High pressure melt dynamics in shock-compressed titanium

TL;DR

This study combines experimental and computational methods to investigate the high-pressure melting behavior of titanium, revealing the coexistence of solid and liquid phases at specific pressures and highlighting the microstructural changes during shock compression.

Contribution

It provides the first experimental evidence of liquid titanium at 86 GPa and combines this with molecular-dynamics simulations to map the melt coexistence range, advancing understanding of titanium's behavior under extreme conditions.

Findings

Liquid titanium observed at 86 GPa

Solid-liquid coexistence predicted at 111-124 GPa

Residual crystalline texture persists above 126 GPa

Abstract

We study the high-pressure melting behavior of titanium using laser-driven shock compression with in situ femtosecond x-ray diffraction and molecular-dynamics simulations based on a machine-learned interatomic potential. The MD simulations predict the solid-liquid coexistence on the Hugoniot in the $\sim$$111-124$ GPa range. Experimentally, we observe the first evidence of liquid at 86 GPa. We also observe pronounced microstructural changes with pressure with strong grain refinement associated with the emergence of liquid, within the solid-liquid coexistence ($\sim$$110-126$ GPa). Above 126 GPa, we observe the persistence of residual levels of highly textured crystalline Ti to $\sim$$180$ GPa, well above the expected melt completion pressure. We discuss the accuracy that current laser-shock experimental platforms have at determining the melt onset and completion pressures.