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

This study presents the manufacturing of an Al-Fe 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 (438.9HV(0.025) with SD: 53.5) than pure Al one (110HV(0.025)).