Study of the Splat-Substrate Interface for a NiCr Coating Plasma Sprayed onto Polished Aluminum and Stainless Steel Substrates

Abstract

In the plasma spraying process, the mechanisms by which molten particles impact on and bond with the substrate are not fully understood. For this study a nickel-chromium powder was sprayed onto mirror polished aluminum 5052 and stainless steel 304 substrates to form single splats. The splats and their interface with the substrate were studied using detailed microstructural characterization with emphasis on the shape of the splats, the nature of the splat-substrate interface, including the degree of contact and the extent of melting of the substrate and mixing with the splat material, and the presence, either on or within the splats of phases such as oxides. It was shown that melting of the substrate, along with intermixing and diffusion between substrate and splat materials, occurred for the steel substrate, but not for the aluminum substrate. Oxides including nickel oxide, chromium oxide, and aluminum oxide were also observed, the type and distribution of these phases depended on the substrate type.

Evidence of Substrate Melting of NiCr Particles on Stainless Steel Substrate by Experimental Observation and Simulations

“…Nickel and stainless steel have the similar lattice parameters and crystal structures, resulting in grain growth between two phases across the interface. The studies, not shown here [32], found that NiCr and stainless steel grains were juxtaposed with the same orientation across the interface. Thus, all these studies, with evidence of diffusion and jetting, suggested that substrate melting has occurred.…”

“…A trace of iron oxide and chromium oxide was observed at the splat-substrate interface where substrate melting occurred. Selected area diffraction patterns were also used in this study (not shown here) [32], to determine the structure of the oxide. Through a range of diffraction analysis, a number of oxides including NiO, Cr 2 O 3 or CrO 3 and FeO were observed.…”

Recent Developments in the Research of Splat Formation Process in Thermal Spraying

“…Melting-Induced Splashing Model. As proposed by the previous researchers, thermal sprayed coating was always mechanical bonded with the substrate [52][53][54][55][56]; however, the substrate melting at the splat-substrate interface during splat collection process was also reported recently with both experimental and numerical simulation [23,78,101,[109][110][111][112][113].…”

“…Zhang et al [101] also detected an intermetallic layer between the molybdenum splat and the mild steel substrate and suggested that substrate melting occurred. Melting of the substrate, along with intermixing and diffusion between substrate and splat materials, was found when the nickel-chromium powder was thermally sprayed onto the �at stainless steel 304 substrate, but not for the aluminum substrate [78,[111][112][113]. Figure 6 [23].…”

Complex Permittivity and Microwave‐Absorbing Properties of Fe/Al2O3 Coatings by Air Plasma Spraying Technique

“…Thermal spraying technologies are widely used to produce various coatings with high deposition rate for structural and functional applications, which certainly give much greater flexibility and could easily be adapted to deposit coatings onto components surface having very different geometries . It allows using the widest range of available materials to obtain different coatings for the application in many industrial fields, such as wear resistance coatings, thermal barrier coatings, and resistance corrosive environment coatings .…”