Mo-Induced Phase Modification of Laser-Cladded TiNbZrMo Coatings and Its Effects on Interfacial Electrochemical Stability

To address the issue of physiological corrosion and its adverse susceptibility on the long-term interfacial stability of TC4 titanium alloy medical implants, multicomponent TiNbZrMo coatings with varying Mo contents were fabricated on TC4 substrates via laser cladding. Microstructural analysis revealed that the introduction of Mo significantly modulated the precipitate morphology, gradually refining the α phase from coarse lath-like structures into acicular and spin dle-like shapes. Notably, the 9 wt % Mo coating exhibited the most pronounced structural refinement along with the highest precipitate density. Electrochemical impedance spectroscopy (EIS) demonstrated a nonmonotonic trend in the charge-transfer resistance ( R ct ) of the coatings with increasing Mo content. Among all samples, the 9 wt % Mo coating exhibited the optimal compositional window effect, yielding a peak R ct value of 3.98 × 10 6 Ω·cm 2, which is nearly 2 orders of magnitude higher than that of the TC4 substrate, thereby demonstrating superior interfacial electrochemical stability. X-ray photoelectron spectroscopy (XPS) analysis further confirmed the formation of a protective composite passive film consisting of Ti-, Nb-, Zr-, and Mo-containing oxides on the coating surface. Correlating the microstructural evolution with electrochemical kinetics, the enhanced interfacial stability is primary attributed to the Mo-induced phase modification. Furthermore, all coatings exhibited favorable in vitro cytocompatibility. These findings provide critical experimental insights into the compositional design and interfacial stability regulation of multicomponent biomedical titanium alloy coatings.