Demand for high-performance permanent magnets is increasing rapidly for applications such as wind turbine generators and electric and hybrid car motors. Samarium-cobalt (Sm-Co) and Neodymium-iron-boron (Nd-Fe-B) rare earth magnets are generally used for such challenging applications. While rare earth magnets are the best currently available permanent magnets, they tend to be brittle, suffer from thermal shock and experience corrosion. Additionally, rare earth mining has been associated with severe environmental degradation and prohibitive energy usage. Nickel-iron, which has been identified in meteorites as the compound Tetrataenite where it transformed from a high temperature phase to a low temperature magnetic phase over thousands of years, has magnetic properties comparable to that of rare earth magnets. This award develops nickel-iron based permanent magnets using quantum-mechanical calculations to predict the effects of alloying and experiments to verify the effects of these additional elements on the transformation kinetics and magnetic properties of these materials. A novel pulsed electrical heating is used to accelerate the phase transformation. The development of novel nickel-iron magnets enables production of permanent magnets at low cost, which impacts the U.S. economy and security. The project engages women and under-represented minorities in multi-disciplinary research activities and develops a website that offers simple virtual experiments to explain to a wide audience magnetism and the materials science of permanent magnets.
The L10-structured compound nickel-iron (NiFe) has the potential to replace rare earth (RE) magnets at low cost. NiFe has a magnetic anisotropy energy, ku, of 1.3 x 106 J.m-3 and a saturation magnetization m0MS of 1.59 Tesla, which is comparable to that of Nd2Fe14B, and it has good corrosion resistance. The challenge is that the binary L10 compound has a very low transformation temperature from the high-temperature face centered cubic (f.c.c.) phase of about 320oC that forms on casting and, thus, orders very slowly at temperatures where it is stable. This project combines ab initio quantum mechanical calculations and experimental work to design new L10-structured NiFe magnets with ternary elemental additions. These ternary compounds potentially have a significantly higher f.c.c.-to-L10 transformation temperatures and higher diffusivities than binary NiFe but have similar saturation magnetizations. Thus, the L10 phase can be produced at higher temperature in short, commercially-viable times utilizing electro-pulse annealing of cold-worked material, which has also been shown to dramatically accelerate recrystallization in NiFe. Commercially, NiFe can be manufactured by continuous electro-pulse annealing of rolls of sheet material or of rods and, being ductile, can easily be machined into various shapes.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
