Improved strength and ductility of Ti₂(CrFeNi)₉₈ multi-principal element alloy at cryogenic temperature with deformation twins induced by BCC precipitates

The mechanical properties of a Ti₂(CrFeNi)₉₈ multi-principal element alloy (MPEA) with heterogeneous microstructures were systematically investigated at room (293 K) and cryogenic (77 K) temperatures, together with the corresponding microstructure evolution. As the temperature decreased from 293 K to 77 K, the yield strength, ultimate tensile strength and ductility increased from 800 MPa to 980 MPa, 1.1 GPa–1.5 GPa and 20%–25%, respectively. Microstructure characterization indicates that the increase of ductility at 77 K is owing to the arising of deformation twins (DTs) in the face-centered cubic matrix adjacent to body-centered cubic precipitates. Finite element analysis confirm that the DTs is induced by locally concentrated stress which exceeds the critical twinning stress, owing to the low stacking fault energy at cryogenic temperature. This work provides a designing strategy for promising Co-free MPEAs with both good strength and ductility at extreme low temperature conditions.