Low cycle fatigue behaviour of Ti alloy Timetal 834 at 873 K

Low cycle fatigue behaviour of a near α titanium alloy Timetal 834 was studied, for a bimodal microstructure with ∼14 vol% of primary α in the matrix of transformed β at different total strain amplitudes (Δεt/2) ranging from ±0.75% to ±1.25%, at 873 K. Cyclic softening was exhibited at all the strain amplitudes, however, the rate as well as degree of softening was found to decrease with increase in strain amplitude. In general the rate of softening was high at all the strain amplitudes during the initial ∼10 cycles, however, it decreased in subsequent cycles and shortly the cyclic stress became almost stable and remained so for the major fraction of life, until the onset of macrocrack propagation to cause rapid drop in the stress leading to fracture. Coffin–Manson (C–M) plot was found to exhibit a single slope at 873 K, in contrast to dual slope at room temperature. Also fatigue life at 873 K was considerably higher than that at room temperature. The results are discussed in terms of increased homogeneity of deformation and higher stability of Ti3Al precipitates at the elevated temperature of 873 K than that at room temperature.