放电等离子烧结-热变形技术制备NdFeB永磁材料

采用放电等离子烧结(SPS)方法烧结HDDRNdFeB粉末,研究烧结温度对制备NdFeB永磁材料密度和磁性能的影响。随着烧结温度在650～900℃范围内升高,剩磁、内禀矫顽力及最大磁能积均呈现先升后降的趋势。800℃烧结所获得磁体的磁性能最佳:Br=0.78T,Hcj=577kA/m,(BH)max=78kJ/m3,其致密度达到了99%。微观组织、XRD图谱及磁性能均表明800℃烧结的磁体出现了一定程度的各向异性。900℃烧结时,晶粒长大明显。进而选择具有最佳磁性能的磁体在800℃进行热变形(HD)处理,制备出各向异性磁体。热变形制备的磁体中,大部分晶粒为扁平片状且c轴取向与热压方向一致;少量异常长大晶粒会使细小Nd2Fe14B晶粒的c轴偏离压力方向。各向异性磁体沿c轴的磁性能为:Br=1.09T,Hcj=384kA/m,(BH)max=114kJ/m3。

NdFeB Magnets Prepared by Spark Plasma Sintering and Hot Deformation

The effects of sintering temperature (Tsps) on the magnetic properties and density of NdFeB magnets prepared by spark plasma sintering (SPS) from HDDR powders were studied. With increasing the sintering temperature in the range of 650-900 °C, the remanence (Br), intrinsic coercivity (Hcj) and maximum energy product ((BH)max) all increased first and then decreased. The optimum magnetic properties of Br = 0.78 T, Hcj = 577 kA/m and (BH)max = 78 kJ/m3 were obtained in the samples SPSed at 800 °C and the density reached 99% of the theoretical. The microstructure, XRD patterns and magnetic properties indicated that the sample (Tsps = 800 °C) was anisotropic to a certain degree. But the grain growth was obvious when the Tsps reached 900 °C. The SPSed magnet with optimal magnetic properties was subjected to hot deformation at 800 °C and an anisotropic magnet was obtained. The hot deformation made the Nd2Fe14B grain orient in such a way that the c-axis of the Nd2Fe14B grain was parallel to the pressing direction. However, the alignment of grains was disrupted by a small amount of abnormal large grains. The magnetic properties parallel to the c-axis of the SPSed + HDed magnet were as follows: Br = 1.09 T, Hcj = 384 kA/m, and (BH)max = 114 kJ/m3