Tribological Performance of Hot-Filament Chemical Vapor Deposited Diamond Coatings on Laser Powder Bed Fusion Fabricated Ti-6Al-4V Alloy Substrates

Abstract This study explores the structural, chemical, and tribological behavior of boron-doped diamond coatings deposited on Ti-6Al-4V alloy substrates using hot filament chemical vapor deposition. The coatings were developed under optimized plasma-enhanced chemical vapor deposition conditions. Their characteristics were assessed through a combination of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and linear reciprocating tribological testing using silicon carbide (SiC) ball counter faces. XRD patterns confirmed the formation of nanocrystalline diamond layers, with prominent reflections corresponding to the (111), (220), and (311) planes. The suppression of diffraction signals from the underlying titanium alloy suggested uniform and complete coating coverage. Raman spectra showed a sharp sp3 carbon peak at 1332 cm−1, along with D and G bands typical of graphitic structures, indicating the presence of structural changes associated with boron doping. Friction and wear testing demonstrated a notably low coefficient of friction (∼0.0189) and a reduced wear-rate (∼4.02 × 10−5 mm3/N · min), marking a sixfold improvement over the uncoated alloy. Post-test SEM analysis revealed a dense, crack-free surface without signs of delamination. EDX analysis supported this observation, showing high carbon content (∼91.8%) and minimal detection of substrate elements. Furthermore, the wear track depth (110.4 µm) and SiC ball scar diameter (∼810 µm) were both significantly reduced in coated samples. These findings highlight the potential of boron-doped diamond coatings to enhance the surface durability, wear resistance, and mechanical stability of titanium-based materials, particularly for demanding applications such as biomedical implants.