MICROSTRUCTURAL STUDY OF HOT-PRESSED HDDR ND-FE-B MAGNETS

Systematic microstructural studies of hot pressed HDDR, fully dense Nd 16Fe76B8 magnets have been carried out. A fine grained, hard magnetic phase structure with a grain size of a few hundreds of nanometres is t he most outstanding microstructural characteristic of these magnets. A part from the compact fine grained microstructure with hardly any Nd-r ich phase, partially isolated, fine hard magnetic grains with a Nd-ric h surrounding were also found. Abnormal grains were observed, arising from the early stages of growth. These grains had a close contact to s mall neighbouring grains as well as larger abnormal grains of up to 10 mu m with straight borders. Other phases identified were the Nd1+epsi lonFe4B4 and Nd5Fe2B6 intergranular platelets.