Abstract
After gas atomization, a quasicrystalline powder based on aluminium was used to prepare a thick coating by high-velocity oxygen-fuel flame torch spraying. This layer was deposited on top of a bond-coat layer on a steel plate. A post-spraying annealing treatment turned the two layers to their stable state, a γ-brass crystal and an icosahedral quasicrystal, respectively. The projection parameters were selected in such a way that the coating behaved like a self-lubricating material, which offered very good wear resistance (duration of pin-on-disk tests superior to 5 km with negligible material loss) and low friction (µ ≤ 6% against sintered tungsten carbide), in contrast to the state of the art. This property was achieved thanks to, on the one hand, excellent bonding to the substrate via the bound coat, and on the other hand, presence at the boundaries between quasicrystalline flakes of a mixture of both threefold and fourfold coordinated carbon originating from spray processing. Application to hard materials used in mechanical devices is appealing, especially because soft, lubricating additives may not be needed, thus considerably increasing the lifetime of the devices and reducing waste of materials.
Highlights
Friction and resistance to wear are applied properties of key importance to mechanical engineering
Worth noticing is the very significant reduction of the friction coefficient measured on the quasicrystal in comparison to that observed on hard steel, despite the fact that they both exhibit similar high hardness
Those experiments were conducted under high vacuum in order to limit oxidation of the wear debris that forms due to adhesion phenomena against the steel pin and contributes to a very significant extent to increase friction if the experiment is performed in ambient air or under oxygen
Summary
Friction and resistance to wear are applied properties of key importance to mechanical engineering. 0.013 10−3 kg s–1 25–45 μm 14°C 120°C and Young modulus Those experiments were conducted under high vacuum (typically 10−7 mbar) in order to limit oxidation of the wear debris that forms due to adhesion phenomena against the steel pin and contributes to a very significant extent to increase friction if the experiment is performed in ambient air or under oxygen. Delaminating materials such as MoS2 or graphite, soft metals such as tin, or polymers, can be used to produce self-lubricating composites that are able to exhibit friction coefficients against steel of the order of a few per cent or less This is at the expense of a loss in hardness and toughness, which may lead to problems with the mechanical functionality of the device. The present article describes a self-lubricating quasicrystalline coating that shows friction against tungsten carbide not larger than 6% and of the order of 6–7% against hard steel, whereas wear resistance is excellent
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