IMECH-IR  > 非线性力学国家重点实验室
金属/陶瓷界面断裂的微观机制研究
Alternative TitleStudy on the Microscopic Mechanism of Metal/Ceramic Interface Fracture
付雪琼
Thesis Advisor魏悦广 ; 梁立红
2019-12
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype博士
Degree Discipline固体力学
KeywordMetal/ceramic Interface, Interface Fracture, Molecular Simulation, Interface Strength, Misfit Dislocation
Abstract

金属/陶瓷界面的优化设计在新材料、纳微电子器件、化学催化等领域起着重要作用,界面的强韧及断裂失效直接影响相关关键结构、部件的使用寿命。与界面宏观断裂相关的微观原子尺度断裂涉及多种作用力及能量耗散机制的竞争。尽管对金属/陶瓷界面的实验及理论研究已经持续了数十年,仍有很多基本问题还不清楚,如与宏观断裂密切相关的界面微观断裂机制。由于实验手段及势函数的限制,目前从位错运动机理及界面原子相互作用出发研究金属/陶瓷界面微观断裂的报道较少。分子模拟结果与宏观实验结果在界面强度及粘结功方面的巨大差异仍难以逾越。对界面断裂能量机制仍缺乏定量分析。本文针对以上三个关键科学问题,采用分子模拟与理论分析相结合的方法,研究了金属/陶瓷界面在剪切及拉伸载荷作用下的微观断裂机制,通过共格界面与半共格界面的对比分析了界面失配位错的重要作用。主要工作及获得的主要结论如下:

Ag/MgO界面的分子模拟揭示了失配位错网滑移主导的界面剪切机理。位错滑移过程中位错能的变化决定了界面剪应力,位错节点的钉扎作用使位错线沿剪切方向发生明显弯曲现象。平衡界面结构原子应变分析表明位错节点区域应变集中程度最高,剪切过程中位错节点结构转变导致界面剪切强度和位错滑移能垒降低。沿不同方向的剪切模拟结果表明Ag/MgO界面沿失配位错伯氏矢量方向发生剪切破坏的可能性最大,该结论可推广到其他类似金属/陶瓷界面。

通过理想界面与含有失配位错的缺陷界面的对比,系统地分析和讨论了界面剪切强度及拉伸强度的微观机理。Ag/MgO理想界面的剪切破坏伴随着界面原子键的整体断裂。与理想界面相比,缺陷界面的界面剪切强度低了一个数量级,界面粘结功低了两个数量级,界面剪切行为更连续。采用基于界面势函数的积分方法得到了与第一原理计算结果一致的理想界面拉伸强度及粘结功。对Ag/MgO界面拉伸断裂过程的分子动力学模拟结果表明金属塑性变形改善了界面接触状态,硬化强度接近理想界面强度。应变率及界面面积增大时界面出现局部微裂纹,造成界面拉伸强度显著降低。

给出了异质界面拉伸灾变破坏过程的弹性模型,该模型成功刻画了界面破坏灾变点及界面断裂的尺寸效应。发现厚模型系统损伤率快,界面断裂模式趋向于脆性断裂。强界面-软金属组合的金属/陶瓷界面系统,断裂破坏模式与厚模型类似;而弱界面-硬金属组合的金属/陶瓷界面系统则趋向于软化现象显著的韧性断裂模式。与之前含有灾变不稳定性的分子模拟结果不同,采用一种新的边界位移-裂纹面位移混合加载模拟方法成功捕捉到了界面灾变破坏过程,发现理想界面与缺陷界面归一化的界面粘结关系遵循同样的指数变化形式。

本文系统地模拟了金属/陶瓷界面剪切及拉伸断裂微观机制,定量分析了界面断裂的能量机制,给出了界面强度及粘结功的关键影响因素。为深入研究金属/陶瓷界面断裂问题及相关界面设计提供理论指导。

Other Abstract

The optimized design of metal/ceramic interfaces plays an important role in fields such as new materials, nano-/micro-electronic devices, chemical catalysis, and so on. The interface strength and toughness, and fracture failure of this interface directly affects the service life of relevant key structures and components. The microscopic interface fracture involves the competition of various forces and energy dissipation mechanisms. Although experimental and theoretical studies on metal/ceramic interfaces have continued for decades, many fundamental problems, such as the interface micro-fracture mechanism responsible for macroscopic fracture, remain unclear. Due to the limitation of experimental methods and interatomic potentials, there are few reports on the microscopic fracture of metal/ceramic interfaces based on dislocation motion and interfacial atomic interaction. The huge difference between the molecular simulation results and the macroscopic experimental results in terms of interface strength and cohesive work is still insurmountable. The interfacial fracture energy mechanism still lacks quantitative analysis. In view of the above three key scientific problems, this dissertation studies the microscopic fracture mechanism of metal/ceramic interfaces under shear and tensile loading by means of molecular simulation and theoretical analysis. Through the comparison between coherent and semi-coherent interfaces, the important role of interfacial misfit dislocation is analyzed. The main work and conclusions are as follows:

Molecular simulations of the Ag/MgO interface reveal the shear mechanism dominated by the gliding motion of misfit dislocation network. The interface shear stress is determined by the change of dislocation energy during dislocation gliding, and the pinning effect of dislocation node causes the dislocation lines to bend significantly along the shear direction. The atomic strain analysis of the equilibrium interface structure shows that the strain concentration in the dislocation node region is the highest, and the interface shear strength and energy barrier of dislocation motion are reduced due to the structural transformation of dislocation node during shearing. Simulation results in different shear directions show that the Ag/MgO interface is most likely to undergo shear failure along the direction of Burger’s vector, and this conclusion can be extended to other similar metal/ceramic interfaces.

The microscopic mechanism of interfacial shear strength and tensile strength is discussed by comparing the ideal interfaces with the defect interfaces containing misfit dislocations. The shear failure of ideal Ag/MgO interface is accompanied with the overall fracture of interfacial atomic bonds. Compared with ideal interface, the shear strength of the defect interface is one order of magnitude lower, the interface cohesive work is two orders of magnitude lower, and the interface shear behavior is more continuous. The ideal interface tensile strength and cohesive work obtained by the integration method based on interface potentials agree with ab initio calculation results. Molecular dynamics simulations of the tensile fracture process of Ag/MgO interface show the plastic deformation of metal improves the interface contact state, and the hardening strength is close to the ideal interface strength. When the strain rate and interface area increase, local microcracks appear at the interface, resulting in a significant decrease in the interface tensile strength.

The elastic model of the tensile catastrophic failure process of heterogeneous interface is presented. This model successfully characterizes the interface catastrophe point and the size effect of interface fracture. It is found that the thick model has a high damage rate and the interface fracture mode tends to be brittle. The fracture failure mode of metal/ceramic interface system with strong interface and soft metal is similar to that of thick model; while the weak interface - hard metal interface system tends to ductile fracture with significant soften phenomenon. Different from the previous molecular simulation results with catastrophic instability, a new boundary displacement-crack displacement hybrid loading simulation method was used to capture the interface catastrophic failure process. It is found that the normalized interface cohesive relation of both ideal interfaces and defect interfaces follow the same exponential function.

In this dissertation, the microscopic mechanism of shear and tensile fracture of metal/ceramic interface is simulated systematically. The energy mechanism of interface fracture is quantitatively analyzed, and the key influencing factors of interface strength and cohesive work are given. It provides theoretical guidance for in-depth study on metal/ceramic interface fracture and related interface design.

Call NumberPhd2019-032
Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/80728
Collection非线性力学国家重点实验室
Recommended Citation
GB/T 7714
付雪琼. 金属/陶瓷界面断裂的微观机制研究[D]. 北京. 中国科学院大学,2019.
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