Mechanism of lamellae deformation and phase rearrangement in ultrafine β-Ti/FeTi eutectic composites

Abstract We report the microscopic mechanism of lamellae deformation in a series of (Ti0.705Fe0.295)100−xSnx (0 ⩽ x ⩽ 4) eutectic comprising of ultrafine FeTi and β-Ti phases with varying lamellae thickness. Furthermore, the microstructural refinement and phase rearrangement upon severe forging have been explored using X-ray diffraction and transmission electron microscopy to reveal the dislocation activity inside the lamellae interior and at the β-Ti/FeTi interface. Nanoindentation tests have been performed at control loading rate and control strain rate modes to evaluate the strain rate sensitivity, activation volume, and to compare them with that of the constituent single phases. The strain rate sensitivity slightly decreases upon Sn addition and with the decrease of the lamellar spacing. However, severe forging increases the hardness, reduces the activation volume without any change of the strain rate sensitivity. The role of dislocation accumulation in the ultrafine lamellae, inter-lamellar sliding, formation of sub-boundaries, evolution of shear bands, cutting, and phase rearrangement towards the deformation-induced nanostructuring of the ultrafine lamellar composites, have been discussed using a micromechanical model.