Properties of alloy steel coatings oxidized during plasma spraying

Plasma spraying of metals in air is usually accompanied by oxidation reactions resulting in the presence of oxides in plasma deposited coatings. Oxides in plasma sprayed high-alloy steel coatings can strongly affect their protective and mechanical properties. Two high-alloy steels were plasma sprayed onto plain steel substrates using a water-stabilized plasma gun. Both coating types, composed as usual of metallic lamellae (splats), contained considerable amounts of oxides present mainly as thin oxide films enveloping the splats. The compressive behaviour of cubic samples cut out of the coatings was studied. The results indicate an appreciable anisotropy of the response to compressive loading. If the pressure is parallel to the coating surface, strong cracking occurs. For loading perpendicular to the surface, cracking is less pronounced and high values of plastic deformation are observed. Though the coating structure and the presence of oxides preclude a satisfactory tensile strength, the coating can withstand high purely compressive loading. In this respect, plasma sprayed steels are comparable to those produced by conventional metallurgy.