INFLUENCE OF Hf ON WELD CRACKING FOR CAST NICKEL BASE SUPERALLOYS

In this paper, the characteristic of physical metallurgy in ehe solidification processes of TIG weld bead had been studied for Hf-bearing cast nickel base superalloys. The results have shown that Hf lowers the sensitivity to weld cracking appreciably, Hf increases the volum percent of eutectic γ+γ' in alloys, widens the solidification temperature range and promotes the interlink of interdendritic small pools in a wide temperature range. Hf-rich melts have good fluidity, wettability and skin effects at the later stage of solidification. The skin melts are a multicomponent eutectic liquid that contains Hf above 6% by wt. and have the capability of self-brazing and the recovery effect on cracks. These results proved that solidification range of alloys is not the only factor influencing weld cracking. The physical and chemical properties of ultimate solidification liquid have also an important effect.