Plasma-sprayed Al₂O₃–ZrO₂ composite coatings with nano-eutectic structures for wear protection: A novel strategy based on feedstock powder design

Thermally sprayed nanostructured ceramic coatings have demonstrated considerable potential for surface protection applications. Nevertheless, the regulation of their microstructure and mechanical properties remains challenging owing to the persistent dependence on reconstituted feedstocks. Herein, a novel nanoeutectic powder prepared by combustion synthesis-air atomization (CS-AA) is used in atmospheric plasma spraying (APS) to fabricate a nanostructured Al₂O₃–ZrO₂ coating for wear protection. The composite coating has a bimodal microstructure featuring the coexistence of a fully melted (FM) region and a partially melted (PM) region. Significantly, the PM region exhibited a multicolony structure composed of fibrous or lamellar nanoeutectic phases with an average spacing of 65 nm. In contrast to the FM region, the PM region has a higher microhardness and contributes to the fracture toughness of the coating through mechanisms such as crack deflection, grain pulling-out, and bridging. An increase in plasma spray power facilitates deposition efficiency, coating densification, and intersplat bonding while causing a reduction in the proportion of the PM region. A coating sprayed at 57 kW exhibited optimized properties, with a microhardness of 1008.39±308.54 HV_0.2, a toughness of 4.22±0.58 MPa·m^1/2, and a wear rate of 5×10⁻⁵ mm³·N⁻¹·m⁻¹ under a 6 N load at 500 r·min⁻¹. This work offers a novel idea for the design of thermal spraying feedstock and provides new insights into the performance optimization of nanostructured ceramic coatings.