Critical electron-vacancy concentrations and sigma formation in Udimet 700

The γ-phase compositions and the γ' volume fractions are tabulated for 12 heats of Udimet 700. Values for the average electron-vacancy concentrations and the critical values for the γ-phase at 8700C are also tabulated. The results support a model of Barrows and Newkirk [Met. Trans., 3: 2889 (1972)] in which the γ phase boundary is described in terms of electron--vacancy concentration and temperature and show that this method can be used with computed γ matrix compositions. Confidence in this method should increase as further comparisons between observed and predicted sigma forming propensities are carried out for other alloys and when the role of non-transition elements such as Al is better understood