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采用气炮作为加载手段, 结合反向碰撞技术和多台阶三层组合飞片技术, 通过精细的样品/窗口波剖面测量, 对典型加载-卸载-再加载路径下铁的相变动力学特性进行了研究. 观测到一次卸载阶段的多波结构及再加载段的双波结构. 获得首次逆相变阈值约为(11.3 ± 0.5) GPa, 首次加卸载相变特征时间为30 ns; 再加载相变起始压力为10—12 GPa, 且随着再加载初始态ε相质量分数降低而降低. 实验显示二次相变压力阈值与ε相残余质量分数以及逆相变子相所含孪晶、缺陷相关, 同时二次加载相转变速率比首次加载更快. 上述结果揭示了多晶铁相变动力学行为与加载路径的强耦合, 为相关研究提供了新的视角和实验支撑.The dynamics of iron under extreme conditions like high temperature and high pressure has been well studied for several decades. But, there have been not many reports about the phase transition kinetics coupled with complicated thermodynamic paths, especially loading-unloading-reloading path, which is closer to the real applications. A three-layer structure impactor with five stages performed in the front-surface experiment is made up to approach the special path. We choose epoxy to be the adhesive as it has low impedance and high strength. Tantalum, the standard material of high impedance which also has single wave structure, is selected for reloading process. The wave profile shows a 3-wave structure in the first unloading period and the inverse phase transition threshold is calculated to be about 11.3 GPa. This onset pressure of reverse phase transition is not consistent with Barker’s result, higher than his result (about 2.5 GPa). By comparing with recalculated result of Jensen’s data, we find that our result is consistent with theirs.In this work the inverse phase transition ends at about 10 GPa, the value from this way which is higher than Barker’s finding, even higher than his result of the threshold pressure of reverse phase transition. And at this state there remains 12%–15% of ε phase. So it cannot be seen as the completed reverse phase transformation. The phase transition onset pressure is 10–12 GPa on the reloading path and it is about 1–2 GPa lower than the first phase transition. By simulating the wave profile, the discrepancy of using different phase transformation characteristic time τas 30 ns and 5 ns is analyzed. It can be seen that the phase transition rate of reloading is faster than that of the first loading process. These phenomena may be caused by the twins and the dislocations which are produced by the inverse phase transition. Also, as unloading time becomes longer, the mass fraction of ε phase becomes lesser and the onset pressure of α → ε phase transition becomes lower. This because with more ε phases transforming into α phase, more twins and dislocations will be produced in material. Therefore, it brings the lower onset pressure.
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Keywords:
- iron/
- shock loaded/
- kinetics of phase transition/
- reload
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材料 $ {{\rho }}_{0}/{({\rm{g}} \cdot {\rm{cm}}}^{-3}) $ $ {{C}}_{0} $/$ ({\rm{km}} \cdot {\rm{s}}^{-1}) $ λ Ta 16.65 3.43 1.19 Epoxy 1.19 2.73 1.49 Fe样品 7.86 3.93 1.58 LiF窗口 2.64 5.21 1.34 
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部件 $ {{\rho }}_{0}/\left({{\rm{g}} \cdot {\rm{cm}}}^{-3}\right) $ 直径
/mm厚度
/mm对应Epoxy
厚度/mmTa 1号台阶 16.65 55 2 2.2 Ta 2号台阶 16.65 15 2.5 1.7 Ta 3号台阶 16.65 15 2.8 1.4 Ta 4号台阶 16.65 15 3.2 1.0 Ta 5号台阶 16.65 15 3.5 0.7 Epoxy 1.19 55 — — Fe样品 7.86 55 1.5 — LiF窗口 2.64 55 20 — 下载:
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$ {W}/(\mathrm{m}\cdot {\mathrm{s}}^{-1}) $ $ {{u}}_{\mathrm{w},\mathrm{H}}/(\mathrm{m}\cdot {\mathrm{s}}^{-1}) $ $ {{u}}_{\mathrm{m}}/(\mathrm{m}\cdot {\mathrm{s}}^{-1}) $ $ {{P}}_{\mathrm{m}}/\mathrm{G}\mathrm{P}\mathrm{a} $ $ {{p}}_{\mathrm{D}}/\mathrm{G}\mathrm{P}\mathrm{a} $ $ {{p}}_{\mathrm{E}}/\mathrm{G}\mathrm{P}\mathrm{a} $ $ {\Delta {t}}_{\mathrm{D}\mathrm{E}}/\text{μ}\mathrm{s} $ Shot No.1 1475 ± 15 986 ± 10 489 ± 10 17.0 ± 0.1 11.2 ± 0.4 10.0 ± 0.2 0.08 Shot No.2 1521 ± 15 1015 ± 10 506 ± 10 17.6 ± 0.1 11.4 ± 0.4 10.0 ± 0.2 0.07 下载:
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Shot No.1 Shot No.2 台阶编号 ε相质量
分数/%二次加载相
变压力/GPaε相质量
分数/%二次加载相
变压力/GPa5 52 11.5 77 12.0 4 27 10.9 36 11.1 3 21 10.6 26 10.8 2 16 10.4 20 10.5 1 12 10.1 15 10.2 下载:
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