Investigating Carbon Coating on Ni-Invar and Ti-6Al-4V Surfaces for Low Friction Performance

This study investigates the deposition of carbon-based coatings on Ni-Invar and Ti6Al-4V substrates using the pack carburization method with cyanide-rich cassava leaves as the carbon source. The coated surfaces were characterized using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), and lateral force microscopy (LFM) to assess their composition, structure, and tribological performance. The results indicate that the coatings exhibit distinct structural and tribological behaviors depending on the substrate. Ni-Invar demonstrated the formation of multi-layered graphene structures with minimal formation of metal carbide within the diffusion layer, resulting in an ultra-low coefficient of friction ( 0.008 in macroscopic tests and 0.0033 in nanoscale friction measurements) on the surface. In contrast, a considerable amount of metallic carbide on the Ti-6Al-4V substrate was observed, leading to a less ordered carbon layer with higher friction coefficient ( 0.1 in macroscopic tests and 0.0147 in nanoscale friction measurements). Monte Carlo simulations and
density functional theory (DFT) calculations revealed that Ni-Invar’s weak carbon-metal interactions promote the clustering of carbon atoms into graphene-rich structures, while the stronger affinity of Ti for carbon leads to metal carbide formation within the diffusion layer. These findings demonstrate that substrate chemistry significantly influences the tribological performance of carbon coatings and highlight the potential of Ni-Invar as an ideal substrate for achieving superlubricity through controlled carbon deposition.