The yielding, deformation and fracture behavior for the Widmanstätten structure of Ti–8Al–1Mo–1V alloy upon high speed impact

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The yielding, deformation and fracture behavior for the Widmanstätten structure of Ti–8Al–1Mo–1V alloy upon high speed impact were studied through characterization and discussion. Seven strain rates ranging from 870 s−1 to 3300 s−1 were applied. The results show that: The yield strength of Widmanstätten structure shows two distinct changing stages among the whole range of strain rates. Under the strain rates below 2250 s−1, Widmanstätten structure exhibits positive strain rate sensitivity. Surprisingly, under the strain rates from 2250 s−1 to 3300 s−1, it shows negative strain rate sensitivity. The increasing importance of twinning in the initiation of plastic deformation with higher strain rate is deemed as the reason causing this phenomenon. The dynamic compression behavior of Widmanstätten structure is described by J-C model, which shows unstable prediction performance. Adiabatic shearing band starts forming under the strain rates above 1950 s−1, from which the fracture behavior of Widmanstätten structure is analyzed. An interesting phenomenon is that the adiabatic shearing band thicknesses at different locations of specimen can be obviously different. This is attributed to the relative orientation of α lamellae to the biggest shear stress plane. Saw-tooth chips start forming at the two end faces of specimen under the strain rates above 2500 s−1, and its formation mechanism is thoroughly discussed. Adiabatic shearing band after post annealing was characterized by EBSD, which shows recrystallized grains with gradient diameters. In addition, it is found that the Burgers orientation relationship of the microstructure outside adiabatic shearing band was generally retained during the dynamic loading and post-annealing process.