Reddy Kolan Madhav, Guo Dezhou, Song Shuangxi, Cheng Chun, Han Jiuhui, Wang Xiaodong, An Qi, Chen Mingwei
State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
Chemical and Materials Engineering Department, University of Nevada, Reno, NV 89557, USA.
Sci Adv. 2021 Feb 17;7(8). doi: 10.1126/sciadv.abc6714. Print 2021 Feb.
The failure of superhard materials is often associated with stress-induced amorphization. However, the underlying mechanisms of the structural evolution remain largely unknown. Here, we report the experimental measurements of the onset of shear amorphization in single-crystal boron carbide by nanoindentation and transmission electron microscopy. We verified that rate-dependent loading discontinuity, i.e., pop-in, in nanoindentation load-displacement curves results from the formation of nanosized amorphous bands via shear amorphization. Stochastic analysis of the pop-in events reveals an exceptionally small activation volume, slow nucleation rate, and lower activation energy of the shear amorphization, suggesting that the high-pressure structural transition is activated and initiated by dislocation nucleation. This dislocation-mediated amorphization has important implications in understanding the failure mechanisms of superhard materials at stresses far below their theoretical strengths.
超硬材料的失效通常与应力诱导非晶化有关。然而，结构演变的潜在机制在很大程度上仍然未知。在此，我们报告了通过纳米压痕和透射电子显微镜对单晶碳化硼中剪切非晶化起始的实验测量。我们证实，纳米压痕载荷-位移曲线中的速率依赖性加载不连续性，即突跳，是由剪切非晶化形成纳米尺寸的非晶带所致。对突跳事件的随机分析揭示了异常小的激活体积、缓慢的成核速率以及较低的剪切非晶化激活能，这表明高压结构转变是由位错成核激活和引发的。这种位错介导的非晶化对于理解超硬材料在远低于其理论强度的应力下的失效机制具有重要意义。
