Plasma duplex treatment of stellite

Despite their excellent tribological properties, the lifetime of stellites in some applications in metallurgical and mechanical engineering is not sufficient. This study describes the development of a duplex treatment for stellite 6B, which consists of either plasma nitriding (PN) or plasma nitrocarburizing (PNC), followed by the deposition of boron-containing hard coatings (TiBN or TiB2). The influence of the process parameters and the gas composition was investigated. Compositional and structural analysis was performed by: profilometry; XRD; SEM; WDS; and GDOS. Knoop hardness measurements, scratch tests, pin-on-disk tests and wear tests by ball cratering were determined in order to describe the mechanical properties. It is shown that plasma duplex treatment combines the advantages of both separate process steps. Case hardening during diffusion treatment offers a mechanical support to the coating, which exhibits a lower coefficient of friction than the diffusion-treated surface. The optimal combination consists of PNC, at high plasma energy, and a boron rich TiBN coating.