THE FEATURES OF DETONATION SPRAYING TECHNOLOGY FOR TUNGSTEN CARBIDE BASED COATINGS

The authors studied the effect of key parameters of detonation spraying process on tungsten carbide-based coatings and their mechanical properties, microstructure, and phase composition. Two main tasks are solved when developing the technology for spraying the carbide-containing materials. The relationship is established between the phase composition of tungsten-based coatings and their strength, hardness, and substrate adhesion. It was established that the WC dissolution in the metal phase promotes the increase of substrate adhesion as well as strength and hardness of coating material. A procedure of spraying coatings in the reduction mode is proposed: i.e., using working gas mixtures with excess acetylene. It prevents the decarbonization of WC carbides under the action of detonation products and environment. The phase composition heterogeneity (both along with the layer thickness and along the spraying spot diameter) is established. This depends on a complex of factors that determine the intensity of heat removal from the area of layer formation. For optimizing the structure and the mechanical characteristics of the coating, we need to control decarbonization of carbide component (WC) and formation of alpha-Ni (W) solid solution at different stages of spraying. Even a minor departure from carbon content leads to either appearance of graphite or formation the fragile eta'-phase (Co3W3C), thus strongly reducing the mechanical properties.