MICROSTRUCTURAL FEATURES AND MECHANICAL-PROPERTIES OF A COBALT-BASED LASER COATING

Electron microscopy, mechanical hardness measurements and pin-on-disc wear experiments were carried out on a laser-coated cobalt based Stell ite alloy. It was found that with optimum laser parameters a poreless coating with a hardness of 11.3 GPa can be attained. The mechanical pr operties of the coating are explained from a rather detailed investiga tion of the microstructural features by transmission electron microsco py. The analysis indicates that solid solution hardening by tungsten a nd chromium, dislocation-dislocation interactions, impenetrable partic le hardening due to the metal-carbides and due to the Co3W precipitate s are responsible For its high hardness. In accordance with theoretica l predictions, cutting of the DO19 ordered Co3W precipitates--which cr eates planar faults like anti-phase boundaries or super lattice intrin sic stacking faults--was not observed. All these microstructural featu res contribute in their own way to the mechanical properties, on the b asis of which the hardness could be explained rather well. Copyright ( C) 1997 Acta Metallurgica Inc.