Effect of surface oxidation on transition temperature of stainless steel substrate uponimpact of aluminum particles

摘要

Experimental studies involving aluminum particles sprayed onto polished AISI304L substrates using the Valuarc200 wire arc previously showed that there exists a transition temperature from splash to disk splats. Increasing thesubstrate temperature above the transition temperature was seen to increase the number of disc splats, thusproducing coatings of improved properties. XPS test results have shown that increasing the substrate temperaturealso results in increased oxygen content on the surface of the substrate. Experiments also show that prolongedheating of a substrate at a particular (fixed) temperature further promotes oxidation of the substrate surface, thusincreasing the surface roughness (Ra). Samples generated on substrates that were held at or above 350°C (aboveTt) for prolonged periods of time (over 20 minutes) were seen to promote splashing. This is in contrast to theprevious findings that showed substrate temperatures above Tt further promoted disc type splats and improvedadhesion between the splat and substrate. Samples generated in this study consistently showed that splashing canbe seen at temperature well above the transition temperature, if the substrate has been heated for too long aduration. The cause of splashing is believed to be related to increased surface roughness resulting from prolongedoxidation of the substrate surface.