Influence of solidification on the microstructural evolution of nickel base weld metal

The effect of segregation resulting from solidification on the microstructural evolution of nickel base alloys was investigated. Two different groups of alloys were produced to simulate either the Hastelloy C type or the Inconel 625/718 type of alloys. Gravitational thermal analysis welding was performed on these experimental alloys and the extent of microsegregation in the weld metal was determined. Using composition profiles obtained from solidified microstructures, predictions of the phase stability of these microstructures were made based on metal d-level (M(d)) calculations. The maximum M(d) values obtained in these microstructures were compared with those critical to the formation of topologically close-packed (TCP) phases such as sigma, P, and Laves. These profiles showed an increase in the M(d) level in the interdendritic regions which was correlated to the formation of TCP phases.