Modeling the Coverage of Splat Areas Arising from Thermal Spray Processes

Abstract

The coverage of a deposited material that arises from the integration of discrete splat areas is an essential parameter that needs to be understood during thermal spray processes. However, there is absence of a theoretical method to predict and estimate the area coverage per pass by a thermal spray torch; for example by the plasma spray process. In this study, a model is presented that calculates the splat area coverage for a thermal spray process of ceramic materials. A focused survey of the published literature takes into consideration experimental observations that are related to this work. The model accounts for physical events in thermal spray processes, such as the use of a mono‐modal feedstock and size of spray stream. The model predictions for the area coverage of plasma sprayed yttria‐stabilized zirconia (YSZ) ranged between 12% and 18% depending on the value assumed for the maximum flattening ratio. The results for the model were demonstrated via wipe studies where microscope glass slides were spray coated with YSZ and image analysis conducted. The average coverage calculated was approximately 13% for the sprayed images. The experiment verifies that the simulation results from the model predict adequately the splat area coverage of a thermal spray process.

A review of testing methods for thermal spray coatings

“…The flattening ratio may be derived from the splat dimensions and depend on the spray method; as compiled in previous work. 5 An illustration of a typical ceramic thermal spray microstructure is depicted in Fig. 8.…”

“…1,2 The so-formed splat anatomy is the result of the spatial interaction of three inputs; i.e., the feedstock distribution and associated physical characteristics, the temperature-velocity field of the heat source, and the temperature-velocity fields of the particles. 3,4 In practical terms, the spreading of the molten particles during splat formation, 5 along with other important artefacts such as oxides and voids can be controlled by the feedstock and thermal spray processes employed. The term 'voids' is inclusive of cracks and porosity.…”

Thermal Spray Techniques for Developing a Carbide Coating

“…the dissemination of feedstock and related attributes, the heat source velocity and temperature, and the temperature and velocity of the particles [7], [8]. The oxides and voids remaining in the coatings (which include cracks and porosity) can be regulated by the types and sizes of feedstock and thermal spray process used [9].…”