Improving the (BH)_max of L1₀-Structured t-MnAl by Processing

L1₀ structured, near-stoichiometric t-MnAl has great potential as a permanent magnet for applications to fill the gap between high-performance rare-earth magnets with an energy product, (BH)_max, up to 470 kJ/m³ and inexpensive low performance ferrites with a (BH)_max of ~32 kJ/m³. The metastable t-phase can display a saturation magnetization, M_S of ~161 Am²/kg, a coercivity, H_C, of 430 KA/m, and has a theoretical (BH)_max of 101 kJ/m³. Unfortunately, simultaneously obtaining a high M_S and a high H_Chas been problematic. Here we present the results of processing by three different methods: high strain rate high-pressure torsion at elevated temperature, back-pressure-assisted equal channel angular extrusion also at elevated temperature of cast billets, and laser powder bed fusion using pre-alloyed powder. The microstructures of the resulting materials were characterized using x-ray diffraction and electron backscattered diffraction imaging in a scanning electron microscope. The latter was used to identify the phases present and their orientations, the grain size and to determine the dislocation density. The extent of cracking was also characterized. The magnetic properties were measured in different directions using a vibrating sample magnetometer and related to the microstructures. This work was supported by the National Science Foundation under awards 1852529 and 2238204.