Microstructural effects on the wear behavior of a biomedical as-cast Co-27Cr-5Mo-0.25C alloy exposed to pulsed laser melting.

Abstract

In this work, the effect of pulsed laser melting on the exhibited microstructure and properties of a cast Co-27Cr-5Mo-0.25C alloy was investigated. In particular, properties such as surface hardness and wear behavior of the laser modified microstructure were determined as a function of the implemented laser melting parameters. It was found that laser melting promotes significant grain refinement while preventing the precipitation of coarse carbide phases. Apparently, a refined dendritic grain structure develops which is surrounded by a fine carbide distribution in the interdendritic regions. Moreover, the high-temperature face centered cubic (FCC) phase remains untransformed at room temperature. Hardness measurements and wear testing using a Pin-On-Disk tribological machine indicate that the modified laser surfaces exhibit both, high wear resistance and high microhardness when compared with the untreated as-cast Co-27Cr-5Mo-0.25C alloy. In particular, it was found that the laser modified surfaces exhibit improved wear and friction properties comparable to the ones found in Co-Cr-Mo alloys with a predominantly hexagonal closest packed (HCP) matrix. However, surface defects associated with the laser process can be detrimental for the improved wear performance and they should be considered in identifying the proper laser parameters in alloy melting.