Surface engineering with lasers:An application to co-base materials

Electron microscopy, mechanical hardness measurements and wear experiments were carried out on laser coated cobalt based Stellite alloys. It was found that with optimum laser parameters, a poreless coating with a hardness of 11.3 GPa can be attained. Detailed 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 Co3W precipitates are responsible for its high hardness. In accordance with theoretical predictions, cutting of the DO19 ordered Co3W precipitates 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. An important parameter which influences these mechanical parameters is the volumetric dilution with the substrate. Ii is this aspect together with the well defined and controllable processing parameters which make the laser coating of Stellite powders superior to other depositing techniques.