Temperature dependence of deformation and fracture in a beta titanium alloy of Ti-22V-4Al

Impact tests and tensile tests were conducted with a beta titanium alloy of Ti-22V-4Al between 77 K and 450 K in order to elucidate the temperature dependence of absorbed-impact energy, yield stress, effective shear stress, activation volume, and activation enthalpy. The absorbed-impact energy decreased with decreasing test temperature, however, this alloy did not undergo low-temperature embrittlement although it has a bcc structure. Tensile tests showed changes in both the work-hardening rate and the temperature dependence of yield stress approximately at 150 K. This suggests a change in the mechanism behind the plastic deformation at the temperature. The temperature dependence of the activation enthalpy for dislocation glide suggests that the process of overcoming the Peierls potential (kink-pair nucleation) controls the dislocation glide at between 150 K and 200 K, while the interaction between a dislocation and solute atoms controls the dislocation glide above 200 K. Superelasticity appears in stress-strain curves tested below 120 K, suggesting that the yielding is controlled by the transformation-induced plasticity below 120 K. The enhanced toughness at low temperatures in these alloys is discussed taking into account the transformation from the viewpoint of dislocation shielding theory.