•A general parametric model is used to optimize the bottom profile of surface texture.•GA-SQP, an intelligent computational approach, is applied.•The optimization results are influenced by the operating parameters of friction pairs.•The mechanism of the optimized bottom profile is revealed.Most of the previous studies on the surface texture were based on pre-determined shapes and distributions, and the global-optimum shapes were uncertain. In this paper, a general parametric model of the groove bottom profile (inner structure, depth profile) of thrust bearings was developed and the GA-SQP hybrid method was adopted to obtain the global-optimum profile of the groove texture bottom. The optimization target was the maximization of the load carrying capacity (LCC) of the oil film. The results verified the superiority of the proposed GA-SQP hybrid method. The mechanism of the optimized bottom profile was investigated using the commercial software FLUENTR.High load carrying capacity can keep stable lubricant film so as to avoid direct contact of the fiction pairs under high load. The load carrying capacity can be solved by Reynolds equation. On the basis of Reynolds equation, it can be found that the change of fluid film thickness is the intrinsic cause of hydrodynamic effect. Moreover, bottom profile of surface texture is one of the determinants of fluid film thickness. A general parametric model of groove bottom profile was developed and GA-SQP hybrid method was adopted to optimize the surface texture bottom profile. The mechanism of the optimized bottom profile is revealed. The optimized bottom profile keeps the cavitation area and suppresses the formation of the vortex in surface texture.Download high-res image (206KB)Download full-size image

Recently, studies on graphene-based lubrication additives have been widely researched, but few refer to their preparation by thermal reduction which shows potential in not only significantly lowering the mass-production cost, but also the simple, nonchemical process. In this study, mild thermal reduction of graphene oxide (MRGO) has been achieved by high temperature (700 °C) treatment and the product used as a lubrication additive. It shows a relatively ordered lamellar structure and a certain level of oxygen by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis, and exhibits excellent tribological properties as a lubrication additive. The friction coefficient can be reduced by as much as 30% and the rubbing surfaces display few scratches at a lower additive concentration (0.5 wt%) compared with that of base oil (Poly Alpha Olefins Type 6: PAO 6) without MRGO additive under the same friction conditions. Based on the advantages of green, low-cost and simple synthesis operation, the MRGO offers significant potential application as a lubrication additive.

•A new synthesis method of thermally reduced graphite oxide in sulfuric acid (SA-tRGO) is proposed.•SA-tRGO has a lamellar structure without obvious fold and wrinkling.•SA-tRGO-based lubricant shows outstanding tribological properties.•The method is simple and efficient, and thus has great potential of industrialization.Graphene as an efficient lubrication additive attracts more and more attentions. The structure and the properties of graphene are influenced by its synthesis process. Although thermal reduction of graphene is an excellent method, such graphene always has some defects including obvious fold and wrinkling. In this study, a new synthesis method of thermally reduced graphite oxide in sulfuric acid (SA-tRGO) is proposed for preparing a graphene additive, and it shows a lamellar structure without obvious fold and wrinkling. The SA-tRGO shows outstanding tribological properties, and even at a high load (1.86 GPa) the friction coefficient and the wear rate still can be decreased by 30% and 75%, respectively. The synthesis method is simple and has great industrialization potential.

•AISI 420 steel was anodic nitrided by active screen plasma nitriding process.•480 °C nitrided sample showed better corrosion and friction performance.•Wear mechanisms are oxidation and slight abrasion after ASPN treatment.•Surface depositions mainly come from the active screen.AISI 420 martensitic stainless steel was treated by active screen plasma nitriding. The test table was placed inside the steel screen but isolated from the cathodic potential. The specimens, together with the furnace wall and test table, were earthed, resulting in formation of anodic potential. Treatments were carried out in NH3 atmosphere of 400 Pa for 6 h at temperature ranging from 440 to 520 °C. The specimens were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and micro-hardness measurement. The results showed that anodic nitriding treatments were able to produce different types of modified surface layers at different temperatures. The thickness of the nitrided layers and surface roughness increased with the nitriding temperature. Dry sliding wear tests and electrochemical corrosion tests were conducted on the untreated substrate and nitrided specimens. It can be concluded that active screen plasma nitriding at anodic potential improved the hardness, wear resistance, and corrosion properties of AISI 420 stainless steel.

•AISI 304 stainless steels were efficiently treated by ASP oxynitriding.•TEM indicates a dual-layer structure of the modified layer was formed.•The deposition layer was composed of Fe3O4 and Fe4N phases.•Wear mechanisms after ASP oxynitriding are oxidative and abrasive.This study investigates the microstructures and tribological behaviour in the modified layers of AISI 304 steel produced by active screen plasma oxynitriding. Compositional analysis of modified layers was carried out by field emission scanning electron microscopy, atomic force microscopy and high-resolution transmission electron microscopy. The results demonstrated that the modified composite duplex layer consisted of an amorphous and nanocrystalline oxynitrided layer (upper layer) and the nitrided layer (lower layer). Additionally, the wear resistance of the active screen plasma oxynitrided specimens was much higher than that of the untreated ones. The wear rate of the treated specimen decreased by approximately 95% compared with that of the untreated one. The analysis of the worn surface indicated that the treated specimen exhibited slight oxidation and abrasive wear, whereas the untreated one showed severe adhesive wear and plastic deformation.

•Fullerene-like hydrogenated carbon film is deposited from CH4 by using a low ion energy source.•The presence of the FL structure is proven to lead to reduced wear and low friction in open air.•The film has better potential engineering application and economic benefit than before.•The film also exhibits high hardness and good elasticity recovery.In this article, we prepared the fullerene-like hydrogenated carbon film by using the chemical vapor deposition (CVD) technique with pure CH4 and low ion energy supply (500 V). The film exhibits high hardness (~16.8 GPa), good elasticity recovery (~82%) and ultra-low friction (~0.023) and wear in humid air. Meanwhile, compared with previous deposition methods, this synthesis method offers advantages such as simpler operation, easier controlling, and lower cost.

•Cobalt has been regarded as one of the most promising barrier metals for IC manufacturing.•The synergetic effect of H2O2 and glycine on the cobalt polishing performance is investigated.•The cobalt static etching rate and removal rate (RR) gradually decrease with increasing pH.•High concentration of H2O2 in slurry can suppress the cobalt RR.Cobalt has been selected as one of the most promising candidates of barrier metals for the next-generation ultra-large scale integrated circuits. This paper investigated the synergetic effect of oxidizer like H2O2 and complexing agent like glycine on the cobalt polishing performance. It is revealed that the cobalt static etching rate (SER) and removal rate (RR) are gradually suppressed with increasing pH due to the formation of compact and passive cobalt oxides on the cobalt surface, and the addition of high concentration of H2O2 can further reduce the cobalt RR. However, by the synergetic effect of H2O2 and glycine at pH 8.00, the cobalt SER and RR can be enhanced due to the formation of soluble Co(III)-glycine complex.Graphical abstract