High-Strength and Ductile TiNbZrTa BCC MPEA With Heterogeneous Microstructure for Orthopedic Implants

In order to develop a promising bio-applicable body-centered-cubic multi-principal element alloy (BCC MPEA) with excellent mechanical and biological properties, Tantalum (Ta) was introduced into TiNbZr alloy based on lattice distortion design, and heterogeneous structure was subsequently constructed. The widespread hetero-structured interfaces alter planar slip mode in recrystallized grains (RGs) via emission and multiplication of geometrically necessary dislocations (GNDs), which generate significant heterogeneous deformation induced (HDI) stress effect. Plentiful subgrains and nano-sized dislocation cells in unrecrystallized grains (UGs, i.e., textures) enable extensive dislocation behavior including annihilation, activation and interaction, effectively alleviating stress concentration in RGs and strain gradient across the interfaces. This process results in an optimal balance of yield strength reaching 925.2 MPa and fracture elongation of 26.1%. In vitro experiments demonstrate that TiNbZr_0.7Ta_0.3 alloy exhibits enhanced cell adhesion, proliferation and osteogenic response compared to TC4 alloy. The remarkable mechanical properties and biocompatibility render it a highly promising candidate for orthopedic implants. This study provides new insights for the design and optimization of biomedical MPEAs with excellent mechanical properties.