Self-adaptive and self-healing nanocomposite tribocoatings

In this thesis the design and exploration of environmental self-adaptive and damage self-healing tribocoating with both an ultralow coefficient of friction and a low wear are studied. Our objective is aimed at producing WS2 in which the porous structure with micocracks are healed and the tribo-system becomes self-repairing and even self-curing. In general the coatings has a coefficient of friction down to 0.02 in dry air (5% RH) and around 0.15 in moisture (55% RH), together with an ultralow wear rate of 10−7 mm3 m−1N−1. The nonreactive WS2/a-C coating is superior to the WS2/a-C:H one for the future development of self-adaptation in varied humidity conditions. HR TEM observations reveal an instant WS2 platelets rearranged parallel to the sliding direction. This corresponds to a short tribological running-period and thus self-adaptive “frictionless” response. Besides, by sliding contact, segmented TMD nanoplatelets are reorientated and bridged to form a closed continuous tribofilm that could consequently repair damages in an adaptive way. In fact, the notched damages are acting as microreservoirs restoring debris which become transformed at a later stage into tribofilm consisting of well aligned WS2 lubricants.. The study sheds new light on the release of the requirement of producing flawless coatings for tribo-applications

Self-adaptive and self-healing nanocomposite tribocoatings

In this thesis the design and exploration of environmental self-adaptive and damage self-healing tribocoating with both an ultralow coefficient of friction and a low wear are studied. Our objective is aimed at producing WS2 in which the porous structure with micocracks are healed and the tribo-system becomes self-repairing and even self-curing. In general the coatings has a coefficient of friction down to 0.02 in dry air (5% RH) and around 0.15 in moisture (55% RH), together with an ultralow wear rate of 10−7 mm3 m−1N−1. The nonreactive WS2/a-C coating is superior to the WS2/a-C:H one for the future development of self-adaptation in varied humidity conditions. HR TEM observations reveal an instant WS2 platelets rearranged parallel to the sliding direction. This corresponds to a short tribological running-period and thus self-adaptive “frictionless” response. Besides, by sliding contact, segmented TMD nanoplatelets are reorientated and bridged to form a closed continuous tribofilm that could consequently repair damages in an adaptive way. In fact, the notched damages are acting as microreservoirs restoring debris which become transformed at a later stage into tribofilm consisting of well aligned WS2 lubricants.. The study sheds new light on the release of the requirement of producing flawless coatings for tribo-applications

Effects of carbon content and argon flow rate on the triboperformance of self-lubricating WS2/a-C sputtered coating

Layered transition metal dichalcogenides (TMD) such as WS2 are materials well-known for their solid lubrication properties [1]. However, the lubricating property degrades through oxidation or moisture and it is also limited by its low hardness and low load-bearing capacity. In contrast amorphous diamond-like carbon (DLC) films are reported to have many features that contribute to excellent tribological characteristics, such as high hardness, anti-wear property with both low friction coefficient and low wear rate[2]. The present research aims at depositing WS2/a-C nanocomposite coatings by magnetron co-sputtering method. The effects of carbon content and argon flow rate on the microstructure and mechanical performance were investigated. The WS2/a-C nanocomposite tribocoating was scrutinized by electron microscopy and mechanical testing. Transmission electron microscopy reveals feathery WS2 platelets, randomly distributed in the amorphous carbon matrix. The nanocomposite coating turns out to be more amorphous-like with increasing carbon content. Nanoindentations tests show that the hardness and elastic modulus of the coating increase with increasing carbon addition while decreasing with a higher argon flow from 10 sccm to 25 sccm. Ball-on-disk tribotests (100Cr6 steel ball as a counterpart) show that the coefficient of friction can be as low as 0.017 in a dry environment (5% relative humidity). It reaches 0.15 in a high humidity surrounding and remains stable within 20000 sliding cycles

Effect of Quench Polish Quench Nitriding Temperature on the Microstructure and Wear Resistance of SAF2906 Duplex Stainless Steel

The effect of quench polish quench (QPQ) nitriding temperature on the microstructure and wear resistance of SAF2906 duplex stainless steel was investigated. Results showed the surface of the nitrided samples was composed of an oxidized layer, a loose compound layer, a compact compound layer, and a diffusion layer. The oxidized layer was composed of Fe3O4. The main phases of the loose compound layer were CrN, alpha(N), Fe2-3N, and Fe3O4. The compact compound layer was composed of CrN, alpha(N), and Fe2-3N. In the diffusion layer, CrN and expanded austenite (S) were the main phases. The nitrided layer thickness increased from 20 to 41 mu m with an increasing temperature of 570 to 610 degrees C. When the nitriding temperature was above 590 degrees C, the precipitates in the diffusion layer became coarsened, and their morphologies gradually changed from spherical particulate to rod-like and flocculent-like. Tribotests showed the cumulative mass loss of QPQ-treated samples was much lower than that of the substrate. The cumulative mass loss of the samples nitrided at 610 degrees C was higher than that at 570 degrees C during the first 29 h. When the test time was over 29 h, the former was lower than the latter