Phase Diagram and Precipitation Behaviour in Ni-Rich Region of Ni-Ta-Al Ternary System
Tantalum (Ta) addition is one of the promising method for increasing the strength of Ni-based wrought alloys such as Inconel 718, because Ta is an element having a high melting temperature. For wrought alloys, it is necessary to make clear the phase relationships at 700~1000°C, but there is a few report on phase diagrams of Ni-Ta and Ni-Ta-Al systems at those temperatures. In this study, the phase diagram in Ni-rich region of Ni-Ta-Al system at 800°C, which is the important temperature for the practical use of the wrought alloys, was investigated. The equilibrium relations of each phase were examined by a conventional XRD, SEM/EDX and TEM observations. It was found that the γ-phase region expanded considerably towards Ta-rich compositional region in Ni-Ta-Al system at 800°C. Also, it was observed that the γ phase precipitated secondarily in the primary precipitated γ’ phase in Ni-10.5mol%Ta-5.5mol%Al alloy. Ni8Ta phase was not detected even in Ni-Ta binary system in this study, although this phase was reported previously.
Young Won Chang, Nack J. Kim and Chong Soo Lee
Y. Tsukada et al., "Phase Diagram and Precipitation Behaviour in Ni-Rich Region of Ni-Ta-Al Ternary System", Materials Science Forum, Vols. 561-565, pp. 2329-2332, 2007