Tantalum-Doped Co–Cr Alloys: Multiscale Effects on Mechanics, Surface Potential, and Biological Responses

High Resolution Image Download MS PowerPoint Slide Cobalt–chromium (Co–Cr) alloys are valued in biomedicine for their mechanical performance and relative bioinertness. Here, Co–Cr alloys containing tantalum (Ta; 0, 3, 6, and 9 wt %) were synthesized by electric-arc melting to assess how Ta content influences bulk and surface properties across scales. X-ray Diffraction (XRD), Vickers Microhardness, Wettability, Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and Atomic Force Microscopy/Kelvin Probe Force Microscopy (AFM/KPFM) were employed. Bioactivity and biocompatibility were evaluated by immersion in simulated body fluid (SBF) and cell-viability assays. Ta addition promoted the coexistence of Co allotropes (εCo and αCo) and the formation of a secondary TaCo 2 phase, resulting in a dendritic microstructure. Microhardness increased significantly, reaching 466 ± 27 HV0.5 for 9 wt % Ta (≈77% above the Ta-free alloy). Surface-potential mapping revealed ≈1500% higher local potential differences and composition-dependent work function distribution, indicating Ta-driven electronic heterogeneity. The alloys were cytocompatible under extract exposure conditions, suggesting that Ta-induced surface changes may indirectly modulate the biological response. SBF tests confirmed improved in vitro bioactivity, with apatite nucleation on all alloys; the 6 wt % Ta composition produced the thickest Ca/P-rich layer (∼1.3 μm). Overall, Ta addition modulated the microstructure, localized deformation resistance, surface electronic response, and in vitro biological behavior of Co–Cr alloys, with 6 wt % Ta showing the most balanced response among the investigated compositions.