Segregation in Stellite powders produced by the plasma rotating electrode process

A hypo-eutectic Stellite-type alloy (Co-28Cr-4.5W-1.1C, in wt%) was atomized by the plasma rotating electrode process (PREP). The microstructures of both powders and electrodes were studied by optical and scanning electron microscopies, electron probe microanalysis, and X-ray diffraction techniques. The powder exhibits three kinds of particles. Most of them are melted and solidified primary dendrites of γ-Co solid solution. The second kind of particles corresponds to melted and solidified interdendritic eutectic. The remaining particles are fragments detached from the electrode in the semisolid stage. The mechanism of segregation is similar to that observed by other authors in centrifugal refining of alloys with large solidification ranges.