Improved oxidation resistance and diffusion barrier behaviors of gradient oxide dispersed NiCoCrAlY coatings on superalloy

NiCoCrAlY has been used as the bond coat material in thermal barrier coating (TBC) to protect the superalloy substrate from oxidation and hot-corrosion. Inter-diffusion of elements between the coating and substrate could degrade the oxidation resistance of the coating and the mechanical properties of the superalloy. In this work, a gradient oxide dispersed (OD) NiCoCrAlY coating was produced onto DZ125 superalloy using electron beam-physical vapor deposition (EB-PVD). For comparison, conventional NiCoCrAlY (OD free) coated specimens were also produced by EB-PVD. The oxidation and inter-diffusion behaviors of the coated specimens at 1373 K were investigated. As compared to OD free coating, the OD coating exhibits not only a lower oxidation rate but also an improved oxide scale adherence because outward diffusion of the elements such as Ta, W and Hf from the superalloy was effectively blocked by the OD zone. Meanwhile, the presence of minor Hf in the OD coating contributes to the improved oxide scale adherence by reactive element mechanism.