Search

Titanium alloy has the advantages of high specific strength, good corrosion resistance, and biocompatibility and is widely used in marine equipment, biomedicine, aerospace, and other fields. However, the application of titanium alloy in special working conditions shows some shortcomings, such as low hardness and poor wear resistance, which seriously affect the long life and safe and reliable service of the structural parts. Tribocorrosion has been one of the research hotspots in the field of tribology in recent years, and it is one of the essential factors affecting the application of passivated metal in corrosive environments. In this work, the characteristics of the marine and human environments and their critical tribological problems are analyzed, and the research connotation of tribocorrosion of titanium alloy is expounded. The research status of surface protection technology for titanium alloy in marine and biological environments is reviewed, and the development direction and trends in surface engineering of titanium alloy are prospected. [ABSTRACT FROM AUTHOR]

Using nanoadditives in lubricants is one of the most effective ways to control friction and wear, which is of great significance for energy conservation, emission reduction, and environmental protection. With the scientific and technological development, great advances have been made in nanolubricant additives in the scientific research and industrial applications. This review summarizes the categories of nanolubricant additives and illustrates the tribological properties of these additives. Based on the component elements of nanomaterials, nanolubricant additives can be divided into three types: nanometal-based, nanocarbon-based, and nanocomposite-based additives. The dispersion stabilities of additives in lubricants are also discussed in the review systematically. Various affecting factors and effective dispersion methods have been investigated in detail. Moreover, the review summarizes the lubrication mechanisms of nanolubricant additives including tribofilm formation, micro-bearing effect, self-repair performance, and synergistic effect. In addition, the challenges and prospects of nanolubricant additives are proposed, which guides the design and synthesis of novel additives with significant lubrication and antiwear properties in the future. [ABSTRACT FROM AUTHOR]

In this study, the tribological behaviors of graphene as a lubricant additive for steel/copper and steel/steel friction pairs were compared. For the steel/copper friction pair, the graphene sheets remarkably decreased the coefficient of friction and wear scar depth under low loads, but these slightly increased under high loads. The steel/steel friction pair showed excellent tribological properties even under high loads. Severe plastic deformation on the copper surface reduced the stability of the graphene tribofilm because of a rough copper transfer film on the steel during the running-in period. The results provide a better understanding of the mechanism of graphene as a lubricant additive. [ABSTRACT FROM AUTHOR]

In order to satisfy the requirements of precise components with tidiness, low power and high stability in the field of biological engineering, medical equipment and semiconductors etc. a pre-stress acoustic transport prototype without horn was proposed in this paper. The mechanism of levitation and transport which is driven by orthogonal waves was revealed by the analysis of waveform and squeeze film characteristics in high-frequency exciting condition; also, the electric, solid and acoustic coupled finite element method (FEM) was established to investigate the effect of pre-stress and acoustic pressure distribution in the near field. The levitation and driving capacity of near field acoustic levitation (NFAL) transport platform without horns can be proved in this experiment and further to achieve the goal of parameters optimization. The theoretical and experimental results indicate that the pre-stress has a significant effect on resonant frequency and levitating stability, the pre-stress are determined by the DC voltage offset which is related to the system working point so that we cannot increase the offset and exciting voltage unlimitedly to improve the stability. At the same time, the calculated pressure distribution of acoustic radiation can generally reflect the regional bearing capacity in near and far field for levitation. These achievements can partly solve the problem of accuracy design of prototype and thickness of gas film, supporting for accuracy close loop control of levitating height. [ABSTRACT FROM AUTHOR]

In direct current plasma nitriding (DCPN), the treated components are subjected to a high cathodic potential, which brings several inherent shortcomings, e.g., damage by arcing and the edging effect. In active screen plasma nitriding (ASPN) processes, the cathodic potential is applied to a metal screen that surrounds the workload, and the component to be treated is placed in a floating potential. Such an electrical configuration allows plasma to be formed on the metal screen surface rather than on the component surface; thus, the shortcomings of the DCPN are eliminated. In this work, the nitrided experiments were performed using a plasma nitriding unit. Two groups of samples were placed on the table in the cathodic and the floating potential, corresponding to the DCPN and ASPN, respectively. The floating samples and table were surrounded by a steel screen. The DCPN and ASPN of the AISI 304 stainless steels are investigated as a function of the electric potential. The samples were characterized using scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffraction, atomic force microscopy and transmission electron microscope. Dry sliding ball-on-disk wear tests were conducted on the untreated substrate, DCPN and ASPN samples. The results reveal that all nitrided samples successfully produced similar nitrogen-supersaturated S phase layers on their surfaces. This finding also shows the strong impact of the electric potential of the nitriding process on the morphology, chemical characteristics, hardness and tribological behavior of the DCPN and ASPN samples. [ABSTRACT FROM AUTHOR]

Annealing regulation plays an important role in improving the mechanical and dynamic properties of bulk metallic glass (BMG), but the influence of annealing on the tribological properties of Zr-based BMG hasn't been investigated. In this study, we comparably investigated the tribological properties of the Zr-based BMG (Zr 61 Ti 2 Cu 25 Al 12 ) under different annealing degrees. The result shows that the anti-friction property of the BMG weakens with the increase of the annealing degree, but their anti-wear property presents an opposite trend. This study makes a contribution to understanding the relationship between the annealing degree and tribological properties, which means the BMG can be further optimized for the application of tribology by annealing regulation. [ABSTRACT FROM AUTHOR]

Recently, we have proposed an Electro-hydrostatic-actuator (EHA) based on a novel linear oscillating motor, which permits nanoparticle additives, such as layered graphene and MoS 2 , using in hydraulic oil. Especially under a super smooth (Ra~5 nm) surface unlike past studies, the tribological properties of these additives is sent more highlight. In addition, oil temperature is introduced into the friction process. We show that the friction coefficient can be decreased to as low as 0.04 when adding MoS 2 nanaosheets for the chemical absorption and forming “available solid lubricant” under smooth surface and high temperature while multilayer graphene performs relatively unstable tribological properties because of agglomerates and crystal defects. It can be concluded that MoS 2 nanosheets possess better potential value for the application. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The tribological properties of the different modified layers of plasma nitrocarburized and post-sulfurized on 38CrMoAl steel under oil lubrication were investigated, and the wear mechanism was proposed. The modified layers were prepared by the plasma nitrocarburized at 520 °C for 5 h and post-sulfurized at 160 °C for 1, 3, and 5 h. The morphology, phase structures, and composition were characterized by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, three-dimensional white light interferometry, X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The sliding-wear characteristics were investigated by ball-on-disk wear tests against GCr15 steel counterparts. The results show that the nitrocarburized layer mainly comprises ε-Fe 2-3 (N, C) and γ ′-Fe 4 (N, C), with a surface hardness of 1250 HV 0.1. The nitrocarburized treatment significantly improved the wear resistance of the 38CrMoAl steel. For the plasma nitrocarburized and post-sulfurized samples, a sulfurized layer mainly consisting of FeS and FeS 2 was formed on the nitrocarburized layer. The wear mass loss and friction coefficient of the duplex samples are significantly reduced due to the thin FeS layer acting as a solid lubricant. A two-step method, plasma nitrocarburized and post-sulfurized duplex treatment, further improves tribological performance, which is crucial for engineering applications. • Plasma nitrocarburized and post-sulfurized duplex treatment can improve tribological performance. • Hollow cathode discharge resolves the main issues present in traditional methods. • The sulfurized layer provides an excellent solid lubrication effect. [ABSTRACT FROM AUTHOR]

Little work has been reported directly compared to the tribological behavior of plasma nitrided pure titanium and those coated with TiN coatings. This work prepared the compound layers and coatings with the same thickness on TA2 pure titanium by plasma nitriding and multi-arc ion plating. The tribological behaviors of sliding against ZrO 2 balls under lubricant conditions were investigated using a UMT-5 tribo-tester. The results reveal that nitrided and coating samples showed the friction coefficients (0.11–0.12) were significantly decreased compared to that (~0.33) of the TA2 pure titanium matrix. It was also found that the wear mechanism is different after nitriding or coating, which is caused by the surface phases, chemical composition, and surface roughness under other processes. [ABSTRACT FROM AUTHOR]