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

结合拉曼显微镜、纳米压痕和高压金刚石压砧，系统研究了单晶B_4C中压力诱导的非晶化，发现局部非晶化在约25GPa的压力下开始，并且在25GPa左右的压力下观察到广泛的非晶化。当施加的压力高达 50GPa 时才有意义，非晶化仅在卸载过程中发生，在加载过程中或仍然处于高压下。低温和高温拉曼光谱研究表明，非晶B_4C由碳芳环和B11C二十面体组成，B_4C的非晶化与C-B-C链的破坏和sp2碳簇的形成有关，这种结构相对较弱。碳 sp2 键被认为是造成 B_4C 在高压下剪切强度损失的原因。通过从头计算研究发现 B-C-B 链结构比其他多型体具有最低的能量，该结构通过具有点对点分辨率的 Cs 校正高分辨率扫描透射电子显微镜进行了实验证实。除了准静态研究之外，在冲击载荷碎片和划伤碎片中也观察到了 B_4C 的非晶化。在冲击压力约为 40GPa 的冲击碎片中，观察到非晶相与纳米晶颗粒的混合，非晶相和纳米晶相的组成与结晶碳化硼相同，表明在冲击载荷过程中发生了多晶型转变。 B_4C在准静态和动态加载下的非晶化表明高压在B_4C的弹性失稳和不可逆高弹性中起主导作用高压引起的变形是卸载过程中非晶化的原因。