Mechanical characterization of boron carbide single crystals
Mechanical characterization of boron carbide single crystals
复制标题
DOI：
10.1111/jace.18065
复制
发表时间：
2021-08
影响因子：
3.9
通讯作者：
A. Zare;M. He;Michael Straker;M. Chandrashekhare;M. Spencer;K. Hemker;J. McCauley;K. Ramesh
中科院分区：
文献类型：
--
作者：
A. Zare;M. He;Michael Straker;M. Chandrashekhare;M. Spencer;K. Hemker;J. McCauley;K. Ramesh
通过纳米压痕实验，研究了碳化硼力学响应的面外各向异性。对于单晶的每个方向，通过监测晶体表面和Berkovich压头尖端之间的相对旋转，还研究了压痕模量和硬度在平面内的变化。压痕模量具有显著的面外各向异性，最高和最低值相差约80 GPa。在压痕硬度中也观察到较小但可测量的面外各向异性。另一方面，数据的散射和压头尖端的几何缺陷显著影响了平面内各向异性。对压痕突入事件的研究表明，在第一次突入之前，变形完全是弹性的。此外，准塑性流动沿单晶取向被发现比其他测试取向更为均匀。对于选定的压痕，横截面透射电子显微镜（TEM）显示，压痕区域形成了晶格旋转形式的准塑性区和各种微观结构缺陷。准塑性区随压痕深度的增加而增大。透射电镜观察还表明，晶体滑移是准塑性的潜在机制，是最终导致开裂和断裂的非晶带形成的前兆。提出的破坏机制为校正碳化硼破坏的本构计算模型提供了有价值的见解。
Out‐of‐plane anisotropy in the mechanical response of boron carbide was studied by performing nanoindentation experiments on four specific crystallographic orientations of single crystals, that is, , , , and . For each orientation of the single crystals, in‐plane variations of indentation modulus and hardness were also studied by monitoring the relative rotation between the crystal surface and a Berkovich indenter tip. A significant out‐of‐plane anisotropy in indentation modulus was observed with ~80 GPa difference between the highest and lowest values. A smaller but measurable out‐of‐plane anisotropy in indentation hardness was also observed. In‐plane anisotropy, on the other hand, was found to be significantly influenced by the scatter in the data and geometrical imperfections of the indenter tip. Investigations of indentation pop‐in events suggested that deformation is entirely elastic prior to the first pop‐in. Furthermore, quasi‐plastic flow along the orientation of the single crystals was found to be more homogeneous than the other tested orientations. For select indents, cross‐sectional transmission electron microscopy (TEM) of the indented regions showed formation of a quasi‐plastic zone in the form of lattice rotation and various microstructural defects. The quasi‐plastic zone grew in size with increasing the indentation depth. The TEM observations also suggested the crystal slip to be a potential mechanism of quasi‐plasticity and a precursor for formation of amorphous bands that could eventually lead to cracking and fragmentation. The proposed failure mechanism provides valuable insights for calibrating constitutive computational models of failure in boron carbide.