Plasma sprayed WC–Co coatings: Influence of spray conditions (atmospheric and low pressure plasma spraying) on the crystal structure, porosity, and hardness

Abstract

Ten WC–Co (12, 17, and 20 wt.% Co) powders manufactured by different techniques (sintering, atomization, coating) were studied. Both open atmosphere Ar–H2 plasma spraying and controlled atmosphere Ar–He chamber plasma spraying were performed. Pressures of 60, 150, 400, and 700 Torr were employed. To optimize controlled atmosphere spray conditions, particles splatted on glass slides rapidly traversing the jet at different distances from the nozzle exit were studied. The melting conditions were determined as a function of the plasma power level, the particle composition, and structure for particles with the same size distribution. Crystal structure analysis showed a strong decomposition of the carbides when sprayed in open atmosphere. Less decomposition occurred in the coated or atomized particles. The decomposition was reduced and coating density increased by reduced pressure spraying. The best results were obtained at 60 Torr. The hardness depended on the cobalt content, the degree of decomposition and on the density of the coatings.