Abstract
A single splat is the building block of a thermal spray coating; thus, investigating single splats is essential to understanding thermal spray coatings and their properties. In this study, the spreading behavior and the morphology of flame sprayed ethylene methacrylic acid (EMAA) splats, deposited at various stand-off distances (SODs) onto glass and mild steel substrates were investigated using optical microscopy, back scattered scanning electron microscopy and secondary electron scanning electron microscopy. The results of this study indicate that the spread factor increases with an increase in the stand-off distance up to 30 cm for glass and 25 cm for steel substrates. Further increase of the stand-off distance results in a decreased spread factor. The aspect ratio of EMAA single splats on both glass and mild steel substrates decreases with increased stand-off distances, indicating that more circular shapes occur at higher stand-off distances. On mild steel substrates, the minimum unevenness ratio (η) occurs at 35 cm SOD. The unevenness ratio (η) on glass substrates decreases from 1.9 (at 20 cm SOD) to 1.77 (at 25 cm SOD), and from 1.8 (at 30 cm SOD) to 1.3 (at 35 cm SOD). The lowest unevenness ratio (η) is found at 35 cm SOD. The highest unevenness ratio (η) is at 25 cm SOD. This paper discusses the effect of surface chemistry on the underside of an EMAA single splat morphology. It includes Raman spectrum analysis of EMAA and the X-ray diffraction of the EMAA powder. This work analyses the splat morphology and classifies the taxonomy of single splats of EMAA.
Highlights
Many parameters influence the structure of a single splat, and the thermal spray coating and its properties
The minimum unevenness ratio (η) on mild steel occurred at 35 cm stand-off distances (SODs) and the highest unevenness ratio (η) arose at 25 cm SOD because the ethylene methacrylic acid (EMAA) particles at 25 cm SOD exhibited a higher temperature and greater velocity
A single splat deposited onto a glass substrate is shown in Figure 7d and indicated that the bottom of the splat was smooth
Summary
Many parameters influence the structure of a single splat, and the thermal spray coating and its properties. The coating formation process is generally determined by the prime processing variables, which include substrate roughness, substrate temperature, impact velocity, stand-off distance (SOD), and the nature of the local atmospheric environment [3,4,5,6]. The second factor includes the composition, thickness and morphology of the oxide layer on the surface of the substrate; these are affected by the preheating rate, temperature and time. The current work aims to investigate the effects of stand-off distance and the surface chemical condition on the splat spreading behavior and morphology
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