Gradient-controlled interfaces in medium/high entropy alloy composites for enhanced mechanical and biocompatibility performance

A critical challenge in developing orthopedic implants is tuning them to achieve high yield strength, low modulus, and enhanced wear resistance. A key strategy involves optimizing matrix-reinforcement interfaces in metal matrix composites. In this study, we incorporated MoNbTaTiZr-based high-entropy alloy (HEA) particles within a Ti-Zr-Nb (TZN) medium entropy alloy matrix. Using powder metallurgy and spark plasma sintering, we developed a graded core-shell structure around the HEA particles, which refines interfacial bonding and optimizes the load transfer mechanism. The resulting heterogeneous alloy exhibited up to a 50 % enhancement in yield strength (>750 MPa), a low elastic modulus (⁓65 GPa), and a significant reduction in the wear rate to the order of 10 −4 to 10 −5 mm 3 /Nm, while retaining substantial tensile ductility (>8 %). Molecular dynamics simulations revealed that the HEA particles act as impenetrable obstacles to dislocation motion, inducing partial wrapping and pile-up at the particle-matrix interface. This leads to localized stress accumulation and the generation of back-stress, which corroborates experimental observations of increased yield strength and interface-driven plasticity reduction. Critically, post-sintering annealing of 10 wt% HEA-TZN samples resulted in an optimized interface thickness via Mo and Ta interdiffusion, restoring ductility to levels comparable to pristine TZN without compromising strength. This compositional gradient inhibited crack propagation and promoted dislocation pile-up while ensuring strong interfacial bonding. Additionally, the sintered heterogeneous alloys showed excellent corrosion resistance in simulated body fluid and enhanced cellular adhesion and proliferation compared to conventional biomaterials. The present approach advances orthopedic implant design by combining wear resistance with low modulus to alleviate stress shielding.