Strength and ductility dual-enhancement of Ni36Co30Fe11Cr11Al6Ti5Nb1 high entropy alloy by directional solidification

Ni36Co30Fe11Cr11Al6Ti5Nb1 high entropy alloys (HEAs) were prepared by directional solidification. The effect of solidification rate on microstructure evolution and mechanical properties was systematically investigated. Re-sults show that the microstructure has a dendritic morphology with uniform orientation. FCC phase rich in Co, Cr and Ni is formed in the dendrite. Laves phase rich in Nb and Ti and FCC phase rich in Ni and Ti are formed between dendrites. With the increase of solidification rate, the dendrites are gradually refined. Tensile results show that the yield strength and elongation increase with the increase of solidification rate. The yield strength and elongation at 100 mu m/s are 606.2 MPa and 27.6 %, respectively, achieving an excellent combination of strength and plasticity. Fine-grain strengthening, second-phase strengthening and solid-solution strengthening are the dominant strengthening mechanisms. The dendrites growing along the directional direction reduce the transverse grain boundaries and avoid the rapid propagation of cracks.