Research On The Properties Of FeCoHfBCu Amorphous And Nanocrystalline Alloys As Well As Its EET Simulation

The HITPERM FeCoHfBCu nanocrystalline alloy appeared at the end of 20th century is a novel nano microcrystalline soft magnetic material. This nanocrystalline alloy is characterized by higher saturation magnetic induction, low coercivity, high permeability and low high-frequency power loss. It has become preferred material for the modern weapons and new motivation system because of its excellent soft magnetic properties. The HITPERM-type nanocrystalline alloy is gained through crystallization of amorphous alloys. Therefore, the study on preparation and stability of amorphous alloys is very important.In this paper, the microstructures and properties of amorphous and nanocrystalline alloys were examined by transmission electron microscopy (TEM), Mossbauer spectra, positron annihilation technique (PAT) and differential thermal analysis (DTA), etc. Moreover, The magnetic moment of amorphous was calculated using the empirical electron theory (EET) and micro crystal model. The main contents were summarized as follows:(1) First, we prepare the amorphous (Fe1-xCox)86Hf7B6Cu1 (x=0.3-0.6) alloys by the single-roller-quenching method using high purity metals as raw materials. There were two ways to add B, injecting pure B or injecting FeB. The surface linear speed of the copper wheel was about 49 m/s and 45m/s. Then, all of the specimens were analyzed with XRD, TEM, Mossbauer spectroscopy and scanning electron microscope (SEM). The result showed that all of the specimens were amorphous state.(2) The properties of amorphous alloy were studied by means of DTA, VSM and PAT. The influences of the surface linear speed of the copper wheel, the adding way of B and the value of x on the thermal stability and the soft magnetic properties of amorphous (Fe1-xCox)86Hf7B6Cu1 alloys were studied. The results obtained by DTA showed that the crystallization activation energy of amorphous alloy was larger for the faster cooling velocity 49m/s as the adding way of B is same. For the same cooling velocity, the crystallization activation energy of the amorphous alloy prepared by injecting pure B is larger than the alloy prepared by injecting FeB. When x is equal to 0.4, the crystallization activation energy of amorphous alloy was the largest in all of the specimens with same cooling velocity and same adding way of B. The PAT results showed that the volume of mono vacancy and vacancy cluster for the specimens (x=0.4) were smaller, and the number of monovacancy was less than others. So the stability of (Fe1-xCox)Hf7B6Cu1 (x=0.4) amorphous alloy was the best according to the results of DTA and PAT. At last, the soft magnetic properties of specimens were measured by VSM. The specimens added pure B displayed more excellent soft magnetic property.(3) Amorphous Fe52Co34Hf7B6Cu1 alloys were treated by medium frequency pulse magnetic field in order to get better soft magnetic property. Then, the treated specimens were analyzed by XRD, TEM and Mossbauer spectroscopy. The results showed that the amorphous were nanocrystallized with different degrees at process of the treatment by pulse magnetic field. Then, the structure defects of the nanocrystalline alloys were studied with PAT. It was found that the volume of monovacancy and vacancy cluster was decreased after treatment by medium frequency pulse magnetic field. It means that pulse magnetic field can lead the structure of alloys relax continuously, and cause various defects to annihilate, format and recombinate, etc. To further eliminate structure defect or residual stress after the treatment of pulse magnetic field, a series of 30min vacuum annealing treatment were carried out at the temperature ranging from 100? to 400 ?. The VSM was used to measure the saturation magnetic induction (Ms) and the coercivity (Hc). The micro-structural changes of some specimens were analyzed by TEM. After vacuum annealing at 100? for 30 min, the distribution of nanocrystalline phases become more homogenous, and the soft magnetic properties of specimens get better than before.(4) The covalence electronic structures and magnetic moment of amorphous were calculated using the bond length difference (BLD) method in the EET. First, we calculated the covalence electronic structures and magnetic moment of six kinds of unit cell, ?-Fe, fcc-Co, ?-Fe-B, ?-Fe-Co, Co-Hf and Fe-Cu, based on short range order model of amorphous alloys, respectively. Then, the magnetic moment of amorphous (Fe1-xCox) 86Hf7B6Cu1 (x=0.4-0.6) alloys were calculated according to the percentage of each unit cell in amorphous alloys. It is found that the error of the computed value with EET theory and experimental value of the magnetic moment is less than 10%, which indicated that we can calculate the magnetic moment of amorphous alloy on the valence electron level.