Effect of a Strong Magnetic Field on the Microstructure of Near-equilibrium Solidified Ni-Co-Mn-Sn Metamagnetic Shape Memory Alloy

Author of the article:ZHAI Qiang 1,2 , BU Fan 1,2 , MA Changyao 1 , LIU Ziyu 1 , HE Yixuan 1,2 , WANG Jun 2 , LI Jinshan 2

Author's Workplace：1. Center of Advanced Lubrication and Seal Materials, Northwestern Polytechnical University, Xi'an 710072, China; 2. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China

Key Words： strong magnetic field; Ni-Co-Mn-Sn alloy; near-equilibrium solidification; microstructure

Abstract：Optimizing the overall performance of Heusler-type Ni-Mn-Co-Sn magnetic shape memory alloys (MSMA) by the application of advanced treatment technology in current smart material research has been a research hotspot. The properties of alloys are strongly related to the solidification microstructures. In this paper, the solidification microstructures of Ni 42 Co 8 Mn 39 Sn 11 MSMA under different magnetic field intensities were studied. The results show that in the absence of magnetic field, the microstructure is mainly composed of D0 3 coarse dendrite trunks and L2 1 interdendrite, embedded with the vermicular γ phase that is Co-rich and Sn-depleted, and the chemical composition of the D0 3 phase shows the opposite tendency. The D0 3 structure is formed due to the chemical segregation of the Heusler L2 1 phase, and the γ phase is hardly obtained from the decomposition of the L2 1 phase in the range of 500~700 ℃. After the application of a 10 T high magnetic field, the phase constituent, chemical composition and morphologies of the alloy remain stable, and no obvious alignments or textures are found due to the enhanced thermal energy rather than the weakened anisotropic magnetic energy. In addition, the fraction of the D0 3 phase decreases efficiently, and the L2 1 phase rises when a magnetic field is applied, i.e., a strong magnetic field could alleviate the chemical fluctuation and contribute to the formation of a more uniform distribution of Heusler phase elements.