Shear Localization and its Related Microstructure Mechanism in a Fine-Grain-Sized Near-Beta Ti Alloy

Shear localization is an important deformation and failure mechanism for the high strength near beta fine-grain-sized titanium alloy used in aircraft’s gear at high rate deformation. Hat-shaped specimens are used to induce the formation of an adiabatic shear band under controlled shock-loading tests. Unstable shear deformation of the alloy emerges after the true flow stress reaches 1147 MPa, the first vibration peak during the split Hopkinson pressure bar testing, and the whole process lasts about 68 μs. The microstructures within the shear band in the alloy are investigated by means of light microscopy, scanning electron microscopy, and transmission electron microscopy. The results show that the grains in the boundary of the shear band are highly elongated along the shear direction, and the core of the shear band consists of ultrafine-equiaxed grains with diameters 0.1-0.3 μm, low dislocation density, and no observed phase transformation. The rotational dynamic recrystallization is used to explain the microstructural evolution mechanism in the shear band. Kinetic calculations indicate that the recrystallized ultrafine grains are formed during the deformation and do not undergo significant growth by grain boundary migration after deformation.