Hot isostatically pressed SmCo5magnets

Two batches of SmCo5alloy powders have been hot isostatically pressed at temperatures considerably lower than used for sintering. The first batch with average powder particle size of 40 μm consisting of samples with nominal compositions in the range of 35.5 to 38.5 wt percent Sm was HIP´ed at 900°C. The second batch with 25 μm particles and composition between 35.5 and 37.0 wt percent Sm was HIP´ed at 950°C. Close to theoretical densities were obtained in both cases. Post-HIPP´ing thermal treatments at temperatures as low as 950°C produced magnetic properties comparable to best available conventional sintered magnets. Samples HIP´ed at 950°C showed remarkably high values of coercivity (about 20 kOe) in the as-HIP´ed condition. The remanence values were high for all samples in the as-HIP´ed condition and showed little change after thermal optimization. This is very different from the behavior reported for hot-pressed magnets where the remanence was quite low initially but increased significantly on post-pressing treatment at temperatures similar to those used for sintering. In sharp contrast to the sintered magnets, the coercivity values of HIP´ed materials were found to be reasonably constant over the entire range of 35.5 to 37.0 wt percent Sm composition.