Laser Cladding of MCrAlY coatings on stainless steel

MCrA1Y alloys (where M stands for Ni,Co or both) are commonly used as overlay protective coatings in gas turbine engine components against high temperature oxidation and corrosion. The protective effect of these alloys is due to the formation of a continuous thermally stable oxide layer on the coating surface. In this work several types of MCrA1Y alloys, differing in their elemental composition, have been deposited on austenitic stainless steel by means of laser cladding. The microstructure of the coatings have been characterized by SEM-EDS and XRD. As expected, elemental composition compatible with gamma Ni/gamma' Ni3A1, gamma Ni/beta-NiAl or gamma Co/beta-(Co,Ni)A1 phases are observed in hypoeutectic or hypereutectic microstructures depending on the alloy composition. The high temperature oxidation behavior of the coatings was evaluated by air furnace oxidation tests at 1100 degrees C for 200 h. The oxidized surface of the samples was examined by SEM-EDS and the oxides present identified by theoretical stoichiometric calculations. Results indicate the formation of a uniform A1(3)O(2) protective oxide scale with NiO, CoO, Y2O3/YA1O(3) and Cr2O3 oxide inclusions.