Effect of microstructure changes on magnetic properties of spark plasma sintered Nd-Fe-B powders

¹ Faculty of Materials Science and Engineering, Woloska 141, 02-507 Warszawa, Poland
² Institute of Non-Ferrous Metals, Sowinskiego 5, 44-100 Gliwice, Poland

Abstract

In this study the SPS method was applied for low RE content (8,5% at.) and high RE content (13,5 % at.) MQ powders. The powders were sintered in a wide range of temperature, for 5 min., under pressure of 35 MPa. The low RE content grade, densified reluctantly and gained the density close to the theoretical value only for 850 °C. The coercivity decreased gradually with increasing sintering temperature. On the other hand, the densification of the higher RE content grade powder occurred much easier and the coercivity, close to the theoretical value, was achieved already at 650 °C. The coercivity of this material also decreased with increasing sintering temperature. Microstructural studies revealed that the SPS sintering process leads to partial decomposition of the Nd₂Fe₁₄B phase. The proportion of the RE-rich and iron phases increases parallel to the increasing sintering temperature. On the basis of the current results one can conclude that fabrication of high density MQ powders based magnets by the SPS method is possible, however the powders having higher RE content should be used for this purpose and the sintering temperature as low as possible, related to density, should be kept.