Ni–Cr Substitution in TiFe: An Integrated Experimental–Modeling Study of Phase Stability and Hydride Thermodynamics

We present an integrated experimental–theoretical investigation of the combined effects of Ni and Cr substitution in TiFe _{(1− x − y )} Cr _x Ni _y on phase stability, lattice properties, and hydrogen sorption behavior. Alloys with fixed total substitution ( x  +  y  = 0.2) were synthesized by arc melting and characterized by X‐ray diffraction, electron microscopy, and pressure–composition–‍temperature measurements, complemented by density functional theory and CALPHAD modeling. Both substituents expand the B2 TiFe lattice and markedly reduce the equilibrium plateau pressure of the monohydride phase, indicating enhanced hydride stability while largely preserving reversible hydrogen capacity. Structural analysis shows that Cr promotes the formation of a C14 Laves secondary phase, whereas Ni stabilizes the B2 matrix; their combined addition leads to composition‐dependent coexistence of B2 and C14 phases in agreement with calculated phase equilibria. Thermodynamic analysis indicates that increased hydride stability correlates with both lattice expansion and the intrinsic hydrogen affinity of the substituents. The integrated experimental and modeling approach provides a coherent interpretation linking composition, phase stability, and hydrogen thermodynamics. These results provide quantitative guidance for tailoring TiFe‐derived hydrides from recycled steel feedstocks, supporting circular‐economy strategies for large‐scale hydrogen storage technologies.