Influence of solidification conditions on grain boundary cohesion in the mushy zone during directional solidification of nickel base superalloy

AbstractThe effect of solidification rates on grain boundary (GB) cohesion in mushy zone during directional solidification was explored. The mushy zone structures were frozen by tin bath quenching. It was found that high solidification rate leads to an extended mushy zone thus vulnerable region, while there are larger areas where dendrites are bridged at higher solidification rate, i.e. there is a high fraction of bridging areas in the mushy zone as solidification rate is increased. The smaller hot tearing susceptibility at higher solidification rate cannot be explained by the greater mushy zone or vulnerable region, but it can be explained by stronger GB cohesion. The results suggest more attention should be paid to the GB cohesion rather than the range of mushy zone or vulnerable region in order to avoid hot tearing at least in some alloys.