Thermal Transformations and Mechanical Properties of All-d-metal Mn2FeCu Heusler-Type Shape Memory Alloy

Abstract All-d-metal Heusler alloys are emerging functional materials in which magnetic ordering, lattice distortion, and mechanical behavior are strongly coupled through d–d electronic interactions. This study systematically investigates the structural, thermal, magnetic, and mechanical properties of Mn₂FeCu synthesized within a Heusler-type compositional framework. SEM/EDS revealed a dual-phase FCC-based microstructure consisting of Mn–Fe–rich and Mn–Cu–rich domains, while XRD confirmed FCC symmetry with compositional partitioning rather than full L2₁ ordering. Differential scanning calorimetry identified partial melting of the Cu-rich phase near ~ 900 °C. Dilatometry showed a thermoelastic FCC → FCT transformation at ~ 770–780 °C with a recoverable strain of ~ 0.067%. Magnetic thermogravimetric analysis determined a Néel temperature of 485 °C, indicating strong antiferromagnetic ordering and magneto-elastic coupling. Mechanical properties were highly processing-dependent. The as-cast condition exhibited the best strength–ductility balance (YS = 434 MPa, UTS = 632 MPa, 51% elongation), the quenched state maximized ductility (67%), and the furnace-cooled condition increased hardness (210.8 HV) but reduced elongation (20%). Fractography revealed transgranular ductile fracture in the as-cast and quenched states and intergranular fracture in the furnace-cooled condition. These findings demonstrate tunable thermo-magneto-structural behavior in Mn₂FeCu and highlight phase stability challenges in all-d Heusler alloys.