Pulverizing anisotropic rapidly solidified Nd-Fe-B materials for bonded magnets

The high (BH)max potential of Nd-Fe-B materials make them excellent candidates for bonded magnets. We have previously shown that anisotropic bonded magnets can be made from hot deformed rapidly solidified materials. The purpose of this paper is to show how hot deformed materials can be pulverized into desired particle size ranges by using specific hydrogen decrepitation (HD) cycles. Specific temperatures for hydriding and desorbing cycles to achieve desired particle size ranges and magnetic values are given. The data shows that there are optimum times and temperatures to achieve the desired magnetic properties. TEM and SEM photomicrographs of mechanically and HD pulverized materials are shown. TEM studies show that stacking faults generated during HD are relieved after desorption. With proper control of HD and desorption, bonded magnets have been produced having (BH)max values as high as 18.9 MGOe.