Evaluation of yield strength anomaly of Alloy 718 at 700-800 °C

Alloy 718 showed enhanced tensile yield strength and reduced ductility at 700 and 800 °C, a possible indication of yield strength anomaly phenomenon. The results of TEM, STEM and EDS verified the formation and precipitation of γ′′ and δ phases at these temperatures that could have contributed to such anomalous behavior of this alloy under tensile loading. Presence of nickel (Ni) and niobium (Nb) was observed in both phases, suggesting a composition of Ni3Nb for them.