Comparison of Stellite coatings on low carbon steel produced by CGS and HVOF spraying

Abstract

Stellite alloys are of great interest in industries due to a unique combination of high temperature mechanical strength, outstanding wear and corrosion resistance. Different thermal spraying processes are used for deposition of stellite alloys on industrial components. However, the investigations on the structure-property relationship of these alloys produced via different deposition process are limited. This study focuses on the microstructure, oxidation, and tribo-mechanical properties of Stellite 21 deposited by cold gas spraying (CGS) and high velocity oxy-fuel (HVOF) process on a low carbon steel substrate. The coating cross- section was characterized by SEM and optical microscopy. The coatings were further characterised by using nanoindentation, adhesion, and ball-on-disk wear tests. Moreover, XRD tests were run on the powder and the coatings to reveal possible phase transformation during spraying, as well as during wear and oxidation tests. The results showed no phase transformation in the as-sprayed CGS coating, besides higher values of porosity and oxide phase in the HVOF coating. However, an fcc-to-hcp phase transformation occurs at the surface layer of both types of coating during the ball-on-disk wear test. The presence of continuous oxide networks in HVOF coatings leads to delamination during the wear test. Overall, the CGS Stellite 21 coatings exhibit better performance than HVOF coatings in wear and oxidation tests.