高压高应变率加载下多晶相变的原位X射线衍射

In situ observation of phase transition in polycrystalline under high-pressure high-strain-rate shock compression by X-ray diffraction

高功率激光可通过直接烧蚀产生高温、高压、高应变率的物质状态,同时也可驱动金属箔产生与之精密同步的超短超强X射线源,成为利用原位X射线衍射技术研究材料在极端高温、高压、高应变率下相变动力学的重要实验平台.本文基于原型高功率激光装置建立高压、高应变率加载下材料相变的原位X射线衍射诊断平台,并以典型金属钒和铁为例开展冲击相变的原位观测.实验表明,在高应变率(10^8-10^9s^-1)冲击加载下,金属钒在69 GPa时依然保持体心立方结构不变,而金属铁在159 GPa时已经由体心立方结构转变为六角密排结构,均与文献报道一致.同时原位X射线衍射实验测量的材料压缩特性与宏观Hugoniot曲线符合得很好.利用原位X射线衍射技术研究高应变率动态加载下材料的相变行为对理解材料相变的应变率效应和动力学过程具有重要的科学意义,同时对提高材料工程服役的可靠性以及突破材料极端环境服役的发展瓶颈具有重要的工程价值.

The knowledge of phase transition of material under dynamic loading is an important area of research in inertial confinement fusion and material science.Though the shock-induced phase transitions of various materials over a broad pressure range have become a field of study for decades,the loading strain rates in most of these experiments is not more than.However,in contrast with the strain rate range where the phase diagram is a good predictor of the crystal structure of a material,at higher strain rate(>10^6s^-1)the phase diagram measured can be quite different not only in shifting the boundary line between various phases,but also in giving a different sequence of crystal structure.High-power laser facility can drive shock wave and simultaneously provide a precisely synchronized ultra-short and ultra-intense X-ray source.Here,based on the Prototype laser facility,an in situ X-ray diffraction platform for diagnosing shock-induced phase transition of polycrystalline material is established.The in situ observation of material phase transition under high-strainrate shock loading is carried out with typical metals of vanadium and iron.Diffraction results are consistent with vanadium remaining in the body-centered-cubic structure up to 69 GPa,while iron transforms from the body-centered-cubic structure into hexagonal-close-packed structure at 159 GPa.The compressive properties of vanadium and iron obtained in in situ X-ray diffraction experiment are in good agreement with their macroscopic Hugonoit curves.The decrease in the lattice volume over the pressure step period yields a strain rate on the order of 10^8-10^9s^-1.The available of the presented in situ X-ray diffraction plateform offers the potential to extend our understanding of the kinetics of phase transition in polycrystalline under high-pressure high-strain-rate shock compression.