Enhanced Wear Resistance of Fine-Grained Ni-Based Coating via Annealing-Induced Phase Transformation

Annealing is widely applied to reduce porosity and enhance the wear resistance of thermally sprayed metallic coatings; however, its effectiveness is often limited by grain coarsening and brittle phase formation. Here, we present a new approach that directly overcomes these limitations by coupling thermal spraying with the crystallization behavior of a rationally designed amorphous alloy powder (Ni 68.6 Cr 8.7 Nb 3 P 16 B 3.2 Si 0.5 ). Upon annealing at 800°C for 1 h, the metastable Mg 6 Cu 17 Si 7 -type phase present in the as-sprayed coating transforms into a well-refined three-phase microstructure, comprising a ductile Ni-based solid solution and hard Ni 3 P and NbNi 3 intermetallic phases, with 51% reduced intersplat density. This microstructural configuration results in a 21% reduction in COF and an 89% reduction in wear rate. The worn surface of annealed coating demonstrates minor thin grooves, lower fractions of oxides, and no sign of spallation, delamination or cracking, presenting a significant improvement in the wear resistance after annealing. This improvement originates from the three-phase composite microstructure in which the ductile Ni-based solid solution provides plastic deformability and crack resistance, whereas the hard Ni 3 P and NbNi 3 phases provide hardness and load-bearing capacity. Annealed coating exhibits mild abrasive wear mechanism coupled with limited plastic deformation. These findings demonstrate that controlled crystallization of thermally-sprayed coatings can be used to engineer beneficial phases, providing a promising strategy for the design of high-performance wear-resistant coatings.