Structual Superplasticity in Intermetallics and Ceramics—Experimental
Like conventional alloys, usually brittle intermetallic alloys (TiAl, Ti3Al, Ni3Al etc.) in a fine-grained condition under a certain temperature-strain rate intervals display superplastic behavior [994–1003]. Phenomenological features like high elongation, low flow stress, high strain-rate sensitivity index and deformation mechanisms were found to be similar to those found in conventional superplastic alloys. The influence of grain size on superplastic deformation temperature in intermetallic alloys was also similar to that of conventional superplastic alloys. In particular, a decrease in grain size down to d ~ 100 nm leads to a significant decrease in the homologous temperature of superplastic deformation [995, 1001]. At the same time, there are some differences as well. One of them is the higher superplastic deformation temperatures, which are normally higher than 0.7Tm against the range of 0.3–0.5Tm for conventional alloys [994, 996, 1000–1003]. Other features observed in the intermetallic alloys are dynamic recrystalization present in the course of superplastic deformation [994, 995, 1004] and a strong negative role of “special” grain boundaries, which can suppress superplastic flow (which is similar to observations concerning conventional alloys, e.g. Al-Li alloys).