高强韧Ti-3Al-5Mo-4Cr-2Zr-1Fe合金低周疲劳性能研究

Low cycle fatigue (LCF) behavior of Ti-3Al-5Mo-4Cr-2Zr-1Fe (Ti-35421) alloy with bimodal microstructure consisting of lath α(α_p) and β_trans was investigated by strain-controlled mode at room temperature. Results indicate that cyclic stress amplitudes of the Ti-35421 alloy with bimodal microstructure show cyclic softening at first, then reach to cyclic stability at high strain amplitude (Δε_t/2=1.0%, 1.2%, 1.4%, 1.6%). However, the cyclic stress response characterizes cyclic saturation at low strain amplitudes (Δε_t/2=0.6%, 0.8%). Only one fatigue crack source is found by fracture morphology observation when Δε_t/2=0.6%, while a large number of small secondary cracks occur on the surface. On the contrary, multiple fatigue crack sources generate when the strain amplitude increases to 1.6%. The number of secondary cracks reduces, but the length and width of the secondary cracks increase significantly. TEM results indicate that a large number of dislocations generate at the α_p/β_trans interface at the low strain amplitude (Δε_t/2=0.6%), which leads to micro-crack nucleation due to the stress concentration. Meanwhile, at high strain amplitude (Δε_t/2=1.6%), deformation inhomogeneity phenomena occur in the α_p phase, a large number of dislocation tangles and dislocation debris form in the α_p phase, and some dislocation pile-ups form in the α_s phase instead of β matrix. Due to the elongated α_p phase, it can improve the compatibility of alloy α phase and β phase deformation, and delay crack nucleation and propagation. Therefore, Ti-35421 alloy has excellent low cycle fatigue performance.