THE EFFECT OF ELEVATED-TEMPERATURE AND SILICON ADDITION ON A COBALT-BASED WEAR-RESISTANT SUPERALLOY

The effects of an elevated temperature and a 5 wt% silicon addition on the resultant microstructure and inherent phases of Stellite 6 were i nvestigated by using room and high temperature optical microscopy, X-r ay diffraction, scanning electron microscopy (SEM) and also bulk hardn ess and microhardness measurements. It has been observed that exposing Stellite 6 to heat treatments at 1000 degrees C results in a characte ristic textured structure and coarsening of interdendritic regions due to bulk diffusion. In addition, both dendritic and interdendritic har dness values increase due to texture formation and increased amounts o f carbide and intermetallic phases, respectively. On the other hand, s ilicon addition to Stellite 6 causes the transformation of the origina l spongy dendritic microstructure in as-cast Stellite 6 to a eutectic dendritic and skeleton interdendritic structure. Also, when silicon ad ded Stellite 6 was heat treated at 1000 degrees C, particulates emanat ing from the interdendritic skeleton become irregularly dispersed in t he dendritic region. In addition, similarly to Stellite 6; a high temp erature heat treatment results in an increase in hardness values of si licon added Stellite 6 due to the presence of an Co2Si intermetallic p hase.