High temperature microstructure stability of Waspaloy produced by Wire Arc Additive Manufacturing

The microstructural stability of Waspaloy produced by wire arc-based Cold Metal Transfer (CMT) was studied in the 700-1050 C-circle temperature range. Major process-induced chemical segregation resulted in heterogeneous gamma' precipitation between dendrite cores and interdendritic spacings up to 1050 C-circle. The coarsening behavior of gamma' followed the Lifshitz-Slyozov-Wagner theory between 760 and 900 C-circle. Diffusion activation energies revealed that kinetics in the dendrite cores are faster than within the interdendritic spacings, although precipitates in the latter appear more stable at higher temperatures. Fine globular (Cr,Mo)(23)C-6 and blocky (Ti,Mo)C carbides were observed to decorate grain boundaries. The formation of plate-like (Cr,Mo)(23)C-6 was found in both interdendritic spacings and grain boundaries. The laths were predominantly aligned along the <110>gamma directions and precipitated as a result of (Ti,Mo)C degeneration associated with the presence of lattice defects such as stacking faults and dislocations. Thermo-Calc (R) calculations were performed and correlated well with experimental Time-Temperature-Transformation diagrams.