【摘要】 基于磁驱动装置CQ-4开展了金属钛的斜波压缩相变实验,研究了窗口特性对钛相变动力学的影响.实验结果显示,钛后表面为较低声阻抗(自由面和Li F窗口)时,相变起始对应的粒子速度特征拐点约408.9 m/s,而高阻抗蓝宝石窗口时约373.9 m/s,这一速度特征拐点对应的压力并不是相变压力.结合基于热力学Helmholtz自由能的多相状态方程和非平衡相变速率模型开展了钛的相变动力学数值模拟研究,计算结果与三种情况的实验结果都基本吻合.计算结果显示,样品在加载面附近速度波形相同,在后表面附近由于阻抗匹配不同,波形幅值差异较大.钛的相变压力为10.5 GPa,且为率相关的非平衡相变.在压力-比容热力学平面,相变前准等熵线与冲击绝热线基本重合,相变过程在一定的压力区间内完成,进入新相后准等熵线在冲击绝热线下方.进入相变后有明显的声速下降,这是由于相变引起的比容间断造成的,相变完成后恢复到体波声速.更多还原

【Abstract】 The phase transition experiments under ramp wave compression of titanium have been done by using a magnetic diven device CQ-4, and the influence of the acoustic impedance of the back surface of titanium on the phase transition has been studied. The experimental results show that when the acoustic impedance of the window is low, free surface or Li F, the particle velocity corresponding to the beginning of phase transition is about 408.9 m/s, while at the high impedance sapphire window, is about 373.9 m/s. The pressures corresponding to the characteristic velocities are not the phase change onset pressures. A simulation was done to well describe this complicated dynamic response including physical models of multi-phase equation of state based on Helmholtz free energy, strength model, and non-equilibrium dynamic equation of phase transition. The calculated results are in excellent agreement with the experimental data, and they exhibit the dynamic physical characteristics of Tin involving the elastoplastic transition and evolution of mass fraction of different phase. The results show that the velocity wave forms of the samples near the loading surface are the same, but the amplitude of the wave forms varies greatly due to the impedance matching of Tin and windows in the vicinity of Tin’s rear surface. The phase transition pressure of Ti is about 10.5 GPa, which is a rate dependent non-equilibrium dynamic process. In the pressure-volume thermodynamic plane, the calculated isentrope coincides with Hugoniot before phase transition, but is below the Hugoniot after phase change. The obvious decrease in sound velocity after phase transition is due to the discontinuity of the specific volume due to phase transition.更多还原