategy for graphene dispersion and an approach for fabricating high-performance metal-modified rGO/CoCrNi MECs.