Intercalation-driven friction reduction in Ti-based MXenes for biomedical applications

Abstract

This thesis investigates the tribological performance of organically intercalated Ti3C2Tx MXene coatings applied to a novel Ti64-5HAP-5CMC composite substrate developed for implant applications. The study aims to evaluate the influence of MXene intercalation chemistry and coating methodology on friction behaviour, wear mechanisms, and tribolayer stability under ambient sliding conditions.Intercalated MXene powders were characterised using PXRD, XPS, and TEM, confirming successful intercalation and increased interlayer spacing, with ODA-intercalated MXene exhibiting a larger interlayer distance compared to HDA-intercalated MXene. Surface roughness and morphology of the coated substrates were analysed using optical profilometry.Tribological testing demonstrated a significant reduction and stabilisation of the coefficient of friction for MXene-coated samples compared to the uncoated reference material. Among the investigated systems, spraycoated ODA-intercalated MXene exhibited the lowest and most stable friction values in short-term tests and was therefore selected for extended long-term investigations. Stable low-friction behaviour was maintained over 24h, 72h. While the wear track width on the sample surface remained comparable to the reference material, a clear reduction in counterbody wear was observed for ODA-intercalated MXene coatings.Comprehensive wear track analyses using LSM, Raman spectroscopy, SEM, and TEM revealed the formation of a mechanically mixed tribolayer. Raman spectroscopy confirmed the presence of the organic intercalant within the wear track after sliding. SEM and TEM investigations showed that MXene flakes undergo pronounced bending, folding, and partial amorphisation while largely retaining their lamellar structure. TEM-EDX analysis demonstrated elemental intermixing between the MXene coating and the porous substrate, as well as reduced material transfer from the counterbody for ODA-intercalated systems. Overall, the results demonstrate that organic intercalation, particularly with ODA, significantly enhances the tribological performance of MXene coatings on the investigated implant substrate.