| Shock-induced phase transformation is an important subject in the Shock-Wave Physics. We could discover the phase transformation, dynamic behavior etc, which are meaningful to built up a complete equation of state of the material, promoting the research of material science, geophysics and so on.Bismuth is a kind of complex-structure metal, which has complex polymorphic transitions and un-normal melting characteristic. However, there are so many divergences about its polymorphic transitions between dynamic and static experiments data, what's more, the study on the high pressure phase of Bi is abecedarian. Thus study on Bi is meaningful to our understanding on polymorphic phase transition, melting characteristic and the constructing of complete EOS.The main contents of this paper are experimental research, with theoretical analysis additively, to studied the shock-induced phase transformation behavior of Bismuth. The modified technique is verified and the main goals obtained can be concluded as follows:(1)The load wave profiles of Bi were measured at about 3 GPa, using distance interferometer system for any reflector (DISAR) by the plate impact. The low pressure experimental result indicated the elastic-plastic behavior, BiⅠ—BiⅡor BiⅡ—BiⅢphase transformation, which were in accord with Asay's report.(2) Bi was ramp compressed (quasi-isentropic) by the ramp wave generator (fused-quartz), to control the strain rate. Our experimental result indicated that the strain rate had a poor relation to the phase transformation pressure.(3) The release wave profiles of Bi were measured at in the shock pressure range 10-45 GPa, using reverse-impact method, and Hugoniot data,sound velocity for Bi has been measured. Our high-accuracy experimental technique solved the problem that the shock wave velocity can not be measured exactly due to the simultaneous connection of the electronic detectors, and avoided measuring the time the shock wave got through the sample accurately. The Hugoniot data (shock wave velocity-particle velocity) we got indicates that the D-u curve did have a discontinuity when the particle velocity was about 0.9 km/s, which may be caused by the shock-induced solid-liquid phase transformation. Through the analysis of sound velocity data, we concluded that Bi was solid at about 16 GPa, and it would melt in the next pressure range.(4) To interpret the shock data, we calculated the phase diagram of Bi on the basis of Johnson and Cox's Gibbs free energy thermodynamic EOS. The calculated results were compared with our experimental results. It was in good agreement with the solid-solid phase transitions at the low pressure range,but differs somewhat with the measured high pressure melting ling.In all, we got the low pressure phase transition pressure and high pressure melting zone of Bi through the conduct of shock experiments and theoretic calculation. This research method is meaningful to the developing of reverse impact technology, the measuring of Hugoniot and sound velocity data and the further study on phase transition characteristics of materials. |
PDF Full Text Request