Yang Shengyao, Zhang Liangchi, Wu Zhonghuai
Laboratory for Precision and Nano Processing Technologies, School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia.
Shenzhen Key Laboratory of Cross-scale Manufacturing Mechanics, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China.
ACS Appl Mater Interfaces. 2021 Sep 1;13(34):41351-41360. doi: 10.1021/acsami.1c12349. Epub 2021 Aug 23.
Potassium dihydrogen phosphate (KDP) is an important nonlinear material due to its excellent physical and optical properties. However, it is also a difficult-to-machine material due to its complex anisotropic microstructure. To better understand the deformation mechanisms under external stresses, this paper aims to carry out systematic nanoindentation simulations using molecular dynamics (MD). To facilitate the structural characterization of KDP, a machine learning-based method was developed. The results showed that the subsurface damage is obviously anisotropic. On the (001) surface, both tetragonal and monoclinic phases appear simultaneously and part of the monoclinic phase transfers to the tetragonal phase. The generated phases close to the surface undergo amorphization and are squeezed out to form pile-ups. On the (100) surface, however, an orthorhombic phase emerges directly from the original structure rather than transforming through the monoclinic phase. No amorphization happens and no pile-ups appear in this case. The first "pop-in" in the load-displacement curve of nanoindentation signified the emergence of phase transformation under the combined hydrostatic and shear stresses. After unloading, the recovery of the deformed KDP is also anisotropic. The maximum recovery takes place when the indentation is on the (100) surface.
磷酸二氢钾（KDP）因其优异的物理和光学性能而成为一种重要的非线性材料。然而，由于其复杂的各向异性微观结构，它也是一种难加工材料。为了更好地理解外部应力作用下的变形机制，本文旨在利用分子动力学（MD）进行系统的纳米压痕模拟。为了便于对KDP进行结构表征，开发了一种基于机器学习的方法。结果表明，亚表面损伤明显具有各向异性。在（001）表面，四方相和单斜相同时出现，部分单斜相转变为四方相。靠近表面生成的相发生非晶化并被挤出形成堆积。然而，在（100）表面，正交相直接从原始结构中出现，而不是通过单斜相转变。在这种情况下，没有发生非晶化，也没有出现堆积。纳米压痕载荷-位移曲线中的第一次“弹出”表示在静水压力和剪切应力共同作用下发生了相变。卸载后，变形KDP的恢复也具有各向异性。当压痕位于（100）表面时，恢复最大。
