A new strategy to improve the mechanical properties of CoCrNi medium-entropy alloys based self-lubricating composite in a wide temperature range

The fact that metal matrix is incompatible with hexagonal boron nitride (h-BN) seriously aggravates the mechanical and tribological properties of solid-lubricating composites. This study successfully introduces a solid-lubricant h-BN@Ag (Ag nano powders generated in-situ on h-BN surface). Adding h-BN@Ag to CoCrNi medium entropy alloys significantly improve the fracture toughness of the CoCrNi/h-BN (increased by 40.1%), which is resulted from decreasing porosity of the composite. In comparison with the CoCrNi/h-BN composite, obvious plasticity characteristics are found in CoCrNi/h-BN@Ag composite. Moreover, the composite containing h-BN@Ag exhibits a low, stable coefficient of friction (COF) in a wide temperature range (RT—600°C). Obviously, the COF of CoCrNi/h-BN@Ag composite is more stable than CoCrNi/Ag composite. Our findings show that adding h-BN@Ag is an effective way to enhance the fracture toughness and tribologicial behaviors of the CoCrNi matrix composites.