Novel B-doped Mn-Ni-Ti-Fe all-d-metal Heusler alloy: large elastocaloric effect and exceptional cycling stability

All-d-metal Heusler alloys, due to the enhanced mechanical properties brought about by d-d orbital hybridization, have become highly promising candidate materials in the field of elastocaloric cooling. However, achieving an optimal balance among high strength, low stress hysteresis, and excellent elastocaloric cycling stability remains a critical challenge. In this study, a novel all-d-metal Heusler alloy (Mn 50 Fe 2 Ni 37 Ti 11 ) 100- x B x ( x = 0, 0.1, 0.2, 0.3) was designed and fabricated. Systematic experimental results demonstrate that the addition of trace amounts of boron significantly optimizes the microstructure and mechanical properties of the alloy. Specifically, the alloy with x = 0.3 exhibits outstanding toughness, with a fracture strength reaching 1760 MPa and fracture strain up to 33.4%. Although its maximum superelastic strain is relatively small (2.2% strain under 450 MPa stress), this alloy features an ideal low critical driving stress and narrow stress hysteresis, thereby reducing energy dissipation during the martensitic phase transformation. Notably, the (Mn 50 Fe 2 Ni 37 Ti 11 ) 99.7 B 0.3 alloy shows exceptional elastocaloric cycling stability, maintaining a stable adiabatic temperature change (Δ T ad ) of 4.5 K after 5000 elastocaloric cycles, with no obvious performance degradation. The novel Mn-Ni-Ti-Fe-B alloy in this study offers a new strategy for developing elastocaloric cooling materials possessing high toughness and excellent elastocaloric cyclic stability.