分子动力学模拟位错和界面的相互作用

摘要

纳米尺度的金属多层膜在屈服应力、塑性、抗腐蚀性能等方面具有特殊的性能。目前它已被广泛应用于航空航天、机械制造、电子技术、光学工程及计算机工程等各个领域。而在薄膜材料的应用过程中,薄膜的使用寿命和可靠性是人们普遍关注的焦点问题。界面的结合性能是影响多层膜寿命和可靠性的关键指标,而位错和界面的相互作用机理决定着界面的结合性能,即位错和界面的相互作用机理在薄膜的使用寿命和可靠性方面扮演着关键角色。因此对位错和界面的相互作用机理的研究就显得特别有价值和意义。随着高性能计算机的发展,原子模拟已成为材料性能预测与设计方面一种有效的方法。本文用三维分子动力学方法研究了位错和界面的相互作用机理,具体如下:首先,用分子动力学方法研究了侧向拉伸载荷下位错从bcc-Fe/Ni界面的形核和发射过程。弛豫后,在Fe(0 0 1)/Ni(0 0 1)和Fe(0 0 1)/Ni(1 1 1)界面观察到无序的失配位错网络,Fe(0 0 1)/Ni(1 1 0)界面观察到长方形的失配位错网络。研究了晶体取向对Fe/Ni 双层膜拉伸性能的影响。不同取向的对比发现Fe(0 0 1)/Ni(1 1 0)系统的屈服强度最低。和Fe薄膜进行了对比,发现Fe/Ni双层膜系统的塑性高于Fe薄膜的,而屈服强度低于Fe薄膜的。模拟结果显示,界面是位错的发射源,滑移位错从界面的失配位错线形核和发射。同时界面也会阻碍位错运动,随着拉伸的进行,Fe层中越来越多的位错被塞积在界面处,当到达到临界值时,迫使位错穿过Fe/Ni界面,从Fe层到Ni层。在Fe基体中位错主要在{1 0 1}面滑移,而在Ni中主要在{1 1 1}面滑移。

其次,用分子动力学模拟了单轴拉伸载荷下不同扭转角的Cu(001)/Ni(001)界面的结合性能。模拟结果显示,当扭转角小于15.124度时,界面形成方格状的失配位错网络,界面失配位错网络的密度随着扭转角的增加而增加。当扭转角大于

15.124度时,在界面形成面缺陷。模拟发现界面构型对Cu/Ni系统的界面强度有着非常显著的影响。随着扭转角的增加屈服应力首先减小,直到扭转角为5.906度的最小值,然后增加,当其达到扭转角为15.124度的最大值后,又开始减小,最后当扭转角约大于20度,屈服应力几乎趋于一稳定的值。

关键词:分子动力学;界面;滑移位错;失配位错

ABSTRACT

Nanoscale multilayered composites often possess extraordinary mechanical properties in terms of yield stress, ductility, and wear resistant. Now it has been widely used in aerospace, mechanical manufacturing, electronics, optical engineering and computer engineering fields. In the applied process of the thin film materials, people commonly focus on the reliability and service life of the thin films. The binding property between the thin film and the substrate is a key indicator of metallic multilayers’the reliability and service l ife, the interaction mechanisms between dislocations and interfaces dominate the binding properties of the interfaces. Therefore, the interaction mechanism between dislocations and interfaces plays a vital role in the field of the reliability and service life of the thin films.So it is an interesting and valuable thing to understand the interaction mechanisms between dislocations and interfaces. With the development of high-performance computer, atomic simulations have become an effective method in the field of material properties forecast and design. In the present work, we have studied the interaction between dislocations and

interfaces with 3D Molecular Dynamic Simulations.

Firstly, molecular dynamics simulations were carried out to investigate the nucleation and emission of dislocations from an

interface in a bcc-Fe/Ni bilayer subjected to transverse loading. After relaxation, disordered types of dislocations were observed at both Fe(0 0 1)/Ni(0 0 1) and Fe(0 0 1)/Ni(1 1 1) interfaces, and rectangular dislocations types at Fe(0 0 1)/Ni(1 1 0) interface. The orientation