Enhancing wear resistance of plasma-sprayed NiCr coatings through ZrB2 and Mo dual-phase reinforcement: Microstructure and tribological performance evaluation

ZrB₂-NiCr and Mo-ZrB₂-NiCr coatings were prepared through atmospheric plasma spraying, and the effects of varying ZrB₂ content as well as the addition of Mo on the microstructure and tribological properties of the coatings were analyzed. Both the hardness and porosity of the coatings increased with the addition of refractory hard phases. The dual-phase reinforced coating achieves its highest hardness of 577.86 HV_0.1 at a ZrB₂ content of 20 wt%. The heat-absorbing protective effect of Mo reduced the formation of oxides within the coating. Friction tests showed that the wear rate of both coatings first decreased and then increased with increasing ZrB₂ content. Coating with 10 wt% ZrB₂ and 5 wt% Mo exhibited optimal wear resistance, with a minimum wear rate of 1.93 × 10⁻⁶ mm³/N·m. Mo reduces friction by forming the laminar structure of MoO₃. It fully spreads out to protect loose debris from being scattered by grinding balls, thereby forming a complete lubricating film on the sliding surface. The wear mechanisms of both coatings are dominated by the hardness and toughness of the materials, transitioning from material removal caused by adhesion and micro-cutting at low hardness to layered fracture caused by brittle interface defects at high hardness.