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铁磁形状记忆合金 (FSMA)是在一定温度范围马氏体相稳定同时又具铁磁性的一类特殊的形状记忆合金。Ni2MnGa铁磁形状记忆合金近年来成为呈现磁场驱动大应变的新型驱动材料 ,这些应变来自磁场诱发马氏体孪晶的重排 ,而不是磁场对奥氏体至马氏体相变的作用。孪晶变体的重排在宏观上呈现为正或切应变 ,一非化学计量比Ni2 MnGa单晶于室温加 0 .4T磁场能产生6 %的应变 ,Ni Mn Ga单晶在高至 15 0Hz的交变磁场仍可得到 2 .5 %的应变。本文阐述了与这种磁控形状记忆效应相关的孪晶界迁动的磁学和晶体学理论。马氏体相的大磁晶各向异性能使磁化沿c轴方向有利 ,穿过孪晶界c轴刚好转动 90度 ,同时 ,这个孪晶界也构成了约 90度的畴界。在各向异性的情况下 ,孪晶界的迁动仅有相邻孪晶变体的Zeeman能差驱动 ,μ0 ΔMis·Hi。磁场和外应力对应变的影响通过对一简单的自由能表达式取极小值来表示 ,自由能表达式包括Zeeman能、磁晶各向异性能和外应力以及在某些情况下需考虑的内部弹性能 ,模型的所有参数可通过应力 应变曲线和磁化曲线测量得到。铁磁形状记忆合金的磁场诱发应变可类比传统热弹性形状记忆效应 ,与更为人们所熟知的磁致伸缩现象不同。
Ferromagnetic shape memory alloy (FSMA) is a type of special shape memory alloy that is stable and ferromagnetic at a certain temperature range. In recent years, Ni2MnGa ferromagnetic shape memory alloys have become the new type of driving materials that exhibit large field-driven strain. These strains come from the rearrangement of magnetic field-induced martensite twins rather than the effect of magnetic field on austenite to martensite transformation. The rearrangement of the twin variants appears as positive or shear strain macroscopically. A non-stoichiometric Ni2MnGa single crystal at room temperature plus 0.4T produces a 6% strain, and the NiMnGa single crystals grow up to 150Hz Of the alternating magnetic field still get 2.5% of the strain. This article describes the magnetoclinic and crystallographic theory of the twin-boundary migration associated with this magneto-shape memory effect. The large magnetocrystalline anisotropy of the martensitic phase enables the magnetization to be favorable in the c-axis direction, passing through the twin c-axis just 90 degrees and at the same time, the twin boundary also forms a domain boundary of about 90 degrees. In the case of anisotropy, the migration of the twin boundaries is only driven by the Zeeman energy difference of adjacent twin variants, μ0ΔMis · Hi. The effect of magnetic field and external stress on strain is expressed by taking a minimum value for a simple free energy expression that includes Zeeman energy, magnetocrystalline anisotropy energy and external stress, and in some cases Internal elastic energy, all the parameters of the model can be measured by the stress-strain curve and the magnetization curve. The field-induced strain of ferromagnetic shape memory alloys can be analogous to the traditional thermoelastic shape memory effect, unlike the more well-known magnetostriction phenomenon.