Unsteady flow softening behaviour of near beta Ti alloy TLM during hot deformation

Ti-3Zr-2Sn-3Mo-25Nb (TLM) titanium alloys are compressed at the 850°C temperature and 0·1 s^-1 strain rate. The behaviour of unsteady flow softening with the oscillation of the flow stress- strain curve is observed during hot compression, and deformation mechanism of unsteady flow softening is investigated. The experimental results show that the stress-strain curve of TLM alloy in hot compression exhibits the character of four stages: the elastic stage, the stress plateau stage, the strain workhardening stage (true strain, 5·1-15%), the steady flow softening stage (true strain, 15-35%) and the obviously unsteady flow softening stage with the oscillation (>35%). Unsteady flow softening behaviour with the oscillation of TLM alloy is related to dynamic recrystallisation, and the flow stress is prone to oscillation with multiple peaks at the thermomechanical processing parameters of 0·1 s^-1 strain rate, deformation temperature of 850°C and initial microstructure with a grain size of 50 μm.