HVOF system definition to maximise the thickness of formed components

The present study aims to establish the potential of producing various hard metal industrial components using the high-velocity oxy-fuel (HVOF) thermal spray process, rather than by the sintering techniques currently used. The HVOF technique is generally used as a coating process, but previously has been employed to spray-form thin tungsten carbide–cobalt (WC–Co) components, flat and cylindrical in shape [Proceedings of Advances in Powder Metallurgy and Particulate Materials, Washington DC 5 (1996) 18.41]. The present work is focused on maximising the thickness of such components. The difficulty in producing thick-formed components using this technique arises from residual stress in the sprayed material. In coatings this stress leads to adhesion loss and interlaminar debonding and, in formed components, cracking or buckling. Residual stress that arises during spraying can be reduced by limiting the rise and fluctuation of the die temperature, and this was carried out in the present study using a carbon dioxide cooling system. This enabled continuous deposition at a steady temperature, and led to the successful production of thick-formed WC–Co components.