Laser Boronizing Functional Strategy for Self-Lubricating Enhancement of CoCrNi Medium-Entropy Alloy

The CoCrNi medium-entropy alloy (MEA) is recognized for its high strength and ductility; however, its wear resistance is limited in harsh environments. While traditional powder-pack boronizing enhances wear resistance, it requires prolonged high-temperature treatments (900–1000 °C for 6–8 h), leading to thermal deformation and restricting scalability for large components. High-energy lasers present a promising solution by enabling rapid, localized melting with a confined heat-affected zone of 2 mm. This study presents a novel laser boronizing functional strategy for CoCrNi MEA that uses prefabricated boron layers (400–1600 μm) to create dual-phase CrB and (Co,Ni)₃B coatings with a dendritic structure. The CoCrNi-800B coating (800 μm boron layer) showed optimal performance: a hardness of 23.5 GPa, an elastic modulus of 258 GPa, a 96% reduction in wear rate in aqueous environments, and a 40% reduction in the friction coefficient. Tribofilm analysis revealed the formation of self-lubricating B₂O₃/H₃BO₃ layers at the friction interface, effectively reducing friction and wear. This ultrafast laser boronizing method (1–5 min, 60 times faster than conventional methods) minimizes thermal deformation while enabling localized boronizing of large components like bearings. This strategy lays the groundwork for the development of wear-resistant materials for offshore wind power and hydropower applications.