Characterization of plasma sprayed Fe-17Cr-38Mo-4C amorphous coatings crystallizing at extremely high temperature

A Fe-17Cr-38Mo-4C alloy powder was plasma sprayed by three processes: an 80 kW low-pressure plasma spray (LPPS), a 250 kW high-energy plasma spray (HPS), and a 40 kW conventional plasma spray (APS), The as-sprayed coating obtained by the LPPS process is composed of only amorphous phase, As-sprayed coatings obtained by the HPS and APS processes are a mixture of amorphous and crystalline phases, The three as-sprayed coatings exhibit a high hardness of 1000 to 1100 DPN. The amorphous phase in these coatings crystallizes at a high temperature of about 920 K, A very fine structure composed of hard chi-phase and carbides is formed after crystallization. The hardness of the coating obtained by LPPS reaches a maximum of 1450 DPN just after crystallization on tempering and retains a high hardness more than 1300 DPN after tempering at high temperatures of 1173 or 1273 K. The corrosion potential of the amorphous coating is the highest among the three coatings and higher than that of a SUS316L stainless steel coating, The anodic polarization measurements infer that the corrosion resistance of the amorphous coating is superior or comparable to SUS316L stainless steel coating in H2SO4 solution.