LASER PROCESSING OF HIGH-CHROMIUM NICKEL-CHROMIUM COATINGS DEPOSITED BY VARIOUS THERMAL SPRAYING METHODS

High-chromium (Cr) nickel (Ni)-Cr coatings were deposited by thermal spraying in air and in an argon (Ar) gas atmosphere. coatings sprayed in Ar gas were free of pores and defects and of the same chemical composition as the spraying material. Following thermal spraying for each coating, laser glazing or laser gas alloying was applied to provide a protective chromium oxide (Cr2O3) film, produced by the intermediate oxidation process on top of the coatings. Five types of coatings were treated: (1) are and (2) flame spraying in Ar, (3) arc and (4) flame spraying in air, and (5) low-pressure plasma spraying (LPPS). Oxide formation mechanisms during laser processing were studied, and the oxidation and hot-corrosion resistance of the coatings in the presence of a sulfate-vanadate fused salt at 900 degrees C in air were examined.