Characterization of plasma sprayed Fe-10Cr-10Mo-(C,B) amorphous coatings

Abstract

Alloys of Fe-10Cr-10Mo containing a large amount of carbon and/or boron were plasma sprayed by low-pressure plasma spraying (LPPS) and high-energy plasma spraying (HPS). The as-sprayed coatings obtained by the LPPS process are composed of only an amorphous phase, while as-sprayed coatings obtained by the HPS process are a mixture of amorphous and crystalline phases. The amorphous phase in these coatings crystallizes on tempering at about 773 to 873 K, and the crystallization temperatures depend on the content of carbon and boron. Thermal stability of the amorphous phase containing boron is higher than those phases containing carbon. A very fine mixed structure of ferrite and carbide, borocarbide, or boride is formed by decomposition of the amorphous phase, bringing about a hardness of 1200 to 1400 DPN (Vickers hardness). The coatings containing carbon retain a hardness of more than 1000 DPN, even on tempering at temperatures of 1073 K or higher. The anodic polarization behavior of the coatings exhibits an activation-passivation transition in 1N H2SO4 solution. The active and passive current densities of the as-sprayed amorphous and tempered crystalline coatings containing carbon is lower than the coatings containing boron. The corrosion resistance of the as-sprayed and crystallized coatings containing carbon is superior to a SUS316L stainless steel coating.