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The operational safety and reliability of a variable gauge train are affected by the anti-fretting wear performance of the locking mechanism. The main purpose of this study is to optimize the surface treatment process for a locking pin material under actual service conditions to alleviate fretting damage. Based on the two basic principles of surface strengthening and friction reduction, a substrate (AISI 4135 steel) surface was treated by laser quenching (LQ), plasma nitriding (PN), and bonded MoS2 coating. Systematic fretting wear tests were conducted, and the wear behavior and damage mechanism of various treated surfaces were comprehensively investigated. The results indicate that the wear resistances of the LQ- and PN-treated surfaces were significantly improved, and their main wear mechanisms were abrasive wear, delamination, and oxidation wear. The MoS2 coating exhibits the lowest friction coefficient and energy dissipation due to its self-lubricating property, but it incurs the highest wear rate and failure in the form of plastic deformation. Furthermore, the rough compound layer with a high hardness on the PN-treated surface is conducive to the formation and maintenance of the third-body contact at the fretting interface, consequently resulting in a significant reduction in wear. An optimal surface treatment process for alleviating fretting damage of the locking pin is recommended via comprehensive evaluation, which provides a reference for the anti-fretting protection of related mechanical components.

This paper investigates the phenomenon of imbalance between the frequencies of thenice andAdj and Adjand nicepatterns from the perspective of humans’ social and limited-processing-capacity attributes. Humans’ social attribute requires that language users stay informative with minimal effort in communication, resulting in the from-the-least-to-the-most-informative information organization in discourse. Their limited-processing-capacity attribute requires that they resort to the production biases of “easy first” and “plan reuse” in order to achieve communicative efficiency in real-time production. The analysis of the occurrences of thenice andAdj pattern and native speakers’ judgment of the degree of informativeness ofnicein these occurrences suggest thatniceis largely delexicalized. Such delexicalization makesnice andAdj consistent with the information organization and allows language users to stay informative with the use of the pattern, thus in line with the social attribute, but not Adjand nice. In the meantime,niceis not only highly frequent but also conceptually salient when it comes to the positive property (Panther & Thornburg, 2009), makingnice andAdj easier to produce and more likely to be reused than Adjand nice, thus in line with the limited-processing-capacity attribute. The analysis of the unbalanced frequency of the two patterns suggests that human attributes should be considered when studying language form, and this should offer insights into English learning.

Through a simple and low-cost way to gain the precursor solution, a conductive and high-quality La0.7Sr0.3MnO3 (LSMO) buffer layer approximately 280 nm thick only by one single coating was successfully deposited on LaAlO3 (LAO) (100) single crystal substrates using an independently developed new method of polymer-assisted chemical solution deposition (PA-CSD). Highly epitaxial YBa2Cu3O7−x (YBCO) superconducting film with thickness of 500 nm managed to be deposited on LSMO/LAO. A study was made on the LSMO buffers and YBCO films with XRD, SEM, and superconducting critical temperature (Tc) analyses. The temperature-dependent resistivities of YBCO on insulating BaZrO3 (BZO) buffer layer and on conductive LSMO buffer layer were also investigated. It was found that the conductive LSMO buffer prepared at 840 °C in argon would possess high-degree out-of-plane and in-plane texturing, good density with a sufficient thickness about 280 nm, and microcrack-free nature. More importantly, the value of the self-field critical current density (Jc) of YBCO superconducting film on LSMO/LAO architecture was 2.8 MA/cm2 at 77 K.

Through a simple and low-cost way to gain the precursor solution, high-quality La2Zr2O7 (LZO) buffer layers approximately 300 nm thick only by one single coating were successfully deposited on the textured Ni-5at%W alloy substrates using an independently developed new method of polymer-assisted chemical solution deposition (PA-CSD) with and without Y2O3 seed layer. Highly epitaxial YBa2Cu3O7−x (YBCO) thin film with thickness of 500 nm is managed to be deposited on LZO/Y2O3/NiW. A study was made on the buffers and YBCO films with XRD, AFM, FIB-SEM, ESEM, and through superconducting critical temperature (Tc) analyses, and it was found that the Y2O3 seed layer had a good effect in improving the c-axis texture for the performance of LZO thin films. More importantly, the value of the self-field critical current density (Jc) of YBCO film on LZO/Y2O3/NiW architecture was 1.6 MA/cm2 at 77 K. Our results indicated that the low-cost and effective way to develop high-performance YBCO-coated conductors on the basis of high-quality LZO buffer layer were suitable candidates.

In this paper, the premature failure of the railway wheel shaft of power locomotive operated three million kilometres in China was investigated. Series of macroscopic and microscopic analysis was conducted to identify the damage degree and failure mechanism of the axle thoroughly, and the root causes of the unexpected failure were fully obtained. The results showed that the different extent damage (fretting damage, fatigue crack and corrosion) occurred in the interference fit of the wheel seats, gear seats and bearing seats without any material defect. In particular, plentiful cracks distributed on the wheel seat were sprouted in the subsurface and exhibited multi-source characteristics, which were fretting fatigue failure caused by interference fit under alternating loads of rotation and bending. The main reason of fatigue crack initiation is that there were numerous tangle and a pile-up of dislocations in the sub-surface of wheel seat position, which resulted in stress concentration at the grain boundary and phase boundary, and when it exceeded the strength limit of the material, the micro-crack would initiate and propagate. Therefore, to reduce the stress concentration at the wheel seat portion, the structure of the axle need to be further optimized, and the surface be strengthened also crucial for resisting the fretting damage.

Contact pressure is a crucial factor which can affect fretting fatigue (FF) life significantly. In this research, the influence of contact pressure on torsional fretting fatigue (TFF) damage of a 7075 aluminum alloy is investigated. According to the experiment results, below 72.5 N⋅m torque as the contact pressure increases, the TFF life decreases firstly and then it reaches to the lowest point at 300 N, while afterward the TFF life increases. The P-N curve shows a C shape. The damage analysis results show that with increasing the contact pressure, the damage becomes severer. The oxidative products are mainly Al2O3 and Al(OH)3, and the loading side is found to be more oxidized than the center position and fixed side.

Fretting fatigue is a complex tribological phenomenon that can cause premature failure of connected components. Combining with the effects of tribological and fatigue, the components have premature fracture, which ultimately leads to disastrous consequences. In this work, the fretting fatigue tests of 316L austenitic stainless steel have been carried out with same normal load and varied torsional torques. The results indicate that the fretting fatigue life significantly depends on the torque amplitude, wear degree of the fretting damage zone, hysteresis loops and energy dissipation. A physical model for fretting crack initiation and propagation is created to explain the failure process of torsional fretting fatigue. The results from X-ray photoelectron spectroscopy analysis show that the extent of oxidation in the fretting damage zone is affected by the amplitude of relative displacement. The tribo-chemical reaction in the slip regime is more activated than that in partial slip regime. It can lead to more severe wear in the slip regime. The wear debris of the fretting damage zone is composed of metallic Fe, Fe2+ and Fe3+.

The torsional fretting fatigue tests of LZ50 axle steel were carried out in a cylinder-on-cylinder contact configuration to investigate the influence of fretting wear and tribo-chemical action in the contact zone on the fretting fatigue life. The S-N curves of the torsional fretting fatigue were drawn. The results indicated that there was a competitive relationship between wear and fatigue in the fretting process. The tribo-chemical action in the fretting damage zone accelerated the wear of material. The Fe element in fretting damage zone existed in consist of Fe0+, Fe2+ and Fe3+.

The role of water in the material removal of single crystal calcium fluoride (CaF2) was studied using a scratch tester with a diamond tip. Water can facilitate the sliding wear of CaF2, and the degree strongly depended on the amount of water molecules involved in the wear process. CaF2 wear increases with the increase of relative humidity (RH). When the sliding wear tests were conducted in dry condition, the wear rate increases linearly with applied load, obeying the Archard wear equation. When water participated in the wear process, the Archard wear equation was failure and a exponential dependence of wear rate on contact stress was given under water condition. The transformation of the applied load (or contact stress) dependence indicates the change of wear mechanism in water condition. In dry condition, the surface damage of CaF2 is mainly attributed to mechanical wear where the stress-induced plastic flow under the activation of the slip systems results in a relatively smooth worn surface. In humid nitrogen or water condition, the plastic wear of CaF2 weakens due to the stress-associated dissolution though the wear volume increases compared to that in dry case. Both the water-associated dissolution itself and induced delamination promote the sliding wear of CaF2 in water. The results may help elucidate the water-associated wear mechanism of CaF2 and optimize the processing parameters in the ultra-precision machining to reduce the residual surface/subsurface defects.

In this paper, the premature failure of the integral droppers in high speed railway catenary in China was investigated. Series of microscopic characterization and analysis were conducted to identify the root causes of the unexpected failure. By numerically simulating the existing crimping behavior, distribution of the contact stress in the dropper was obtained. It was found that there was stress concentration at the dropper sliced end, which became the primary reason for the permanent distortion and damage on the droppers, and consequently resulted in the untimely final fracture with bending fretting fatigue acting. Through the failure analysis and numerical simulation, a scheme of the improvements in measuring the existing crimping was brought up. Meanwhile, a plan was also put forward to change the current crimping model and reduce the depth of indentation of clamp tube. Static tensile tests and bending fretting fatigue tests were carried out to evaluate the optional plans, which would help extend the service life of integral dropper in practice.

Space irradiation-induced damage to onefold lubricants including four multialkylated cyclopentanes (MACs) space greases, Chromium doped diamond-like carbon (Cr-DLC) and molybdenum disulfide (MoS2) films was first investigated under simulated space environment (atomic oxygen (AO) and proton (PR)). Then solid-grease synergistic lubrication systems were prepared via spinning four space greases on Cr-DLC and MoS2 film, and their tribological behaviors were evaluated under simulated space environment including ultra-vacuum, AO and PR irradiation, low temperature (−100 °C). The irradiated damage mechanism and friction mechanism were explored by surface/interface analysis techniques. The results demonstrates that Cr-DLC film have better space adaptability than MoS2 film because irradiation induced partial transition of Cr-DLC’s micro-structure with the decrease in ID/IG ratio from 1.50 to 1.26 and the increase of sp3 content from 0.24 to 0.59, while the surface morphology and micro-structure of MoS2 film have dramatically changed. Solid-grease synergistic lubrication systems provide excellent friction-reducing and anti-wear behaviors (friction coefficient can be reduced up to below 0.05 under the special working conditions). Such excellent tribological performance of Cr-DLC-grease lubrication coatings is attributed to the friction-induced graphitization at the sliding interface, while that of MoS2 film mainly depends on its original structure/merits under greases lubrication.

Previous studies demonstrated that the continuation task has great language learning potential and that various task-related factors may affect the extent to which the potential can be exploited (e.g. Wang & Wang, 2015). This study investigates the effect of one understudied factor, the linguistic complexity of the input text, on English as a foreign language (EFL) learners’ alignment, writing fluency, and writing accuracy in the continuation task. Two comparable groups of Chinese undergraduate EFL learners read and continued a simplified and unsimplified version of the same incomplete story whose linguistic complexity matched and exceeded their production ability, respectively. Compared to the unsimplified version, the simplified version resulted in more automatic alignment and greater improvement in writing fluency and accuracy. The implications of these findings for writing pedagogy are discussed.

A torsional fretting test of 7075 aluminum alloy is carried out on a fretting fatigue test rig, which is independently designed based on a multi-axis fatigue testing machine, and thus the S-N curve for this material is established. The damage regions of torsional fretting fatigue are analyzed with 3-D profilometer, Scanning Electron Microscopy and Electron Probe Microanalyzer. The results reveal the damage mechanism of the torsional fretting fatigue on different regimes, and the fatigue life is greatly reduced due to the fretting acting. The S-N curve of the torsional fretting fatigue presents characteristics of a Z-shaped curve. The coefficient of friction increases with the torque, while when the fretting is running in the mixed fretting and slipping regimes, oxidation of the damage regions near the loading end becomes severe, accompanying with micro-cracks; while in the partial slipping regime, the oxidation is mild without micro-cracks.

In the work, new type composites of acrylonitrile butadiene rubber (NBR) and polyurethane-sericite (PU-sericites) hybrid materials was prepared by melt blending method. The PU-sericite hybrid phase was formed via the reaction of NCO groups of NCO terminated PU prepolymer and OH groups of sericites. It was indicated by dynamical mechanical analysis that the damping property of NBR decreases as the amount of PU increases, whereas the mechanical properties at low temperature are enhanced. When PU of 10 wt% was added in, a better damping property can be obtained. The damping property of NBR/PU composites would decrease when adding in sericites, however, the mechanical properties at low temperature would be improved. With PU-sericites hybrid added, the compatibility between sericites and NBR/PU composites would be enhanced and the quasi-interpenetrating polymer network structures would be formed, resulting in a better mechanical property of NBR/(PU-sericites) composites.

This study investigated the fretting wear behavior of the nuclear power material Inconel 690 alloy. An improved PLINT high-temperature fretting tester was used on an Inconel 690 tube against a 1Cr13 cylinder at different temperatures (25 ℃ and 300 ℃) under alternating load conditions. The fretting-wear mechanism and the kinetic characteristic of Inconel 690 alloy were analyzed. Results showed that the fretting running behavior was closely related to the normal excitation frequency. In parallelogram shaped Ft– D curves, the friction fluctuates periodically, and accordingly the fretting was running in the slip regime. The steady-state friction force at room temperature in air was higher than that at 300 ℃. Moreover, the damage behavior of the fretting for Inconel 690 alloy strongly depended on the normal load, displacement amplitude, temperature, and excitation frequency in atmospheric environment. A superposition effect of fretting wear behavior was discovered because of the combined effect of alternating normal and tangential forces; thus, delamination became more significant. Abrasive wear and delamination were the major mechanisms in Inconel 690 alloy at room temperature in ambient air. The dominant mechanisms at 300 ℃ were the abrasive wear, oxidation wear, and delamination.

Fluorides are promising host materials for optical applications. This paper reports the photoluminescent (PL) and cathodoluminescent (CL) characteristics of barium hexafluorogermanate BaGeF6 nanowires codoped with Ce3+, Tb3+ and Sm3+ rare earth ions, produced by a solvothermal route. The synthesized BaGeF6 nanowires exhibit uniform morphology and size distribution. X-ray diffraction divulges the one-dimensional growth of crystalline BaGeF6 structure, with the absence of any impurity phases. Visible luminescence is recorded from the nanowires in green and red regions, when the nanowires are codoped with Ce3+/Tb3+, and Ce3+/Tb3+/Sm3+, respectively, under a UV excitation source. The PL emission from the codoped BaGeF6 nanowires, when excited by a 254 nm source, originates from the efficient energy transfer bridges between Ce3+, Tb3+ and Sm3+ ions. The decay time of the visible luminescent emission from the nanowires is in the order of subnanoseconds, being one of the shortest decay time records from inorganic scintillators. The CL emission from the BaGeF6 nanowires in the tunable visible range reveals their potential use for the detection of high-energy radiation. The PL emissions are sensitive to H2O2 at low concentrations, enabling their high-sensitivity detection of H2O2 using BaGeF6 nanowires. A comparison with BaSiF6 nanowires is made in terms of decay time and its sensitivity towards H2O2.

Inorganic materials with short radiative decay time are highly desirable for fast optical sensors. This paper reports fast photoluminescence (PL) from a series of barium hexafluorosilicate (BaSiF6) superlong nanowires with high aspect ratios, codoped with Ce3+/Tb3+/Eu3+ ions, with a subnanosecond decay time. Solvothermally synthesized BaSiF6 nanowires exhibit a uniform morphology, with an average diameter less than 40 nm and aspect ratios of over several hundreds, grown in the c-axis direction with {110} surfaces. The PL emission from the codoped BaSiF6 nanowires, when excited by a 254 nm source, is dependent on Tb3+ concentration, and the energy transfer from Ce3+ to Tb3+ and to Eu3+ ions allows efficient emissions in the visible spectra when excited by a near UV source. Annealing BaSiF6 nanowires at 600 °C in a vacuum produced barium fluoride (BaF2) nanowires composed of nanocrystals. Both BaSiF6 and BaF2 nanowires exhibit fast emissions in the visible spectra, with enhanced intensities compared with their codoped microparticle counterparts. The decay time of codoped BaSiF6 nanowires is found to be shorter than that of codoped BaF2 nanowires. The energy transfer is also observed in their cathodoluminescence spectra with high-energy irradiation.

A running condition fretting map of 690 alloy tubes against 405 stainless steel plates was established through various fretting tests at room temperature. Three fretting regimes were observed: partial slip regime (PSR), mixed regime (MR), and gross slip regime (GSR). In the PSR, slight damage associated with the lowest friction coefficient (COF) and an adhesion layer due to adhesive wear were detected. In the GSR, severe damage corresponding to a higher COF and delamination were observed. In the PSR, Fe2O3 may be one of the main components of the wear particles. The spinel oxides of NiCr2O4 and/or FeCr2O4 may have existed in the debris layer in the MR and GSR.

The effect of slippage on the crack behavior of pearlitic steel induced by rolling-sliding friction has been investigated to elucidate the wear damage. The results show that the crack-initiated site occurred at sub-surface sites of the severely deformed phase structure — which is due to the exhausted ferrite ductility — and was accompanied by a series of adjacent connected voids. As the slippage increased, more cracks were observed with the dissolved cementite structure, ranging from lamellae to fragments and particles. The slippage effect on the wear and fatigue competition was demonstrated by comparing the crack propagation rate and wear loss of the material during the rolling-sliding friction process. The length and depth of initiated cracks were key parameters in evaluating the wear damage.

In this study, low velocity impact tests were performed to MoS 2 /Pb nanocomposite coating and its substrate (304-stainless steel, for comparison). The machine is controlled based on kinetic energy and can achieve dynamic response during the tests. The MoS 2 /Pb coating exhibits better impact wear resistance, as shown by its favorable dynamic response. The energy absorption ratio evolution of MoS 2 /Pb coating indicates there were several impact damage forms during the tests, which was relevant to varied dominant impact damage mechanisms. In addition, tests with varied impact conditions were conducted, and distinct results were obtained, revealing the effects of tests parameters. Moreover, comparative analysis between values obtained from the Hertz theory and the measured revealed that the yield strength of MoS 2 /Pb coating was approximately 686.5 MPa, and the substrate was always under elastoplastic deformation although its impact kinetic energy was the lowest. The low velocity impact morphology was characterized by fatigue delamination because of the shearing stress in the subsurface.

The study focuses on understanding how to govern the fretting wear behaviors under dry lubricated contact to find out the keys to develop new coatings for rubber seal applications. Fretting wear behaviors of acrylonitrile-butadiene rubber (NBR) against steel substrate, diamond-like carbon, and graphene coatings were comparatively investigated under dry conditions. Dynamic analyses were performed in combination with examinations through scanning electron microscopy (SEM), 3D surface profilometry, and X-ray photoelectron spectroscopy (XPS). Experimental results show that, there was significant difference between the fretting running regime for graphene coating and the fretting running regimes for diamond-like carbon (DLC) coating and steel substrate; the mixed fretting regime (MFR) disappeared and the boundary between the partial slip regime (PSR) and the slip regime (SR) shifted to the direction of smaller amplitude displacement in running condition fretting map (RCFM). Moreover, it had excellent anti-friction and wear-resistant performances under fretting condition. However, the fretting running behaviors of the DLC coating are similar to those of the steel substrate, so the DLC coating could not migrate the fretting running regimes effectively. The damage on all the tribopairs in partial slip regime was very slight and the adhesion was the main damage mechanism for the DLC coating and the steel substrate in the MFR and SR. The sticky layers on the worn surface played an important role. For the graphene coating, no obvious damage could be observed on the tribopairs. Therefore, the graphene coating exhibited widely potential applications for alleviating fretting wear.

This study investigated the effects of electrical contact resistance (ECR) on pogo pins used in mobile phones, chargers, digital cameras, Bluetooth headsets, medical equipment, and other electronic products with different surface roughness. Experimental results revealed that metallic wear debris is generated by fretting motion and formation of a third body on rough surfaces without removal by fretting motion, thus increasing ECR. Wear debris does not easily form the third body at contact areas of smooth surfaces and causes formation of metal–metal contact pattern. Results showed low ECR with fretting motion. 3D and 2D profiles of contact area verified the definition of contacting high spots, further explaining increases in ECR.

The impact fretting wear has largely occurred at nuclear power device induced by the flow-induced vibration, and it will take potential hazards to the service of the equipment. However, the present study focuses on the tangential fretting wear of alloy 690 tubes. Research on impact fretting wear of alloy 690 tubes is limited and the related research is imminent. Therefore, impact fretting wear behavior of alloy 690 tubes against 304 stainless steels is investigated. Deionized water is used to simulate the flow environment of the equipment, and the dry environment is used for comparison. Varied analytical techniques are employed to characterize the wear and tribochemical behavior during impact fretting wear. Characterization results indicate that cracks occur at high impact load in both water and dry equipment; however, the water as a medium can significantly delay the cracking time. The crack propagation behavior shows a jagged shape in the water, but crack extended disorderly in dry equipment because the water changed the stress distribution and retarded the friction heat during the wear process. The SEM and XPS analysis shows that the main failure mechanisms of the tube under impact fretting are fatigue wear and friction oxidation. The effect of medium(water) on fretting wear is revealed, which plays a potential and promising role in the service of nuclear power device and other flow equipments.

Surface photovoltage inversion was found in PbI2 microcrystals, manifested as a significant increase in the absolute value of surface barrier height under sub-bandgap illumination. The corresponding surface states located at 0.43 eV above the valence band was detected, and the magnitude of photovoltage inversion was found to increase with increasing applied field strength. Besides, transient surface photovoltage responses and the time constants of the relaxation showed a dependence on the wavelength of illumination. When irradiated with 518–632 nm, the exciton together with the lead ion vacancy caused the population of holes in the surface state; while under 700-nm light irradiation, holes depopulation occurred on the surface. Transient surface photovoltage results show that the relaxation of the sub-bandgap surface photovoltage is exponential with long time constant. The different charge transportation processes agree well with the photocatalytic degradation of MO experiments under different wavelength irradiation. It is revealed that the exciton and the surface states could significantly affect the movement of photogenerated charge carriers, which lead to different degradation results of MO. These findings demonstrate a model involving photostimulated population of surface states for the study of surfaces of wide energy gap semiconductors, which shows the highly selective control of photogenerated charge carriers’ behaviors by tuning the wavelength of irradiation.

Fretting is the small amplitude relative oscillatory motion between two solid contact surfaces. Many factors would make impacts on the fretting process, the body stress and contact pressure can be regarded as two major independent factors resulting in the fretting fatigue. The effects of torque and contact pressure on torsional fretting behavior of 316 L austenitic stainless steel are studied in a cylinder-on-cylinder contact configuration. The results indicate that torsional fatigue life drops rapidly due to fretting. The S-N curves of torsional fretting fatigue show a shape of “ C ”. Along with increasing the contact pressures, the fretting fatigue life decreases and enters to a platform area. The variety law of friction coefficient under different contact pressures is obtained. Both fatigue fracture and fretting scar are analyzed with SEM, EDX, XPS and three-dimensional white light interferometer (3D). The study shows that the torsional fretting fatigue is influenced by fretting running behavior. Meanwhile, the depth of crack initiation position would also be affected by contact pressure. In this paper, we proposed the failure mechanisms of the fretting zone, including plastic deformation, delamination, plow and oxidative wear.

The elevated temperature can cause serious failure of electrical contact. The fretting wear behavior of two typical materials (aluminum and silver) and contacts at elevated temperatures (from RT to 300 °C) and normal loads (10 N) is addressed in this paper. The morphology and wear surface was analyses by 3D profile and SEM. The results show that elevated temperature significantly affected the contact resistance. Easily oxidized metal usually have higher ECR value under elevated temperature. Elevated temperature accelerated the formation of oxide film and lead to debris which oxidizes, forming an insulating layer. Metal with good ductility and resistant to oxidation shows lower ECR.

Potential Sm1−xCaxBiO3 (x = 0.1, 0.2, 0.3, and 0.4) buffer layers for REBa2Cu3O7−x(REBCO, RE = Y or Nd, Sm, Gd, Dy, etc) coated conductors (CCS) has been deposited on (00l) LaAlO3 substrate via a self-developed polymer-assisted chemical solution deposition (PA-CSD) route, and then studied by XRD, SEM, AFM and current-voltage (I–V) characteristics. Highly c-axis oriented, dense, smooth and crack-free buffer layers have been obtained. We found that its resistivity does not decrease obviously. The pseudo-cubic lattice parameter of Sm1−xCaxBiO3 matches well with the in-plan lattice parameters of corresponding REBCO compounds. YBCO superconducting epitaxial film with high performance is successfully deposited on Sm0.6Ca0.4BiO3 layer by dc sputtering. Our results offer a new avenue to search for better lattice matched buffer layer for CCS, particularly to REBCO.

The fretting wear behavior of the nuclear power material Incoloy 800 was investigated in this study. A PLINT high-temperature fretting tester was used on an Incoloy 800 cylinder against a 304SS cylinder at vertical cross contact under different temperatures (25, 300, and 400°C). During testing, a normal load of 80 N was applied, and the displacement amplitudes ranged from 2 to 40 µm. The fretting wear mechanism at high temperatures and the kinetic character of the materials of the Incoloy 800 steam generator tube were analyzed. Results showed that the fretting running regimes varied little with ncreasing temperature, and some microcracks were observed in both the mixed fretting regime (MFR) and the partial slip regime (PSR) at high temperatures. Slight abrasive wear and microcracks were the main wear mechanisms of the Incoloy 800 alloy in PSR, whereas those in the MFR and the gross slip regime were oxidative wear, abrasive wear, and delamination.

To address the poor dispersibility and incompatibility of graphene toward potential applications, we propose an approach to prepare high-density modified graphene sheets by combining solvent exfoliation of graphite with chemical modification of ionic liquids (ILs). Graphite is exfoliated into graphene sheets along with in situ modification in ILs-containing solution, and ILs–modified multilayer graphene (MLG) is formed because as-exfoliated graphene sheets with the charged groups of ionic liquids can undergo self-assembly together through electrostatic interaction. Here, three ILs–modified MLG was prepared using different alkyl imidazolium ILs, and their structures and tribological properties were investigated in detail. High-density coverage of IL cation and anion moieties is achieved, remarkably enhancing the dispersibility of the graphene in lubricant. MLG hybrid nanofluids show excellent friction-reducing and anti-wear ability for the contact of steel/steel because of the synergistic effect of a physical adsorption film and a tribo-chemical reaction film on the sliding surfaces.

Axial load distribution and self-loosening behavior of bolted joints were numerically studied in this work. Finite element (FE) models with fine mesh threads were generated by analyzing the clearance of different thread fit qualities and thread profiles of MJ and Spiralock internal threads. By changing the thread clearance value, thread profile, engagement length, pitch value, and friction coefficients, their effects on axial load distribution, loosening behavior, and the dynamic response of bolted joints were explored with accurate three-dimensional FE models. In addition, experiments were conducted to investigate the dynamic response of bolted structures. Numerical results agreed with the theoretical results. For varying friction coefficients between the contact threads and between the bolt head and the bearing surfaces, the clamping force of bolted joints excited by torsional load changed in three cases: continuously decreasing, initially decreasing and then remaining constant, and initially decreasing and then fluctuating. Agreement was achieved by comparing between hysteresis loops generated by numerical and experimental methods.

To understand the microstructural evolution of a pearlitic rail steel during rolling–sliding contact friction, phase structure and mechanical properties of deformed layers, from top surface to inner matrix, were investigated gradually by scanning electron microscopy, electron probe microanalysis (EPMA), X-ray diffraction, transmission electron microscopy (TEM) and nano-hardness indentation. Focused ion beam method was used to prepare site-specific TEM specimens to study the thickness-dependent deformed microstructure. After the deformation, a white etching layer (WEL), was formed on the top surface, which appeared in white color under an optical microscope. Quantitative EPMA analysis revealed slightly lower carbon concentration, inhomogeneously distributed within the WEL. According to high-resolution TEM observation and quantitative electron diffraction analysis, it was found that the WEL was indeed composed of uniform nano-grains of martensite and ferrite, where no cementite and austenite were found. All the results supported that the WEL was formed by severe plastic deformation, and the hardness value of WEL reached 12 GPa by nano-hardness indentation.

Bonded MoS2 solid lubricant coatings are widely used in tribology for their friction-reducing and antiwear properties. However, such coatings have been rarely investigated in complex fretting conditions, such as dual-rotary fretting (DRF). DRF is a complex fretting wear mode that combines torsional fretting with rotational fretting. In this work, the antiwear properties of bonded MoS2 solid lubricant coating under dual-rotary fretting conditions were studied. Results indicated that the MoS2 coating had better friction-reducing and antiwear properties than the substrate for alleviating DRF wear. The coating can greatly influence the fretting regimes and reduce the coefficient of friction. Furthermore, the service life of the coating was strongly dependent on the competition of the two fretting components and was reduced as the rotational fretting component increased.

The aim of this paper is to assess the effect of water temperature (room temperature – RT, 60 °C and 90 °C) on fretting wear behavior of 690 alloy tubes against 405 stainless steel plates, and compare it with fretting in dry condition. Due to the lubrication effect, the presence of a thin water film likely precluded the metal-metal contact, and resulted in less wear. During the fretting process, water also washed the wear particles away from the contact zone leading to a decrease of abrasive wear. Consequently, the wear scars showed “U” shape profile along the fretting direction in water, while “W” shape in air.

Rotational fretting which exist in many engineering applications has incurred enormous economic loss. Thus, accessible methods are urgently needed to alleviate or eliminate damage by rotational fretting. Surface engineering is an effective approach that is successfully adopted to enhance the ability of components to resist the fretting damage. In this paper, using a high-velocity oxygen fuel sprayed (HVOF) technique WC-17Co coating is deposited on an LZ50 steel surface to study its properties through Vickers hardness testing, scanning electric microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffractrometry (XRD). Rotational fretting wear tests are conducted under normal load varied from 10 N to 50 N, and angular displacement amplitudes vary from 0.125° to 1°. Wear scars are examined using SEM, EDX, optical microscopy (OM), and surface topography. The experimental results reveal that the WC-17Co coating adjusted the boundary between the partial slip regime (PSR) and the slip regime (SR) to the direction of smaller amplitude displacement. As a result, the coefficients of friction are consistently lower than the substrate’s coefficients of friction both in the PSR and SR. The damage to the coating in the PSR is very slight. In the SR, the coating exhibits higher debris removal efficiency and load-carrying capacity. The bulge is not found for the coating due to the coating’s higher hardness to restrain plastic flow. This research could provide experimental bases for promoting industrial application of WC-17Co coating in prevention of rotational fretting wear.

Herein, we report a type of core–shell structured NixCo3−xS4 (x = 1, 1.5 and 2) through tuning the ratios of Ni to Co by a simple two-step hydrothermal method. Scanning electron microscopy and transmission electron microscopy images of all the Ni–Co sulfides show high porosity and uniform spherical morphology. Moreover, this study demonstrates that controlling the appropriate ratio of Ni to Co in the core–shell structure is crucial for improving the electrochemical performance in a hybrid supercapacitor. Among them, NiCo2S4 with core–shell structure possesses the highest capacity of 155 mA h g−1, whereas as Ni1.5Co1.5S4 shows the excellent rate-capability of up to 80% from 1 to 20 A g−1 and cycling stability, which retains 74% after 2000 cycles. Therefore, tuning the metal element contents provides a feasible approach to achieving the desired high-rate performance and cycling stability of electrode materials in polynary metal sulfides for hybrid supercapacitors.

This paper presents an experimental study on the loosening behaviour of threaded fasteners under cyclic shear displacement. The effects of the initial preload and the amplitude of the shear displacement on the loosening behaviour of the common zinc-coated bolts are investigated. Diamond-like carbon (DLC) coating is utilised to treat the surface of bolts for improving the wear resistance of threads. The thread damage is analysed after the tests. Results show that fatigue wear is the major wear mechanism on the first thread surface. The looseness of threaded fasteners is small under high initial preload and low amplitude of shear displacement. For DLC-coated bolts, the thread damage is slight, and DLC-coated bolts have a better anti-loosening property comparing with zinc-coated bolts.

The fretting capabilities of 690 alloy against 405 stainless steel were evaluated through a series of tube-plate tests in different experimental conditions. The results indicated that as the temperature increased in air, the wear volume and wear depth increased first until reaching a maximum value at 90 °C and then decreased. This was attributed to spinel oxides formed above 200 °C in combination with adhesive wear, which contributed to oxidation resistance and a reduction of interfacial wear, resulting in the decrease of wear volume and wear depth. Metallic nickel, iron and chromium were observed in water, which indicated low oxidation, associated with lower wear damage.

A systematic experimental investigation was conducted to study the effect of oxygen environment of different pressure on the fretting wear behavior of Ti6Al4V titanium alloy. In order to well probe the real tribo-chemical state, in this work, an in-situ X-ray photoelectron spectroscopy (XPS) analysis test developed by a self-designed high precision fretting wear tester integrated with an XPS equipment was used. The tribo-oxidation formed at the different oxygen pressure and its effect on the fretting wear mechanism and the resulting fretting wear volume in the different fretting run regime were discussed. Results show that the oxygen environment of different pressure has significant influence on the wear resistance of titanium alloy depending on the fretting run regime. In the partial slip regime (PSR), different oxygen pressure plays a little influence on fretting wear behavior, while a significant influence for the mixed fretting regime (MFR) and slip regime (SR). The tribo-oxidations produced at the oxygen environment of different pressure for the different fretting run regimes are found to correlate well with the resulting fretting wear mechanism and the fretting wear resistance.

In this work, to investigate the role of the third body in the fretting behavior of 690 alloy, the fretting capabilities of 690 alloy against 405 stainless steel have been performed under various experimental conditions. The testing normal force and temperature varied from 10 N to 40 N and from room-temperature (RT) to [Formula: see text]C, respectively, at 5 Hz and 200 [Formula: see text]m. The results demonstrated that the profile shape of wear scar was dependent on the action of the wear particles. Three typical profile shapes were examined in this work: “U” shape, “W” shape and “M” shape. The balance of the formation and ejection of wear particles led to a steady value of the coefficient of friction (COF) and friction energy.