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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

本文采用拉曼显微镜、纳米压痕和高压金刚石对顶砧相结合的方法，系统研究了单晶B_4C的压力诱导非晶化。研究发现，在25 GPa左右的压力下，合金开始发生局部非晶化，当压力达到50 GPa时，合金发生了广泛的非晶化。有趣的是，非晶化只发生在卸载过程中。在加载期间或仍然在高压下没有看到相变。低温和高温拉曼光谱研究表明，非晶B_4 C由碳芳香环和B11 C二十面体组成。B_4C的非晶化与C-B-C链的破坏和sp2碳团簇的形成有关。B_4C的这种无序结构和较弱的碳sp_2键被认为是导致其在高压下剪切强度降低的原因。用从头计算方法研究了B_4C分子链结构的可能多型性。的 ...更多信息发现B-C-B链结构比其他多型体具有最低的能量。该结构通过Cs校正的高分辨扫描透射电子显微镜（点-点分辨率优于1.0埃）进行了实验证实。除准静态研究外，在冲击载荷碎片和划痕碎片中也观察到B_4C的非晶化。在冲击压力约为40 GPa的冲击波碎片中，存在大量的非晶相和纳米晶颗粒。非晶相和纳米晶相的组成与结晶碳化硼相同，表明在冲击载荷期间发生多晶型转变。在准静态和动态加载条件下对B_4C非晶化的观察表明，高压是B_4C弹性失稳的主要原因，卸载过程中高压引起的不可逆高弹性变形是B_4C非晶化的主要原因。少