Splat Interface Bonding Formation During Atmospheric Plasma Spraying of High Temperature Oxide-Shell-Free Nicralyc Molten Droplet

Abstract

In this study, carbon-containing NiCrAlY powders are used to generate high temperature oxide-shell-free NiCrAlYC droplets by APS to examine the effect of the droplet condition for the carbon in-situ deoxidizing on the formation of metallurgical bonding at splat-substrate interface. Cross-section of the splat interface samples are prepared by focus ion beam (FIB) technique and the bonding state of splat with the superalloy substrate is examined by high-resolution transmission electron microscopy (TEM). Results reveal that regular disk NiCrAlY splats can deposited by oxide-shell-free molten droplets through APS. The examination into splat samples by FIB reveals that the interfacial bonding ratio reaches over 80% between the splat and superalloy substrate. TEM results provide clear evidence of localized substrate melting and chemical inter-mixing between the splat and the substrate for metallurgical bonding. The NiCrAlYC coating presents a much lower porosity and oxide content and significantly improved cohesion and adhesion strength as compared with the NiCrAlY coating. Tensile adhesion tests yield an adhesion strength of > 83 MPa for the APS NiCrAlYC coating on a polished Ni-based superalloy substrate.

Keywords: Atmospheric plasma spraying, In-flight oxidation, In-situ deoxidizing, Splat, Metallurgical bonding