Low cycle fatigue behavior of Ti-Mn alloys: Fatigue life

The effect of morphology, particle size, β grain size and volume fraction of β, from 0.025 to 1.0, on the low cycle fatigue life of α-β Ti-Mn alloys, have been studied under total strain control. In general, Widmanstätten plus grain boundary (W+GB) α structures show shorter fatigue lives than equiaxed (E) α structures, and this has been ascribed to the formation of much larger surface cracks and ease of transfer of slip from α to β. For Eα structures, fatigue life increases with decreasing α particle size and when the alloy is single phase β fatigue life increases with decreasing grain size. At high total strains the nearly all α alloy had the longest fatigue life and at lower strains the β alloy, with the higher yield strength, had the longest fatigue life. Fatigue life was correlated with strain hardening. The nearly all α alloy which had the highest strain hardening, over the plastic strains encountered, had the highest fatigue life, while the β alloy, with the lowest strain hardening, had the lowest fatigue life. For a portion of the fatigue life curves, it was found that as the average Baushinger strain (ABS) increased, the Coffin-Manson exponentc decreased. The results are discussed.