Heterophase interfacial strengthening mechanism in CrNiCux medium-entropy alloys fabricated by laser-directed energy deposition

The unique structure and formation mechanism of medium-entropy alloys (MEAs) generally result in better comprehensive properties than traditional alloys. However, the strength-ductility trade-off remains a bottleneck, which limits their applications. In this study, we designed novel high-performance CrNiCux MEAs with a heterophase composition by incorporating a Cu-rich phase, and they were fabricated using laser-directed energy deposition (LDED). The results show that synergistic strengthening from multiple phases significantly improved the mechanical properties of the alloys, resulting in a tensile strength of 675 MPa and a ductility of 34.4%, demonstrating an excellent combination of high tensile strength and ductility. The improved mechanical properties of the CrNiCux medium-entropy alloys are primarily due to the heterophase interfacial strengthening mechanism. In the alloy, numerous semi-coherent and coherent interfaces formed between the Cr-rich phase, Cu-rich phase, and the matrix, creating extensive lattice distortions at the interfaces. An increase in the Cu-rich phase content promoted the interaction between phases, enhancing the strain energy of the alloy and the barrier strength of the interfaces. The calculated τintvalues, ranging from approximately 5.92–6.69 GPa, are significantly higher than those found in traditional alloys, providing a benchmark for designing new high-performance medium-entropy alloys.