Small punch creep testing of thermally sprayed Stellite 6 coating: A comparative study of as-received vs post-heat treatment

Abstract

Abstract Thermally sprayed Stellite 6 coatings offer high wear and corrosion-erosion resistance at high temperature but the creep behaviour of such coatings is not well understood. In this paper, the microstructure and creep behaviour of a HVOF Stellite 6 coating was investigated. The coating was tested in the as-sprayed condition and after an isothermal heat-treatment of 1\u202fh at 1050\u202f°C. The as-sprayed coating comprised FCC Co-Cr-W solid solution with 2–3\u202fwt% HCP phase, whereas the heat-treated coating comprised FCC Co-Cr-W solid solution, 11\u202fwt%\u202fM23C6 carbides and 7\u202fwt%\u202fM7C3 carbides. Small punch creep tests were conducted at 700\u202f°C on the as-sprayed and heat-treated coatings. The heat-treated coating exhibited minimum steady-state strain rates approximately 2 orders of magnitude lower than the as-sprayed coating when tested at similar loads, leading to times to failure approximately two orders of magnitude longer for the heat-treated coating within the selected load range. Fracture analysis showed cracking along powder particle boundaries was the main mode of cracking in the as-sprayed coating whereas for the heat-treated coating, fracture along the carbide / matrix interface was the main fracture mechanism.