Anisotropic and supercooled melting in shock compressed silicon carbide

An understanding of the pressure and temperature conditions of melt at extreme levels of compression is important for planetary interior and impact models, inertial confinement fusion designs, and the construction of predictive equation of state models. For many materials, shock compression studies provide the only method for experimentally constraining melt at extremes, but the material states accessed by such rapid compression remain unclear. In this study we constrain the phase diagram of silicon carbide and draw direct comparisons with melt theory by conducting laser-compression experiments along the shock Hugoniot with in situ X-ray diffraction, velocimetry, and pyrometry measurements to simultaneously determine crystal structure, microstructural texture, temperature, density, and pressure. Uniaxial shock compression of 4H single crystals from the ambient B4 phase (wurtzite structure) into the high pressure B1 phase (rocksalt structure) results in a highly textured microstructure consistent with the Limpijumnong phase transformation mechanism. We observe the onset of melt at ∼300 GPa and ∼6300 K in agreement with predictions from quantum accurate molecular dynamic shock simulations. Our combined shock front temperature and bulk structural data suggests the formation of a transient supercooled liquid state at the shock front followed by recrystallization into the high pressure B1 phase, consistent with predictions of shear induced melting in other systems.