Texture and training of magnetic shape memory foam

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• 作者：Cassie Witherspoon^a ; ¹ ; Peiqi Zheng^b ; Markus Chmielus^a ; ² ; Sven C. Vogel^c ; David C. Dunand^b ; Peter Mü ; llner^a ; ^{PeterMullner@BoiseState.edu}
• 关键词：Martensitic phase transformation ; Neutron diffraction ; Thermal cycling ; Ni2MnGa ; Heusler alloys
• 刊名：Acta Materialia
• 出版年：2013
• 出版时间：April, 2013
• 年：2013
• 卷：61
• 期：6
• 页码：2113-2120
• 全文大小：826 K

文摘

Magnetic shape memory alloys display magnetic-field-induced strain (MFIS) of up to 10 % as single crystals. Polycrystalline materials are much easier to create but display a near-zero MFIS because twinning of neighboring grains introduces strain incompatibility, leading to high internal stresses. Pores reduce these incompatibilities between grains and thus increase the MFIS of polycrystalline Ni-Mn-Ga, which after training (thermo-magneto-mechanical cycling) exhibits MFIS as high as 8.7 % . Here, we show that this training effect results from a decoupling of struts surrounding pores in polycrystalline Ni-Mn-Ga during the martensitic transformation. To show this effect in highly textured porous samples, neutron diffraction measurements were performed as a function of temperature for phase characterization and a method for structure analysis was developed. Texture measurements were conducted with a magnetic field applied at various orientations to the porous sample, demonstrating that selection of martensite variants takes place during cooling.