Co-Fe-Ni系磁性高熵合金的组织与性能

发布时间：2018-04-16 07:11

本文选题：高熵合金 + 组织结构　；参考：《北京科技大学》2017年博士论文

【摘要】：在过去的十几年中,高熵合金的出现打破了传统合金的设计理念。高熵合金由于其独特的相结构以及优异的性能而备受瞩目。高熵合金中高的混合熵容易稳定固溶体相,从而抑制有序相及金属间化合物相的析出；其严重的晶格畸变以及缓慢扩散效应导致合金往往具有较高的强度、硬度、良好的抗高温软化能力等等。此外,已有研究显示,高熵合金在功能方面,例如磁性材料方面具有潜在的应用前景。传统软磁材料,例如硅钢、Fe-Co合金、非晶合金,以及磁控形状记忆合金Ni-Mn-Ga,其应用往往由于合金的脆性而受到限制。那么,寻求合金的磁性能与力学性能间的平衡至关重要。高熵合金通过成分设计可以兼具较高的强度与良好的塑性,但是其磁性能研究甚少,而现有的高熵合金体系往往含有铁磁性元素Co、Fe、Ni,因而,研究具有良好综合性能的磁性高熵合金势在必行。因此,本文旨在开发和制备多种磁性高熵合金,系统地研究高熵合金的相形成和磁性能。根据高熵合金的概念,本文首先在CoFeNi基础上添加A1和Si,设计出CoFeNi(AlSi)x系高熵合金,并深入研究了其组织和性能。研究结果显示,合金的饱和磁化强度随着非铁磁性元素A1、Si含量的增多呈直线下降趋势,而合金的屈服强度和硬度不断升高,然而,过量的Al、Si(x0.5)使得合金的塑性变差。其中,真空电弧熔炼的CoFeNi(AlSi)0.2合金具有良好的综合性能,其延展性好,饱和磁化强度高(1.15 T),电阻率高(69.5μΩ·cm),但是矫顽力偏大(1400 A/m)。由于铸态合金不可避免地存在一些组织和结构上的缺陷,如枝晶偏析、孔洞等,同时还会存在内应力,这必将影响合金的性能。因此,后续采用铜模吸铸,热处理以及Bridgman定向凝固技术来改善合金的磁性能,合金的矫顽力得到了明显降低。与高硅钢相比,CoFeNi(AlSi)o.2合金软磁磁性能好、易加工,表现出良好的应用前景。其次,为了制备出具有磁控形状记忆效应的高熵合金,在CoFeNi基础上添加Mn和Ga,并调节Co和Fe的含量设计出CoxFe1-xNiMnGa系多元合金,试图通过元素取代而改善Ni2MnGa磁控形状记忆合金的塑性。实验结果显示,虽然大量的元素替代使得合金的混合熵提高,有序化程度降低,但马氏体相变被推迟到-170℃以下或相变消失,该系合金并未呈现形状记忆效应。此外,元素替代并未完全改变合金的脆性断裂,合金的断裂机制为沿晶断裂和解理断裂相结合。Co的添加使得合金的饱和磁化强度、居里温度大幅提高,CoNiMnGa合金表现出了很好的高温使用优势。由于在Ni-Mn-Ga类合金中,合金的磁矩主要源于Mn。本文在CoFeNi三元合金的基础上单独添加Mn,研究Mn对合金性能的影响。此后,又添加磁控形状记忆合金中经常出现的Al、Ga、Sn元素设计出CoFeNiMnX (X=Al, Ga, Sn)系列高熵合金,研究元素添加对合金结构和磁性能的影响。研究结果显示,Al、Ga、Sn的添加均使得合金有序化增强,合金基体均转变为有序结构,合金的强度升高、塑性变差。密度泛函模拟(DFT)显示,这三种元素的添加使得Mn在CoFeNiMn合金中所表现出的反铁磁性得到抑制,向铁磁性转变。CoFeNiMnAl合金具有最高的饱和磁化强度,147Am2/kg,与CoFeNi合金相当。然而,A1的添加并非越多越好。对于铸态下的CoFeNiMnAlx(x=0.25,0.5,0.75,1.0,1.25,1.5,1.75,2.0)系合金,其饱和磁化强度随着Al含量的增多先增加后减小,在等原子比CoFeNiMnAl合金处达到最大值。过量Al的添加对合金的饱和磁化强度起削弱作用。此外,合金的饱和磁化强度与晶体结构密切相关,对于同一合金而言,其BCC相含量越多,合金的饱和磁化强度越高。
[Abstract]:In the past decade, emergence of high entropy alloy has broken the traditional design concept of alloys. High entropy alloy due to its unique structure and excellent performance has attracted attention. The entropy of mixing high entropy alloy and high stability to solid solution phase, thereby inhibiting the ordered phase and intermetallic compound phase precipitation; the serious lattice distortion and slow diffusion effect of lead alloy often has high strength, hardness, high-temperature softening ability and so on. In addition, studies have shown that high entropy alloy in the aspect of function, for example, has a potential application prospect of magnetic materials. The traditional soft magnetic materials, such as silicon steel, Fe-Co alloy, non amorphous alloy, and magnetic shape memory alloy Ni-Mn-Ga, its application is often due to the brittleness of the alloy is limited. So, the magnetic alloy can seek the balance between vital and mechanical properties of high entropy alloys through. The design can be both high strength and good plasticity, but little research on the magnetic properties, and high entropy alloy existing system often contains ferromagnetic elements Co, Fe, Ni, and magnetic properties of high entropy alloy has good comprehensive performance research is imperative. Therefore, this paper aims at the development and preparation of a variety of high magnetic entropy alloys, systematic study of high entropy alloy phase formation and magnetic properties. According to the concept of high entropy alloy, firstly, the addition of A1 and Si on the basis of CoFeNi design CoFeNi (AlSi) x high entropy alloys, and in-depth study of its microstructure and properties. The results of the study show that the saturation magnetization of alloy with the non ferromagnetic elements of A1, the increase of Si content was decreased, and the yield strength of the alloy and the hardness increase, however, excess Al, Si (x0.5) makes the plasticity of the alloy becomes worse. The vacuum arc melting of CoFeNi alloy with 0.2 (AlSi) Good comprehensive performance, its good ductility, high saturation magnetization intensity (1.15 T), high resistivity (69.5. Cm), but the coercivity is larger (1400 A/m). The cast alloy inevitably has some tissue and structural defects, such as dendrite segregation, such as holes, with when will the internal stress, which will affect the performance of the alloy. Therefore, the follow-up by suction casting, heat treatment and Bridgman directional solidification technique to improve the magnetic properties of the alloy, the coercivity of the alloy has been significantly reduced. Compared with high silicon steel, CoFeNi (AlSi) soft magnetic properties of O.2 alloy, easy processing that shows a good application prospect. Secondly, in order to prepare high entropy alloy with shape memory effect of the addition of Mn and Ga magnetron, on the basis of CoFeNi, CoxFe1-xNiMnGa alloy content design and adjustment of Co and Fe, attempts to replace and improve the elements of Ni2MnGa magnetic shape memory The ductility of the alloy. The experimental results show that although the entropy of mixing a large number of elements substitution made of alloy, reduce the degree of ordering, but martensitic transformation was delayed to -170 DEG C or phase disappeared, the alloys did not show shape memory effect. In addition, element substitution did not change the end of brittle fracture of alloy, fracture mechanism the alloy is intergranular fracture and cleavage fracture combined with the addition of.Co alloy makes the saturation magnetization, Curie temperature increase, CoNiMnGa alloy exhibits the advantages of good high temperature. Due to the Ni-Mn-Ga alloy, the main source of Mn. in magnetic alloy based on CoFeNi three yuan on the single addition of Mn alloy and the influence of Mn on the properties of the alloy. Since then, often added magnetic shape memory alloy in Al, Ga, Sn elements design CoFeNiMnX (X=Al, Ga, Sn) series of high entropy alloy elements on tim Influence on the structure and magnetic properties of the alloy. The results showed that Al, Ga, Sn were added to make alloy ordering enhanced alloy matrix into ordered structure, increase the strength of the alloy, plastic variation. Density functional simulation (DFT) showed that the addition of these three elements to Mn the CoFeNiMn alloy antiferromagnetic to ferromagnetic transition is suppressed, the.CoFeNiMnAl alloy has the highest saturation magnetization, 147Am2/kg, and CoFeNi alloy. However, the addition of A1 is not the more the better. For as cast CoFeNiMnAlx (x= 0.25,0.5,0.75,1.0,1.25,1.5,1.75,2.0) alloys, the saturation magnetization with the increase of Al content increased first and then decreased, in Equiatomic CoFeNiMnAl alloy at maximum. The addition of excess Al on the saturation magnetization of the alloy has weakened. In addition, alloy saturation magnetization and crystal structure closely In relation to the same alloy, the more the BCC phase content, the higher the saturation magnetization of the alloy.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG146.16

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