| Nanocomposite permanent magnetic materials consist of both nano-scale hard and soft phase, which get excellent magnetic performance through exchange coupling between their neighboring atomic magnetic moments. If the nanocrystals of the two phase nanocomposite magnets are orientated, their potential upper limit of maximum energy product can exceed 1000 kJ/m3, which is higher than that any single phase permanent magnetic materials. In addition to the high maximum energy product that may be achieved, nanocomposite magnets are of commercial interest because they require less of an expensive rare earth element. However, in the bulk nanomaterials, it is a difficult and significant work to prepare the orientated, ultra-fine and homogeneous nanocrystals.Amorphous crystallization method is an important technique to prepare the nanomaterials; moreover, the research of amorphous crystallization under high pressure is the front edge in the materials sciences. Therefore, to investigate the nanostructure transformation of magnetic amorphous alloy Nd9Fe85B6 under high pressure is not only help to develop the nanocomposite permanent materials, but also help to learn the rule of amorphous crystallization under high pressure.By means of X-ray diffraction (XRD), Transmission electron microscopy (TEM), Electron diffraction (ED) and Six-Side Anvil Cell, the nanostructure transformation of amorphous alloy Nd9Fe85B6 under high pressure has been investigated in this paper. The main research contents and results are followed:The oriented growth of nanocrystals in the amorphous matrix under high pressure has been investigated. The results show that the pressure can induce the preferential growth of nanocrystals of Nd2Fe14B phase in amorphous matrix. Nd2Fe14B nanocrystals with a strong crystallographic texture along with [410] orientation have been produced under a pressure of 6 GPa at 923 K. This is attributed to that the diffusion of different size atom is discrepant in amorphous matrix under the high pressure. The plane which is mainly composed of the smaller atom is easier to form under the high pressure.The effect of high pressure on the microstructure in crystallizing amorphous Nd9Fe85B6 alloy has been studied. It is found that application of high pressure makes the microstructure of crystallized alloy much more homogeneous. This is attributed to the homogeneous distribution of the cluster which is formed under high pressure. There two effects of pressure on the microstructure of crystallized alloy: One is to constrain atomic diffusion, which makes atomic mobility more difficult. The low atomic mobility constrains the growth of crystals during the crystallization process. The other is to decrease the critical free energy required to form a nucleus, which promotes the growth of crystals. The average grain size of Nd2Fe14B phase decreases with the increase of pressure, while the size ofα-Fe phase first increase when a pressure of 1 GPa was applied and then decreases with further increase of pressure. The pressure also change the sequence of crystalliztion. Under the low pressure (1 GPa), theα-Fe phase is the first crystallized phase, while under the high pressure (6 GPa), the Nd2Fe14B phase becomes the first crystallized phase. Furthermore, the amorphous Nd9Fe85B6 alloy can transform into the nanocrystals under high pressure at room temperature.The activation volume for nanocrystals growth in amorphous Nd9Fe85B6 alloy has been investigated. The activation volume ofα-Fe and Nd2Fe14B phase areΔV ?= (0.76±0.04) ? and (0.57±0.05) ?, respectively. This indicates the growth ofα-Fe and Nd2Fe14B nanocrystals is dependent on atomic diffusion mediated by vacancy-type thermal defects. The growth of Nd2Fe14B nanocrystals in the amorphous Nd9Fe85B6 may take a collective diffusion mechanism involving Nd, Fe and B atoms, which leads to a relatively small activation.
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