E. Y. Chen, D. R. Bice, Transition45 Technologies, Inc., Orange, CA; Q. Li, University of Nevada, Reno, Reno, NV; D. C. Dunand, Northwestern University, Evanston, IL
Unlike fine-structure superplasticity which relies on grain-boundary sliding and necessitates fine, stable grains below 10 micrometers, transformation superplasticity relies on internal stresses produced during thermal cycling around an allotropic transformation temperature, and is thus expected to be active even for very large grain sizes. This investigation tests this prediction by subjecting as-cast, coarse-grained CP-Ti and Ti-6Al-4V to thermal cycling under stress, in order to demonstrate superplastic deformation under both uniaxial deformation and multiaxial dome forming. These results on superplastic properties for the present cast, coarse-grain CP-Ti and Ti-6Al-4V are compared to previous results on powder-metallurgy CP-Ti and Ti-6Al-4V with intermediate grain size.
Summary: Unlike fine-structure superplasticity which relies on grain-boundary sliding and necessitates fine, stable grains below about 10 micrometers, transformation superplasticity relies on internal stresses produced during thermal cycling around an allotropic transformation temperature, and is thus expected to be active even for very large grain sizes. This investigation tests this prediction by subjecting as-cast, coarse-grained CP-Ti and Ti-6Al-4V to thermal cycling under stress, in order to demonstrate superplastic deformation under both uniaxial deformation and multiaxial dome forming.
