Microstructural softening induced adiabatic shear banding in Ti-23Nb-0.7Ta-2Zr-O gum metal

Ti-23Nb-0.7Ta-2Zr-O gum metal (GM) is an attractive candidate material for applications that require superior mechanical properties. In our earlier investigation of the GM [1], geometrical softening and the generation of adiabatic shear bands (ASBs) were proposed as primary reasons for the documented anisotropic impact response. In the present study, electron backscattered diffraction (EBSD) analysis reveals two different deformed microstructures, i.e., deformed ultrafine grains (UFGs) and dynamically recrystallized UFGs, formed in the ASBs of GM samples processed by extrusion equal channel angular pressing (ECAP), respectively. Additional calculation of temperature rise during dynamic compression suggests that the above microstructure differences in the ASBs was originated from their different maximum ASB temperatures (608 K for extruded GM and 1159 K for ECAP-processed GM). Moreover, our calculation on the temperature at the onset of ASBs indicates that microstructural softening is the primary cause for the development of ASBs in both extruded GM (321 K) and ECAP-processed GM (331 K).