Coupling precipitation strengthening and transformation induced plasticity to produce a superior combination of strength and ductility in a high entropy alloy

The strength-ductility trade-off has always been a difficult issue in the development of highperformance structural materials. In this work, a new non-equiatomic Fe37.5Ni30Co22.5Al5Ti5 (at%) high entropy alloy (HEA) was developed, which shows both excellent strength and ductility. The yield strength of the aged HEA reached 1094 MPa, which is more than twice that of the solid-solution HEA, while the ultimate tensile strength was 1275 MPa, and the elongation to failure was ∼38%. The high yield strength resulted from precipitation strengthening provided by a high number density of L12-Ni3(Al, Ti) nanoprecipitates. Both a small grain size and the nanoprecipitates can induce high local stresses, enhancing the phase transformation from face-centered cubic (FCC) to martensite that occurs in this HEA, and which can lead to the good ductility. As much as possible to keep strength-ductility through the coupling between precipitation strengthening and TRIP effect is a suitable strategy to overcome the strength and ductility trade-off.