Investigation of the impact fracture behavior of in-situ TiC particle-reinforced high-entropy alloy composite coatings through experiments and molecular dynamics simulations

Abstract

To enhance the overall mechanical performance of Co-free AlCr_1.75CuFeNi₂ high-entropy alloy (HEA) coating, in-situ TiC particle-reinforced AlCr_1.75CuFeNi₂ HEA composite coatings were fabricated by laser cladding with controlled (Ti + C) additions. The effects of TiC content on the microstructural evolution, hardness, and impact fracture behavior of the coatings were systematically investigated through a combination of experimental characterization and molecular dynamics (MD) simulations. The results show that the in-situ TiC particles significantly refine the dendritic microstructure and promote the formation of an interconnected BCC/B2 spinodal structure in the interdendritic regions. The average grain size decreases from 29.3 μm to 12.9 μm, while the average microhardness value increases from 384.3 HV_1.0 to 497.3 HV_1.0. Charpy impact tests reveal that excessive TiC particles deteriorate impact toughness owing to stress concentration and interfacial debonding, whereas moderate TiC contents maintain relatively high impact energy absorption. MD simulations demonstrate that TiC particles impede dislocation motion through an Orowan bypass mechanism, induce dislocation pile-up, and promote crack deflection. In addition, the high-density BCC/B2 spinodal structure effectively alters crack propagation paths, resulting in enhanced crack-growth resistance and progressive fracture behavior. The combined experimental and simulation results reveal a multiscale synergistic strengthening mechanism involving grain-refinement strengthening at the micrometer scale, strengthening by uniformly dispersed fine in-situ synthesized TiC particles at the submicrometer scale, and energy dissipation associated with high-density disordered/ordered phase interfaces at the nanometer scale. The in-situ TiC particle-reinforced composite coatings achieve an increased strengthening effect while maintaining relatively high impact energy absorption, thereby alleviating the strength-toughness trade-off.