High pressure and shock induced amorphization in boron carbide

高压和冲击引起碳化硼非晶化

基本信息

批准号：
16206064
负责人：
CHEN Mingwei
金额：
$ 32.86万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

项目摘要

By combining Raman microscopy, nanoindentaion and high-pressure diamond anvil cell, the pressure-induced amorphization in single-crystal B_4C have been systemically investigated. The localized amorphization was found to start with the applied pressure at about 25GPa and extensive amorphization was observed with the applied pressure up to 50GPa. Interestingly, the amorphization only occurs during unloading. Phase transitions have not been seen during loading or still at high pressures. Low- and high-temperature Raman spectroscopy study reveals that amorphous B_4C is composed of carbon aromatic rings and B11C icosahedra. The amorphization of B_4C is associated with the destruction of the C-B-C chains and the formation of sp2 carbon clusters. This disordered structure with relatively weak carbon sp2 bonds is believed to be responsible for the loss of B_4C shear strength at high pressures. The possible polytypes of the chain structure in B_4C was investigated by ab initio calculations. The … More B-C-B chain structure was found to have the lowest energy than other polytypes. The structure was experimentally confirmed by Cs-corrected high-resolution scanning transmission electron microscopy that owns the point-to-point resolution better than 1.0 angstrom. In addition to the quasi-static study, amorphization of B_4C was also observed in the shock-loaded fragments and scratched debris. A large amount of amorphous phase mixed with nanocrystalline particles was characterized in the shock fragments with the impact pressure of about 40GPa. The compositions of the both amorphous and nanocrystalline phases are the same as the crystalline boron carbide, suggesting a polymorphic transition occurs during shocking loading. The observations of amorphization of B_4C under both quasi-static and dynamic loading indicate that the high pressures play the dominant role in the elastic instability of B_4C and irreversible high elastic deformation caused by high pressures is responsible for the amorphization during unloading. Less

通过结合拉曼显微镜，纳米INDENTAION和高压钻石细胞，已系统地研究了单晶B_4C的压力诱导的非晶化。发现局部非晶化是从约25GPA的施加压力开始，并且在50GPA的施加压力下观察到了广泛的非晶态。有趣的是，无形化仅发生在卸载期间。在加载期间或仍处于高压时，没有看到相变。低温和高温拉曼光谱研究表明，无定形的B_4C由碳芳环和B11C Icosahedra组成。 B_4C的无形化与C-B-C链的破坏和SP2碳簇的形成有关。据信这种碳SP2键相对较弱的无序结构是导致高压下B_4C剪切强度损失的原因。通过从头算计算，研究了B_4C中链结构的可能多型。发现…比其他多型型的B-C-B链结构具有最低的能量。通过CS校正的高分辨率扫描透射电子显微镜实验证实了该结构，该透射电子显微镜比1.0 Angstrom更好地具有点对点分辨率。除了准静态研究外，还观察到B_4C的非晶化在减震片段和刮擦的碎屑中。在冲击片段中表征了大量与纳米晶体颗粒的无定形相，其冲击压力约为40GPA。无定形和纳米晶体相的组成与碳纤维结晶硼相同，这表明在震动的载荷期间发生了多态性过渡。在准静态和动态载荷下，B_4C无形化的观察结果表明，高压在B_4C的弹性不稳定性和高压引起的不可逆的高弹性变形中起主要作用，导致液压在卸载过程中。较少的