Splat taxonomy of polymeric thermal spray coating

The geometry of a powder particle and the splat that it gives rise to during the thermal spray process are key parameters that determine the physical attributes of a coating. The splat shape is an important feature that requires accurate characterization, preferably by means of a quantified metric, so that the rapid solidification process of thermal spray deposition can be understood.In this work we report on a polypropylene (PP) powder that was sprayed onto a glass substrate at room temperature using the flame spray process, at various stand-off distances (SODs). Several statistical concepts were employed using image analysis techniques that were complemented by optical microscopy, scanning electron microscopy, and 2D profilometry: methods that measured the splat metrics of formation, including an estimate of splash area. Measurement of equivalent diameter, degree of splashing, spreading factor, deposition efficiency and circularity have quantified splats so that thermal spray parameterization can be related to the process efficiency.The results of this study indicated that increasing the SOD from 10 cm to 25 cm reduced the splat thickness and deposition efficiency; while other metrics (as listed earlier) were not routinely correlated, though an increase in splash area was demonstrated. Splat circularity was steady around 0.9, indicating that the deposited particles exhibited a circular shape at all SODs.

Research Highlights
► The feedstock and impacted particle shape factors were measured via routine software.
► Stand-off distance has a major effect on splat morphology and their metrics.
► Splashing of the polymer deposit is strongly influenced by stand-off distances.
► Increase in stand-off distance increases the degree of splashing and spread factor.
► Increase in stand-off distance decreases deposition efficiency and splat thickness.