Microstructures of laser-clad nickel-based hardfacing alloys

Distinctive microstructures of laser-clad passes with three nickel-based hardfacing alloys were observed. The boride-hardened Colmonoy 6 consisted of a structure of gamma-nickel dendrites and interdentritic eutectics of gamma-nickel, nickel borides and nickel silicides; carbide-hardened Colmonoy 88 consisted of mixed carbides, while WC-strengthened AI-1236 consisted of partially dissolved WC particles embedded in a similar microstructure to Colmonoy 6. For a given laser beam intensity, the microstructures of the clad layers are significantly influenced by the powder feed rate (PFR) employed and, to a lesser extent, the translation speed (TS) of the laser beam. A cellular-to-dendritic transition for Colmonoy 6, a morphology change of the mixed carbide from coarse leaflike to fine, equiaxed but angular shape for Colmonoy 88, and a lesser degree of dissolution of WC particles for AI-1236 occurred with increasing PFR. At sufficiently high TS, the nucleation and growth of the mixed carbide phases in the Colmonoy 88 layer can be suppressed, especially when the PFR is low. The effect of PFR and TS on the clad microstructure can be understood in terms of the specific energy input (E-S) and the specific heat energy (E-h) available, respectively. (C) 1998 Elsevier Science S.A.