After heating quickly up to 748 K and holding for 10 min, tensile tests were conducted under a superplastic condition (temperature: 748 K; nominal strain rate: 10° s−1) on a hydraulic testing machine. During the test, the load and extension were recorded on a chart recorder, and nominal stress sn and nominal strain on were converted into true stress s and true strain o by using the well-known relations, s=sn(1+on) and o= ln(1+on). The alloy was supposed to be in a state of solid solution at the deformation temperature, 748 K.