Research On Mechanism Of Mechanically Assisted Hydrogenation-disproportionation And Process Of Desorption-recombination

Nanocrystalline Nd-Fe-B permanent magnets have attracted much attention recently for exhibitting high remanence, intrinsic coercivity, and energy product. However, the magnetic properties of such nanocomposite magnet currently prepared by various processing methods are far from its theory values. Hence, a new technique, which combines mechanically activated disproportionation and desorption-recombination in situ sintering, has been proposed to obtain nanocrystalline Nd-Fe-B magnets. Mechanically activated hydrogenation–disproportionation of Nd-Fe-B alloy by mechanical milling in hydrogen and subsequently desorption–recombination in vacuum were investigated systematically.The thermodynamics and kinetics of the DR process was studied by experimental investigation and numerical simulation. The effect of processing parameters on magnetic properties of Nd-Fe-B magnetic material was studied.At first, the thermodynamic mechanisms were analyzed and the kinetic equation for the mechanically actived hydrogenation-disproportionation of Nd-Fe-B alloy in hydrogen was derived based on milling parameters. Then, the thermodynamic aspects of the desorption-recombination experiments of disproportionated Nd-Fe-B alloy were analyzed. And the kinetic equation for the recombination was also derived. Based on the study of the kinetics of the recombination, applying the Monte Carlo method, we have setted up a simulation software of the desorption-recombination of the disproportionated Nd-Fe-B alloy, where the program was written with the fortran language. The desorption-recombination behavior of as-disproportionated Nd-Fe-B alloy during vacuum sintering was investigated by the means of XRD, M?ssbauer spectra, and TEM analysis, and furthermore, analysis was made about some of the simulation results compared to the experiments. We found the affected law of the temperature and time to the reaction rate and the size of the grains at the end of the recombination. Lastly,the magnetic properties of the nanocrystalline Nd-Fe-B magnets were measured by VSM, then the optimal processing parameters were obtained. The simulation results provide a new study idea to the optimization of sintering process.