Shock temperature measurements in metals New results for an Fe alloy

The temperature of a Fe-Cr-Ni alloy (304 stainless steel) has been measured during shock compression using a high-speed radiometric technique. Experiments were performed on highquality thick films deposited on sapphire and LiF windows. The samples had no observable porosity or defects and closely meet the ideal criteria for shock temperature measurements. Data obtained with both A1203 and LiF windows axe internally consistent, indicating that they remain transparent to high pressures and axe thus suitable windows for shock temperature measurements. Our data yield stainless steel melting temperatures ranging from 45704-310K at 138 GPa to 57104-340 K at 215 GPa, and additionally provide bounds on the initial Hugoniot temperatures of the sample between 56004-340 K at 234 GPa (near the solidus) and 65804-440 K at 283 (in the liquid field). Taken together, these data define a smooth curve for melting of the alloy up to 271 GPa and 5860 K, which should represent a point on the liquidus. Melting along the Hugoniot begins at approximately 234 GPa and 5600 K, as compared with 242 GPa and 6400 K for pure Fe. At the pressure of the inner core-outer core boundary, the melting point of 304 stainless steel is lower than that of pure Fe by m1450 K, as compared with only 110 K at I atm. These results demonstrate that upon alloying with Ni and Cr the melting point depression of Fe and thus material likely to comprise the inner core increases with increasing pressure.