Molybdenum Sound Velocity And Shear Strength Softening under Shock Compression

We measured the longitudinal sound velocity in molybdenum shock compressed up to 5 Mbar on the Hugoniot. Our measured sound speeds increase linearly with pressure up to 2.6 Mbar and level off slightly below the melting pressure of 3.7 Mbar. This suggests a decrease of shear strength near the melt. A linear extrapolation of our data to zero pressure is in good agreement with the sound speed measured at ambient conditions. The results indicate that molybdenum remains in the bcc phase on the Hugoniot up to the melting pressure. There is no evidence for a bcc → hcp phase transition on the Hugoniot as previously reported. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.