O元素会影响亚稳β型钛合金的塑性变形方式，从而影响合金的低温力学性能。利用HRTEM、FIB、EBSD、SEM、OM和配备了低温系统的电子万能试验机等研究了2种不同O含量(0.2%和0.4%，质量分数)的β型Ti-15Mo合金(分别命名为0.2O和0.4O合金)在20 K下的拉伸力学性能。结果表明，20 K下，0.2O合金具有较好的抗拉强度(1825 MPa)和延伸率(7.5%)匹配，呈现典型的微孔聚集型断裂特征；而0.4O合金具有高的抗拉强度(1973 MPa)，但延伸率较低(1.5%)，呈现典型的解理断裂特征。2者超低温力学性能的差异主要取决于O含量对{332}<113>孪晶形成的影响，前者中形成了大量孪晶，而后者仅在断口附近产生了少量孪晶。0.2O合金高的强度归因于{332}<113>孪生的临界分切应力大幅提高，而较高的延伸率则是因为大量孪晶的产生阻碍了局部塑性变形。此外，该合金的拉伸曲线呈现典型的锯齿状特征，并且拉伸试样出现了多处缩颈。缩颈区域产生的孪晶阻碍了局部塑性变形的进行，进一步提高了强塑性匹配。因此，有效利用间隙元素O能够调控亚稳β型钛合金的超低温力学性能。

Ti and titanium alloys are preferred for cryogenic applications, particularly at a liquid hydrogen temperature of 20 K, in aerospace due to their high specific strength, good corrosion resistance, low magnetic permeability, and low thermal expansion coefficient. Currently, the most common cryogenic titanium alloys are extra-low interstitial α-type and near α-type alloys. However, they exhibit inadequate age hardening and low cold-forming ability. Furthermore, they do not meet the enhanced strength-ductility requirements for cryogenic structural components. Metastable β-type titanium alloys with a {332}<113> twinning-induced plasticity (TWIP) effect have shown enhanced mechanical properties, such as a favorable balance of strength-ductility at ambient and cryogenic temperatures. Therefore, they are considered promising titanium alloy candidates for cryogenic applications. The content of interstitial elements, particularly the O content, has a substantial impact on the cryogenic ductility of titanium alloys. Therefore, all cryogenic titanium alloys have extremely rigorous requirements regarding the O content. However, the effect of O content on the cryogenic tensile behavior of {332}<113> TWIP alloys remains unclear. This study investigated the cryogenic tensile behavior of Ti-15Mo alloy with O contents of 0.2% and 0.4% (mass fraction, the same below) at 20 K. The tests were conducted using HRTEM, FIB, EBSD, SEM, OM, and a tensile testing machine fitted with a cryogenic system. Results show that the alloy comprising 0.2%O content (0.2O alloy) exhibits a good combination of tensile strength (1825 MPa) and elongation (7.5%). This alloy displays typical microvoid coalescence fracture characteristics. Alternatively, the alloy with 0.4%O content (0.4O alloy) presents a high tensile strength of 1973 MPa, a relatively low elongation of 1.5%, and typical cleavage fracture characteristics. The discrepancy in cryogenic tensile properties between the two alloys can be attributed to the effect of O content on the formation of {332}<113> twins. Several {332}<113> twins appear in the 0.2O alloy, whereas only a small number of twins are observed near the fracture region in the 0.4O alloy. The exceptional strength of the 0.2O alloy is attributed to the enhanced critically resolved shear stress of twinning, while the impressive elongation is attributed to the formation of numerous twins that impede local plastic deformation. The 0.2O alloy exhibits a noticeably serrated tensile curve and multiple necking. The activation of twins in the necking region hinders local plastic deformation and necking, thus enhancing the strength-ductility combination. Hence, by effectively using the interstitial element O, the cryogenic mechanical properties of metastable β-type titanium alloys can be effectively tailored as per requirements.