Cold Sprayed MCrAlY as a Bondcoat Candidate for TBC Application

Abstract

Abstract As an emerging technique, cold gas dynamic spray is one of the latest tools for dimensional repair and coating applications. Cold spray (CS) utilizes high velocity particles as feedstock rather than high temperature to produce a coating without over melting feedstock, and thereby achieves a free-oxide coating. One of today’s critical coating applications is thermal barrier coating (TBC) for high efficiency turbine engine components, assisting and enabling today’s super alloys for turbine components to operate at a higher firing temperature. Many studies reveal that the formation of thermally grown oxide (TGO) on MCrAlY bondcoat, and the surface morphology profile of the bondcoat play paramount roles in failure modes and lifetimes of TBCs. This work has been focused on exploring the feasibility of CS MCrAlY as a bondcoat candidate for TBC application by comparing with those deposited by thermal spray processes, mainly plasma spray (APS) and high velocity oxygen fuel (HVOF). In this work, the features and properties of CS coatings were characterized mainly on microstructure, surface morphology, and TGO formation in isothermal oxidation test at 1100°C. Also, CS bondcoat and its thermal barrier coating were tested together with APS and HVOF formed TBC coatings. CS NiCoCrAlY coatings are identified with some unique aspects and characteristics: A desirable microstructure can be achieved, with oxide-free and high density. Solid solution of NiAl phase at local regions of grain boundaries is discovered; CS-bondcoat has a honeycomb network-like surface morphology. Long-range roughness is characterized from all honeycomb networks, and short-range roughness from the peaks within individual network cells; Kinetic curve of isothermal oxidation test at 1100°C indicates that a low-rate and stable TGO scale is formed on CS-bondcoat; and thermal cycling test demonstrates that CS-bondcoat TBC and APS-TBC have higher resistance to the spallation of ceramic topcoat.