Analysis of shear stress promoting void evolution behavior in an alpha/beta Ti alloy with fully lamellar microstructure

With the help of X-ray synchrotron tomography, in situ tensile tests have been performed on Ti-6Al-4V titanium alloy with full lamellar microstructure. The rendered 3D images have shown that void could nucleate as soon as the material yields, although local stress triaxiality (T = 0.472) seems not to be high and even tends to maintain a constant value in the following damage steps(T = 0.474-0.510). It can be inferred that local stress triaxiality could not be the dominating factor during damage development in this current work. By combining this result with the result of post mortem analysis by SEM and EBSD, it can be found that voids preferentially nucleate and propagate along either the alpha/beta interface, or along shear bands within one grain/colony, or at grains/colonies boundary. This could be interpreted by the role of shear stress during this processing. Based on the location of voids, shear stress can be taken into consideration at a/I3 interface, shear band within one grain and grains/colonies boundaries, respectively. The origins of shear stress at different scales seems correlated to local microstructure inhomogeneity and subsequent heterogeneous plastic deformation at different scales. Void nucleation and propagation could depend on this local shear stress instead of stress triaxiality.