Ni-Fe-Ga-Co磁致形状记忆合金超弹性行为及磁驱相变研究

发布时间：2018-03-15 03:06

本文选题：磁致形状记忆合金　切入点：Ni-Fe-Ga-Co　出处：《北京理工大学》2016年博士论文　论文类型：学位论文

【摘要】：磁致形状记忆合金是一种集大应变输出和磁控快速响应于一体的新型智能材料,有望成为首选的驱动器材料,其中由于Ni-Fe-Ga合金具有强的磁晶各向异性能和热加工性能优异等优点,成为了磁致形状记忆合金研究的热点之一。本文采用真空电弧熔炼和吸铸的方法制备了不同Co浓度Ni55-xFe18Ga27Cox合金样品(x=5.5,5.7,6,6.5,9,10,12),利用光学悬浮区炉对其中四个成分的合金制备了单晶样品,其Co浓度为x=5.5,5.7,6,6.5,对合金的晶体结构、相变行为、磁学性能、磁致应变以及超弹性行为进行了系统研究,同时研究了B和Cr元素的添加对Ni-Fe-Ga-Co合金相变行为和机械性能的影响。本文依据实验数据,建立了Ni55-xFe18Ga27Cox合金随Co含量变化的相图,研究发现:在Ni55-x Fe18Ga27Cox合金体系中,Co含量x=9,10的合金在降温过程中发生马氏体相变,低温相为单一的非调制马氏体结构;Co含量x=5.5-6.5区域,合金的晶体结构、相变行为以及力学行为对合金成分变化非常敏感,发生马氏体相变时生成亚稳态的斑驳结构(Mottled Structure);Co含量x=12的合金为应变玻璃态,降温过程中没有马氏体相变发生。通过原位中子衍射实验对Ni46Fe18Ga27Co9和Ni45Fe18Ga27Co10合金的晶体结构和相变进行了研究,结果表明两种合金具有相同的晶体结构,高温相为立方L21 Heusler奥氏体结构,低温相为L10非调制马氏体结构,合金中没有发生中间马氏体相变。对Ni46Fe18Ga27Co9合金进行单轴压缩原位中子衍射实验,发现合金在室温下表现为超弹性,当外加应力达到200MPa时,表现出了应力诱发马氏体相变行为。对成分差异仅为0.3%的Co浓度为x=5.7和6的合金的微观结构、相变行为和力学行为进行了研究分析,并对x=6的合金的磁学性能和磁致应变进行了研究。Co浓度为x=5.7和6的合金在室温下为结构不同的预马氏体相,在马氏体相变过程中两种合金都生产了以超点阵衍射斑点为特征的马氏体相,超点阵对应的结构称之为斑驳结构,两种合金的斑驳结构对应的超点阵衍射花样不相同,该结构为亚稳态,x=5.7的合金在133K时小部分斑驳结构转变为稳态的7层调制马氏体结构,x=6的合金在170K时斑驳结构转变为相对稳定的两相共存结构(非调制和7层调制马氏体结构共存);在co6合金为两相共存态时(150k)施加应力,合金随着应力的增加发生了两次相转变和一次变体选择,转变顺序为:(i)7层调制马氏体结构转变为非调制马氏体结构;(ii)非调制马氏体结构发生变体选择;(iii)部分非调制马氏体结构转变成为4层调制马氏体结构。通过力学实验对x=5.7和6的单晶在不同温度下的应力-应变特征进行了研究,实验结果表明在马氏体相变开始温度以上,x=5.7和6的单晶的屈服应力平台随温度的下降而减小,相同温度下x=5.7的合金的屈服应力小于x=6的合金,而在马氏体相变开始温度以下,x=5.7和6的合金单晶的屈服应力平台随温度的下降而升高,在243k时,x=5.7和6的合金的屈服应力最小,分别为20mpa和5.5mpa。相对于x=5.7的单晶,x=6的单晶屈服应力更小,这意味着该合金更容易在磁场诱发下产生应变,因此对x=6的合金的磁学性能和磁致应变行为进行了研究,实验结果表明,在x=6的合金中,零场冷和场冷的磁化强度-温度(m-t)曲线在低温下发生了严重偏离;磁场(1t)导致了伴随马氏体相变的应变减小;合金对磁场下的相变过程具有记忆效应;在相变过程中合金的磁化强度在恒温时具有时间依赖性;磁场可以诱发合金产生应变,磁致应变表现出了时间依赖性特征并且随温度的降低而减小。经过分析,本文认为这些特性是由于磁场诱发亚稳态的斑驳结构向稳态非调制马氏体结构转变导致的。此外,通过原位高能x射线衍射实验对co含量相差1%的x=5.5和6.5的合金的微观结构和相变行为进行了初步研究,结果表明这两种合金在室温下亦为预马氏体相,x=5.5的合金在150k时奥氏体未能全部转变为马氏体,为非调制马氏体、调制马氏体和残余奥氏体共存,而x=6.5合金在150k时奥氏体转变完全,为非调制马氏体和调制马氏体共存。利用中子衍射和高能x射线技术原位研究了应变玻璃态ni43fe18ga27co12合金在单轴压缩过程中的超弹性行为,揭示了该合金准线性超弹性行为的物理机制。研究发现在应力诱发马氏体相变前弹性模量发生了软化,该现象与温度诱发预马氏体相变表现出来了的特征相似。此外,在弹性阶段衍射峰宽随应力的增加持续宽化,通过williamson-hall分析方法发现衍射峰宽化是由晶粒内部应力场的短程波动造成的,我们认为受限马氏体相变合金中的弹性模量具有空间异质性。在ni46-xfe18ga27co9bx(at.%,x=0,0.1,0.5)合金中用b元素替代部分ni元素,合金的延伸率和抗压强度同时得到了提高,其相变温度随b含量的增加而降低。在ni46-xfe18ga27co9crx合金中用0.5%的cr替代ni元素,适当的热处理工艺可使得晶粒异常长大,晶粒尺寸可达到2mm,这为单晶的制备提供了新的思路,同时Cr元素的添加使合金的屈服强度增大。
[Abstract]:Magnetic shape memory alloy is a new smart material master strain output and magnetron rapid response in one, is expected to become the preferred drive material, because the Ni-Fe-Ga alloy has the magnetocrystalline anisotropy and thermal processing performance of the outstanding advantages, has become one of the hot research of magnetic shape memory alloy. The alloy with different Ni55-xFe18Ga27Cox Co the concentration of samples were prepared by vacuum arc melting and suction casting method of the system (x=5.5,5.7,6,6.5,9,10,12), of which four components alloy prepared single crystal samples using optical floating zone furnace, the Co concentration is x=5.5,5.7,6,6.5, the crystal structure of the alloy, phase transition, magnetic properties, magnetic field induced strain and super elastic behavior were studied at the same time, the influence of adding of B and Cr elements on the phase behavior and mechanical properties of Ni-Fe-Ga-Co alloys. On the basis of experimental data, construction The study found that Ni55-xFe18Ga27Cox alloy phase diagram, the vertical change with the Co content in Ni55-x Fe18Ga27Cox alloy system, the content of Co x=9,10 alloy martensite transformation during the cooling process, the low temperature phase is non modulated martensite structure is single; the content of Co x=5.5-6.5, and the crystal structure of gold, phase behavior and Mechanical behavior is very sensitive the alloy composition changes, formation of mottled metastable structure occurred during the martensitic transformation of Co alloy (Mottled Structure); x=12 was strain glass state, the cooling process has no martensite transformation. Were studied through in situ neutron diffraction experiment of crystal structure and phase transformation of Ni46Fe18Ga27Co9 alloy and Ni45Fe18Ga27Co10 alloy, the results showed that two the alloy has the same crystal structure, high temperature phase austenite structure of cubic L21 Heusler, low temperature phase is L10 non modulated martensite structure, no alloy Happen in the middle of martensitic transformation. Ni46Fe18Ga27Co9 alloy subjected to uniaxial compression in situ neutron diffraction experiments found that the alloy at room temperature is super elastic, when the applied stress reached 200MPa, showed the stress induced martensitic transformation behavior of components. The difference is only 0.3% of the concentration of Co was x=5.7 and 6 alloys the microstructure, phase transformation behavior and mechanical behavior were studied, and the magnetic properties of x=6 alloy and magnetostrain was studied.Co concentration of x=5.7 and 6 alloys at room temperature for the pre martensitic structure of different phase in martensite transformation process two alloy martensite in production dot matrix diffraction spots for the characteristics of the phase structure of super lattice correspondence called mottled structure superlattice diffraction pattern corresponding to the two kinds of alloy mottled structure is not the same, the structure is metastable, x=5.7 alloy in 133K small spot Barge structure into 7 layer modulated martensite structure, change the mottled structure at 170K x=6 alloy for two-phase relative stable coexistence structure (coexistence and the 7 layer structure of non modulated martensite; coexistence phase modulation) in CO6 alloy (150k) alloy applied stress, with the increase of stress occurred the two phase transition and a variant selection, change order: (I) 7 layer modulated martensite structure into non modulated martensite structure; (II) non modulated martensite structure variant selection; (III) part of the non shift modulated martensite structure become 4 martensitic structure. Through mechanical modulation experimental study on x=5.7 and 6 single crystal under different temperature stress strain characteristics, experimental results show that at the beginning of the martensitic transformation temperature, yield x=5.7 and 6 single crystal stress platform decreases with the decrease of the temperature of the x=5.7 alloy under the same temperature The yield stress of the alloy is less than x=6, while the starting temperature of martensitic transformation in the yield of x=5.7 and 6 alloy single crystal stress platform increases with the decrease of temperature, 243K, x=5.7 and 6 of the yield stress of the alloy is smallest, respectively 20MPa and 5.5mpa. relative to the x=5.7 crystal, x=6 crystal. Less stress, which means that the alloy is more prone to strain induced by magnetic field, so the magnetic properties of x=6 alloy and magnetostrictive behavior were studied. The experimental results show that in x=6 alloy, zero field cooling and field cooling magnetization temperature (M-T) curve has a serious deviation in low temperature; magnetic field (1t) led to a strain with martensitic transformation process of alloy decreases; magnetic field has memory effect; magnetization of alloy in the process of phase transformation with time dependence in constant magnetic field can induce alloy strain, The magnetostrictive strain showed a time dependent feature and decreases with the decreasing of temperature. After analysis, this paper argues that these properties are due to magnetic field induced metastable mottled structure leads to the change in non steady state modulated martensite structure. In addition, phase transformation behavior and microstructure by in situ high-energy X ray diffraction experiments on the content of CO is 1% x=5.5 and 6.5 alloys were studied. The results showed that the two kinds of alloy at room temperature is also pre martensitic phase, x=5.5 alloy austenite in 150k can not be transformed into martensite, non modulated martensite, coexisting modulated martensite and residual austenite, and x=6.5 alloy in 150k austenite change completely, coexistence is non modulated martensite and martensite. Modulated by neutron diffraction and high energy X ray technique in situ study of strain glass state of ni43fe18ga27co12 alloy under uniaxial compression super Elastic behavior, reveals the physical mechanism of the quasi linear superelasticity alloy. Study found that the stress induced martensitic transformation before the elastic modulus soften, characteristics of the phenomenon of temperature induced martensitic transformation pre show similar. In addition, with the increasing stress of continuous broadening in the elastic phase diffraction peak width and found that the width of diffraction peak is caused by the fluctuation of short grain internal stress field by Williamson-Hall analysis method, we think that the elastic modulus of constrained martensitic alloys has spatial heterogeneity. In ni46-xfe18ga27co9bx (at.%, x=0,0.1,0.5) B alloys to replace part of the Ni element, the elongation of the alloy and the compressive strength at the same time improved, increasing the temperature of phase transition with the content of B decreased by 0.5% cr. Instead of Ni elements in ni46-xfe18ga27co9crx alloy, the appropriate heat treatment process can make the grain of The grain size can be up to 2mm, which provides a new idea for the preparation of single crystal. At the same time, the addition of Cr elements makes the yield strength of the alloy increase.

【学位授予单位】：北京理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG139.6

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