Laser Cladding of MCrAlY Alloys

Laser cladding (LC) and laser metal deposition (LMD) can be innovative methods to current thermal spray techniques to obtain dense and high-quality bond coats using nickel- and cobalt-based superalloys in thermal barrier coating (TBC) systems for high-temperature applications. In this work, MCrAlY coatings (M = Ni + Co) were obtained on a stainless steel substrate using a coaxial LMD technique with two different Ni/Co and Al proportions. This chapter describes the development of the laser cladding process for such alloys by looking closely at the obtained microstructure and mechanical properties. Finally, the high-temperature oxidation behavior of the MCrAlY laser coatings is analyzed. The as-built resulting microstructure consists of γ-Ni/β-NiAl or γ-Co/β-(Co,Ni)Al phases, depending on the alloy’s chemical composition. The γ/β-phases formed in the MCrAlY coating microstructure resulted in a lower elastic modulus than the austenitic stainless steel substrate, while an inverse behavior for hardness was observed due to the presence of the aluminum-rich β-phase. At high temperatures, the growth and formation of oxide layers protect the underlying coating and substrate from oxidation high temperatures. The possible formation and morphology of oxides on oxidized surfaces, and the evaluation of the thickness and phases present on thermally grown oxide (TGO) scales, were evaluated by advanced characterization techniques. The results show that the as-built microstructure of the laser cladding MCrAlY alloys plays an important role in the behavior of the coatings at high temperature.