Abstract
During heat treatment of Cr3C2-NiCr thermal spray coatings, regions of carbide dissolution have been observed to precipitate very small grains that grow into finely structured carbide networks. This study investigates the potential of developing tailored submicron carbide composites based on that process. The approach taken is to spray a conventional Cr3C2-NiCr powder under high-power plasma conditions to generate a supersaturated solid solution of Ni-Cr-C from which carbides could be precipitated via heat treatment. Preliminary trials assessed the effect of a broad range of plasma parameters to determine what conditions generate the greatest carbide dissolution with the lowest carbon loss. Follow-up trials investigated the most promising parameters in more detail to determine the effect of spray distance, with and without shrouding, on carbon loss and carbide dissolution. This paper presents the results from one of these trials in which an Ar-H2 plasma was sprayed with a low-velocity nozzle. Gas shrouding had a minimal effect on carbide dissolution but was effective in reducing air entrainment in the plasma and the degree of decarburization.
