Effect of substrate temperature on the splat formation of flame sprayed polypropylene

Abstract

Polypropylene (PP) powder particles were thermally sprayed via a flame spray onto mild steel substrates at room temperature (RT), 70 °C , 120 °C, and 170 °C. Single solidified splats were collected from polished substrates. The splat morphology was characterized using optical microscopy and scanning electron microscopy (SEM). Micro-Raman spectroscopy examined the effect of substrate preheating on the molecular structure of the PP splats. The splat–substrate interface, porosity and a qualitative interpretation of the interface adhesion were obtained by cross-sectioning and imaging using the focused ion beam (FIB) technique. This study indicated that increasing the substrate temperature from room temperature to 170 °C produces PP splats of larger diameter that would be expected to exhibit improved adhesion. The influence of preheating dominates the splat formation and splat morphology. The Raman spectra indicate that the degree of crystallinity of the PP particles rises with increasing substrate temperature. Comparison of the spectra of the feedstock and the deposited PP particles confirms that there is no thermal degradation of the material under these processing conditions. This work demonstrates the influence of substrate chemistry on the PP splat morphology. Microstructural characteristics are related to the flame spray process variables for polymeric coatings.