Development of high carbide dissolution/low carbon loss Cr3C2–NiCr coatings by shrouded plasma spraying

Abstract

During heat treatment of Cr3C2–NiCr coatings it has been observed that zones of high carbide dissolution precipitate high concentrations of small carbide grains which develop into finely structured and interconnected networks. The variation in carbide structures developed in this way raises the possibility of producing tailored carbide morphologies with unique composite structures. The first step in exploring this concept for Cr3C2–NiCr composite coatings is to produce a coating with a supersaturated solid solution of Ni–Cr–C from which high concentrations of carbides could be precipitated with heat treatment. The approach taken in this work to generate such a supersaturated solid solution was to spray a conventional Cr3C2–NiCr powder under high power plasma conditions. The effect of key plasma parameters (nozzle geometry, plasma gas composition and flow rate, plasma power) on generating carbide dissolution into the Ni alloy binder was analyzed. Shrouded and unshrouded trials were compared to determine the effect of shrouding on the magnitude of decarburization.