Multi-scale coupling effects on flow localization during micro-compression deformation of Ti–6Al–4V alloy

Abstract

In this study, the initial microstructure dependency of flow localization behavior was investigated for Ti–6Al–4V alloys with equiaxed, duplex, basket-weave and widmannstatten microstructures. The flow localization behavior was conducted using micro-compression hot deformation tests and the microstructures were characterized by Electron backscatter diffraction (EBSD). The results reveal that initiation of micro shear bands in basket-weave is driven through the absorption of dislocations to colony boundaries, whereas it is implemented via the pinch-off of α lamellae in widmannstatten. A semi-quantitative result based on EBSD observations indicates that the high globularization rate of micro shear bands in basket-weave are found in α lamellae with soft orientation where the c-axis of crystal is tilted of 15–75° from the compression axis or the geometric orientation of lamellae is perpendicular to the shear direction. However, the globularization of widmannstatten is no longer subject to the effects of geometric or crystal orientation, suggesting that there is a noteworthy coupling size effects. In addition, accompanying with the microstructure change from duplex through basket-weave to widmannstatten, the decrease of interlamellar spacing for α lamellae increases the strength of materials through Hall-Petch. At the same time, the decrease of interlamellar spacing promotes slip transmission via the proposed mechanisms of boundary absorption and pinch-off, resulting in easier flow softening, earlier flow localization, more intense shear deformation, narrower and sharper shear bands.