INFLUENCE OF SOLIDIFICATION ON THE MICROSTRUCTURAL EVOLUTION OF NICKEL-BASE WELD METAL

The effect of segregation resulting from solidification on the microst ructural evolution of nickel base alloys was investigated. Two differe nt groups of alloys were produced to simulate either the Hastelloy C t ype or the Inconel 625/718 type of alloys. Gravitational thermal analy sis welding was performed on these experimental alloys and the extent of microsegregation in the weld metal was determined. Using compositio n profiles obtained from solidified microstructures, predictions of th e phase stability of these microstructures were made based on metal d- level (M(d)) calculations. The maximum M(d) values obtained in these m icrostructures were compared with those critical to the formation of t opologically close-packed (TCP) phases such as sigma, P, and Laves. Th ese profiles showed an increase in the M(d) level in the interdendriti c regions which was correlated to the formation of TCP phases.