Microstructure evolution of Stellite 6+WC by high power laser cladding

The microstructure evolution of the cladding layer formed by high power CO2 laser cladding Stellite+WC on low carbon steel E24 was investigated, the Stellite and WC powders were delivered respectively with different feeding rates by a powder feeder. Two significantly different solidification structures were found. The first is consisted of dendrites and inter-dendrite eutectics when WC content from 0% to 36% (volume fraction), in which the added WC was completely melted into the melt pool and the re-solidified structure contained alpha-Co, sigma-CoCr and various carbides such as MtauC3. The second is consisted of the matrix and various faceted dendrites with flowery, butterfly and star shapes when WC content from 45% to 100%, in which most of VC was melted, the microstructure contained re-solidified WC, Co, and various Co-W-C/Fe-W-C complex carbides. The dissolution of W into the matrix was limited to maximum of about 26% but reached to 64.6% in the faceted dendrites. A unique microstructure was discovered in laser cladding pure WC, in which a double colored structure with different compositions appeared in the larger block shaped faceted dendrite, the inner structure contained W up to 91.2%(mass fraction) while its exterior contained 68.1% W. Such a structure is probably the frozen result of the peritectic reaction during laser cladding rapid solidification.