Effect of boron addition on transformation behavior and tensile properties of Ti–Nb–Al alloy

Effects of 0.05 mass% boron addition on the transformation behavior and the tensile properties at room temperature were investigated for Ti–24 at.% Nb–3 at.% Al (TiNbAl). The martensitic transformation temperatures (Ms) measured by differential scanning calorimetry decreased upon the addition of boron. The tensile properties were evaluated by a cyclic loading–unloading tensile test with a constant strain increment of 1% carried out at room temperature. It was found that superelasticity appeared regardless of boron addition. By considering the residual strain and the maximum applied stress per cyclic deformation, relationships between maximum stress and residual strain were evaluated. It was found that flow-stress of the B-added TiNbAl was higher than that of TiNbAl, and that the critical stress for slip (σSLIP) became higher upon boron addition: boron addition is effective for strengthening. The stress for inducing the martensitic transformation (σSIMT) became higher by the boron addition, mainly due to the lowering of martensitic transformation temperature. When increasing the number of deformation cycles, σSIMT becomes lower regardless of boron addition. However, the reduction of σSIMT per cycle is smaller in B-added TiNbAl than TiNbAl, due to strengthening by boron addition.