Cold spraying of thermally softened Ni-coated FeSiAl composite powder: Microstructure characterization, tribological performance and magnetic property

Abstract

The low retainability of reinforcing particles in functional composite coatings fabricated by cold spray (CS) is a major problem in maximizing coating properties. In this work, the Ni-coated FeSiAl composite powders were used to fabricate soft magnetic composite (SMC) coatings via CS. The feedstock particles were preheated prior to the entrance of nozzle to improve the retainability of FeSiAl particles and the coating properties. Our results showed that the dense Ni/FeSiAl coatings containing the uniformly-dispersed and crack-free FeSiAl particles were produced. The thermal softening effect of Ni layer, as a result of particle preheating, can effectively increase the volumetric content of FeSiAl particle (from 24.3% to 46.2%) in the composite coating. Particle preheating also conducted to the significant improvement of coating thickness due to enhanced deposition efficiency. Dry-sliding test showed that the tribological performance of SMC coating with particle preheating weakens, owing to lowered microhardness. Enhanced magnetic property was achieved with higher soft ferromagnetic characteristic and decreasing coercivity value at higher particle preheating temperatures. The study on coating formation mechanism highlighted that thermal softening effect can give rise to adiabatic shear instability of Ni layer. This results in the significantly improved retainability of FeSiAl particles and soft magnetic performance.