Design of NbNiTaTi refractory high-entropy alloy via NiTi eutectic phase

Refractory high-entropy alloys (RHEAs) hold far reaching application potential in high temperature structural materials fields due to their high melting points and excellent softening resistance. However, the trade-off between strength-ductility and oxidation resistance of RHEAs has become a critical problem for their processing and application. In this work, we reported a strategy to enhance ductility of NbNiTaTi RHEA by applying the eutectic reaction of NiTi shape memory alloys. Experimentally, NbNiTaTi RHEA exhibited BCC phase and eutectic structure composed of IM phase and NiTiB2 phase. The RHEA showed a compressive strength of 2140 +/- 30 MPa and a compressive plastic strain of 34 +/- 2% at room temperature. Actually, the ultrafine eutectic structure with ductile NiTiB2 phase and hard IM phase could greatly enhance the ductility of NbNiTaTi RHEA while ensuring its strength. Meanwhile, The BCC phase with high solidification temperature remedied the weakness of high temperature stability of RHEA after adding non-high melting point elements. Besides, NbNiTaTi RHEA showed good corrosion resistance and its passive film remained stable across a wide range of potential. These results provided theoretical guidance for the application of ductile phase in RHEA field.