Plastic deformation mode and α/β slip transfer of Ti–5Al-2.5Cr-0.5Fe-4.5Mo–1Sn–2Zr–3Zn titanium alloy at room temperature

Abstract

The plastic deformation mode and slip transfer between the α and β phases of Ti–5Al-2.5Cr-0.5Fe-4.5Mo–1Sn–2Zr–3Zn titanium alloy were investigated using a combination of ex-situ scanning electron microscopy tensile tests and electron backscatter diffraction characterization. With increasing tensile strain, local orientation changes (which lead to the sub-grain boundary generation and migration) occurred in the α phase, resulting in grain subdivision/coalescence. Afterward, the elongated α grains were subdivided (in general) into small equiaxed grains. Abrupt changes in the crystal orientation of the continuous β-matrix were, however, rare. Three primary slip systems (prismatic and basal slip: α phase and {110}<111> slip: β phase) accounted for more than 70% of the total slip system activity at each strain level. These systems could be activated with very low Schmid factors (<0.1) at high strains. The compatible deformation between the α and β phases was realized mainly through the slip transfer correlated with the three primary slip systems, and the prismatic slip system was the most active system. In general, the α phase underwent plastic deformation first and compelled plastic deformation of the separated β grains. Subsequently, the deformed β grains transmitted the strain between an adjacent α grain and other α grains, leading to deviations from the uniaxial stress state in the local region. This resulted in wide distributions of the activated slip systems with various Schmid factors, and considerable strain concentration and failure in the α phase near the phase boundaries.