Elastic deformation behavior of multi-functional Ti-Nb-Ta-Zr-O alloys

Abstract

We investigated the effect of cold working on the elastic properties of a newly developed multi-functional β titanium alloy, GUM METAL, using in-situ XRD and EBSP analysis. Mechanical and physical properties are changed dramatically by cold working. The alloy has a low elastic modulus (40GPa), high strength (more than 1100MPa), high elastic deformability (2.5%) and super-plastic like deformability at room temperature without work hardening. The elastic behavior of the cold worked specimen shows non-linearity, with the gradient of the stress-strain curve in the elastic region continuously decreasing with a stress increase. In-situ XRD measurements during tensile loading show that all β peaks shift monotonically to higher 2θ angles with increasing tensile strain up to 2.7%. This result suggests that the elastic behavior in the alloy is not accompanied by phase transformations, such as stress-induced α″. Additionally, EBSP analysis reveals that the deformation mode in the alloy does not relate to (112}(111) or (332}(113) twinning. The microstructure of the alloy during deformation is characterized by localized distorted regions ranging in size from several tens of micrometers to submicrometers, with elastic strain located hierarchically in the alloy. It is likely that this microstructure is attributable to its elastic anomaly, which arises at this specific alloy composition of the multifunctional alloy. The above elastic anomaly in the alloy seems to contribute to the development of the unique microstructure during plastic deformation, as well as to its macroscopic elastic behavior. © 2005 The Japan Institute of Metals.