Propagation behavior of long and small fatigue cracks from notch root in reactive-sintered TiAl intermetallic compound

摘要

Smooth and notched specimens of reactive-sintered Ti-45at％Al-1.6at％Mn intermetallic compound with lamellar and equiaxedγ microstructures were fatigued under cyclic axial tension compression at room temperature. The effect of microstructures on the crack propagation behavior was investigated in comparison with cast Ti-47.2at％Al with larger grain size. Fatigue crack paths were tortuous in the lamellar microstructure in contrast to the straight crack paths in the equiaxed γmicrostructure. In comparison with cast TiAl, reactive-sintered TiAl exhibited higher crack propagation rates when compared at the same stress intensity range. The values of stress intensity range at threshold were greater in cast TiAl. Those threshold values bad a tendency to increase with the roughness of the fracture surface. The rate of increase in crack opening stress intensity factor at threshold with non-propagating crack length was smaller than that of cast TiAl. Predicted fatigue limits for crack initiation and propagation based on the fatigue-crack-growth resistance-curve method were in agreement with the experimental results. The fatigue limits of notched specimens were smaller than those of cast TiAl in spite of the superior mechanical properties of reactive-sintered TiAl.