Hierarchical microstructures and strengthening mechanisms of nano-TiC reinforced CoCrFeMnNi high-entropy alloy composites prepared by laser powder bed fusion

Abstract

High entropy alloys (HEAs) have recently received extensive attention due to their appealing mechanical performance given their simple phase formation. This study utilized laser powder bed fusion (LPBF) to fabricate high-performance HEA components. By processing respective powder blends, LPBF enabled the fabrication of stronger composites with a uniformly distributed reinforcing phase. Here, the impact of varying content of nano-scale TiC (1 wt.%-3 wt.%) particles for strengthening the CoCrFeMnNi HEA was explored. The microstructural features and mechanical properties of the HEA composites were investigated in detail. The introduction of nano-scale TiC into the HEA matrix encouraged the development of cross-scale hierarchical microstructure and eliminated the formation of oxide inclusions. Incorporating more nano-TiC led to a higher dislocation density and more refined microstructure in the HEA composites, whereas posed little influence on the anisotropy of the HEA matrix which typically featuring a <001> texture along the building direction. With an optimized content of nano-TiC (1 wt.%-2 wt.%) used, the strength-ductility trade-off can be overcome by exploiting multiple strengthening mechanisms encompassing grain boundary strengthening, solid solution strengthening, Orowan strengthening, and dislocation strengthening. The HEA composites showed a favored strength-ductility combination with a yield strength of 748-882 MPa, ultimate tensile strength of 931-1081 MPa, and fracture elongation of 23%-29%. This study demonstrates that introduction of nano-scale TiC is an effective way to simultaneously improve the strength and ductility of additively manufactured HEA materials.