Effect of Heat Treatment Assisted with Magnetic Field on Microstructure and Magnetic Properties of Co-Ni-Al Alloy

The control of microstructures and properties of magnetic shape memory alloys is one of the important research topics in the field of smart materials. In this study, the Co₃₈Ni₃₃Al₂₉ ternary magnetic shape memory alloys are annealed at 1 100 ℃under different intensities of strong magnetic fields, and the influences of microstructural evolution and magnetic properties of the annealed Co₃₈Ni₃₃Al₂₉ alloys are investigated. Results show that the as-cast alloy presents a hypoeutectic characteristic of β austenite phase as primary dendrites and β+γ lamellar eutectics within the interdendritic regions. The γ secondary phase is rich in Co and Ni solutes, presenting ferromagnetism, while the β phase is in paramagnetic state, rich in Al element. As the magnetic field intensity increases to 3 T, the fraction of the γ phase increases, the γ phase becomes refined, presenting orientation tex- tures along the direction of external magnetic field, and the direction of magnetization tends to be parallel to the magnetic field. The saturation magnetization, magnetic anisotropy coefficient and magneto-strain of alloys also increases. If the magnetic field is further increased to 6 T and 9 T, respectively, the amount of γ phase reduces slightly and the magnetic properties are not altered obviously. This work can provide guidance for further optimization of the microstructure and properties of alloys.