Laser additive manufacturing of nano-TiC particles reinforced CoCrFeMnNi high-entropy alloy matrix composites with high strength and ductility

Abstract

CoCrFeMnNi high-entropy alloy (HEA) matrix composites reinforced with nano-sized TiC particles were successfully fabricated by laser powder bed fusion (LPBF), which is widely used laser additive manufacturing technology. The microstructural evolution and mechanical properties of the HEA composites fabricated at various processing conditions, were investigated. The LPBF-fabricated HEA composites showed typical hierarchical microstructure characteristics including epitaxially grown columnar grains, submicron-sized cellular substructures, nano-sized precipitates, and a high density of dislocations. The rapid solidification process inherent to LPBF resulted in micro segregations of Mn and Ni along the cell walls, which contributed to a pronounced impurity-drag effect toward the present dislocations. TiC1-x with a size of 35–100 nm uniformly precipitated along the cell boundaries as well as inside the cells. Entangled dislocations easily formed around the cell walls and the nano-TiC1-x precipitates leading to a high dislocation density in the LPBF-fabricated HEA composites. The HEA composites with 1 wt% nano-TiC addition exhibited a promising mechanical performance readily characterized by a yield strength of 779 MPa, tensile strength of 940 MPa and an elongation of 30%. The advantageous combination between strength and ductility can be attributed to the prevailing subgrain boundaries, solid solution strengthening, grain refinement, nano-precipitation hardening, dislocation hardening, plasticity and storage. This work demonstrates the importance of hierarchical microstructures of HEA materials via incorporation of nano-sized TiC particles for imparting exceptional mechanical properties.