High strain-rate behavior of copper–titanium alloy

Plate-impact experiments were conducted on Cu–Ti alloy (with 4.8 wt. % Ti) samples to determine its dynamic strength properties, e.g., yield strength and spall strength, under high strain rate-loading conditions. The as-received samples were subjected to microscopic analysis through x-ray diffraction and electron back scattering diffraction (EBSD) measurements before using in experiments. In a series of planar shock loading experiments carried out at different impact speeds, the shock stress and free-surface velocity history (FSVH) were measured and utilized to generate the Hugoniot data of the Cu–Ti alloy up to 18 GPa. The analysis of FSVH yielded the Hugoniot elastic limit (HEL) varying from 1.49 to 2.12 GPa, following an increasing trend up to 7.35 GPa. The dynamic yield strength averaged to be ∼0.97 GPa, which is 18% higher than the quasi-static value of 0.82 GPa. The spall strength as a function of shock pressure was found in the range of 1.95–2.71 GPa with a slightly increasing trend up to a pressure of 7.35 GPa and a monotonically decreasing trend thereafter. The analysis of EBSD patterns of samples recovered from peak shock stress of 7.35 and 15.38 GPa indicated a significant increase in fracture facilitating deformation twins together with the high-angle grain boundaries at 15.38 GPa, thus resulting in reduced spall strength. Furthermore, microstructural observations revealed progressive grain refinement, enhanced plastic deformation, and dynamic recovery with increasing shock pressure. The Hugoniot, HEL, and spall strength have been compared with those of unalloyed Cu available in the literature.