Microstructural features and mechanical properties of a cobalt-based laser coating

Abstract

Electron microscopy, mechanical hardness measurements and pin-on-disc wear experiments were carried out on a laser-coated cobalt based Stellite alloy. It was found that with optimum laser parameters a poreless coating with a hardness of 11.3 GPa can be attained. The mechanical properties of the coating are explained from a rather detailed investigation of the microstructural features by transmission electron microscopy. The analysis indicates that solid solution hardening by tungsten and chromium, dislocation-dislocation interactions, impenetrable particle hardening due to the metal-carbides and due to the Co 3W precipitates are responsible for its high hardness. In accordance with theoretical predictions, cutting of the DO 19 ordered Co 3W precipitates—which creates planar faults like anti-phase boundaries or super lattice intrinsic stacking faults—was not observed. All these microstructural features contribute in their own way to the mechanical properties, on the basis of which the hardness could be explained rather well.