Liquid-phase sintering of nanodiamond composite coatings on aluminum A319 using a focused laser beam

Laser-induced phase transition and sintering of nanodiamond (ND) powders (4-8 nm) were used to produce 50-75 µm thick, strongly adherent composite coatings of nanodiamond, amorphous carbon and aluminum on cast alloy A319. First, ND powders, produced by detonation synthesis, were electrostatically sprayed on the surfaces of aluminum substrates. Second, a continuous wave CO2 laser was used to heat the ND powder and aluminum substrate in a controlled fashion to cause liquid-phase nano-sintering that led to a dispersion and phase transformation of ND particles in a molten pool of aluminum. Raman spectroscopy, scanning electron microscopy, optical profilometry, and microhardness, nanoindentation and friction/wear tests were used to evaluate the coating characteristics. Tribology tests showed that the coefficient of friction was under 0.2 in the beginning and then increased to an average value of 0.39. By comparison, the uncoated substrate exhibited a much higher friction (up to 1.03) despite having the finer surface (1.8 µm Ra). Wear loss is also reduced by over 500% in the laser-sintered coupon compared to the uncoated aluminum. The potential application of the work is hard and wear-resistant coatings for lightweight engine components and biomedical implants to improve the tribological characteristics.