Dynamic behavior and adiabatic shearing formation of the commercially pure titanium with explosion-induced gradient microstructure

The commercially pure (CP) titanium has been processed by explosion hardening to produce a gradient microstructure. The hardness distribution of CP titanium after explosion hardening was measured. The microstructure of explosion hardened CP titanium was revealed by transmission electron microscopy and optical microscopy. The split Hopkinson pressure bar was used to study the effect of explosion hardening on dynamic behavior and adiabatic shearing formation of CP titanium. The experimental results showed that explosion hardening induced the gradient hardened microstructure with a depth of 2.6 mm in CP titanium. The explosion hardened specimens present enhanced static and dynamic compressive strengths, which was caused by grain refinement, the α-ω phase transition, and micro-defects’ proliferation. The gradient deformation and gradient ASB occurred in explosion hardened specimen after dynamic loading, whereas the homogeneous deformation and a bipyramid-shaped adiabatic shear band were observed in untreated specimen. The ASBs were easier to nucleate, propagate, bifurcate and interact in the explosion hardened CP titanium during dynamic loading, especially in the shocked side due to the higher-density micro-defects. This was attributed that the ω phase particles and the proliferation of twinning/dislocations during explosion hardening promoted the dynamic recovery process during the nucleation stage of ASBs. The gradient microstructure in CP titanium with explosion hardening delayed the propagation of ASBs and cracks under dynamic loading.