Dynamic characteristics of the γ→α phase transition of cerium at room temperature
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摘要: 通过试样组件尺寸匹配设计的被动围压SHPB实验，获得了99.8%纯铈在1.7GPa静水压内的、包含γ↔α相变和逆相变过渡区的室温动态静水压-体应变连续曲线。研究显示：室温铈γ→α相变是具有明显滞后现象的一级相变，而非以往研究认为的体积跃变的一级相变；相变过渡区的静水压范围是0.8~1.3GPa。逆相变过渡区的静水压范围是0.6~1.1GPa；逆相变过渡区的静水压-体应变曲线滞后于相变过渡区的静水压-体应变曲线0.15GPa静水压；在相变和逆相变过渡区内，静水压-体应变曲线按照约4.2GPa体积模量的线性关系演化；演化机制为γ和α两相均匀混合、静水压驱动两相组份转化。基于该演化机制，构建了描述相变前后和相变过程的静水压-体应变响应的三段线性模型。Abstract: The γ→α phase transition of 99.8% purity cerium was investigated using the passive confined split Hopkinson pressure bar experiment under a hydrostatic pressure up to 1.7GPa and at room temperature, the relationship of the hydrostatic pressure with the volume strain covering the whole process of γ↔α phase transformation was obtained, and the hysteresis loop was observed. The results show that the γ→α phase transition is the first-order with hysteresis rather than the first-order with volume discontinuity as recognized in previous researches. The γ →α phase transition occurs under the hydrostatic pressure ranging from 0.8 GPa to 1.3 GPa, whereas the inverse phase transition occurs under the hydrostatic pressure ranging from 1.1 to 0.6 GPa. The hysteresis loop shows a gap of 0.15 GPa hydrostatic pressure between the curve of hydrostatic pressure and volume strain during the γ→α phase transition and that during the inverse phase transition. The curves of the hydrostatic pressure and volume strain during the γ↔α phase transition were linear with the bulk modulus of 4.2 GPa. The mechanism behind the γ↔α phase transition is that the hydrostatic pressure drives the conversion between the phases of γ and α, which coexist during the γ↔α phase transition. Based on the mechanism of phase transition, a tri-segment linear model was constituted to describe the response of the hydrostatic pressure and volume strain in the process of γ→α phase transition. The modeled curve is found to be in good agree with the experimental curve.
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Key words:
- cerium /
- phase transition /
- hydrostatic pressure /
- phase transition model
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图 2 室温铈的静水压-体应变曲线
Figure 2. Curves of hydrostatic pressure and volume strain of cerium at room temperature
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