Iron-based soft magnetic amorphous alloy has broad application prospects in power electronic devices such as transformers, motors, sensors, etc. It is an important energy-saving and green environmental protection new material. Soft magnetic properties and mechanical deformation capabilities are two important factors affecting the application of amorphous alloys. Generally, the original amorphous alloy sample has good mechanical deformation ability, but the residual stress frozen in the non-equilibrium preparation process will deteriorate the soft magnetic properties. Annealing can reduce residual stress and greatly improve soft magnetic properties, but tends to make amorphous alloys brittle. The annealing process mainly uses the relaxation phenomenon to control the properties of amorphous alloys. However, the relaxation mode of amorphous alloys is very complicated, and there are coupling effects between different relaxation modes. Studying the relaxation phenomenon in amorphous alloys, and clarifying the influence of different relaxation modes on the performance and the microscopic physical mechanism are of great significance to solve the problem of different performances.
Song Lijian, He Nana and Ouyang Crisp, Key Laboratory of Magnetic Materials and Devices, Institute of Materials Technology and Engineering, Chinese Academy of Sciences, under the guidance of researcher Wang Junqiang and associate researcher Huo Juntao, etc., isothermal relaxation around amorphous alloys since 2015 The behavior of Henan and its influence on magnetic properties and microscopic mechanisms have been studied in depth. Relevant achievements and topics have been published and patented in the first half of 2018. Firstly, the relaxation dynamics behavior of different alloy systems under isothermal annealing conditions was studied by using a high-precision, ultra-fast temperature-speed flash scanning calorimeter (Flash DSC). It was found that the isothermal annealing process is not a single relaxation mode, but a transition from β relaxation to α relaxation (see Fig. 1). That is, when annealing at a low temperature for a short time, the amorphous alloy undergoes β relaxation, and when the annealing temperature is sufficiently high or the annealing time is long enough, the α relaxation behavior is triggered. This isothermal transformation process is caused by the quenching of the free volume of the aligned loose areas resulting in enhanced atomic motion. These results indicate that precise regulation of different relaxation modes in amorphous alloys can be achieved, as published in Intermetallics 93, 101–105 (2018).
They further controlled the relaxation mode in iron-based amorphous alloys and found that the β relaxation phase can effectively improve the soft magnetic properties (reduced coercivity, increased magnetic permeability) while maintaining good mechanical properties; α relaxation The stage has no obvious influence on the soft magnetic properties, the coercive force and magnetic permeability remain basically unchanged, but the mechanical deformation ability is deteriorated, and the amorphous alloy becomes brittle (see Fig. 2). The above work shows that different relaxation modes have different effects on the different properties of amorphous alloys. By precisely controlling the relaxation mode in amorphous alloys, the problems of different performances can be solved and the comprehensive performance can be improved. Relevant work is being compiled and submitted, and has applied for a national invention patent (201810310296.5).
In view of the relationship between β relaxation and microstructure inhomogeneity, and the relationship between macroscopic magnetic properties and microscopic magnetic domain structure, in order to further study the microscopic mechanism of β relaxation affecting soft magnetic properties, the team studied magnetic domain motion and structural non-uniformity. Coupling between sexes. The in-situ study of the magnetic domain wall around the nanoindentation under the applied magnetic field shows that the amorphous alloy magnetization is determined by the movement of the magnetic domain wall. The closer the nanoindentation is to the magnetic domain wall, the more difficult it is to move, meaning that the magnetic permeability is lower. The microscopic inhomogeneity around the indentation was studied by amplitude-modulation atomic force microscopy (AM-AFM). The closer the indentation is, the higher the viscous loss energy is, which is related to the dilatation deformation mechanism in the amorphous alloy. The microscopic inhomogeneity under tensile state was studied in situ, and it was found that there is a linear relationship between external stress and viscous loss energy. Based on the above experimental results, they found a significant correlation between magnetic domain wall mobility and viscous loss energy (see Figure 3). The relationship can be fitted by the magnetoelastic coupling theory. The fitting results show that the magnetic domain wall thickness in the soft magnetic amorphous alloy is about 36 nm, which is similar to the viscoelastic ratio uniformity. The relevant results are published in Phys. Rev. Materials 2, 063601 (2018).
The above results prove that amorphous alloys have different relaxation mode transitions during isothermal annealing, and the influence of β and α relaxation on magnetic properties and mechanical properties, and the microscopic mechanism of β relaxation affecting magnetic properties are clarified. The result is universal in amorphous alloys and is expected to be applied to actual production processes to improve the overall performance of amorphous alloys.
The above work was supported by the National Natural Science Foundation of China and the Youth Project, the Zhejiang Provincial Natural Science Foundation Outstanding Youth Fund, the Chinese Academy of Sciences Hundred Talents Program and the National Key Research and Development Program.
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