Residual stress in HVOF thermally sprayed thick deposits

Due to the nature of the high velocity oxy-fuel thermal spray process, residual stress build up in thick deposits is a significant and a limiting problem. The residual stress-state that evolves in a deposit is largely dependent on the thermal conditions to which the system has been subjected, and is a combination of quenching stresses, which arise during deposition, and cooling stresses, post-deposition. It follows that precise control of these phenomena is essential, if a thick deposit is to be thermally sprayed. This paper applies an analytical technique to calculate residual stress in thermally sprayed deposits based on geometric properties. Residual stress results for WC–Co (tungsten carbide–cobalt) samples are compared to experimental results (X-ray diffraction and hole-drilling method). A change in deposit stress-state from tensile to compressive stress with deposit thickness is analysed in terms of quenching and cooling stresses.