DYNAMIC PROCESSES DURING HIGH-VELOCITY OXYFUEL SPRAYING

High velocity oxyfuel spraying is a new, rapidly developing technology for coating formation which is now challenging plasma spraying. Dynam ic processes during HVOF spraying have considerable influence on the c oating quality. The dynamic processes considered are as follows: combu stion and gas dynamics, mechanical and thermal inflight behaviour of t he powder particles, and droplet flattening. The corresponding literat ure is also reviewed. The following points are taken into account: flu id behaviour inside and outside a spraying gun; fluid-particle interac tions; particle shape and morphology; internal heat conduction in powd er particles; mass transfer (dissolution, diffusion, etc.) inside the composite particles; particle heating, fusion, cooling, and solidifica tion; surface roughness, splat solidification, and mass loss of the dr oplet liquid phase during droplet flattening. Good agreement between t heoretical and experimental results is shown to exist. The results obt ained can be used for prediction of the optimum conditions of spraying . (C) 1996 The institute of Materials and ASM International.