Splat Morphology and Spreading Behaviour due to Oblique Impact of Droplets in Plasma Spray Coating Process

摘要

Individual splats produced by plasma spraying of Yttria-parlially-stabilised (8%) Zirconia on flat and inclined substrates are examined by Scanning Electron Microscopy and optical surface profiler. This study is focused on the effect of oblique angle of impact on the final splat morphology and spreading behaviour. The spreading behaviour is quantified by measuring the spread factor (ξ) and the aspect ratio (ψ). The splats resulting from droplets impacting perpendicularly to the part surface are well known to be circular. In the case of oblique impact, the resultant splat is oval or elliptical in shape hence the aspect ratio (ψ) is defined by the ratio of the major to minor diameters of the ellipse. The spread factor (ξ) is defined as the ratio of the splat circular equivalent diameter to the droplet diameter. The two parameters are to be used in future numerical simulation for prediction of deposit profiles of realistic engineering parts having complex curved surfaces. This paper presents the results of the experiments quantifying the spread factors and aspect ratios of individual splats at different substrate inclinations and comparison to available literature. Curve fitted quadratic equations for spread factor and aspect ratio are proposed.