Deformation of Ti-36Nb-2Ta-3Zr-0.3O (Gum Metal)

In-situ loading X-ray diffraction experiments were performed on 90% cold worked Ti-36Nb-2Ta-3Zr-0.3O (wt. %) alloy (Gum metal). A self-consistent (Eshelby-Kröner-Kneer) model was used to infer the single crystal elastic constants from the measured diffraction elastic constants. The results show that (C₁₁ — C₁₂) is ~ 50 GPa and not approaching 0 as predicted in this material. This implies that τ_max for ideal shear is well above the yield stress of this alloy and therefore this material is not vulnerable to perfect shear. In addition, X-ray diffraction peak broadening, combined with work hardening during rolling and the observation of dislocations in TEM, all suggest that this material does deform with the aid of dislocation glide, in contrast to what has previously been reported. Stress-lattice strain results indicate that the elastic region is linear at the microscopic level and not non-linear as observed macroscopically. Also, elastic moduli of the diffracting planes indicate that this material is nearly elastically isotropic. Further work is needed to understand the mechanism of formation of the giant faults previously observed during the early stages of plastic deformation.