Ni47Mn32Ga21多晶合金的磁熵变和磁感生应变

对定向凝固方法制备的Ni₄₇Mn₃₂Ga₂₁多晶合金,通过扫描电镜、金相、电子能谱等手段研究其组份和组织形貌,通过对合金磁化强度与温度关系、等温磁化曲线及磁感生应变曲线等的测量分析,研究了合金结构相变和磁相变过程中的磁熵变及不同压力下的磁感生应变. 研究结果表明:合金组份与设计组份基本一致,室温下合金大部分为马氏体相. 升温过程中合金的磁熵变在居里温度(365 K)附近有最大值,并有较大的磁熵变峰值半高宽,747 kA/m的磁场下该磁熵变最大值为-1.45 J/kg ·K,磁熵变峰值的半高宽为21 K. 合金在室温(298 K)下有较好的双向可恢复磁感生应变,480 kA/m磁场下,无压力时合金的磁感生应变值达到-670×10^-6,并趋饱和;而在与磁场方向平行的27.3 MPa外压力作用下合金的磁感生应变值增大到-1300×10^-6,且未饱和. 关键词： Ni-Mn-Ga 铁磁形状记忆合金 磁熵变 磁感生应变

Magnetic entropy change and magnetic-field-induced strain in polycrystalline Ni47Mn32Ga21 alloy

The Ni₄₇Mn₃₂Ga₂₁ polycrystalline alloy is prepared by the directional solidification technique. The components and the microstructure of the alloy are investigated using SEM, metallography and EDS methods. The magnetic entropy change in the process of the structural and magnetic phase transition, and magnetic-field-induced strains with pressure are also studied through analyzing the magnetization as a function of temperature, and the isotherm magnetization and magnetic field-induced strain curves. The results show that there is little difference between the component and the designed component. The alloy is comprised mainly of martensitic phase at room temperature. In the heating process, the magnetic entropy change reaches a maximum value and has a larger peak half width near Curie temperature(365 K). The maximum value of the magnetic entropy change is -1.45 J/kg ·K in a magnetic field of 747 kA/m and its peak half width is 21 K. The Ni₄₇Mn₃₂Ga₂₁ alloy exhibits excellent free recoverability of the magnetic-field-induced strains at room temperature(298 K). The magnetic-field-induced strain reaches a saturated value of -670×10^-6 without extra stress in a field of 480 kA/m. When the compressive stressis parallel to the direction of the magnetic field, the magnetic-field-induced strain increases evidently with the increase of the pressure, which reaches -1300×10^-6 under a pressure of 27.3 MPa. Meanwhile the strain does not reach the saturated value.