Abstract
In the present work thin Al2O3 coating was obtained mainly by low pressure plasma spray (LPPS). Low-porosity and low-roughness deposits resulted from the optimized spray conditions, i.e. plasma parameters, grit blasting, powder feed rate and specimen rotation speed. Results showed that LPPS processing was highly beneficial for densifying the ceramic coatings, especially when coupled to a moderate powder feed rate. Coating average surface roughness (Ra) ranged from 1.5 to 2.5 µm for a coating thickness of less than 30µm and an original substrate Ra of 1.1µm. The spray conditions were optimized particularly for a low feed rate and a high specimen rotating speed to lower surface roughness. Moreover, a specific atmosphere/temperature control device was developed (using local gas injection close to the specimen to be coated). This resulted in improving cooling efficiency, which reduced microcracking in the deposits. Mechanical pull-off adhesion test was also carried out to evaluate these low-roughness thin coatings. Adhesion was shown to be satisfactory for direct coating (i.e. without any bond coat) of a low-roughness (Ra=1.1µm) AISI 316L substrate.
