Improving strength-ductility balance of a brittle Al-doped FeCrNi multi-principal element alloy by introducing a heterostructure with hard phase enveloping soft phase

In the present work, a heterostructure was created in a brittle Al-doped FeCrNi multi-principal element alloy via thermomechanical treatment. This heterostructure consists of a hard phase surrounding a soft phase, with the soft defect-free face-centered cubic (FCC) phase formed through phase transformation evenly distributed within the hard body-centered cubic (BCC) matrix. This unique heterostructure promotes more uniform deformation, thereby enhancing the deformability of the original hard BCC matrix. As a result, the elongation was increased from 2.4 % to 17 %, while the ultimate tensile strength was just decreased from 1076 MPa to 1021 MPa. The maintenance of strength is primarily attributed to the hetero-deformation-induced (HDI) strengthening effect provided by this distinctive heterostructure. Overall, this special heterostructure formed through phase transformation opens up new possibilities for developing alloys with both high strength and ductility.