Phase transformations and spall fractures of high-purity cerium under explosive loading

1. VNIITF results on compressibility of high-purity unalloyed cerium when it is explosively loaded in the region of its initial γ-phase and in regions of its γ-α and α-liquid phase transformations are presented. All available experimental data were verified and generalized. Boundaries of one-, two-, and three-wave configurations in cerium were determined in the (D, u)-, and (σ_xx, V/V₀)- coordinates. 2. New data on the stress-wave structure and parameters and their variation throughout the wedges for four explosive loading conditions realized with different loading-pulse amplitudes and durations were obtained on wedge samples using the photochronographic optical-lever method. Not only the smeared γ-α-phase precursor but also the elastic precursor were reliably recorded in the high-purity unalloyed cerium in the realized modes of its explosive loading. 3. Our experiments confirmed theoretical prediction that the Hugoniot does not cross the α-ε-phase equilibrium boundary. At σ_xx ≤16 GPa, the optical lever method registered a sudden drop in the intensity of the light reflected from the sample's free surface and this can be explained by the shock-wave melting of cerium. 4. Experimental velocity profiles for the free surface of wedge samples, as well as the calculated longitudinal and bulk sound velocities, i.e. 1.9 km/s and 1.2 km/s, were used to estimate the first spall thickness and cerium spall strength, i.e. 0.2-0.4 GPa, which depend on stress pulse gradient in the tensile region.