Bioinspired directional structures for inhibiting wetting on super-melt-philic surfaces above 1200°C

Over the past two decades,superhydrophobic surfaces that are easily created have aroused considerable attention for their superior performances in various applications at room temperature.Nowadays,there is a growing demand in special fields for the development of surfaces that can resist wetting by high-temperature molten droplets(>1200°C)using facile design and fabrication strategies.Herein,bioinspired directional structures(BDSs)were prepared on Y2O3-stabilized ZrO2(YSZ)surfaces using femtosecond laser ablation.Benefiting from the anisotropic energy barriers,the BDSs featured with no additional modifiers showed a remarkable increase from 9.2°to 60°in the contact angle of CaO–MgO–Al2O3–SiO2(CMAS)melt and a 70.1%reduction in the spreading area of CMAS at 1250°C,compared with polished super-CMAS-melt-philic YSZ surfaces.Moreover,the BDSs demonstrated exceptional wetting inhibition even at 1400°C,with an increase from 3.3°to 31.3°in contact angle and a 67.9%decrease in spreading area.This work provides valuable insight and a facile preparation strategy for effectively inhibiting the wetting of molten droplets on super-melt-philic surfaces at extremely high temperatures.

Effect of Different Laser Energy Nitriding on the Fretting Wear Performance of Zr Alloy

The zirconium(Zr)alloy fuel cladding is one of the key structural components of a nuclear reactor and the first and most important line of defense for accommodating fission products.During the operation of nuclear reactors,Zr alloy fuel cladding is subjected to extreme harsh environments,such as high temperature,high pressure and high flow rate for a long period of time.The wear and corrosion resistance of Zr alloys is important for the safe operation of nuclear reactors.Surface modification can effectively improve the corrosion and wear resistance of fuel cladding.Compared with coating technology,nitriding technology does not have problems for bonding between the coating and the substrate.Current research on surface nitriding of Zr alloys mainly focuses on plasma nitriding and ion implantation techniques.Research on laser nitriding of Zr alloy surfaces and their fretting wear characteristics is scarce.In this study,the surface of Zr alloy was treated with laser nitriding at different laser energies.The microstructure of Zr alloy treated with different laser energies and its fretting wear performance were studied.The results showed that after nitriding with different laser energies,the surface of the Zr alloy showed a typical molten state after melting,vaporizing and cooling under the thermal effect of the laser,and this state was more obvious with the increase of the laser energy.At the same time,doping of N atoms and formation of the ZrN phase led to different cooling rates in the molten zone that produced large tensile stresses after cooling.This led to cracks on the surface of Zr alloys after laser nitriding at different energies,and the crack density increased with increasing laser energy.This also led to an increase in the surface roughness of the Zr alloy with increasing laser energy after laser nitriding treatment.Due to the presence of water in the industrial nitrogen,nitrides were generated on the surface of the sample along with some oxides.When the laser energy was 100 mJ,there was no ZrN generation,and N existed mainly as a diffusion layer within the Zr alloy substrate.ZrN generated when the laser energy reached 200 mJ and above,which increased with the increase of laser energy.Due to the generation of ZrN phase and the presence of some oxides,the surface Vickers hardness of Zr alloys after laser nitriding treatment at different energies increased by 37.5%compared to Zr alloys.After laser nitriding treatment,the wear mechanism of Zr alloys changed.For the untreated Zr alloys,the wear mechanism was dominated by delamination and spalling wear,accompanied by oxidative and abrasive wear.The phenomenon of delamination and peeling decreased with the increase of laser energy.Wear mechanisms changed to predominantly abrasive wear with oxidative wear and delamination spalling.The wear volume of sample nitriding with laser energy 400 mJ was reduced by 46.5%compared with that of untreated Zr alloy.

Fretting Wear Characteristics of Nuclear Fuel Cladding in High-Temperature Pressurized Water

In pressurized water reactor(PWR),fretting wear is one of the main causes of fuel assembly failure.Moreover,the operation condition of cladding is complex and harsh.A unique fretting damage test equipment was developed and tested to simulate the fretting damage evolution process of cladding in the PWR environment.It can simulate the fretting wear experiment of PWR under different temperatures(maximum temperature is 350℃),displacement amplitude,vibration frequency,and normal force.The fretting wear behavior of Zr-4 alloy under different temperature environments was tested.In addition,the evolution of wear scar morphology,profile,and wear volume was studied using an optical microscope(OM),scanning electron microscopy(SEM),and a 3D white light interferometer.Results show that higher water temperature evidently decreased the cladding wear volume,the wear mechanism of Zr-4 cladding changed from abrasive wear to adhesive wear and the formation of an oxide layer on the wear scar reduced the wear volume and maximum wear depth.

Well-Dispersed Graphene Enhanced Lithium Complex Grease Toward High-Efcient Lubrication

Graphene as a lubricating additive holds great potential for industrial lubrication. However, its poor dispersity and compatibility with base oils and grease hinder maximizing performance. Here, the infuence of graphene dispersion on the thickening efect and lubrication function is considered. A well-dispersed lubricant additive was obtained via trihexyl tetradecyl phosphonium bis(2-ethylhexyl) phosphate modifed graphene ([P_(66614)][DEHP]-G). Then lithium complex grease was prepared by saponifcation with 12-OH stearic acid, sebacic acid, and lithium hydroxide, using polyalphaolefn (PAO20) as base oil and the modifed-graphene as lubricating additive, with the original graphene as a comparison. The physicochemical properties and lubrication performance of the as-prepared greases were evaluated in detail. The results show that the as-prepared greases have high dropping point and colloidal stability. Furthermore, modifed-graphene lithium complex grease ofered the best friction reduction and anti-wear abilities, manifesting the reduction of friction coefcient and wear volume up to 18.84% and 67.34%, respectively. With base oil overfow and afux, well-dispersed [P_(66614)][DEHP]-G was readily adsorbed to the worn surfaces, resulting in the formation of a continuous and dense graphene deposition flm. The synergy of deposited graphene-flm, spilled oil, and adhesive grease greatly improves the lubrication function of grease. This research paves the way for modulating high-performance lithium complex grease to reduce the friction and wear of movable machinery.

Investigation of Experimental Devices for Finger Active and Passive Tactile Friction Analysis

Complicated tribological behavior occurs when human fingers touch and perceive the surfaces of objects.In this process,people use their exploration style with different conditions,such as contact load,sliding speed,sliding direction,and angle of orientation between fingers and object surface consciously or unconsciously.This work addressed interlaboratory experimental devices for finger active and passive tactile friction analysis,showing two types of finger movement.In active sliding experiment,the participant slid their finger freely against the object surface,requiring the subject to control the motion conditions themselves.For passive sliding experiments,these motion conditions were adjusted by the device.Several analysis parameters,such as contact force,vibration acceleration signals,vibration magnitude,and fingerprint deformation were recorded simultaneously.Noticeable friction differences were observed when comparing active sliding and passive sliding.For passive sliding,stick-slip behavior occurred when sliding in the distal direction,evidenced by observing the friction force and the related deformation of the fingerprint ridges.The employed devices showed good repeatability and high reliability,which enriched the design of the experimental platform and provided guidance to the standardization research in the field of tactile friction.

Gaps,challenges and possible solution for prediction of wheel-rail rolling contact fatigue crack initiation

The prediction of wheel/rail rolling contact fatigue(RCF)crack initiation during railway operations is an important task.Since RCF crack evolution is influenced by many factors,its prediction process is complex.This paper reviews the existing approaches to predict RCF crack initiation.The crack initiation region is predicted by the shakedown map.By combining the shakedown map with various initiation criteria and the critical plane method,the crack initiation life is calculated.The classification,methodologies,theories and applications of these approaches are included in this paper.The advantages and limitations of these methods are analyzed to provide recommendation for RCF crack initiation prediction.This review highlights that wheel/rail dynamic characteristic,complex working conditions,surface defects and wear all affect the RCF crack initiation.The optimal selection of criteria is essential in the crack initiation prediction.Based on the research gap regarding the challenging process of crack initiation prediction detailed in this review,a proposed prediction process of RCF crack initiation is proposed to achieve a more accurate result.

Experimental Study on Wear and Spalling Behaviors of Railway Wheel

The current researches of the wear and spalling behaviors of wheel/rail materials focus on the field investigation rather than the mechanism. However, it is necessary and significant for clarifying the mechanism and relationship between the wear and spalling damage of railway wheel to test and reproduce the wheel damages in laboratory. The objective of this paper is to investigate the wear and spalling damage behaviors of railway wheel using a JD-1 wheel/rail simulation facility, which consists of a small wheel serving as rolling stock wheel, and a larger wheel serving as rail. The damage process of wheel roller is explored in terms of the creep ratio, axle load, and carbon content by means of various microscopic examinations. The experimental results show that the wear volume growth of wheel roller is proved to be proportional to the increase of the creep ratio and normal load between simulating wheel and rail. The increase of carbon content of wheel material causes a linear reduction in the wear volume. The microscopic examinations indicate that the rolling wear mechanism transfers from abrasive wear to adhesive and fatigue wear with an increase of tangential friction force, which results in the initiation of fatigue crack, and then aggravates spalling damage on the wheel roller surface. The surface hardness of material depends strongly upon its carbon content. The decrease of the carbon content of wheel material may alleviate spalling damage, but can cause a significant growth in the wear volume of wheel roller. Therefore, there is a competitive relationship between the wear and spalling damage of wheel material. This research proposes an important measure for alleviating or preventing the wear and spalling damage of railway wheel material.

Improving impact wear resistance of Ti-6Al-4V alloy treated by laser shock peening

The effects of laser shock peening (LSP) on the impact wear behavior of Ti-6Al-4V alloys were investigated by a homemade impact wear test rig. The microstructure and mechanical properties of the peened samples were studied. During the impact wear test, the energy absorption, impact force, wear contact time and wear mechanism of all the test samples were investigated in terms of the influence of the impact kinetic energy. The results showed that microhardness, elastic modulus and residual compressive stress of the treated samples were markedly improved. The wear resistances of both treated samples were highly improved after LSP, and a higher pulse energy corresponded to a more obvious effect. Besides, the wear in all test samples involved a combination of abrasive and oxidation wear and fatigue spalling.

Friction and wear of 7075 aluminum alloy induced by torsional fretting

The torsional fretting wear tests of 7075 aluminum alloy flat against 52100 steel ball in dry condition were carried out on a new high-precision torsional fretting-wear tester.The kinetics behaviors and damage mechanism of 7075 aluminum alloy under different angular displacement amplitudes were investigated in detail.The results show that the torsional fretting running behaviors of 7075 aluminum alloy can be defined by three fretting regimes(i.e.partial slip regime(PSR),mixed fretting regime(MFR) and slip regime(SR)) with the increase of angular displacement amplitudes.In PSR,the damage occurs at the lateral portion of the contact zone with a slight annular shape.However,in MFR and SR,more severe damages are observed and the debris layer covers the wear scars.Friction torque and dissipation energy which are strongly dependent upon the imposed angular displacement amplitudes and presented in three stages were discussed in detail.The mechanisms of torsional fretting wear of aluminum alloy are mainly oxidative wear,abrasive wear and delamination in the three fretting regimes.In addition,the oxidative debris plays an important role during the torsional fretting wear processes.

Friction-Induced Nanofabrication: A Review

As the bridge between basic principles and applications of nanotechnology,nanofabrication methods play significant role in supporting the development of nanoscale science and engineering,which is changing and improving the production and lifestyle of the human.Photo lithography and other alternative technologies,such as nanoimprinting,electron beam lithography,focused ion beam cutting,and scanning probe lithography,have brought great progress of semiconductor industry,IC manufacturing and micro/nanoelectromechanical system(MEMS/NEMS)devices.However,there remains a lot of challenges,relating to the resolution,cost,speed,and so on,in realizing high-quality products with further development of nanotechnology.None of the existing techniques can satisfy all the needs in nanoscience and nanotechnology at the same time,and it is essential to explore new nanofabrication methods.As a newly developed scanning probe microscope(SPM)-based lithography,friction-induced nanofabrication provides opportunities for maskless,flexible,low-damage,low-cost and environment-friendly processing on a wide variety of materials,including silicon,quartz,glass surfaces,and so on.It has been proved that this fabrication route provides with a broad application prospect in the fabrication of nanoimprint templates,microfluidic devices,and micro/nano optical structures.This paper hereby involved the principals and operations of friction-induced nanofabrication,including friction-induced selective etching,and the applications were reviewed as well for looking ahead at opportunities and challenges with nanotechnology development.The present review will not only enrich the knowledge in nanotribology,but also plays a positive role in promoting SPM-based nanofabrication.

Fretting wear of micro-arc oxidation coating prepared on Ti6Al4V alloy

Micro-arc oxidation(MAO)coating was prepared on Ti6Al4V alloy surface and its characterizations were detected by Vickers hardness tester,profilometer,scanning electric microscope(SEM),energy dispersive X-ray spectrometer(EDX)and X-ray diffractometer(XRD).Fretting wear behaviors of the coating and its substrate were comparatively tested without lubrication under varied displacement amplitudes(D)in a range of 3-40μm,constant normal load(Fn)of 300 N and frequency of 5 Hz.The results showed that the MAO coating,presenting rough and porous surface and high hardness,mainly consisted of rutile and anatase TiO2 phases.Compared with the substrate,the MAO coating could shift the mixed fretting regime(MFR)and slip regime(SR)to a direction of smaller displacement amplitude.In the partial slip regime(PSR),lower friction coefficients and slight damage appeared due to the coordination of elastic deformation of contact zones.In the MFR,the friction coefficient of the coating was lower than that of the substrate as a result of the prevention of plastic deformation by the hard ceramic surface.With the increase of the displacement amplitude,the degradation of the MAO coating and the substrate increased extremely.The fretting wear mechanisms of the coating were abrasive wear and delamination with some material transfer of specimen.In addition,the coating presented a better property for alleviating fretting wear.

3D Profile Filter Algorithm Based on Parallel Generalized B-spline Approximating Gaussian

Currently, the approximation methods of the Gaussian filter by some other spline filters have been developed. However, thesc methods are only suitable for the study of one-dimensional filtering, when these methods are used for three-dimensional filtering, it is found that a rounding error and quantization error would be passed to the next in every part. In this paper, a new and high-precision implementation approach for Gaussian filter is described, which is suitable for three-dimensional reference filtering. Based on the theory of generalized B-spline function and the variational principle, the transmission characteristics of a digital filter can be changed through the sensitivity of the parameters （t1, t2）, and which can also reduce the rounding error and quantization error by the filter in a parallel form instead of the cascade form, Finally, the approximation filter of Gaussian filter is obtained. In order to verify the feasibility of the new algorithm, the reference extraction of the conventional methods are also used and compared. The experiments are conducted on the measured optical surface, and the results show that the total calculation by the new algorithm only requires 0.07 s for 480×480 data points; the amplitude deviation between the reference of the parallel form filter and the Gaussian filter is smaller; the new method is closer to the characteristic of the Gaussian filter through the analysis of three-dimensional roughness parameters, comparing with the cascade generalized B-spline approximating Gaussian. So the new algorithm is also efficient and accurate for the implementation of Gaussian filter in the application of surface roughness measurement.

Effect of Cycling Low Velocity Impact on Mechanical and Wear Properties of CFRP Laminate Composites

The mechanical and wear properties of CFRP laminate were investigated using a method of cycling low velocity impact, to study the trend and mechanism of impact resistance of the CFRP laminate under repeated impact during its service process. The interface responses of CFRP laminate under di erent impact kinetic energy during the cycling impact process were studied were studied experimentally, such as impact contact duration, deformation and energy absorption. The worn surface morphologies were observed through optical microscopy and a 3?D surface profiler and the cross?sectional morphologies were observed through SEM to investigate the mechanism of impact material dam?age. Based on a single?degree?of?freedom damping vibration model, the normal contact sti ness and contact damp?ing of the material in di erent wear stages were calculated. It shows the failure process of CFRP laminate damaged by accumulated absorption energy under the cycling impact of di erent initial kinetic energy. The results indicate that the sti ness and damping coe cients will change at di erent impact velocities or cycle numbers. The damage mechanism of CFRP laminates under cycling low kinetic energy is delamination. After repeated experiments, it was found that there was a threshold value for the accumulated absorption energy before the failure of the CFRP laminate.

Fretting wear behavior of Ti/TiN multilayer film on uranium surface under various displacement amplitudes

Ti/TiN multilayer film was deposited on uranium surface by arc ion plating technique to improve fretting wear behavior. The morphology, structure and element distribution of the film were measured by scanning electric microscopy（SEM）, X-ray diffractometry（XRD） and Auger electron spectroscopy（AES）. Fretting wear tests of uranium and Ti/TiN multilayer film were carried out using pin-on-disc configuration. The fretting tests of uranium and Ti/TiN multilayer film were carried out under normal load of 20 N and various displacement amplitudes ranging from 5 to 100 μm. With the increase of the displacement amplitude, the fretting changed from partial slip regime（PSR） to slip regime（SR）. The coefficient of friction（COF） increased with the increase of displacement amplitude. The results indicated that the displacement amplitude had a strong effect on fretting wear behavior of the film. The damage of the film was very slight when the displacement amplitude was below 20 μm. The observations indicated that the delamination was the main wear mechanism of Ti/TiN multilayer film in PSR. The main wear mechanism of Ti/TiN multilayer film in SR was delamination and abrasive wear.

Investigation into rail corrugation in high-speed railway tracks from the viewpoint of the frictional self-excited vibration of a wheel–rail system

A finite element vibration model of a multiple wheel-rail system which consists of four wheels, one rail, and a series of sleepers is established to address the problem of rail corrugation in high-speed tracks. In the model, the creep forces between the wheels and rail are considered to be saturated and equal to the normal contact forces times the friction coefficient. The oscillation of the rail is coupled with that of wheels in the action of the saturated creep forces. When the coupling is strong, self- excited oscillation of the wheel-rail system occurs. The self-excited vibration propensity of the model is analyzed using the complex eigenvalue method. Results show that there are strong propensities of unstable self-excited vibrations whose frequencies are less than 1,200 Hz under some conditions. Preventing wheels from slipping on rails is an effective method for suppressing rail corrugation in high-speed tracks.

Wear Characteristics of the Nuclear Control Rod Drive Mechanism(CRDM)Movable Latch Serviced in High Temperature Water

The current research of nuclear control rod drive mechanism(CRDM)movable latch only makes a simple measurement of wear mass.The wear volume and difference in various claw surfaces are ignored and the degradation mechanism of each claw surface is not clear.In this paper,a detailed degradation analysis was carried out on each claw surface of movable latch combined with wear result and worn morphology.Results indicate that the boundary of carbide is preferred for corrosion because carbide presents a nobler Volta potential compared to the metal matrix or boundary region.Due to the oscillation of drive shaft between the claw surfaces of movable latch,the dominant wear mechanism on the upper surface of claw(USC)and lower surface of claw(LSC)is plastic deformation caused by impact wear.Mechanical impact wear will cause the fragmentation of carbides because of the high hardness and low ductility of carbides.Corrosion promotes the broken carbides to fall off from the metal matrix.The generated fine carbides(abrasive particles)cause extra abrasive wear on USC when the movable brings the drive shaft upward or downward.As a result,USC has a higher wear volume than LSC.This research proposes a method to evaluate the wear on the whole movable latches using a 3D full-size scanner.

Study on the fatigue and wear characteristics of four wheel materials

The fatigue and wear characteristics of four different steel wheel materials are investigated in detail by using rolling contact fatigue and wear bench tests on a JD-1 apparatus, analyzing chemical composition and hardness, and performing profile analysis and micro-morphology analysis. The wear and fatigue behavior of one of the materials under different operation speeds is also investigated. The results show that the wear resistance of the materials has a positive correlation with their carbon content, while fatigue resistance has a negative correlation. Based on hardness analysis as a function of depth into the specimen, the thickness of layers with a steep hardness gradient has a negative correlation with the initial surface hardness in the tests using different materials. The hardness increments, however, have a positive correlation with initial surface hardness. The rolling tests on one material using different rotation speeds show that the hardness increments and the thickness of layers with a steep hardness gradient increase with the rotation speed. The analyses and experimental results demonstrate that two of the four materials exhibit good wear resistance and rolling contact fatigue resistance, making them suitable for either highspeed or heavy axle railroad operations.

Sliding Wear Behavior of Plasma Sprayed Zirconia Coating on Cast Aluminum against Silicon Carbide Ceramic

The sliding wear behaviors of ZrO2-22 wt pct MgO （MZ） and ZrO2-8 wt pct Y2O3（YZ） coatings deposited on a cast aluminum alloy with bond layer （NiCrCoAlY） by plasma spray were investigated under dry test conditions at room temperature. Under all load conditions, the wear mechanisms of the MZ and YZ coatings were almost the same. The material transfer and pullout were involved in the wear process of the studied coatings under the test conditions. The wear rate of the MZ coating was less than that of the YZ coating. While increasing the normal load, the wear rates of the MZ and YZ coatings increased. SEM was used to examine the worn surfaces and to elucidate likely wear mechanisms. Energy dispersive X-ray spectroscopy （EDX） analysis of the worn surfaces indicated that material transfer occurred in the direction from the SiC ball to the disk. Fracture toughness had a significant influence on the wear performance of the coatings. It was suggested that the material transfer played an important role in the wear behavior.

Friction and Wear Properties of High-velocity Oxygen Fuel Sprayed WC-17Co Coating under Rotational Fretting Conditions

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-17 Co 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-17 Co 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-17 Co coating in prevention of rotational fretting wear.

A Study of Effect of Various Normal Force Loading Forms on Frictional Stick-Slip Vibration

In this work,a comparative study is performed to investigate the influence of time-varying normal forces on the friction properties and friction-induced stick-slip vibration(FIV)by experimental and theoretical methods.In the experiments,constant and harmonic-varying normal forces are applied,respectively.The measured vibration signals under two loading forms are compared in both time and frequency domains.In addition,mathematical tools such as phase space reconstruction and Fourier spectra are used to reveal the science behind the complicated dynamic behavior.It can be found that the friction system shows steady stick-slip vibration,and the main frequency does not vary with the magnitude of the constant normal force,but the size of limit cycle increases with the magnitude of the constant normal force.In contrast,the friction system under the harmonic normal force shows complicated behavior,for example,higher-frequency larger-amplitude vibration occurs and looks chaotic as the frequency of the normal force increases.The interesting findings offer a new way for controlling FIV in engineering applications.