Novel Co-free CrFeNiNb0.1Ti high-entropy alloys with ultra high hardness and strength

A new class of materials called high-entropy alloys (HEAs) possess unusual structural and thermal features, which could contribute to the mechanical performance. However, the high cost and sole-phase insufficiently strong for engineering applications are greatly limit the practical application of the HEAs. Therefore, developing HEAs with high strength/hardness and low cost is urgent. In this work, we designed a novel HEA system by minor additions of Nb and Ti. The microstructures and mechanical behaviors of the CrFeNiNb0.1Tix high-entropy alloys were investigated. The results showed that with the Ti addition, the content of FCC phase decreased, while the BCC/B2 and HCP phase proportion increased, which dramatically improved the hardness and yield strength. With the x value increased from 0.2 to 0.4, the Vickers hardness value of the alloys enhanced from 512.35 HV to 866.92 HV, and compressive yield strength increased from 1250 MPa to 2223 MPa, respectively. Different from the improvement in yield strength, the fracture strain decreased with the Ti addition. In addition, the microstructure evolution and strengthening mechanism were discussed.