Some heat treatment experiments for Nd-Fe-B alloys

Since the Curie temperature (Tc) of R-Fe-B permanent magnets is lower than conventional 1/5 and 2/17 magnets, the irreversible loss due to the change of coercivity is critical when considering their application. The simple way to guarantee the thermal properties is to raise the coercivity at room temperature. The effect of heat treatment on coercivity was studied. The typical heat treatment is as follows: (1) The first heating at T1, 900°C × 2 hrs is followed by the continuous cooling at the rate of 1.3°C/min to room temperature. (2) The second heating at T2, near the eutectic temperature for 1 hr is followed by quenching. When employing this heat treatment, the following magnetic properties were obtained for Nd(Fe0.92B0.08)6. Br=13800 G, bHc=9150 Oe, iHc=9200 Oe and (BH)max=44.0 MGOe.