Formation mechanisms of in-situ Al based intermetallic coatings manufactured by very-low pressure plasma spraying

This study presents the manufacturing of an AlFe based intermetallic coating by the Very Low Pressure Plasma Spraying (VLPPS) process. Coating microstructure and mechanical properties are carried on with a focus on the in-situ reaction. An aluminum powder was sprayed with a plasma torch under a working pressure of 150 Pa on a stainless steel substrate to get the reaction. The microstructural analysis shows that the Al-based intermetallic coating, containing phases such as Al13Fe4, Fe3Al and Al8Cr5 is formed by the in-situ reaction between the high temperature of the aluminum coating manufacturing and the substrate. Moreover, the dense coating obtained, with a supposed metallurgical bonding to the steel substrate, featured a packed columnar microstructure mixed with nano-sized particles. Finally, the intermetallic coating presents a higher (438.9HV0.025 with SD: 53.5) than pure Al one (110HV0.025).