IR-Laser Treatment of Thermal Sprayed MCrAlY Coatings and Their High Temperature Corrosiion Behavior

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Abstract
To improve the corrosion resistance of MCrAlY (M=Ni, Co) coatings, IR-laser modification was attempted by a combination of (i) gas-flame and plasma spraying in air followed by laser-glazing (in air and Ar), (ii) low-pressure plasma spraying (LPPS) and laser-glazing (Ar), and (iii) LPPS and laser-gas (oxygen) alloying. Glazing in both argon and air of oxide containing CoNiCrAlY coatings promoted formation of weakly adherent agglomerates of A1YO3 and a solid solution of alumina-chromia. LPPS CoNi/Ni-CrAlY glazed in an inert atmosphere showed formation of NiAl and NiAl3, besides the formation of Al-Y compounds in the top layer. The gas alloying reaction of these coatings: produced continuous and adherent chromia-alumina oxide layers containing yttrium. This work describes metallurgical and chemical changes of MCrAlY alloys during the surface modification, and the oxidation resistance of glazed coatings at 900°C in air. The role of yttrium in the behavior of the oxides formed during laser-glazing, laser-alloying and oxidation is discussed.