With low density, high temperature strength, oxidation resistance and creep resistance, high niobium base alloy is the most promising light and high temperature structural material in aerospace and other fields. Through the accumulation of years of research, at present the high niobium TiAl alloy composition design, organization, regulation, forming processing and conventional mechanical properties have basic control, but for the micro mechanical behavior and deformation mechanism of the high temperature fatigue deformation research is relatively lack, in addition, for improving comprehensive mechanical properties of high niobium TiAl alloy method research is not enough broad and comprehensive, at this stage is mainly by regulating the composition and organization or by the preparation of preferred orientation of many twin synthetic crystal (PST) method to improve the performance of high niobium TiAl alloy. Based on the above research background, this paper combined the methods of scanning electron microscopy, transmission electron microscopy and high energy X-ray of synchrotron radiation to study the behavior, deformation mechanism and fracture mode of high temperature and low cycle fatigue deformation of high niobium niobium alloy with full lamellar structure and double-state structure.
The mechanical properties of high niobium niobium alloy at high temperature were improved by introducing gradient structure through pretorsional deformation. Based on this, the influence of pretorsional deformation on microstructure and micromechanical behavior of high niobium base alloy and the mechanism of improving mechanical properties of high niobium base alloy by means of transmission electron microscopy and synchrotron radiation were revealed. The research on low-cycle fatigue deformation behavior of high niobium base alloy shows that the cyclic stress-strain response behavior of high niobium base alloy with different tissues is different. There are three cyclic stress-strain responses in high niobium niobium alloy with full lamellar structure, which are cyclic stability, cyclic softening and cyclic hardening. There are two cyclic stress-strain responses in high niobium niobium alloy with two-state structure, namely cyclic stability and cyclic softening. The research on the mechanism of high temperature and low cycle fatigue deformation shows that in the low cycle fatigue deformation of high niobium base alloy with the whole lamellar structure, the main phase bears compressive strain/stress in the initial phase of cyclic deformation, and tensile strain/stress in the stable phase and softening phase of cyclic deformation. The strain/stress borne by phase ii in cyclic deformation is contrary to the strain/stress borne by phase ii, which is mainly related to the distribution of stress in the surface/phase ii layer during deformation. The o phase always bears the tensile strain/stress during cyclic deformation.
