Exploration of Pseudobinary Alloys (Al–Mn)‐(Co–Fe–Ni) to Design High‐Entropy and Compositionally Complex Alloys to Stabilize the τ Phase in Al–Mn‐Based Ferromagnetic Alloys

This study examines alloys in the ðAl 46 -Mn 54 Þ x ðCo -Fe -NiÞ 100 -x pseudobinary system. The objective is to gain a deeper understanding of the thermodynamic limits of the ferromagnetic Al-Mn τ phase within the broader context of high-entropy alloys (HEAs) and CompositionallyComplex Alloys (CCAs). Although this phase shows promise as a rare-earth-free permanent magnet, its industrial application remains challenging due to its intrinsic instability. The present work investigates nine distinct compositions located along a line in a four-dimensional compositional space, combining an ðAl -MnÞ alloy with ðCoFeNiÞ in varying proportions. The alloys have been produced using a cold-crucible levitation furnace, heat-treated, and studied in their as-cast condition. Characterization methods included X-ray diffraction (XRD) and magnetic propertymeasurements. The experimental findings highlight a complex interplay between composition, phase stability, and magnetic response, demonstrating that conventional HEA design strategies are insufficient for this alloy system. The study concludes that a more robust, thermodynamically informed approach is required to efficiently explore the design space of HEAs and CCAs based on metastable phases. Furthermore, the magnetic properties evolve significantly with composition. This evolution is not reflected in the XRD patterns, indicating that it arises not only from crystal structure changes but also from factors such as local atomic ordering.