Ni-Ti基合金薄膜相变行为及其力学特性研究

发布时间：2018-03-18 12:39

本文选题：Ni-Ti基薄膜　切入点：沉积温度　出处：《南京大学》2015年博士论文　论文类型：学位论文

【摘要】：Ni-Ti基合金薄膜由于具有优异的形状记忆性和伪弹性等特性被广泛地应用于微机电系统(MEMS)中。随着微电子器件向微型化的方向不断发展,薄膜的特征尺寸(如薄膜厚度、晶粒尺寸等)持续减小,其相变行为和力学特性表现出强烈的尺寸依赖性,甚至出现反常的物理与力学特性,导致无法正确预测微电子器件的工作可靠性与寿命；另一方面,Ni-Ti基合金薄膜的相变行为和力学特性与组元、成分和热处理工艺密切相关。因此,研究Ni-Ti基合金薄膜的特征尺寸、组元等对其相变行为和力学特性的影响,对设计和制备具有响应快、相变温度高和力学性能优异的形状记忆合金薄膜具有重要的科学意义。基于以上考虑,本文采用直流磁控溅射法,通过改变沉积温度和退火温度制备了一系列的三元Ni-Ti-Al薄膜和Ti/Ni多层膜。利用能谱分析、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化学组成、相组成和微观结构；利用四探针电阻测试法研究了薄膜的相变行为；利用纳米压痕法表征薄膜的伪弹性、硬度、模量和应变速率敏感性等力学特性；研究了薄膜特征尺寸(晶粒尺寸、多层膜的调制周期)、压痕深度、析出相和应变速率等对Ni-Ti基合金薄膜相变行为和力学性能的影响及其作用机制。主要结论如下：(1)制备了具有高伪弹性的L21相-N143Ti3gAl19合金薄膜,发现薄膜的伪弹性和硬度表现出明显的尺寸依赖性。其伪弹性随晶粒尺寸和压入深度的减小而逐渐增高,在晶粒尺寸最小为12 nm和压痕深度最小为30nm时达到最高值92.7%。薄膜的伪弹性随晶粒尺寸的减小而增加的原因是应力诱导的马氏体转变所需的弹性应变和临界应力随晶粒尺寸的减小而增加。随着晶粒尺寸从28nm减小至12 nm,薄膜的硬度先增加后减小,在晶粒尺寸为16 nm时达到最大值13.8 GPa,在晶粒尺寸≤16 nm时,薄膜硬度随晶粒尺寸展现出反Hall-Petch效应。(2)发现富Ni析出相的生长能明显提高Ni-Ti-Al合金薄膜的马氏体相变温度和硬度、减小其相变滞后。不同沉积温度制备的Ni49.7Ti45.3Al5薄膜的马氏体相变开始温度均高于室温,随着富Ni析出相的生长,马氏体相变温度逐渐升高、马氏体相变滞后温度减小了一半、二阶的B2→R→B19'相变路径转变为了B2→B19'一阶相变。随着富Ni析出相的生长,Ni44Ti32Al24合金薄膜的马氏体相变温度由-37.5℃增加到-33.7℃,且相变展现出零相变滞后。由于富Ni析出相的强化作用,Ni49.7Ti45.3Al5和Ni44Ti32Al24合金薄膜的硬度随着富Ni析出相的生长分别增加了12.8%和22%。(3)通过Ti/Ni多层膜设计,选用原位加热沉积和退火处理相结合,制备出超高硬度的Ni-Ti合金薄膜,这证实了最初引入界面实现性能强化的设想。退火态Ti/Ni多层膜的合金化和力学性能都明显依赖于薄膜的调制周期,随着调制周期减小至5.4 nm,多层膜实现了充分合金化,层界面消失。沉积态和退火态的Ti/Ni多层膜的硬度都随调制周期的减小先增大后减小,均在调制周期为5.4 nm时达到最大值。随着压入深度的增加,调制周期为13.5和27 nm的多层膜的硬度出现异常软化,可以发现其载荷-位移曲线上产生了明显的"pop-in"和载荷急剧下降现象。"pop-in"和载荷下降现象由应力诱导的马氏体相变引起,同时诱导马氏体相变的临界载荷随着调制周期的减小而增加。(4)研究了应变速率对退火态Ti/Ni多层膜力学性能和相变行为的影响。发现调制周期为13.5和27 nm的退火态Ti/Ni多层膜的硬度具有负的应变速率敏感性,而其他调制周期的多层膜的硬度不随应变速率变化。应力诱导的马氏体相变是调制周期为13.5和27 nm的退火态Ti/Ni多层膜的硬度出现负的应变速率敏感性的内在原因。另外,发现引起马氏体相变的临界载荷随应变速率的加快而逐渐增大,这是由于应变速率越快,更多的相变(奥氏体-马氏体相变)潜热来不及消散,这有利于奥氏体相保持稳定,导致驱动相变所需的应力变大。
[Abstract]:Ni-Ti based alloy film with shape memory and pseudo elastic properties excellent is widely used in microelectromechanical systems (MEMS). With the continuous development of microelectronic devices to miniaturization, the feature size of films (such as film thickness, grain size, etc.) continued to decrease and the phase behavior and mechanical properties a strong dependence on the size of the physical and mechanical properties, and even lead to abnormal work, can not correctly predict the reliability and life of microelectronic devices; on the other hand, Ni-Ti based alloy thin film phase transition behavior and mechanical properties of the element composition and heat treatment process are closely related. Therefore, the feature size of Ni-Ti based alloy thin films so, component effect on the phase behavior and mechanical properties, the design and preparation of fast response, high phase transition temperature and excellent mechanical properties of shape memory alloy film has an important branch Significance. Based on the above considerations, this paper by DC magnetron sputtering by changing the deposition temperature and annealing temperature to prepare a series of three Ni-Ti-Al films and Ti/Ni multilayers. The energy spectrum analysis, chemical composition of X ray diffraction, scanning electron microscopy and transmission electron microscopy were used to characterize the phase composition and film. Micro structure; phase behavior of thin films are studied by using four probe method; using pseudo elasticity, by nanoindentation hardness, modulus and mechanical properties of strain rate sensitivity; studied feature size (the modulation period of multilayers grain size), indentation depth, precipitation and strain rate, etc. the phase transition behavior of Ni-Ti based alloys and the mechanical properties and mechanism. The main conclusions are as follows: (1) with high pseudo elastic L21 phase -N143Ti3gAl19 alloy thin film was prepared and found thin The film of the pseudo elasticity and hardness show obvious size dependence. The pseudo elasticity with the grain size and the penetration depth decreases gradually increased, reached the highest value of pseudo elastic 92.7%. films in the minimum grain size of 12 nm minimum and indentation depth is 30nm with the decrease of grain size and the reasons for the increase of martensite change of stress induced required elastic strain and the critical stress increases with the decrease of the grain size. The grain size decreases from 28nm to 12 nm, the hardness of the film increased first and then decreased, the grain size of 16 nm reaches the maximum value of 13.8 GPa in grain size less than 16 nm, the hardness of the films as the grain size showed anti Hall-Petch effect. (2) found that Ni rich precipitates can significantly improve the growth of Ni-Ti-Al alloy films on martensitic transformation temperature and hardness, reduce the hysteresis. Ni49.7Ti45.3Al5 thin films prepared by different deposition temperature The starting temperature of martensitic transformation was higher than that at room temperature, with the growth of Ni rich precipitates, the martensitic transformation temperature increased gradually, the martensitic transformation temperature hysteresis is reduced by half, B19'transition path of order two B2 - R - B2 - B19' transformation to a first-order phase transition. With rich Ni precipitates the growth of martensite the phase transition temperature of Ni44Ti32Al24 alloy film increased from -37.5 DEG to -33.7 DEG, and the phase change show zero hysteresis. Due to the strengthening effect of Ni rich precipitates, Ni49.7Ti45.3Al5 and Ni44Ti32Al24 alloy films with hardness of Ni rich precipitates growth were increased by 12.8% and 22%. (3) through the design of Ti/Ni multilayer film, using in situ heating deposition and annealing treatment, preparation of ultrafine Ni-Ti alloy films with high hardness, which confirmed the initial introduction of the interface to realize performance enhancement. And the mechanical properties of the alloy annealed Ti/Ni films have obvious dependence The modulation period on film, with the modulation period is reduced to 5.4 nm, multilayer achieved full alloying layer interface disappeared. Ti/Ni multilayer films deposited and annealed hardness with the decrease of modulation period increased first and then decreased in the modulation period is reached the maximum value of 5.4 nm. With the increase of pressure the depth of the modulation period of multilayers of 13.5 and 27 nm the hardness of abnormal softening, can be found that the load displacement curve has obvious "pop-in" and a sharp decline in load phenomenon. "Pop-in" decreases and the load phenomenon caused by the martensite transformation induced by stress, critical load and induced martensitic transformation increased with the decrease of modulation period. (4) studied the effect of strain rate on the properties and phase behavior of annealed Ti/Ni films annealed Ti/Ni mechanics. Found that multilayer modulation period is 13.5 and 27 nm hardness has a negative The strain rate sensitivity, and other periodic multilayer film hardness with strain rate change. The martensitic transformation is induced by the annealed Ti/Ni multilayer modulation period of 13.5 and 27 nm, the hardness of the negative strain rate sensitivity of the intrinsic reason. In addition, that leads to the critical load of martensite phase transition when the strain rate is accelerated gradually increases. This is due to the strain rate is faster, more phase (austenite martensite transformation) to latent heat dissipation, which is conducive to maintain the stability of austenite phase, resulting in the stress driven phase transition required larger.

【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.2

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