【作者】 王振华；

【导师】 郭二军；

【作者基本信息】 哈尔滨理工大学 ， 材料学， 2019， 博士

【摘要】 Ni-Mn-Sn磁驱动形状记忆合金薄膜具有响应频率高、输出应力大和磁热效应明显等优点,因而被广泛关注,但是薄膜制备过程中易受到衬底束缚,导致晶化温度较高,限制了其在MEMS领域中的应用。本文采用磁控溅射技术制备了Ni-Mn-Sn无约束形状记忆合金薄膜,解决了衬底对薄膜束缚的影响,研究了Ni-Mn-Sn薄膜的晶化行为,获得了合金的MEAM势函数参数,为薄膜固态相变研究提供了参考依据。论文研究了溅射工艺对薄膜表面形貌及化学成分的影响规律;通过X射线衍射分析、原子力显微镜观察、示差扫描量热法（DSC）和振动样品磁强计（VSM）等方法系统研究了薄膜的晶化行为、马氏体相变和磁性能;阐明了Co掺杂对薄膜的相组成和晶化行为的影响规律;采用第一性原理辅助构建Ni-Mn-Sn合金的势函数,并通过修正嵌入原子方法对Ni-Mn-Sn合金的势函数进行修正,给出一种适用于Ni-Mn-Sn合金的MEAM势函数参数。在此的基础上,研究了升温速率对Ni-Mn-Sn合金晶化行为的影响规律,揭示了升温速率对薄膜晶化形核的影响机制。研究表明,磁控溅射工艺对Ni-Mn-Sn无约束薄膜的化学成分及表面粗糙度有显著影响。溅射薄膜的表面呈现随机柱状颗粒,并且柱状颗粒密度随着Ar工作压强和溅射功率的增大而增加,近邻的柱状颗粒逐渐合并生长,形成不规则的岛状颗粒。当溅射功率为100 W时,随着Ar工作压强的增大,合金薄膜中Ni含量小幅减少,Sn含量小幅增加,而Mn含量几乎保持不变。当Ar工作压力为0.15 Pa时,Ni和Mn的含量随着溅射功率的增大而减少,但Sn含量小幅增加。非等温晶化试验结果表明,升温速率对Ni-Mn-Sn无约束薄膜的晶化开始温度（T_x）和峰值温度（T_p）影响显著。非晶薄膜的T_x和T_p随升温速率的增大而升高,薄膜在低温区放出能量的时间随之减少,导致薄膜a阶段的形核过程随着升温速率的增大而减小;另外,分别用Kissinger峰值法和Ozawa峰值法计算出的晶化表观激活能分别为195.63±5.2 kJ/mol和195.66±4.98 kJ/mol,两种计算方法得到结果基本一致。等温晶化试验结果表明,晶化温度对Ni-Mn-Sn无约束薄膜晶化的形核和核长大方式影响显著。随着晶化温度的升高,Ni-Mn-Sn无约束薄膜的晶化孕育时间缩短,薄膜晶化生长方式随之改变。当晶化温度为520 K时,Avrami指数n=1,薄膜呈现出受扩散控制的预存晶核生长。当晶化温度>520 K时,Avrami指数n=1.5,薄膜呈现出二维扩散控制的晶核生长。试验结果表明,Co掺杂对Ni-Mn-Sn薄膜起到了细化晶粒的效果,晶粒尺寸减小,薄膜晶格畸变程度随着Co含量的增加而增大,薄膜的晶化表观激活能、T_x和T_p均随之增大。随着Co掺杂含量的增大,Ni-Mn-Sn薄膜均表现出受界面能控制的二维扩散式生长特征。模拟结果表明,基于第一性原理和LAMMPS模拟构建的MEAM势函数,能很好的反映Ni-Mn-Sn薄膜中原子间的相互作用关系。当升温速率为0.1 K/ps时,Ni-Mn-Sn薄膜在300⁶00 K温度区间内出现一放热峰,薄膜晶化温度T_p为523 K,模拟结果与试验结果相吻合,表明结晶行为具有明显的动力学性质。晶化试验结果表明,晶化温度对Ni-Mn-Sn无约束薄膜晶体结构、马氏体相变和磁性能影响显著。晶化后的Ni-Mn-Sn薄膜均具有典型的奥氏体L2₁结构,其XRD衍射峰A（220）和A（422）强度随着晶化温度的升高而增大,晶粒尺寸随之增大,并且马氏体相变温度和磁性能随晶化温度升高而升高,薄膜的M-T曲线可以观察到顺磁-铁磁-反铁磁的变化过过程。更多还原

【Abstract】 Ni-Mn-Sn magnetic shape memory alloys thin films have attracted considerable attention due to their high response frequency,high output stress and obvious magnetic thermal effect.However,the high crystallization temperature and substrate constraints of Ni-Mn-Sn thin flmes greatly limit their development and application in MEMS.In this thesis,the free-standing Ni-Mn-Sn thin flims have been prepared by magnetron sputtering technique,and the effect of substrate on film binding are solved.The crystallization temperature of free-standing thin films is calculated by crystallization kinetics.The parameters of Modified Embedded Atom Method（MEAM）potential function of Ni-Mn-Sn thin films are obtained.It provides a reference for the study of solid phase transition of thin films.The results clarify the effect of sputtering parameters on surface morphology and chemical compositions of free-standing Ni-Mn-Sn thin films,revealing the physical mechanism of composition variations.At the same time,crystallization behavior,martensitic transformation and magnetic performance of thin films have been systematically investigated by mean of XRD,AFM,DSC and VSM,respectively.The effects of Co doping on phase composition and crystallization behavior of thin films are investigated.The potential function of Ni-Mn-Sn thin films is constructed by first principles and is modified by Modified Embedded Atom Method（MEAM）.Based on the potential function of MEAM,the effect of heating rate on the crystallization behavior of free-standing Ni-Mn-Sn alloy is studied,revealing the mechanism of crystallization and nucleation of Ni-Mn-Sn thin films.It is found that process parameters of magnetron sputtering technique have remarkable influence on surface roughness and chemical compositions of free-standing Ni-Mn-Sn thin films.The random columnar particles are observed on the surface of the sputtered films,and the density of columnar particles increases with the increasing Ar working pressure and sputtering power.Neighboring columnar particles are gradually merged,and irregular island particles are formed on the surface of the thin films.When the sputtering power is 100 W,the Ni content slightly decreases and the Sn content increases with increasing Ar working pressure,whereas Mn content does not change with the increasing Ar working pressure.When the Ar working pressure is 0.15 pa,the content of Ni and Mn is decreased gradually with the increasing sputtering power,and the Sn content slightly increases with the increasing sputtering power.The results show that the heating rate of non-isothermal crystallization has an important influence on the T_x and T_p for the crystallization of free-standing Ni-Mn-Sn thin films.The T_x and T_p of amorphous thin films increase with the increasing heating rate.Resulting in the fact that the release energy time of the films is decreased in the low temperature zone.The start of nucleation process of thin film decreases with the increasing heating rate.The activation energy of free-standing Ni-Mn-Sn thin films are calculated by Kissinger method and Ozawa method,and the value of activation energy is 195.63±5.2 kJ/mol and 195.66±4.98 kJ/mol,respectively.Two methods of results are obtained basically consistent.The results show that the isothermal temperature of crystallization has an important influence on the nucleation and nucleus growth of free-standing Ni-Mn-Sn thin films.With the increase of crystallization temperature,the incubation time of crystallization of free-standing Ni-Mn-Sn thin films is shortened,and the growth mode of crystallization of thin films is changed with the increasing crystallization temperature.When the crystallization temperature of thin film is 520 K,the value of Avrami exponent is 1.The crystallization process of thin film is pre-existing nuclei growth by diffusion-controlled.When the crystallization temperature of thin film is higher than 520 K,the value of Avrami exponent is 1.5.The value of n ranges from 1 to 1.5 for the thin films indicating that the crystallization process are two dimension diffusion-controlled growths.It is found that the effect of Co doping on refining grain of free-standing Ni-Mn-Sn thin films.When the thin films are crystallized,the number of grain boundary of thin films increases with the increasing Co content.The grain growth of thin films is affected by interfacial energy.Thus,the crystal activation energy,T_x and T_p of free-standing Ni-Mn-Sn-Co thin films increase with the increasing Co content.Meanwhile,the lattice distortion of thin films increases with the increasing Co content.The growth of the free-standing Ni-Mn-Sn thin films is controlled by the interface energy,and the film grows in a two-dimensional diffusion mode.The simulation results that the potential function of MEAM of Ni-Mn-Sn thin films is carried out by first-principles and LAMMPS simulation accordingly.The potential function of MEAM can be reflected the interaction between atoms in Ni-Mn-Sn films.When the heating rate is 0.1k/ps,the curves of DSC have a single exothermic peak related to the crystallization process in the range of300⁶00 K.The T_p is 523 K,indicating that the simulation results are consistent with the experimental results.This phenomenon indicates that the crystallization behaviors in a marked kinetic nature.The experimental results indicate that crystallization temperature has influence on the crystal structure,martensitic transformation and magnetic properties of free-standing Ni-Mn-Sn thin films.As demonstrated by the XRD profile,the pattern of Ni-Mn-Sn free-standing thin films is a cubic single-phase austenite phase（L2₁）.All the peaks of freestanding alloy thin films increase with the increasing crystallization temperature,and the relative intensity of peaks A（220）and A（422）enhance gradually.The grain size,martensitic transformation temperature and magnetic energy increase with the crystallization temperature increasing for thin films.Upon temperature variation,undergo a change of magnetization typical for the first order martensitic transition and at higher temperatures a second order ferromagnetic-paramagnetic transition at Curie temperature of austenite.更多还原