Torsional Fatigue of Ti15Mo Titanium Alloy

This study investigates the torsional fatigue behavior of Ti-15Mo alloy through comprehensive analyses of its mechanical properties, microstructure, fatigue stress-life curves, and fracture surfaces, providing valuable insights into its fatigue characteristics. The hot-forged and air-cooled Ti15Mo alloy exhibited a microstructure predominantly consisting of equiaxial β phase grains, deformation twins, and ω athermal phase. Mechanical testing revealed a microhardness of 347.4 HV, yield and ultimate tensile strengths of 873 MPa, elongation of 20.7%, Young's modulus of 83.7 GPa, ultimate shear strength of 673 MPa, shear modulus of 30.5 GPa, and a fatigue strength limit of 190.2 MPa, as estimated by Basquin's model at 5 x 106 cycles. Fracture analysis indicated that crack nucleation predominantly occurred on the surface under pure torsion loading. In high-cycle fatigue (HCF) tests, cracks propagated at approximately 45° (Mode I), while in low-cycle fatigue (LCF) tests, propagation occurred at around 90° (Mode III). Fracture profiles also revealed significant number of deformation twins and instances of intragranular fracture near the fracture surface.