Shear localization behavior in hat-shaped specimen of near-αTi−6Al−2Zr−1Mo−1V titanium alloy loaded at high strain rate

The microstructure characteristics in early stage shear localization of near-αTi−6Al−2Zr−1Mo−1V titanium alloy were investigated by split Hopkinson pressure bar(SHPB)tests using hat-shaped specimens.The microstructural evolution and deformation mechanisms of hat-shaped specimens were revealed by electron backscattered diffraction(EBSD)method.It is found that the nucleation and expansion of adiabatic shear band(ASB)are affected by both geometric and structural factors.The increase of dislocation density,structure fragment and temperature rise in the deformation-affected regions provide basic microstructural conditions.In addition to the dislocation slips,the extension twins detected in shear region also play a critical role in microstructural fragmentation due to twin-boundaries effect.Interestingly,the sandwich structure imposes a crucial influence on ASB,which finally becomes a mature wide ASB in the dynamic deformation.However,due to much larger width,the sandwich structure in the middle of shear region is also possible to serve as favorable nucleation sites for crack initiation.

Experiment and modeling of TiB_(2)/TiB boride layer of Ti−6Al−2Zr−1Mo−1V alloy

The influence of the boriding conditions on the boride layers was examined by boriding Ti−6Al−2Zr−1Mo−1V alloy in the temperature range of 920−1120℃.The experimental results show that the boride layers were composed of a continuous thin outer layer of TiB_(2) and a thick inner layer of TiB with whiskers or needle-like morphologies that extended into the substrate.Thick and compact boride layers were obtained when the boriding temperatures were 1000−1080℃,and the treatment time exceeded 8 h.The boride layer depth increased with the boriding temperature and time,and the growth kinetics of the boride layers was characterized by a parabolic curve.The growth kinetics of the boride layers,including both TiB_(2) and TiB layers,were predicted by establishing a diffusion model,which presented satisfactory consistency with the experimental data.As a result,the activation energies of boron in the TiB_(2) and TiB layers were estimated to be 223.1 and 246.9 kJ/mol,respectively.