Grain Boundary Sliding and Amorphization are Responsible for the Reverse Hall-Petch Relation in Superhard Nanocrystalline Boron Carbide
Grain Boundary Sliding and Amorphization are Responsible for the Reverse Hall-Petch Relation in Superhard Nanocrystalline Boron Carbide
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DOI：
10.1103/physrevlett.121.145504
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发表时间：
2018-10-04
影响因子：
8.6
通讯作者：
An, Qi
中科院分区：
文献类型：
--
作者：
Guo, Dezhou;Song, Shuangxi;An, Qi
最近在纳米晶陶瓷中观察到的霍尔-佩奇逆关系为传统脆性陶瓷提供了一种可能的途径，即通过纳米尺寸效应来提高延展性，就像纳米晶金属和合金一样。然而，纳米晶陶瓷的潜在变形机制还没有很好地建立起来。在这里，我们结合反应分子动力学(RMD)模拟和实验透射电子显微镜来确定纳米碳化硼(B4C)的原子级形变机制。我们对晶界尺寸从4.84(135050个原子)到14.64 nm(3702861个原子)的三种晶界模型的有限剪切变形进行了大规模(多达3 700000个原子)REAxff RMD模拟。在纳米晶B4C中，我们发现了一个反向的Hall-Petch关系，该关系的变形机制主要是晶界滑移。这种GB滑移导致在预畸变的二十面体GB区形成非晶带，并在非晶带内引发空化。通过在压痕实验中观察到的晶间非晶态Gb相的压痕实验，验证了模拟结果的正确性。这些理论和实验结果从原子角度解释了晶界对纳米陶瓷变形行为的影响，解释了反向的Hall-Petch关系。
The recent observation of the reverse Hall-Petch relation in nanocrystallinc ceramics offers a possible pathway to achieve enhanced ductility for traditional brittle ceramics via the nanosize effect, just as nanocrystalline metals and alloys. However, the underlying deformation mechanisms of nanocrystalline ceramics have not been well established. Here we combine reactive molecular dynamics (RMD) simulations and experimental transmission electron microscopy to determine the atomic level deformation mechanisms of nanocrystalline boron carbide (B4C). We performed large-scale (up to similar to 3 700000 atoms) REAxFF RMD simulations on finite shear deformation of three models of grain boundaries with grain sizes from 4.84 (135 050 atoms) to 14.64 nm (3 702 861 atoms). We found a reverse Hall-Petch relationship in nanocrystallinc B4C in which the deformation mechanism is dominated by the grain boundary (GB) sliding. This GB sliding leads to the amorphous band formation at predistorted icosahedral GB regions with initiation of cavitation within the amorphous bands. Our simulation results are validated by the experimental observations of an intergranular amorphous GB phase due to GBs sliding under indentation experiments. These theoretical and experimental results provide an atomistic explanation for the influence of GBs on the deformation behavior of nanocrystalline ceramics, explaining the reverse Hall-Petch relation.