Low cycle fatigue behavior of Ti-6AI-2Sn-4Zr-6Mo: Part II. Cyclic deformation behavior and low cycle fatigue

Abstract

A series of strain-controlled low cycle fatigue tests have been carried out on Ti-6-2-4-6 at room temperature primarily for solution-treated and aged material. Tension-compression testing at R = 1 produced softening, irrespective of the morphology of the primary α. The amount of softening increased with increasing strain. Tension-tension testing for R = 0 produced strengthening. Unaged specimens showed behavior similar to aged material for both R = −1 and R = 0 testing. Annealing at 621 °C produced hardening for R = −1 and softening for R = 0 testing. Aging at 210 °C of R = −1 specimens produced strengthening. Fatigue life data revealed longer fatigue life for equiaxed (E) structures than for Widmanstätten plus grain boundary (W +GB)α structures. ForEα, increasing α particle size tends to reduce fatigue life. For W +GBα alloys the situation is more complex, and both a decrease and increase in fatigue life may be seen for increasing particle sizes. There is also a prior β grain size dependency. As a result of softening, the slope of the log Δε _p/2 vs logN _f curve continuously decreases with increasingN. Explanations of the softening and hardening behavior in terms of dislocation rearrangement are offered. An explanation of the role of microstructure on fatigue life has been offered in the companion paper.