Low cycle fatigue behavior of Ti alloy IMI 834 at room temperature

Abstract

Low cycle fatigue behavior of the Ti alloy IMI 834 was studied, for a bimodal microstructure with ≈14 vol.% primary α (αp) in the matrix of transformed β, at different total strain amplitudes (Δεt/2) from ±0.75 to ±1.7%, at room temperature. TEM examination revealed silicide particles at the interface of secondary α platelets in the transformed β, at the boundary of αp and transformed β, and extremely fine precipitates of ordered Ti3Al in the matrix. Cyclic softening was observed at all the above strain amplitudes. However, the degree as well as the rate of softening increased markedly at Δεt/2⩾1%. Cyclic softening was much less at low strain amplitude (Δεt/2⩽0.8%). The increase in the degree and the rate of softening at higher strain amplitudes is associated with increase in the number and more complete shearing of the ordered Ti3Al precipitates, from increase in the number of slip bands and glide dislocations. The increase in the number of glide dislocations in each cycle, with increase in strain amplitude occurs from increase in the effective strain rate to maintain the cyclic frequency at constant level. Bi-linearity was observed in the Coffin–Manson relationship and it was found to be associated with change in the deformation behavior from low to high strain amplitude.