Development of New High Temperature and High Performance Permanent Magnet Materials

Permanent magnet materials capable of operating at high temperatures equal or greater than 400 deg C are required for advanced aerospace power systems. Prior to the UDRI AMPS teams successful program, the best available high temperature permanent magnets could not operate above 300 deg C. The problem for higher temperature operation has been that the strength of conventional magnets, as characterized by their intrinsic coercivity MHc drops sharply upon heating. The MHc of the best 217 rare earth-transition metal permanent magnets previously available drops from 20 to 30 kOe at room temperature to only 1 to 3 kOe at 500 deg C. This also results in nonlinear 2nd-quadrant induction demagnetization curves B curves at temperatures above 200 to 300 deg C. A linear B curve is critical in all dynamic applications such as in generators and motors. The UDRI AMPS team also proposed a new theory of coercivity mechanisms in permanent magnet materials based on this breakthrough result. This new theory explains the variations in the temperature dependencies of coercivity and provides important guidance to the RD of new magnetic materials. In addition, EEC has successfully commercialized the new high temperature permanent magnets. These advances represent a major breakthrough in high temperature permanent magnet materials.