MICROSTRUCTURES OF LASER-CLAD NICKEL-BASED HARDFACING ALLOYS

Distinctive microstructures of laser-clad passes with three nickel-bas ed hardfacing alloys were observed. The boride-hardened Colmonoy 6 con sisted of a structure of gamma-nickel dendrites and interdentritic eut ectics of gamma-nickel, nickel borides and nickel silicides; carbide-h ardened Colmonoy 88 consisted of mixed carbides, while WC-strengthened AI-1236 consisted of partially dissolved WC particles embedded in a s imilar microstructure to Colmonoy 6. For a given laser beam intensity, the microstructures of the clad layers are significantly influenced b y the powder feed rate (PFR) employed and, to a lesser extent, the tra nslation speed (TS) of the laser beam. A cellular-to-dendritic transit ion for Colmonoy 6, a morphology change of the mixed carbide from coar se leaflike to fine, equiaxed but angular shape for Colmonoy 88, and a lesser degree of dissolution of WC particles for AI-1236 occurred wit h increasing PFR. At sufficiently high TS, the nucleation and growth o f 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.