Intrinsic residual stresses in single splats produced by thermal spray processes

Abstract

Changes in processing parameters strongly affect the structure and properties of thermally sprayed coatings and, consequently, their performance. Residual stress in the deposits is a factor that needs consideration, since it has direct influence on the processability and integrity of the sprayed material. In order to enhance the understanding of this phenomenon, a study of measurements of residual stresses on a single particle level was undertaken. The deposit is built-up with the successive impingement of micron-sized droplet and therefore an understanding of the single splat microstructure and properties will provide a fundamental understanding of the underlying mechanisms. Residual stresses in thin coatings, as well as isolated particles—splats—deposited on stainless steel substrates were investigated using X-ray microdiffraction. Plasma sprayed molybdenum and cold sprayed copper were studied. The key process parameters considered were: in-flight particle energy and substrate temperature in the first case, and particle velocity in the latter. The results will be discussed with respect to the influence of each of these parameters, contribution of quenching and thermal stress component and splat formation. Further, the coating build-up from individual particles and the associated factors influencing residual stress will be discussed.