Plasma Transferred Arc is the only thermal spray process that results in a metallurgical bond with the substrate. When compared with other welded coatings finer microstructures are observed after PTA processing, which have been associated with the faster solidification rate imposed by this technique. However, the powdered/atomized material used that forms the thermal spray, can play an important role in the solidification of coatings depending on their chemical composition and their grain size. This study analyzed the solidification of PTA coatings processed with an atomized cobalt based alloy (Stellite 6) with different average grain sizes. Typically, solidification of a welded coating follows solidification principles regarding the nucleation and growth of their microstructure determined mainly by the solidification rate. The role of the powdered feedstock in the solidification of coatings is analyzed based on the assumption that solidification is influenced by the initial interface energy of the atomized grains that melt in the plasma arc before reaching the melt pool. A commercial atomized Stellite 6 alloy was divided in two groups according to their grain size, below and over 125 microns, and deposited with the same processing parameters. Coatings were characterized by laser confocal microscopy and Vickers microhardness. Differences in coatings hardness and microstructure of coatings were associated with the grain size of the deposited alloy and subsequent solidification.

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