Laser beam weld-metal microstructure in a yttrium modified directionally solidified Ni3Al-base alloy

The microstructure of laser beam weld-metal of an yttrium doped directionally solidified alloy IC 6A, with chemical composition Ni-16Al-8.5Mo-0.12B-0.05C-0.03Y (at.%) was studied. The dendritic microsegregation observed within the fusion zone indicated that dendrite cores were slightly depleted in molybdenum and aluminum and the interdendritic regions were also considerably enriched in yttrium. Severe cracking in the weld-metal was observed and was found to be closely associated with interdendritic eutectic-type microconstituents identified as consisting of γ, γ′ and Ni-Mo phases. An yttrium-rich phase (Ni3Y) was observed in some interdendritic regions containing the eutectic γ, γ′ and Ni-Mo products. Their formation was discussed in relation to plausible microsegregation induced alteration of primary solidification path during cooling from welding temperatures.