TEM INVESTIGATION OF RAPIDLY SOLIDIFIED NDFEB HARD MAGNETIC MATERIAL

The surface condition and microstructure of near stoichiometric (Fe۸۲۳Ndll.۸B۵.۹) Nd-Fe-B alloy ribbons and the effect of melt spinning parameters were investigated using optical, scanning and transmission electron microscopes (SEM, TEM). The formation of gas pockets on the roll surface of the ribbons during melt spinning can prevent heat transform and result in local coarse grains. The local thickness would also be less in these places and thus perforates preferentially during ion beam milling. Therefore different areas of the sample should be carefully observed in the TEM. Reducing inert gas pressure in the chamber will eliminate the gas pockets. As a general trend, decrease in the ribbon thickness and mean Nd۲ Fe۱۴B grain size were observed on increasing the roll speed. By careful adjustment of the melt spinning parameters, the nanostructure will develop. An orientation relationship was found between Nd۲ Fe۱۴B and ;#۹۴۵-Fe precipitates for coarse grain samples melt spun at low roll speed. Dark field image of such grain also shows that some of these ;#۹۴۵-Fe precipitates have the same orientation. X-ray diffraction evident the development of texture by decreasing the roll speed.

کلیدواژه ها:

Transmission electron microscope ، TEM ، Scanning electron microscope ، SEM ، Hard magnetic ، Rapid solidification ، NdFeB ، Melt spinning