Strengthening Fe1.4Co0.8Ni0.8Cr high-entropy alloy composites via in-situ synthesis of TiC: Perspective from experiments and first principles calculations

Abstract

Achieving a harmonious balance between strength and plasticity is a long-standing problem in single-phase face-centered-cubic (fcc) high-entropy alloys (HEAs). Herein, in-situ TiC ceramic particle reinforced fcc-structured Fe1.4Co0.8Ni0.8Cr HEAs is designed and investigated by combining the experiments and first-principate calculations. The results show that the y(TiC)-Fe1.4Co0.8Ni0.8Cr (y=0, 2.5, 5.0, 7.5 and 10.0%, y: volume fraction) composites consist of fcc phase with submicron/micron TiC after the co-addition of Ti and C element, and the formation of TiC facilitates to refine the microstructure of the composites. Such microstructural evolutions significantly enhance the mechanical performances of the composites. Particularly, the 7.5%(TiC)-Fe1.4Co0.8Ni0.8Cr composite exhibits a high yield strength of ∼562.7 ± 7.7 MPa and tensile strength of ∼971.3 ± 5.4 MPa, which are respectively increased by 169.0% and 88.3% as compared with the Fe1.4Co0.8Ni0.8Cr based alloy, yet with the fracture elongation decreases to 35.9 ± 0.3%. The increment in yield strength is mainly driven from the combined effect of the grain refinement strengthening, dislocation strengthening and precipitation strengthening. Density functional theory (DFT) results reveal that the increase of C-Ti bonds and the formation of covalent bonds in the 7.5%(TiC)-Fe1.4Co0.8Ni0.8Cr composite lead to relatively higher strength and lower ductility, which are well agreed with the experimental results.