Synthesis of diamond-like carbon coatings on aluminum 6061 T-91 substrates by laser sintering of ultra-nanocrystalline diamond powders

Diamond-like carbon (DLC) coatings have been prepared on aluminum 6061 T-91 substrates with the aid of electrostatic spray deposition (ESD) of ultra-nanocrystalline diamond powders (2-8 nm) followed by direct laser sintering technique. A continuous-wave CO2 laser was utilized, producing a dense, adherent DLC coating with a nominal thickness of 10 μm under optimal laser parameters that included laser power of 200 W, spot size of 1 mm by 0.1 mm and scanning speed of 254 mm/s. The evidence of DLC formation and its purity was obtained by characterizing the samples with Raman spectroscopy, X-ray diffraction and scanning electron microscopy/energy dispersive spectroscopy. Functional evaluation of DLC coatings was performed using scratch, micro-hardness, fracture toughness and surface roughness tests. Raman measurements showed the presence of a broader peak at around 1332 cm− 1 (characteristic of pure diamond) for electrostatically deposited samples and the presence of DLC with a broad asymmetric hump in the region of 1000 to 1600 cm− 1 for laser-sintered samples. X-ray diffraction and energy dispersive spectroscopy confirmed the presence of carbon phases in the coatings. Scanning electron microscopy examination showed a fairly uniform and dense coating with a nominal thickness of 10 μm and a heat affected zone of 60–80 μm. These coatings exhibited micro-hardness in the range of 2150 to 2350 kg/mm2 when measured using a Vickers diamond pyramid indenter at a load of 0.5 N. In some localized regions, hardness of 9000 kg/mm2 was obtained. Scratch tests revealed a fairly homogenous coating with strong adhesive nature having almost four times the average critical force when compared against the electrostatically deposited sample. Fracture toughness and surface roughness are well within the acceptable ranges of DLC coatings. The capability of laser sintering to produce thick DLC coatings with outstanding mechanical and tribological properties and excellent bonding with aluminum offers the possibility to tailor an extreme lightweight, strong and wear-resistant material.