Shock-induced Phase Transformation Research Articles

Phase transformation in bismuth under shock loading

The behavior of bismuth under shock loading was studied by means of a shock-detection technique based on the electrical response of bimetallic junctions and on the polarization effect of thin dielectric sheets under shock. The experiments were performed in the pressure range 50–180 kbar. A new shock-induced phase transformation was found to take place at about 70 kbar. A rough estimate of the temperature increase associated with shock loading, and comparison with data of static compression experiments suggest that this new shock-induced phase change in bismuth corresponds to the Bi III-V transformation, previously observed only under static pressure loading.

Stability of the magnetic phase transformation in shocked Fe-Ni alloys

Abstract Hugoniot-equation-of-state data recently published by Christou indicated that the addition of nickel to iron increased the pressure required to bring about the shock-induced martensitic phase transformation. The data were said to agree with previous experimental measurements. It was also implied that the increase in transition pressure was in agreement with theory. The purpose of this communication is to point out that Christou's measurements are in disagreement with all previous experimental measurements and theoretical predictions which show that the transition pressure decreases with increasing nickel content.

Stability of the magnetic phase transition in shocked Fe-Ni alloys

Abstract Shock deformation of Fe-Ni alloys with composition of 5 wt.% Ni to 30 wt.% Ni results in a shock-induced phase transformation. The addition of nickel to iron raises the transition pressure from 133 kbar for pure Fe to more than 150 kbar for Fe-30 Ni. The values for susceptibility have been found to follow a Curie-Weiss law indicating the occurrence of irreversible demagnetization as a result of deformation above 150 kbar. Saturation magnetization studies for the Fe-10 Ni and Fe-30 Ni alloys have detected a residual reduction in magnetization due to work hardening and the retention of the high-pressure phase.

High-Pressure Phase Transition and Demagnetization in Shock Compressed Fe–Mn Alloys

Shock deformation of Fe–Mn alloys up to 14 wt% Mn results in a shock-induced phase transformation. It has been shown that bcc martensite with manganese in the range 4–16 wt% transforms to a stable close-packed phase under pressure without the occurrence of reversion. The addition of manganese to iron also decreases the transition pressure from 133 kbar for pure Fe to less than 70 kbar for Fe–14Mn. X-ray diffraction, electron-probe microanalysis, electron microscopy, and density results indicate that for the Fe–4Mn and Fe–7Mn alloys, the fcc phase has been stabilized after shock deformation, while the ε phase has been stabilized for the Fe–14Mn alloy. Saturation magnetization studies have detected a residual reduction in magnetization due to the retainment of the high-pressure phase.

Galvanomagnetic effects in shock-deformed iron alloys

Abstract The transverse magnetoresistivity of annealed and shock-deformed Fe, Fe-7·37 wt. % Mn and Fe-30 wt. % Ni was measured as a function of B/p0 -The deformed material yields a curve which is in general shifted from the annealed metal. The shift in Fe is due to anisotropic scattering of conduction electrons by dislocations. In Fe Ni and Fe Mn the shift can be explained by a shock-induced second-order phase transformation occurring above 90 kbars.

Temperature Dependence of Shock-Induced Phase Transformations in Iron

Shock-induced phase transformations in iron have been investigated in the temperature range 78° to 1158°K. The pressure for transformation over this temperature range has been determined by a technique that depends on microstructural changes associated with a phase transformation. A discontinuity in the temperature-pressure relationship was observed at 115 kbars and 775°K. Two distinct transformation microstructures were observed. It is postulated that the results obtained above 775°K are due to the expected transformation from alpha iron to gamma iron whereas the results below 775°K are related to a transformation from alpha iron to a presently undetermined new phase.