Effect of Copper Content on the Microstructure and Mechanical Properties of As‐Cast Refractory MoNbTi Multiprincipal Element Alloys

Multiprincipal element alloys (MPEAs) exhibit a wide range of microstructures and mechanical properties, depending on composition and processing. In this study, the impact of Cu addition on the microstructure and mechanical performance of MoNbTi MPEAs is investigated. Cu plays a dual role, promoting the formation of strengthening intermetallic phases while, at higher concentrations, potentially increasing brittleness. It also influences diffusion kinetics and phase transformation, leading to dendritic refinement and the formation of Cu–Ti intermetallics. Phase diagram simulations predict the behavior of Cu x MoNbTi alloys with varying Cu content ( x = 0, 0.25, 0.5, 1.0, and 2.0). The alloys are synthesized by arc casting and analyzed using X‐ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Mechanical properties are evaluated through Vickers hardness and compressive testing. The results show that Cu enhances densification and refines the dendritic structure, increasing hardness and strength. However, excessive Cu content leads to an increased fraction of Cu‐rich intermetallics. Hardness ranges from 515 ± 54 HV to 614 ± 47 HV, while UTS peaks at ≈2000 ± 80 MPa for Cu 0.5 MoNbTi, nearly doubling that of MoNbTi. The well‐distributed precipitate network in Cu 0.5 MoNbTi enables effective plastic deformation by reducing stress concentrations and delaying crack formation. Cu tailors MPEA microstructures, optimizing properties for applications.