纳米多重孪晶金属薄膜的尺度效应及其力学性能研究

发布时间：2018-06-22 23:56

本文选题：薄膜 + 孪晶　；参考：《南京大学》2015年硕士论文

【摘要】：金属薄膜由于具有优异的综合性能被广泛应用在微机电系统中,其中力学性能直接影响微机电系统的服役寿命。传统的材料强化机制主要是在材料内部引入各种缺陷阻碍位错运动来实现,包括固溶强化、弥散强化和细晶强化等,但这些途径不可避免地会影响材料的塑性形变能力,导致其韧性降低。研究发现,在材料中引入纳米孪晶结构,提高材料强度的同时保证其韧性不受影响,并且发现孪晶的形成表现出很强的尺度依赖性。然而目前关于纳米孪晶的形成机制和尺度效应的研究主要是关于平行孪晶,在实验过程中除平行孪晶以外,经常可以观察到多重孪晶(如二重(即V型孪晶)、三重、四重和五重孪晶),但是对于多重孪晶的形成机制、尺度依赖性及其对材料性能的改善仍然存在着许多争议。基于以上考虑,本文以制备Cu薄膜、Ag薄膜以及Ag/Cu多层膜为研究对象,采用直流磁控溅射法,通过改变退火温度制备了一系列Cu、Ag薄膜以及具有不同调制周期的Ag/Cu多层膜。利用X射线衍射、扫描电子显微镜和透射电子显微镜等方法表征薄膜的微观结构,并利用纳米压痕法表征薄膜的硬度。研究了退火处理后Cu薄膜和Ag薄膜中V型孪晶的尺度效应和形成机制,以及沉积态和退火态Ag/Cu多层膜中力学性能与多重孪晶之间的关系。主要结论如下：1.通过对不同退火温度金属Cu薄膜的研究发现,V型孪晶数量随着晶粒尺寸的减小,先增加后降低,在晶粒尺寸为40m附近达到最大,表现出明显的反晶粒尺寸效应。2.通过对不同退火温度金属Ag薄膜的研究同样发现V型孪晶数量遵从反晶粒尺寸效应,但是由于Ag的层错能非常低,造成与Cu薄膜中V型孪晶的尺度效应存在差异,其峰值晶粒尺寸出现在60 nm左右,且V型孪晶的最大晶粒尺寸(155 nm)大于Cu薄膜(121 nm)。3.从能量角度上提出一种新的多重孪晶形成机制,即V型孪晶是由退火驱动的晶界迁移和晶粒转动协同产生的,并且其形成过程包括形核和增殖两个阶段。4.基于Cu薄膜和Ag薄膜中V型孪晶在临界晶粒尺寸时出现最大密度,设计了一种调制比为2的Ag/Cu多层膜,并对不同调制周期的沉积态和退火态多层膜进行研究,发现沉积态Ag/Cu多层膜的硬度随尺度的变化表现出非单调性,在调制周期为45 nm时硬度达到最大值3.42 GPa。当对调制周期为45 nrn的Ag/Cu多层膜进行100℃退火处理后,其硬度值相比沉积态时进一步提高到3.59 GPa,这是由于退火后Ag/Cu多层膜中出现大量多重孪晶,多重孪晶界可以阻挡不同方向上的不全位错。这为制备超高强度多层膜的设计提供了新思路。
[Abstract]:Metal films have been widely used in microelectromechanical systems because of their excellent comprehensive properties. Mechanical properties directly affect the service life of microelectromechanical systems. The traditional material strengthening mechanism mainly introduces various defects to prevent dislocation motion in the material, including solid solution strengthening, dispersion strengthening and fine grain strengthening, but these are the main reasons. The approach inevitably affects the plastic deformation ability of the material and leads to the reduction of its toughness. It is found that the nano twin structure is introduced in the material, the strength of the material is increased and the toughness is not affected, and the formation of the twins shows a strong scale dependence. However, the formation mechanism and the ruler of the nanocrystalline twins are present. The study of the degree effect is mainly about parallel twins. In addition to parallel twins in the experiment, multiple twins (such as double (V type twins), three weight, four weight and five twins) are often observed. However, there are still many controversies on the formation mechanism of multiple twins, the scale dependence and the improvement of the material properties. Considering the preparation of Cu films, Ag films and Ag/Cu multilayer films, a series of Cu, Ag films and Ag/Cu multilayer films with different modulation periods were prepared by DC magnetron sputtering, and the microscopes of the thin films were characterized by X ray diffraction, scanning electron microscopy and transmission electron microscopy. The microhardness of the thin films was characterized by nano indentation. The scale effect and formation mechanism of V twin in Cu and Ag films after annealing, and the relationship between mechanical properties and multiple twins in the deposited and annealed Ag/Cu multilayer films were investigated. The main conclusions are as follows: 1. through the metal Cu films at different annealing temperatures It is found that the number of V twins increases first and then decreases with the size of grain size, and reaches the maximum in the vicinity of the grain size of 40m, showing an obvious reverse grain size effect..2. also finds that the number of V twins follows the anti grain size effect through the study of different annealing temperature metal Ag thin films, but because the Ag's stacking fault energy is very low The scale effect is different from the V type twin in the Cu film, the peak grain size appears at about 60 nm, and the maximum grain size of the V type twin is greater than that of Cu film (121 nm).3., which is a new multiple twin formation mechanism from the energy point of view, that is, the V twin crystal is produced by annealing driven grain boundary migration and grain rotation. The formation process consists of two stages of nucleation and proliferation, which is based on the maximum density of the V twin in the critical grain size of the V type twins in the.4. and Ag films. A Ag/Cu multilayer film with a modulation ratio of 2 is designed, and the deposition and annealed multilayer films of different modulation periods are studied, and the hardness of the deposited Ag/Cu multilayer films is found. When the modulation period is 45 nm, the hardness reaches the maximum value of 3.42 GPa.. When the Ag/Cu multilayer film with a modulation period of 45 NRN is annealed at 100 C, the hardness value is further increased to 3.59 GPa compared to the deposited state, which is due to a large number of multiple twins and multiple twins in the Ag/ Cu multilayer film after annealing. Grain boundaries can block incomplete dislocations in different directions. This provides a new idea for the design of ultrahigh strength multilayers.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG14;TB383.2

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