The impact of oxygen content on low-temperature mechanical properties and deformation mechanism of powder metallurgy Ti–6Al–4V
Chenwei Tao, Xiaotao Liu, Jinbao Long, Junhua Zhang, Ji Gu, Xuan Luo, Dongdong Li, Jie Pan, Ning Li
Abstract
The mechanical behavior and deformation mechanism of powder metallurgy Ti alloys with oxygen content ranging from 1300 ppm to 4600 ppm is comprehensively studied. It is surprisingly found that the powder metallurgy Ti6Al4V with the oxygen contents of 1300 ppm–4600 ppm possesses exceptional mechanical properties synergy, reaching the strength of 940–1041 MPa and the elongation of 16.2 %∼15.7 %, at the ambient temperature. It can be possibly attributed to the remarkable increase of <c+a> dislocations though the basal <a> dislocations were significantly suppressed as the oxygen contents altering from 1300 ppm to 4600 ppm. With being subjected to the liquid nitrogen temperature, the ultimate tensile strength of the powder metallurgy Ti6Al4V switches to 1486–1671 MPa while the elongation can still maintain at the level of 16.5 % to 10.4 % at the designed oxygen range. The strength enhancement is due to the strain strengthening effect, which stems from the significantly boosted shear stress for the motion of dislocations at the low temperatures. Meanwhile, it is observed that as the increase of oxygen amount, much more wavy basal <a> dislocations transform to planar <a> dislocations at the temperature of 77 K. In addition, the type of {10–12} deformation twins are activated with respect to the specimen of 1300 ppm, allowing more relaxation of strain during the deformation and hence achieving higher ductility. This differs significantly to the counterparts where no deformation twins can be detected for the samples with the oxygen content of 4600 ppm.