Melting and refreezing of zirconium observed using ultrafast x-ray diffraction

Ultrafast (130-fs) x-ray diffraction at the Linac Coherent Light Source has been applied to observe shock melting, which is driven by a rapid (120-ps) laser pulse impinging on a thin (few micrometers) bilayer of aluminum/zirconium. At a pressure of 100 GPa in the aluminum (130 GPa in the zirconium), there is rapid melting of both metals and the recrystallization of zirconium into the bcc beta phase. We observe the solidification of the melt starting a few hundred picoseconds following the shock melting, out to 50 ns when the zirconium is fully crystallized into the bcc beta phase at a residual temperature of approximately 2000 K. The pressure is obtained directly from the early time x-ray data, whereas the additional information from the x-ray line width and intensity at longer times inform a model of crystal nucleation and growth.