Preparation and microwave absorption properties of NdFeB alloys

In order to improve the microwave absorbing properties of NdFeB alloys, as-jet milled powders were further processed in a planetary mill. The phase structure, morphology and particle size of the alloy powders were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and laser diffraction-based particle size analyzer, respectively. The saturation magnetization and electromagnetic parameters of the powders were determined by a vibrating sample magnetometer （VSM） and a vector network ana-lyzer （VNA）, respectively. The results showed that the saturation magnetization decreased as the milling time increased. The mini-mum absorption peak frequency shifted towards the lower region and the reflection loss values increased with increasing the ball mill-ing time. The minimum absorption peak value of the powders milled for 15 h on the basis of jet milling reached–44.4 dB at 11.04 GHz, and the bandwidth of R〈–10 dB was 1.2 GHz with the best matching thickness of 1.8 mm.

Study on Characteristics of Crystal Growth of NdFeB Cast Alloys

The characteristic of crystal growth of NdFeB cast alloys was studied. It is found that the crystal growth orientation of conventional ingots is along <410> or <411>. As the cooling rate increases, the crystallization orientation changes from a axis to c axis, along which the grain is easy to be magnetized. Meanwhile, by analyzing the change of crystallization orientation, the influence on the property of magnets was discussed.

Calculating the proportion of Nd-rich phase in NdFeB alloy via Matlab software

Nd-rich phase plays an important role in the magnetic properties of sintered NdFeB alloy. The proportion of Nd-rich phase to all the other phases was calculated by using MATLAB 6.5 software. Especially, post-sintered alloy, post-high-temperature tempered alloy and post-high and low-temperature tempered alloy were analyzed. It was found that the proportion of Nd-rich phase in the three alloys based on SEM (scanning electron microscope) images was about 8.22%, 8.03% and 8.00%, respectively.

Microstructure Variation of Nd_(15)Fe_(77)B_(8) Alloy in Hydrogenation-Disproportionation-Desorption-Recombination Process

In the present paper the microstructure variation of Nd 15 Fe 77 B 8 alloy has been investigated using scanning electron microscopy, optical microscopy and X ray diffraction in the hydrogenation disproportionation desorption recombination(HDDR) process. By making use of the so called“solid HDDR” treatment, the microstructure features of Nd 15 Fe 77 B 8 alloy at different disproportionation stages were revealed. It has been deduced that the disproportionation is controlled by diffusion of hydrogen atom, which takes place preferentially in the boundary region, including phase boundary and grain boundary, and some definite crystallographic orientation of Nd 2Fe 14 B phase. It has also been confirmed that the coarse α Fe dendrite can be removed in a short time in the hydrogen desorption and recombination stage of HDDR procedure. The rapid remove of α Fe dendrite has been discussed. It has been suggested that the very fine grain sized nanocrystalline structure obtained by disproportionation is responsible for fast diffusion process required by the rapid removing of coarse α Fe dendrite.

Differences of element distribution between free and wheel side surface of NdFeB/α-Fe ribbons

The ribbons of NdFeB/College of Material Science ＆ Engineering, Xihua University, Chengdu 610039, China-Fe composite alloy were prepared by melt spinning and post crystallizing technique. The element distri- butions and phase component of both surfaces of as-spun ribbons were measured by energy dispersive spectrometry （EDS） and X-ray diffraction （XRD）. Because of the centrifugation, a segregation of B, Fe, and Nd concentrations was observed at the cross section. After crystallizing annealing, the element concentration segregation still existed in the as-crystallized ribbons. Due to the segregation of B, Fe, and Nd, the B-rich phase was observed near the wheel side surface. The B-rich phase may deteriorate the magnetic property of NdFeB/a-Fe composite alloy.

Effects of lanthanum substitution on microstructures and intrinsic magnetic properties of Nd-Fe-B alloy

（Ndl-xLax）30Fe69B （x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6） alloys were prepared by inducting melting, and the effect of substitution of La for Nd on their microstructure and intrinsic magnetic properties were investigated. With the increase of La content, Curie tem- perature （Tc） decreased from 582.4 to 557.4 K, saturation magnetization （Ms） decreased from 1.59 to 1.37 T, and anisotropy field （HA） decreased from 5394 to 3911 kA/m. However, the reductions of the intrinsic magnetic properties were relatively gentle as La content increased, which meant that the intrinsic magnetic properties still had the potential to fabricate permanent magnets. Moreover, further microstructure observations showed that La tended to diffuse into the Nd-rich grain boundary phase instead of main phase during the substitute process. Such aggregation behavior was beneficial to fabricating La containing magnet with high Ms.