Mechanism of Strength Enhancement of Ceramics Superlattice Coating Films and Its Application to Design of Microstructure

陶瓷超晶格是一种纳米尺度的异质陶瓷复合层状结构，是制备高性能涂层的重要途径之一。由于超晶格薄膜在特定的层压周期内显示出显著的压痕硬度和耐磨性的增强，因此它有望成为经受重摩擦的涂膜材料。本研究旨在阐明陶瓷超晶格的微观结构与力学性能之间的相关性，为高性能陶瓷涂层的设计提供指导，用分子动力学（MD）方法对TiN/SiO2复合材料的单轴和双轴强度进行了计算机模拟。对电弧离子镀TiN/AlN陶瓷超晶格薄膜的显微压痕实验结果表明，薄膜的硬度随层压周期的增加而增加， 关于我们 通过对第一性原理计算结果的拟合，提出了岩盐结构陶瓷TiN、AlN和ZrN的原子间相互作用势函数。利用原子间相互作用势函数，成功地对超晶格陶瓷及其薄膜的单轴和双轴强度进行了分子动力学模拟，模拟结果表明，在超晶格薄膜中，AlN层和TiN层分别存在残余拉应力和残余压应力。断裂起始强度随着层压周期的减小而减小。在双向加载下，AlN和TiN层分别发生裂纹扩展和塑性变形。而断裂和变形在TiN/AlN界面处停止。超晶格薄膜的叠层周期越长，裂纹扩展的时间越长。这导致了压合周期越长，超晶格薄膜的压痕硬度越低。MD模拟结果表明，压入硬度的提高存在一个最佳的压入时间，MD模拟可以从原理上理解陶瓷超晶格的微观结构与力学性能之间的关系，并为陶瓷超晶格的结构设计提供有用的工具。少

Ceramics superlattice, which has a laminated structure of heterogeneous ceramics combination in nanometer scale, is one of the promising approaches for highly functional coating films. As a superlattice film shows remarkable enhancement in indentation hardness and wear-resistance with a specified laminating period, it is expected to be a material of coating films subjected to heavy friction. However, the mechanism of strength enhancement has not been understood well.In this research, to clarify the correlation between the microstructure and mechanical properties of ceramics superlattice and to establish the guidelines for design of highly functional ceramics coating films, molecular dynamics (MD) computer simulations of uniaxial and biaxial strength testing are carried out on TiN/AIN superlattice films with various laminating periods.Experimental results of microindentation on arc ion-plated TiN/AIN ceramics superlattice films show that the hardness increases as the laminating period d … More ecreases and that the highest hardness enhancement is observed on the film with 2.5 nm laminating period.Interatomic potential functions are proposed for ceramics with rock salt structure, such as TiN, AiN are and ZrN, by the fitting with the results of first- principle calculations. Using the interatomic potential functions, MD simulations of uni- axial and biaxial strength testing of the ceramics and superlattice films composed of the ceramics are carried out successfully.The MD simulations show that residual tensile and compressive stresses are observed in the layers of AIN and TiN, respectively, in the films with superlattice structure. The strength for fracture initiation decreases as the laminating period decreases. Under the biaxial loading, crack extension and plastic deformation occur in the layers of AIN and TiN, respectively. However, the fracture and deformation are stopped on the TiN/AIN interface. The longer the laminating period of superlattice film, the longer the crack extension. This results in the lower indentation hardness on the superlattice film with longer laminating period. The results of the MD simulations suggest that there is an optimum laminating period for highest enhancement of indentation hardness.MD simulation can be an useful tool for clear understanding in principle the correlation between miorostructure and mechanical properties and for structure design of ceramics superlattice. Less