Tribological behavior of Stellite 21 modified with yttrium

Cobalt-base alloys have found a wide variety of tribological applications particularly at elevated temperatures or in corrosive environments in many industries, such as aerospace, automotive, power and gas turbines. One of the standard Co-base alloys, Stellite 21, is used predominantly to resist the synergistic effects of corrosion and mechanical attack, especially at elevated temperatures and continuing efforts have been made to improve its properties. One approach is to add reactive elements, such as yttrium, in order to beneficially affect its oxidation behavior. Research was conducted to investigate the effects of Y additions on Stellite 21 on its microstructure, mechanical behavior, and high-temperature wear performance. These studies employed various experimental tools, such as micro-mechanical probe, XRD, SEM, EDS, and high-temperature tribometer. The effects of Y addition on the properties of the oxide film formed on Stellite 21 were also investigated using grazing XRD and nano-mechanical probing techniques. It has been demonstrated that Y additions benefited the wear behavior of Stellite 21, especially at elevated temperatures. The oxide scale developed at 600 °C also showed markedly enhanced mechanical properties when Y was alloyed to the alloy.