A nanofluid is a dispersion of nanoparticles in a base fluid and it has been a hot topic of great interest in recent years primarily due to its potential application in various fields. This review ...presents an overview of the remarkable progress on nanofluids during the past two decades. Nanoparticles have been investigated intensively as an additive for lubricants due to their special tribological properties. This article is focused on various synthetic methods and characterization techniques of nanofluids. Factors enhancing the stability and lubrication mechanism have been delineated in detail. Although nanofluids are potential candidates for tribological applications, there are still many challenges to overcome. These challenges involve the long term stability of nanofluids and validation of lubrication mechanisms. Especially, nanofluid stability and high costs of production are obstacles for the application of nanofluids. The current review also discusses the problems of nanofluids applied in lubrication.
This article is focused on various synthetic methods and characterization techniquesof nanofluids. Factors enhancing the stability and lubrication mechanism have been delineated in detail as well.
The water-based MoS2 nano-lubricant was prepared and tentatively applied in cold rolling lubricant recirculation systems to investigate its recycling prospect and sustainable lubrication mechanism. ...The tribological properties and rolling lubrication performance of recycled nano-lubricants with different cycle stages were preliminarily evaluated using four-ball tribotester and two-high rolling mills. To determine the phase transformation of MoS2 in recycled nano-lubricants, the already used MoS2 nano-lubricant was collected, dried and then analyzed by means of X-ray diffraction (XRD). Molecular dynamics simulation was conducted to analyze the specialized lubrication mechanism of reused MoS2 nano-lubricant. The results revealed that the MoS2 was considered to gradually transform into MoO3 during cold rolling process. Those oxidizing metamorphic MoS2 nano-lubricants still had excellent friction reducing and wear resistance. That indicated MoS2 nano-lubricant could be recycled in cold rolling process. The recirculation of MoS2 nano-lubricant reduced the use of lubricants, the discharge of waste liquid and the production cost. Not only the pollution to environment was relieved, but also resources and costs were saved. The calculation results of adsorption energy between nanoparticles and steel surface further demonstrated the absorbing type of lubricating film in different cycle stages. A lubrication model suitable for MoS2 nano-lubricants under steel strip cold rolling lubrication circulation condition was established to explain their sustainable lubrication mechanism.
•MoS2 nano-lubricant used in cold rolling process was confirmed to be recyclable.•The existence of recycled MoS2 nano-lubricant improved the quality of rolled surface.•The phase transformation of nano-MoS2 during long time recirculation was studied.•Lattice parameter was calculated to explain the sustainable lubrication performance.•Lubrication film evolution model was established to explain lubrication mechanism.
Copper strips experience severe corrosion when rolled with an oil-in-water (O/W) emulsions lubricant. The effects of rolling reduction on the pitting corrosion behavior and surface microstructure of ...Cu strips were studied in detail using electrochemical measurements and electron back scattered diffraction (EBSD) analysis. It was found that the corrosion current densities of the rolled Cu strips increased with accumulated reduction, which also lowered the pitting potentials and weakened their corrosion resistances. Therefore, the corrosive tendency of Cu strips under different rolling reductions (ε) followed the order of ε
< ε
< ε
< ε
. The Cu surface easily reacted with chlorine, sulfur, and carbon components from O/W emulsions to generate pitting corrosion. Under the interactive effect of pitting corrosion and stress corrosion, pits expanded along the rolling direction. The aggregation of anions in surface defects, such as dislocations, metastable pits, and microcracks, further accelerated the pitting corrosion of the surface.
Thermal-assisted and stress-induced triboreactions at friction interface.
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Tribology plays a crucial role in progress of industry and engineering. The dependence of interface ...conditions and interfacial reactions provides the strategies for friction reduction as well as anti-wear in industrial processes. That is to modify the surface structure of materials or tune the properties of lubricants. This review provides an overview on the important interface conditions and surface-induced tribological reactions with emphasis on the underlying of their formation and action mechanism. The tribological features of asperity, debris and surface texture are firstly dictated. Then the main surface-induced physicochemical reactions including wetting/dewetting, deposition/adsorption are discussed. In particular, the thermal, mechanical and electrical effects that trigger tribochemical reactions are also addressed. Finally, some deficiencies in related investigations are summarized, with perspectives for the development of tribology in both science research and industrial application.
The tribological properties of nanofluids are influenced by multiple factors, and the interrelationships among the factors are deserving of further attention. In this paper, response surface ...methodology (RSM) was used to study the tribological behavior of reduced graphene oxide–Al2O3 (rGO-Al2O3) nanofluid. The interaction effects of testing force, rotational speed and nanoparticle concentration on the friction coefficient (μ), wear rate (Wr) and surface roughness (Ra) of steel disks were investigated via the analysis of variance. It was confirmed that all the three input variables were significant for μ and Wr values, while testing force, nanoparticle concentration and its interaction with testing force and rotational speed were identified as significant parameters for Ra value. According to regression quadratic models, the optimized response values were 0.088, 2.35 × 10−7 mm3·N−1·m−1 and 0.832 μm for μ, Wr and Ra, which were in good agreement with the actual validation experiment values. The tribological results show that 0.20% was the optimum mass concentration which exhibited excellent lubrication performance. Compared to the base fluid, μ, Wr and Ra values had a reduction of approximately 45.6%, 90.3% and 56.0%. Tribochemical reactions occurred during the friction process, and a tribofilm with a thickness of approximately 20 nm was generated on the worn surface, consisting of nanoparticle fragments (rGO and Al2O3) and metal oxides (Fe2O3 and FeO) with self-lubrication properties.
Nonequilibrium molecular dynamics (NEMD) simulations were performed to investigate the tribology behaviors of Al
2
O
3
and MoS
2
nanoparticles confined between iron (Fe) slabs. Results indicated that ...the combined use of these two nanoparticles yielded the lowest and most stable friction force, normal force, interface temperature and wear rate, which exhibited a significant synergistic lubrication effect. A novel parameter the rolling/sliding motion coefficient (
K
rs
) was proposed to evaluate the motion pattern of spherical Al
2
O
3
. There were 51% rolling + 49% sliding motion when used alone and 91% rolling + 9% sliding in the existence of MoS
2
. Similarly, about 72.3% of the friction was shared by interlayer sliding of MoS
2
monolayers in the presence of Al
2
O
3
, which was higher than used alone (54.8%). Then, the diffusion of atoms at the friction interface was explored to reveal the synergistic lubrication mechanism. The tribofilm formed by the diffusion of Fe and S atoms could protect the metal surfaces from further wear. The adsorption of S atoms to Al
2
O
3
nanoparticle could promote its rolling effect and prevent it from embedding into iron matrix. Besides, Al
2
O
3
could also facilitate the separation of MoS
2
monolayers to enhance their interlayer sliding effect.
Stainless steel has attracted significant attention in industrial and engineering applications. To improve its corrosion resistance, there are two major approaches that are to optimize the elemental ...composition and tune the microstructure. A comprehensive review of the main findings on the corrosion of stainless steel is presented, and some controversial issues are highlighted. First, the functional roles of alloying elements are discussed, including nonmetallic (B, C, and N) and metallic (Cr, Ni, Cu, and Mo) elements. Additionally, their detrimental and positive effects, as well as the corresponding mechanisms, are highlighted. Second, the microstructure‐induced corrosion of stainless steel is discussed, including the crystallographic‐orientation‐dependent corrosion, the dual influence of grain size and grain boundary distribution, texture, and defects in the matrix. In addition, nanostructured materials are mentioned herein. Third, challenges as well as research trends in the future are proposed with perspectives for the development of novel stainless steel in research and industrial applications.
The positive and negative effects of nonmetallic and metallic alloying elements on the corrosion resistance of stainless steel are shown. Their positive effects involve promoting the passive film formation, stabilizing passive film, as well as the unique intensifying effects of B, C, N. In particular, nonmetallic elements can suppress the anodic dissolution of metal by releasing oxyanions and stabilizing the electronic structure of Fe.
In this study, a novel lubricant additive nitrogen-doped carbon quantum dot (N-CQD) nanoparticle was prepared by the solvothermal method. The synthesized spherical N-CQD nanoparticles in the diameter ...of about 10 nm had a graphene oxide (GO)-like structure with various oxygen (O)- and nitrogen (N)-containing functional groups. Then N-CQDs were added to MoS
2
nanofluid, and the tribological properties for steel/steel friction pairs were evaluated using a pin-on-disk tribometer. Non-equilibrium molecular dynamics (NEMD) simulations for the friction system with MoS
2
or MoS2 + N-CQD nanoparticles were also conducted. The results showed that friction processes with MoS
2
+ N-CQD nanofluids were under the mixed lubrication regime. And MoS
2
nanofluid containing 0.4 wt% N-CQDs could achieve 30.4% and 31.0% reduction in the friction coefficient and wear rate, respectively, compared to those without N-CQDs. By analyzing the worn surface topography and chemical compositions, the excellent lubrication performance resulted from the formation of tribochemistry-induced tribofilm. The average thickness of tribofilm was about 13.9 nm, and it was composed of amorphous substances, ultrafine crystalline nanoparticles, and self-lubricating FeSO
4
/Fe
2
(SO
4
)
3
. NEMD simulation results indicated the interaction between S atoms in MoS
2
as well as these O- and N-containing functional groups in N-CQDs with steel surfaces enhanced the stability and strength of tribofilm. Thereby the metal surface was further protected from friction and wear.
Reducing friction and increasing lubrication are the goals that every tribologist pursues. Accordingly, layered graphene materials have attracted great research interest in tribology due to their ...anti-friction, anti-wear and excellent self-lubricating properties. However, recent studies have found that other forms of graphene derivatives not only perform better in tribological and lubricating applications, but also solve the problem of graphene being prone to agglomeration. Based on a large number of reports, herein, we review the research progress on graphene derivatives and their nanocomposites in tribology and lubrication. In the introduction, the topic of the article is introduced by highlighting the hazards and economic losses caused by frictional wear and the excellent performance of graphene materials in the field of lubrication. Then, by studying the classification of graphene materials, the research status of their applications in tribology and lubrication is introduced. The second chapter introduces the application of graphene derivatives in improving tribological properties. The main types of graphene are graphene oxide (GO), doped graphene (doped elements such as nitrogen, boron, phosphorus, and fluorine), graphene-based films, and graphene-based fibers. The third chapter summarizes the application of graphene-based nanocomposites in improving friction and anti-wear and lubrication properties. According to the different functional modifiers, they can be divided into three categories: graphene-inorganic nanocomposites (sulfides, metal oxides, nitrides, metal nanoparticles, and carbon-containing inorganic nanoparticles), graphene-organic nanocomposites (alkylation, amine functionalization, ionic liquids, and surface modifiers), and graphene-polymer nanocomposites (carbon chain polymers and heterochain polymers). Graphene not only exhibits an excellent performance in traditional processing and lubrication applications, but the fourth chapter proves that it has a good application prospect in the field of ultra-low friction and superlubricity. In the application part of the fifth chapter, the lubrication mechanism proposed by graphene as a nano-lubricant is introduced first; then, the main application research status is summarized, including micro-tribology applications, bio-tribology applications, and liquid lubrication additive applications. The last part is based on the following contents. Firstly, the advantages of graphene-based nanocomposites as lubricants and their current shortcomings are summarized. The challenges and prospects of the commercial applications of graphene-based nanocomposites in tribology and lubrication are further described.
Recent studies have found that other forms of graphene derivatives perform better in tribological and lubricating applications. This paper reviews the research progress of graphene derivatives and their nanocomposites in tribology and lubrication.
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