Microstructure of laser melted/rapidly solidified γ/Cr₃Si metal silicide "in situ" composites

In order to improve the ductility of Cr₃Si metal silicide alloys, rapidly solidified γ/Cr₃Si metal silicide "in situ" composites were fabricated by laser melting/rapid solidification technology using Cr-Si-Ni alloy powders. Microstructure of the γ/Cr₃Si "in situ" composites was characterized by OM, SEM, XRD and EDS. The effect of Ni content in the alloy powder on microstructure and hardness of the γ/Cr₃Si composites was investigated. The γ/Cr₃Si metal silicide "in situ" composites have high hardness and rapidly solidified fine microstructure consisting of primary Cr₃Si dendrites and the interdendritic γ/Cr₃Si eutectics. The volume fraction of the Cr₃Si primary dendrites in the laser melted/rapidly solidified γ/Cr₃Si metal silicide "in situ" composites decreases with the increasing nickel content. Because of the presence of the ductile nickel-base solid solution and the rapidly solidified fine microstructure, the γ/Cr₃Si metal silicide "in situ" composites are expected to have adequate combination of strength and toughness. The results demonstrate that laser melting/rapid solidification for γ/Cr₃Si metal silicide "in situ" composites is a promising toughening method for improving the ductility of Cr₃Si metal silicide alloys.