铈γ→α相变的室温动态特性

Dynamic characteristics of the γ→α phase transition of cerium at room temperature

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。

The γ→αphase 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 7 and a, 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.