Processing map-microstructure evolution correlation of hot compressed near alpha titanium alloy (TiHy 600)

Abstract

Hot compression tests on TiHy 600 alloy (equivalent to IMI 834) is performed using Gleeble-3800® thermo-mechanical simulator. The hot deformation behavior of TiHy 600 alloy is characterized on the basis of flow stress variation with true stress-true strain curves at different strain rates ranging from 10−3 s−1 to 10 s−1 and hot deformation temperatures ranging from 900 °C to 1050 °C, with maximum engineering strain up to 50%. The flow stress is found to be strongly dependent on deformation temperature, strain rate and strain, and it decreases with increasing temperature and decreasing strain rate. The flow curves at various temperatures and strain rates also showed dynamic recrystallization process at temperature range (900 °C–975 °C) in all strain rates and dynamic recovery process at high temperature range (1000 °C and above) in all the strain rates. Using flow stress values from the true stress-true strain curves and by applying dynamic material modeling approach, processing maps are developed at various true strains of 0.3, 0.4, 0.5 and 0.6. Processing maps exhibited safe and unsafe domains with varying efficiency of power dissipation values. Safe and unsafe domains at 0.6 strain are derived from their flow curves are correlated with its related microstructures and misorientation distribution profiles. Hot compression at 900 °C (α-rich region) mostly resulted into new fine dynamic recrystallized equiaxed α grains along grain boundaries of large deformed α grains. Higher temperature (950 °C–975 °C) compression in the (α+β) region generated mixture of deformed large alpha grains containing subgrain boundaries and secondary α laths generates from deformed β. Further compression at higher temperature (1000 °C -β-rich region and 1050 °C -single β region) resulted in the formation of secondary α laths from deformed β with few equiaxed α grains at 1000 °C sample only. The misorientation profile of α phase corroborates with the deformation mechanism in α region through its equiaxed α grains and in β region through its secondary α variant laths misorientations.