DEVELOPMENT OF A COLD FLOW DEPOSITION PROCESS FOR THE APPLICATION OF COATINGS USING THE HVOF SPRAY PROCESS

Cold spraying is the latest development in thermal spray processes. It is a method of applying hard coatings through high velocity impacts of powders on the substrate, however at low temperature or cold flow conditions. The aim of this project was to design and develop a mechanism to produce cold-sprayed hard coatings on substrates using the HVOF (High Velocity Oxy-Fuel) spray process. The first part of the research involved studying the parameters that should be considered in the manufacture of the cold spray gun. This study led to the development of different concepts, of which the most feasible and effective was chosen for further development. The final design involved modifications to a HVOF thermal spray gun to suit the cold spray process. This was done by producing a de Laval type nozzle that could insert into the gun and application of heat to the exterior of the nozzle using a band heater. The cold spray gun was designed and produced and was then tested for the various parameters that control the cold spray process to determine which concept areas were most successful and to determine what modifications could be made to improve the design. Coatings were produced using an external powder injector into the flow of compressed air.