Designing Additive‐Manufactured High‐Performance CoCrNi Matrix Composites Based on Grain Boundary Segregation

ABSTRACT Through grain boundary segregation engineering, a crack‐free high‐strength CoCrNi medium‐entropy alloy (MEA) can be successfully fabricated via laser powder bed fusion (PBF‐LB). The influence of micron‐sized TiC particles on microstructural evolution, grain boundary segregation behavior, and mechanical properties was systematically investigated in the present study. Additionally, the high‐temperature oxidation mechanism of the CoCrNi alloy was elucidated. At an optimal TiC content of 3 wt%, carbon segregation at grain boundaries significantly reduced the grain boundary energy, hence destabilizing the liquid film and promoting grain coalescence during solidification. This process effectively suppressed hot cracking. Partial dissolution of TiC during PBF‐LB processing led to the formation of nano‐sized Cr 23 C 6 precipitates and TiC/TiO 2 core–shell structures at grain boundaries. These precipitates acted as effective Zener pinning sites, which inhibited columnar grain growth and refined the grain structure. As a result, the CoCrNi–3 wt% TiC composite exhibited markedly superior mechanical properties and excellent high‐temperature oxidation resistance. Furthermore, this composite demonstrated excellent high‐temperature oxidation resistance. The fine‐grained microstructure facilitated selective Cr oxidation, which led to the rapid formation of a dense Cr 2 O 3 protective scale. Simultaneously, the relatively high diffusion coefficient of Cr enabled its migration toward loosely packed TiO 2 regions, contributing to the formation of a continuous and self‐healing Cr 2 O 3 layer. Altogether, these mechanisms provide improved oxidation protection and long‐term stability at elevated temperatures.