Effect of Zr and B on castability of Ni-based superalloy IN792

The effect of Zr and B on hot tearing susceptibility of the Ni-based superalloy IN792 during directional solidification (DS) was studied. The Zr and B concentrations in the experimental alloys ranged from 0 to ~550 ppm. The results indicate that Zr or B does not influence the castability when added individually. However, when both Zr and B are present in the alloy, high hot tearing susceptibility was found, the effect being particularly strong if Zr concentration was high. The castability results cannot be explained by simple solidification characteristics such as total freezing range (obtained from differential scanning calorimetry (DSC)) or by the amount of eutectic liquid (derived from the fraction of interdendritic [gamma]/[gamma]' obtained from quantitative metallography). However, the present results can be interpreted in terms of formation of continuous films of liquid at grain boundaries (GBs) during the final stages of solidification rather than enclosed pockets. Such thin films of liquid may reduce GB cohesion and promote hot tearing. [PUBLICATION ABSTRACT]