Superior cryogenic strength-ductility synergy in a crack-free additively manufactured multicomponent L12-strengthened medium-entropy alloy

Developing advanced ultrastrong-yet-ductile structural alloys at both room and cryogenic temperatures is a long-standing challenge in the materials community. In this study, we present an integrated strategy combining compositional design with additive manufacturing (AM) to fabricate a medium-entropy alloy (MEA) with a high L1 2 vol fraction (∼44.2%) via laser powder bed fusion (LPBF). The newly designed alloy exhibits excellent printability with a high relative density of 99.97%. Thermodynamic and thermal-fluid simulations reveal that the extremely high cooling rate (∼7 × 10 6 K/s), steep temperature gradient (∼7 × 10 7 K/m), and narrow solidification range (248 K). It promotes a single-phase face-centered-cubic (FCC) solidification path while reducing cracking susceptibility. Upon the post-heat treatment, coherent L1 2 nanoparticles are controllably introduced, producing a distinctive dual-phase microstructure. The heat-treated MEA (HT-MEA) exhibits exceptional tensile properties with a yield strength (σ y ) of 1240 MPa and an ultimate tensile strength (σ u ) of 1646 MPa, combined with a ductility of 25.0% at room temperature. More prominently, the σ y and σ u further increase to 1413 MPa and 2011 MPa at 77 K accompanied by the uniform elongation of 27.3%. Detailed microstructural examinations indicate that the temperature-dependent mechanical responses originate from the sequential activations of various deformation substructures. These findings demonstrate a new alloy design paradigm that realizes both superior mechanical properties and excellent AM printability, which could effectively empower the development of advanced structural materials operable under extreme service conditions.