Improving strength and ductility at cryogenic temperature via microstructure-engineered deformation twinning in Ti1Al3(CrFeNi)96 multi-principal element alloys

• Increasing Al content progressively refines grains and introduces heterogeneous microstructures. • The Ti 1 Al 3 (CrFeNi) 96 alloy exhibits simultaneous improvement in strength and ductility at cryogenic temperature. • Enhanced tensile properties in Ti 1 Al 3 (CrFeNi) 96 arise from the synergistic effect of deformation twins, heterogeneous microstructure and coherent L1 2 precipitates. To achieve simultaneous improvements in strength and ductility of single-phase FCC-structured multi-principal element alloys (MPEAs), we systematically investigated the microstructural evolution and mechanical properties of Ti 1 Al x (CrFeNi) 99-x (at.%, x = 1, 2, 3) at both room temperature (293 K) and cryogenic temperature (77 K). The findings demonstrate that increasing Al content leads to progressive grain refinement. At 293 K, higher Al content enhances strength at the expense of ductility. At 77 K, the alloy containing 3 at.% Al demonstrates remarkable synergistic enhancement in both strength and ductility. Compared to 293 K, it achieves a 54 % increase in strength to 1479 MPa while simultaneously showing a 2.3-fold improvement in elongation, reaching 28 %. Microstructural analysis and corresponding theoretical calculations reveal that the concurrent improvement in low-temperature strength and elongation originates from the development of a heterogeneous microstructure, coherent interfaces between L1 2 precipitate and matrix, and deformation twinning activated by body-centered cubic (BCC) precipitates. This study establishes a comprehensive microstructural design paradigm integrating multiple strengthening mechanisms, providing a critical guidance for developing cobalt-free MPEAs with exceptional cryogenic performance. These key insights will drive innovation in materials for extreme-environment applications.