本文選題：磁致形狀記憶合金　切入點：Ni-Fe-Ga-Co　出處：《北京理工大學》2016年博士論文　論文類型：學位論文

【摘要】：磁致形狀記憶合金是一種集大應變輸出和磁控快速響應于一體的新型智能材料,有望成為首選的驅動器材料,其中由于Ni-Fe-Ga合金具有強的磁晶各向異性能和熱加工性能優(yōu)異等優(yōu)點,成為了磁致形狀記憶合金研究的熱點之一。本文采用真空電弧熔煉和吸鑄的方法制備了不同Co濃度Ni55-xFe18Ga27Cox合金樣品(x=5.5,5.7,6,6.5,9,10,12),利用光學懸浮區(qū)爐對其中四個成分的合金制備了單晶樣品,其Co濃度為x=5.5,5.7,6,6.5,對合金的晶體結構、相變行為、磁學性能、磁致應變以及超彈性行為進行了系統(tǒng)研究,同時研究了B和Cr元素的添加對Ni-Fe-Ga-Co合金相變行為和機械性能的影響。本文依據(jù)實驗數(shù)據(jù),建立了Ni55-xFe18Ga27Cox合金隨Co含量變化的相圖,研究發(fā)現(xiàn):在Ni55-x Fe18Ga27Cox合金體系中,Co含量x=9,10的合金在降溫過程中發(fā)生馬氏體相變,低溫相為單一的非調制馬氏體結構;Co含量x=5.5-6.5區(qū)域,合金的晶體結構、相變行為以及力學行為對合金成分變化非常敏感,發(fā)生馬氏體相變時生成亞穩(wěn)態(tài)的斑駁結構(Mottled Structure);Co含量x=12的合金為應變玻璃態(tài),降溫過程中沒有馬氏體相變發(fā)生。通過原位中子衍射實驗對Ni46Fe18Ga27Co9和Ni45Fe18Ga27Co10合金的晶體結構和相變進行了研究,結果表明兩種合金具有相同的晶體結構,高溫相為立方L21 Heusler奧氏體結構,低溫相為L10非調制馬氏體結構,合金中沒有發(fā)生中間馬氏體相變。對Ni46Fe18Ga27Co9合金進行單軸壓縮原位中子衍射實驗,發(fā)現(xiàn)合金在室溫下表現(xiàn)為超彈性,當外加應力達到200MPa時,表現(xiàn)出了應力誘發(fā)馬氏體相變行為。對成分差異僅為0.3%的Co濃度為x=5.7和6的合金的微觀結構、相變行為和力學行為進行了研究分析,并對x=6的合金的磁學性能和磁致應變進行了研究。Co濃度為x=5.7和6的合金在室溫下為結構不同的預馬氏體相,在馬氏體相變過程中兩種合金都生產(chǎn)了以超點陣衍射斑點為特征的馬氏體相,超點陣對應的結構稱之為斑駁結構,兩種合金的斑駁結構對應的超點陣衍射花樣不相同,該結構為亞穩(wěn)態(tài),x=5.7的合金在133K時小部分斑駁結構轉變?yōu)榉�(wěn)態(tài)的7層調制馬氏體結構,x=6的合金在170K時斑駁結構轉變?yōu)橄鄬Ψ�(wěn)定的兩相共存結構(非調制和7層調制馬氏體結構共存);在co6合金為兩相共存態(tài)時(150k)施加應力,合金隨著應力的增加發(fā)生了兩次相轉變和一次變體選擇,轉變順序為:(i)7層調制馬氏體結構轉變?yōu)榉钦{制馬氏體結構;(ii)非調制馬氏體結構發(fā)生變體選擇;(iii)部分非調制馬氏體結構轉變成為4層調制馬氏體結構。通過力學實驗對x=5.7和6的單晶在不同溫度下的應力-應變特征進行了研究,實驗結果表明在馬氏體相變開始溫度以上,x=5.7和6的單晶的屈服應力平臺隨溫度的下降而減小,相同溫度下x=5.7的合金的屈服應力小于x=6的合金,而在馬氏體相變開始溫度以下,x=5.7和6的合金單晶的屈服應力平臺隨溫度的下降而升高,在243k時,x=5.7和6的合金的屈服應力最小,分別為20mpa和5.5mpa。相對于x=5.7的單晶,x=6的單晶屈服應力更小,這意味著該合金更容易在磁場誘發(fā)下產(chǎn)生應變,因此對x=6的合金的磁學性能和磁致應變行為進行了研究,實驗結果表明,在x=6的合金中,零場冷和場冷的磁化強度-溫度(m-t)曲線在低溫下發(fā)生了嚴重偏離;磁場(1t)導致了伴隨馬氏體相變的應變減小;合金對磁場下的相變過程具有記憶效應;在相變過程中合金的磁化強度在恒溫時具有時間依賴性;磁場可以誘發(fā)合金產(chǎn)生應變,磁致應變表現(xiàn)出了時間依賴性特征并且隨溫度的降低而減小。經(jīng)過分析,本文認為這些特性是由于磁場誘發(fā)亞穩(wěn)態(tài)的斑駁結構向穩(wěn)態(tài)非調制馬氏體結構轉變導致的。此外,通過原位高能x射線衍射實驗對co含量相差1%的x=5.5和6.5的合金的微觀結構和相變行為進行了初步研究,結果表明這兩種合金在室溫下亦為預馬氏體相,x=5.5的合金在150k時奧氏體未能全部轉變?yōu)轳R氏體,為非調制馬氏體、調制馬氏體和殘余奧氏體共存,而x=6.5合金在150k時奧氏體轉變完全,為非調制馬氏體和調制馬氏體共存。利用中子衍射和高能x射線技術原位研究了應變玻璃態(tài)ni43fe18ga27co12合金在單軸壓縮過程中的超彈性行為,揭示了該合金準線性超彈性行為的物理機制。研究發(fā)現(xiàn)在應力誘發(fā)馬氏體相變前彈性模量發(fā)生了軟化,該現(xiàn)象與溫度誘發(fā)預馬氏體相變表現(xiàn)出來了的特征相似。此外,在彈性階段衍射峰寬隨應力的增加持續(xù)寬化,通過williamson-hall分析方法發(fā)現(xiàn)衍射峰寬化是由晶粒內(nèi)部應力場的短程波動造成的,我們認為受限馬氏體相變合金中的彈性模量具有空間異質性。在ni46-xfe18ga27co9bx(at.%,x=0,0.1,0.5)合金中用b元素替代部分ni元素,合金的延伸率和抗壓強度同時得到了提高,其相變溫度隨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,適當?shù)臒崽幚砉に嚳墒沟镁Я．惓ｉL大,晶粒尺寸可達到2mm,這為單晶的制備提供了新的思路,同時Cr元素的添加使合金的屈服強度增大。
[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.

【學位授予單位】：北京理工大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG139.6

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