The response of dislocations, low angle grain boundaries and high angle grain boundaries at high strain rates

As a most widely applied structure material, the deformed characteristics of steels primarily presented the adiabatic shear band (ASB) formation and phase transitions, instead of its intrinsic structure evolution at different strain rates. In previous works, seldom investigations on the high strain rates dependence of the dislocations, low angle grain boundaries (LAGBs) and high angle grain boundaries (HAGBs) were reported, and the transition mechanism among the three microstructural factors was not clear. Here, we used a gas gun to generate shock wave to compress the AISI 1045 steels and investigated their structures under different stain rates of 4.3 × 10⁵ s⁻¹ (low) and 3.3 × 10⁶ s⁻¹ (high), respectively. A gradient structure was formed along shock compression direction. Surprisingly, the structure evolution of the steel has a strong rate effect. At high strain rates, the dislocations would form the LAGBs, while the LAGBs would difficultly transform into HAGBs. At low strain rates, the LAGBs preferred to transform into HAGBs. Furthermore, the LAGBs to HAGBs transformation was accompanied with the grain rotation. The texture under the low strain rates was changed from annealing {111} <211> to R-Cube {001} <110>, while that of the high strain rates became R-Goss {110} <110>→Goss {011} <100>→Cube {001} <100>. These results indicate that the rate effect of the structures under loading plays an important role in guiding the materials design and applications.