Microstructural Evolution and Mechanical Properties of a Ni-Based Superalloy, TMW-4

The microstructural evolution and mechanical properties were examined in a Ni-based superalloy, TMW-4, with high Co and Ti contents at temperatures ranging from 700 A degrees C to 1200 A degrees C for various times up to 1000 hours. The results showed that solution treatments (temperatures: from 1100 A degrees C to 1200 A degrees C; time: 4 hours) essentially affected the fraction and size of primary and secondary gamma' precipitations and grain size. No eta-Ni(3)Ti phase was observed in all solution heat-treatment samples. On the other hand, small amounts of eta phase were observed in the samples after homogenization at 1220 A degrees C and aging at temperatures ranging from 1000 A degrees C to 1175 A degrees C. Based on the investigations, a time-temperature-transition (TTT) curve for the eta-phase formation was constructed. These microstructural effects were successfully combined to obtain an increase of tensile properties in terms of both strength and ductility.