It is reasonable within the range from 45 ° to 90 °. It shows that it is maximum of the efficient resolved tensile and shear stress at 90°. The twin is the most active around 45 ° roughly the most active range is 22.5 to 67.5°. Therefore we believe that the possibility of twin is relatively high. The effective stress according to s2eff=ss2+tc2-2sstc cos (90°+ϕ) and the adapted effective stress s2eff=ss2+tc2 likely excludes a little deviation with 0~4MPa in Ti2AlNb. The deviation is largest with 4MPa in ϕ of 42.5° in Ti2AlNb. The range rate is 0.5%. According to efficient stress & twins and dislocation happen at λ=45°and 90°.