Seeking to improve the wear resistance of the Ti6Al4V (Ti64) alloy for biomedical applications, carbon nanotubes (CNTs) and calcium phosphate (CaP) ceramics were added to Ti64 powder and successfully 3D-printed using a commercial laser engineered net shaping (LENS™) system. It was hypothesized that CNTs would allow for in situ carbide formation during laser processing, resulting in increased surface hardness. It was also hypothesized that CaPs would allow for protective tribofilm formation during wear, reducing material loss from wear-induced damage. Scanning electron microscopy images reveal defect-free microstructures with fine carbides evenly distributed, while X-ray diffraction confirms the presence of carbides without additional unwanted intermetallic phases. Vickers microhardness shows an increase in surface hardness in coatings containing both CNTs and CaPs. In vitro tribological studies found reduced coefficient of friction, reduced wear rates, and reduced metal ion-release concentrations in coatings containing both CNTs and CaPs. This study demonstrates the efficacy of CNTs and CaPs to improve wear resistance of Ti64 for potential applications in articulating surfaces of load-bearing implants.

The oxidation mechanism and thermal stability of nickel oxide (NiO)/carbon nanotube (CNT) composites were investigated by examining composites with different NiO contents by thermogravimetric analysis and transmission electron microscopy (TEM). NiO acts as a catalyst in the oxidation of CNT in the composite. CNTs can be oxidized, even in a vacuum, by reducing NiO to nickel at temperatures lower than the normal oxidation temperature of CNTs. This phase transition was confirmed directly by in situ heating TEM observations. In air, reduction by CNT occurs simultaneously with reoxidation by gaseous O2 molecules, and NiO maintains its phase. The thermal stability decreased with increasing NiO content because of defects in the CNT generated by the NiO loading.