In situ XRD Observation of the α-ω Phase Transition in Titanium During Shock Loading

The response of titanium (Ti) under shock compression is of fundamental importance due to its wide applications. Here we carry out a series of time-resolved x-ray diffraction (XRD) measurements for Ti under shock loading and release at the Matter in Extreme Conditions (MEC) beamline of the Linac Coherent Light Source (LCLS). Samples were laser shock loaded to a peak stress above the phase transition boundary between α phase and the high-pressure ω phase. Time-resolved XRD captured a complete transition to the ω phase under shock compression and reversion to the α phase during release process. Some amount of ω phase was retained for tens of nanoseconds (ns). The fraction of back-transformed α phase was observed to increase after the onset of spallation, and ultimately, a complete reversion to the α phase was observed at 85 ns after the onset of release. The time evolution of the phase fractions indicates that spallation promote back transformation, likely due to the rise in temperature and uniaxial tension experienced by the spall region.