Radiation-Conditioned Ti–hBN Coatings for Space Mechanisms: Bridging Tribology and Irradiation Effects from Laboratory to Low-Earth Orbit

The longevity of tribological components in extraterrestrial environments is challenged by abrasive regolith,
extreme temperatures, and ionizing radiation. This study evaluates the performance of vacuum plasma
sprayed (VPS) Ti-2vol.% hexagonal boron nitride (hBN) coatings applied to joint mechanisms such as rod
and slot, ball and socket, and hinge assemblies, fabricated from Al6061 and Ti6Al4V for planetary
structures. Coated and uncoated samples were tested under vacuum with lunar regolith simulant (JSC-1A),
followed by environmental exposures including electron radiation and thermal cycling. Results show that
coated samples consistently outperformed uncoated counterparts across all configurations. Wear depth in
coated components was reduced by over 80%, as confirmed by 3D profilometry and surface imaging. SEM
analysis revealed severe abrasion and localized plastic deformation in uncoated surfaces, while coated
samples retained structural integrity due to synergy of hard protective phases formed during deposition and
retained hBN providing solid lubrication in the sliding surface. Coated and exposed samples exhibited
smoother actuation profiles and reduced friction, indicating a beneficial "conditioning" effect from
environmental exposure. The coatings-maintained performance even on complex geometries with minimal
delamination. These findings demonstrate the potential of VPS Ti-hBN coatings to extend the operational
life of lunar mechanisms, bridging laboratory-scale tribology with flight-relevant mechanical applications.