Influence of Parameters of Reactive Magnetron Sputtering on Tribomechanical Properties of Protective Nanostructured Ti–Al–N Coatings

The influence of substrate temperature and bias voltage on the structure and tribomechanical properties of the Ti–Al–N coatings obtained by reactive magnetron sputtering technique has been investigated. The structure and elemental and phase compositions have been studied by scanning electron microscopy, Rutherford backscattering, and X-Ray diffraction. The results of friction and wear experiments indicated that the lowest coefficient of friction (three times lower than 12Cr18Ni10Ti) corresponded to a coating deposited at a bias voltage of–200 V and a substrate temperature of 340°С, while the most wear-resistant coating (under a load of 700 mN and the testing time of 1080 s) was Ti–Al–N sputtered at a bias voltage of–200 V and a substrate temperature of 440°С.     

Chromium and Detonation Nanodiamond Based Coatings of the Chromium–Carbon System: Deposition by Magnetron Sputtering,Peculiarities of Phase Composition,and Tribological Properties

The structure, the chemical and phase compositions, and the micromechanical and tribological properties of chromium–carbon coatings obtained by the magnetron sputtering of composite and/or sintered chromium–nanodiamond targets are investigated. The coatings possess the composite multiphase structure composed of chromium and its phases formed as a result of the chemical interactions of the target material’s components both between each other and with the reactive gas if present in a sputtering atmosphere. Several technological factors influencing the structural and phase peculiarities of the coatings, their nanohardness, and the dry friction behavior at high contact pressures are studied.     

Tribological Properties of Twin Electron-Beam Evaporated Cr–N and Al–Cr–N Coatings Under Laboratory Sliding and Drill Experiments

The tribological behavior of substoichiometric Cr–N and Al–Cr–N coatings prepared by twin electron-beam evaporation at 450 °C was studied. Al–Cr–N coatings with Al to Cr ratios in the range of 1–8 (and nitrogen concentrations of ~45 at.%) were synthesized and compared to Cr–N reference samples. The focus of this work is on Al–Cr–N (Al ≥ 30 at.%) coatings with the aim of (a) replacing Cr with Al due to environmental concerns and (b) achieving improved mechanical properties, and tribological performance. The composition, structure, mechanical and tribological properties of the coatings were determined using X-ray photoelectron spectroscopy, X-ray diffraction, and scanning electron microscopy in combination with nanoindentation measurements, laboratory controlled ball-on-disk sliding experiments, and wet and dry drilling experiments. It was found that all Al–Cr–N coatings exhibit higher hardness values compared to Cr–N coatings. Al–Cr–N coatings with Al contents and Al/Cr ratios of ≤38 at.% and ≤1.7, respectively, showed better performance than the rest of the coatings during both drilling and laboratory tribological experiments.     

Arc Evaporation of Ti–Al–Ta–N Coatings: The Effect of Bias Voltage and Ta on High-temperature Tribological Properties

Recently, titanium aluminium tantalum nitride (Ti–Al–Ta–N) coatings have been shown to exhibit beneficial properties for cutting applications. However, the reason for the improved behaviour of these coatings in comparison to unalloyed Ti–Al–N is not yet clear. Here, we report on the tribological mechanisms present in the temperature range between 25 and 900 °C for this coating system, and in particular on the effect of the bias voltage during deposition on the tribological response. Based on these results, we provide an explanation for the improved performance of Ta-alloyed coatings. An industrial-scale cathodic arc evaporation facility was used to deposit the coatings from powder metallurgically produced Ti₄₀Al₆₀ and Ti₃₈Al₅₇Ta₅ targets at bias voltages ranging from −40 to −160 V. X-ray diffraction experiments displayed a change with increasing bias voltage from a dual-phase structure containing cubic and hexagonal phases to a single-phase cubic structure. Investigations of the wear behaviour at various temperatures showed different controlling effects in the respective temperature ranges. The results of dry sliding tests at room temperature were independent of bias voltage and Ta-alloying, where the atmosphere, i.e. moisture and oxygen, were the most important parameters during the test. At 500 °C, bias and droplet-generated surface roughness were identified to determine the tribological behaviour. At 700 and 900 °C, wear depended on the coating’s resistance to oxidation, which was also influenced by the bias voltage. In conclusion, Ta-alloyed coatings show a significantly higher resistance to oxidation than unalloyed Ti–Al–N which could be an important reason for the improved performance in cutting operations.     

Tribological Properties and Wear Mechanisms of NiCr–Al2O3–SrSO4–Ag Self-Lubricating Composites at Elevated Temperatures

NiCr–Al₂O₃–SrSO₄–Ag self-lubricating composites were prepared by powder metallurgy method and the tribological properties of composites were evaluated by a ball-on-disk tribometer against alumina ball at wide temperature range from the room temperature to 1,000 °C in air. The linear coefficient of thermal expansion was evaluated for investigation of thermal stability of composites. The tribo-chemical reaction films formed on the rubbing surfaces and their effects on the tribological properties of composites at different temperatures were addressed according to the surface characterization by SEM, XRD, and XPS. The results show that the NiCr–Al₂O₃ composite with addition of 10 wt% SrSO₄ and 10 wt% Ag exhibits satisfying friction and wear properties over the entire temperature range from room temperature to 1,000 °C. The composition of the tribo-layers on the worn surfaces of the composites is varied at different temperatures. The synergistic lubricating effect of SrAl₄O₇, Ag, and NiCr₂O₄ lubricating films formed on worn surfaces were identified to reduce the friction coefficient and wear rate from room temperature to 800 °C. Meanwhile, at 1,000 °C, the SrCrO₄ and NiAl₂O₄ was formed on the worn surfaces during sliding process, combining with the NiCr₂O₄, Al₂O₃, Cr₂O₃, Ag, and Ag₂O, which play an important role in the formation of a continuous lubricating film on the sliding surface.     

Dry-Sliding Tribological Properties of Bronze–Graphite Composites

Bronze-uncoated and nickel-coated graphite composites were fabricated by powder metallurgy route. The tribological behaviors of composites sliding against AISI52100 steel ball under dry sliding condition were studied using a ball-on-disk tribometer. The nickel-coated graphite composites showed much better tribological properties in comparison with bronze and uncoated graphite composite. The friction coefficient of nickel-coated graphite composites decreased with increasing nickel-coated graphite content. However, the specific wear rate increased with the increase in nickel-coated graphite. The composite containing 15?wt% nickel-coated graphite showed the best self-lubricating properties because the compacted and stable mechanical mixed layer was formed on the worn surfaces. The wear mechanism of bronze 663 is adhesive wear and abrasive wear. The uncoated nickel-coated graphite composite shows the adhesive wear and delamination characteristics. However, the wear mechanism of nickel-coated composites is mildly abrasive wear.     

Tribological Performance of PTFE–Metal Binary Coatings in Rolling/Sliding Contact

Tribological performance of surface coatings with embedded PTFE reservoirs in rolling/sliding contact is reported. Using two different coating materials and two shapes and patterns of PTFE reservoirs test samples in the form of discs were prepared and tested in a four-ball contact configuration under loads corresponding to nominal contact pressure of 0.5 and 1.0 GPa. It was found that one coating, namely aluminium–bronze with embedded PTFE reservoirs is suitable for applications where rolling is also associated with a degree of sliding and there is no external lubrication.     

Test Analysis of Friction Couples With Solid Lubricant Coatings under Ground–Space Conditions and Prediction of Tribological Characteristics

As a result of an analysis of the literature data on ground–space tribological tests of friction couples with solid lubricant coating (SLC) ARSRI PP 212, the dependences for evaluating the starting antifriction characteristics have been determined. The wear life and coefficient of friction have been compared. According to results, calculation algorithms of tribological characteristics of friction couples with SLC for considered operational conditions have been developed and implemented.     

Tribological Properties of a C/C–SiC–Cu Composite Brake Disc

A life-size composite brake disc was produced from Si, carbon–carbon composite, copper, and phenol resin. The disc had an outer radius Ø380, inner radius Ø180, and thickness of 36 mm. Chopped carbon fibers were used to reinforce frictional and structural layers. To obtain a preform of each layer, resin and carbon-fibers were mixed and hot-pressed. The preforms were pyrolyzed, and bonded by hot pressing. Finally Si and Cu infiltration in vacuum atmosphere was carried out to obtain a C/C–SiC–Cu _x Si _y composite brake disc. The density of the disc was 2.17 g/cm³. The bending strength was 61 MPa. The heat transfer coefficients in vertical and horizontal directions were 30.7, and 85.2 W/m-°C at 25°C, respectively. Friction coefficients of the C/C–SiC–Cu _x Si _y brake disc were more stable than those of C/C–SiC brake discs. X-ray diffraction analysis showed that Cu formed a compound, Cu₃Si.     

Effects of Deposition Conditions and Counter Bodies on the Tribological Properties of Pulsed DC Magnetron Sputtered TiN–MoS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Composite Coating

In the current study, TiN–MoS _x composite coatings were deposited by co-sputtering of MoS₂ and Ti targets under a mixture of Ar and N₂ gas environment using pulsed DC closed-field unbalanced magnetron sputtering. The tribological response of TiN–MoS _x composite coatings was studied against two different counter bodies: cemented carbide (WC–6% Co) ball and pin made of aluminium alloy (AlSiMg). First, the effect of substrate bias was studied on tribological properties using cemented carbide ball. Lowest coefficient of friction in the range of 0.03–0.04 was obtained for the specimen deposited at a substrate bias of −60 V. Wear coefficient was also found to be minimum for the same specimen. Coatings were further deposited at an optimum bias of −60 V in order to vary MoS _x content of TiN–MoS _x composite coating. Effect of variation of chemical composition of the coating was then studied on tribological performance of the coating against aluminium alloy counterface. Excellent anti-sticking property of MoS _x was found to have enabled the TiN–MoS _x composite coating to achieve considerably low coefficient of friction against aluminium alloy. It was shown that with optimum MoS _x content of TiN–MoS _x composite coating, it was possible to attain as low coefficient of friction as 0.09 against aluminium alloy even under normal atmospheric condition.     

Microstructural,Mechanical, and Tribological Properties of Rice Husk–Based Carbon: Effect of Carbonizing Temperature

In this study, we investigated the microstructural, mechanical, and tribological properties of rice husk (RH)-based carbon carbonized at various carbonizing temperatures under dry conditions. All samples exhibited amorphous carbon structures and the X-ray diffraction spectra of the samples carbonized at 1300 and 1400?°C indicated the presence of a polymorphic crystals of silica. The hardness increased with temperature due to the densification of the structure and the presence of the hard crystalline silica. At low normal loads, the mean friction coefficient of the material decreased as the carbonizing temperature was increased from 600 to 800?°C and slightly decreased as the carbonizing temperature was further increased from 800 to 1400?°C. At the highest load, all samples, except for that carbonized at 600?°C, exhibited extremely low friction coefficients (around 0.05). The wear rates of the all samples were smaller than 10^?5 mm³/N·m, indicating that RH carbon exhibits sufficient wear resistance. A Raman spectroscopic analysis of the worn surface of a steel ball revealed that the transfer layer at 600?°C had a less graphitic structure compared to the other carbonizing temperature. Based on these findings, we recommend an optimal carbonizing temperature for applications of sliding materials exposed to dry sliding contact.     

Tribological behaviors of Ti–6Al–4V modified by chemical methods

In order to improve the tribological properties of titanium-based implants, sodium hydroxide (NaOH), hydrogen peroxide (H₂O₂) solutions, sol–gel hydroxyapatite (HA) film, thermal treatment and combined methods of NaOH solution/HA film, H₂O₂ solution/HA film are used to modify the surfaces of Ti–6Al–4V (coded TC4). The chemical states of some typical elements in the modified surfaces were detected by means of X-ray photoelectron spectroscopy (XPS). The tribological properties of modified surfaces sliding against an AISI52100 steel ball were evaluated on a reciprocating friction and wear tester. As the results, complex surfaces with varied components are obtained. All the methods are effective in improving the wear resistance of Ti–6Al–4V in different degrees. Among all, the surface modified by the combined method of NaOH solution/HA film gives the best tribological performances. The friction coefficient is also greatly reduced by the modification of NaOH solution. The order of the wear resistance under 3 N is as following: Ti–NaOH–HA>Ti–NaOH>Ti–HA>Ti–H₂O₂–HA>Ti–H₂O₂ >Ti–500; under 1 N is Ti–HA, Ti–NaOH–HA>Ti–NaOH. For Ti–H₂O₂, a very low friction coefficient and long wear life over 2000 passes is obtained under 1 N. SEM observation of the morphologies of worn surfaces indicates that the wear of TC4 is characteristic of abrasive wear. Differently, abrasion, plastic deformation and micro–crack dominate the wear of Ti–HA; slight abrasive wear dominate the wear mechanism of Ti–NaOH and microfracture and abrasive wear for Ti–NaOH–HA and Ti–H₂O₂–HA, while the sample modified by thermal treatment is characterized by sever fracture. The superior friction reduction and wear resistance of HA films are greatly attributed to the slight plastic deformation of the film. NaOH solution is superior in improving the wear resistance and decreasing the friction coefficient under relative higher load (3 N) and H₂O₂ is helpful to reduce friction and wear under relatively lower load (1 N). Combined method of Ti–NaOH–HA is suggested to improve the wear resistance of Ti–6Al–4V for medial applications under fretting situations.     

Effect of Extrusion on the Microstructure and Tribological Behavior of Copper–Tin Composites Containing MoS2

This article deals with the effect of extrusion on the microstructures and tribological properties of powder metallurgy–fabricated copper–tin composites containing MoS₂ by optical microscopy, scanning electron microscopy (SEM), and tribotesting. The extrusion decreases the number of pores and increases the density and hardness and thus improves the tribological properties of the composites. Results demonstrated that abrasion is the dominant wear mechanism in all extruded composites, whereas a combination of adhesion and delamination appears to be the governing mechanism for prepared composites. The developed hot-extruded composites exhibited lower coefficient of friction and wear rates compared to prepared composites. Design Expert software was used to develop contour map.     

Structural and Tribological Performance of Solid NiCr-WSe2-BaF2·CaF2-Y-hBN and NiCr-WSe2-BaF2·CaF2-Y Lubricant Coatings Produced by Atmospheric Plasma Spray

NiCr matrix WSe₂-BaF₂·CaF₂-Y-hBN and WSe₂-BaF₂·CaF₂-Y powders were prepared by mechanical granulation and crushing, and composite coatings were fabricated by atmospheric plasma spray technology. The microstructures and phase compositions of the powders, as well as the coatings, were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The friction coefficient and the wear behavior of the coatings from ambient temperature to 800°C were evaluated using a ball-on-disk tribometer. From the investigation of the worn surfaces, it was concluded that brittle fracture and delamination were the dominant wear mechanisms of the coatings at low temperature. At higher temperatures, a dense and protective oxide layer (BaCrO₄ and NiO) is generated on the worn surfaces of the coatings. Layered hexagonal BN particles reduce the direct contact and severe adhesion between friction pairs. Thus, the friction coefficient of the NiCr-WSe₂-BaF₂·CaF₂-Y-hBN coating is stable at the evaluated temperatures relative to the non-hBN coating. These fluorides exhibit excellent properties in these coatings over a large temperature range.     

The Preparation and Tribological Investigation of Ni–P Amorphous Alloy Nanoparticles

Amorphous Ni–P alloy nanoparticles were synthesized by chemical reduction of nickel acetate in water reacted with sodium hypophosphite under stirring. The nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Results of XRD and TEM showed that nanoparticles have an average diameter 100 nm. And XPS analysis indicated that part of the surface of Ni–P amorphous alloy nanoparticles was oxidized. The tribological properties of the prepared Ni–P nanoparticles as an additive in lithium grease were evaluated with a four-ball friction and wear tester. The worn surfaces of the lubricated GCr15 steel were analyzed by means of XPS and scanning electron microscopy (SEM). The lubricating mechanisms were discussed on the basis of XPS and SEM analyses of the worn steel surfaces. The results show that these nanoparticles as a grease additive can effectively enhance the friction-reduction and antiwear ability of lithium grease. Tribochemical reactions were involved for steel–steel frictional pair lubricated with the lithium grease containing amorphous Ni–P alloy nanoparticles, with the formation of a boundary lubricating and protecting film composed of additives of lithium grease and tribochemical reaction products (iron phosphate, iron oxides, nickel oxide, nickel, etc.) of the lubricants. This contributes to improve the tribological properties of the lithium grease.     

In Situ Growth of Graphene on Carbon Fabrics with Enhanced Mechanical and Thermal Properties for Tribological Applications of Carbon Fabric–Phenolic Composites

ABSTRACT

Though the premature failures of wind turbine gearboxes are often attributed to bearing fatigue from overloading, there is compelling evidence that wear from underloading is a significant contributor. Here we attempt to gain insight into the relative contributions of over- and underloading by assessing planet bearing reaction forces from the Gearbox Reliability Collaborative (GRC) standard gearbox within a typical utility-scale wind turbine under realistic conditions. The results demonstrate that non-torque load sharing by the planetary stage increases and decreases planet bearing reaction forces at different locations within each rotor cycle regardless of wind speed. Planet bearing reaction forces exceeded the fatigue limit at wind speeds above 12 m/s and fell below the minimum load rating at wind speeds below 7 m/s. Based on analyses of published wind spectra from 10 U.S. sites, the expected fatigue life of the planet bearings ranged from 42 to 529 years even after accounting for non-torque load sharing. At the same 10 sites, planet bearings were underloaded (below 2% of the dynamic load rating) once per rotor cycle 40–70% of the time. Underloaded bearings are susceptible to surface damage when suddenly exposed to common transient events, such as yaw, wind gusts, braking, and grid faults. The resulting surface damage can initiate premature failure via wear (e.g., micropitting) or by reducing bearing fatigue life. The results suggest that carrier bearing clearance, non-torque load sharing, and planet bearing underloading are significant contributors to the premature failures of wind turbine planet bearings.     

Tribological Performance of Halogen-Free Ionic Liquids in Steel–Steel and DLC–DLC Contacts

The tribological performance of halogen-free ionic liquids at steel–steel and diamond-like carbon (DLC)–DLC contacts was investigated. Hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon (ta-C) were used as test specimens. Friction tests were carried out on steel–steel, a-C:H–a-C:H, and ta-C–ta-C contacts by using a reciprocating cylinder-on-disk tribotester lubricated with two different types of halogen-free ionic liquids: 1-ethyl-3-methylimidazolium dicyanamide ([BMIM][DCN]) and 1-butyl-3-methylimidazolium tricyanomethanide ([BMIM][TCC]). From the results of friction tests, the ta-C–ta-C tribopair lubricated with [BMIM][DCN] or [BMIM][TCC] exhibited an ultralow friction coefficient of 0.018–0.03. On the other hand, ultralow friction was not observed at the steel–steel and a-C:H–a-C:H contacts. Measurements obtained with a laser scanning microscope and an atomic force microscope (AFM) showed that a chemical reaction film, derived from the ionic liquid lubricant used, was formed on the steel surfaces. However, this chemical reaction film was not observed on either of the DLC surfaces. The AFM results showed that there were high-viscosity products on the ta-C surfaces, that the wear tracks on the ta-C surfaces exhibited low frictional properties, and that the ta-C surfaces were extremely smooth after the friction tests. Based on these results, it was concluded that an ionic liquid–derived adsorbed film formed on the ta-C surface and resulted in the ultralow friction when lubricated with a halogen-free ionic liquid.     

高温真空分解V2O5制备VO2

尝试采用真空分解V2O5熔体的方法制备高纯度的VO2,通过XRD和SEM等方法进行了分析。结果表明,该方法可以直接获得高纯度的VO2的沉积层,沉积层为连续单相多晶组织。当熔体以小于10℃/h的升温速率加热到1350℃,真空度控制为10-6atm,所获得的沉积层的电阻突变量级达到最大为4~5,相变温度为68℃,相变温度滞后为1℃~2℃。     

Tribological Properties of Spark-Plasma-Sintered ZrO2(Y2O3)–Al2O3–Ba x Sr1?x SO4 (x?=?0.25, 0.5, 0.75) Composites at Elevated Temperature

Self-lubricating ZrO₂(Y₂O₃)–Al₂O₃–Ba _x Sr_1−x SO₄ (x = 0.25, 0.5, 0.75) composites have been fabricated by spark plasma sintering (SPS) method. The tribological properties have been evaluated using a high-temperature friction and wear tester at room temperature and 760 °C in dry sliding against alumina ball. The composites exhibit distinct improvements in effectively reducing friction and wear, as compared to the unmodified ZrO₂(Y₂O₃)–Al₂O₃ ceramics. The ZrO₂(Y₂O₃)–Al₂O₃–Ba _x Sr_1−x SO₄ (x = 0.25, 0.5, 0.75) composites have great low and stable friction coefficients of less than 0.15 and wear rates in the order of 10^− 6mm³/Nm at 760 °C. Delamination is considered as the dominating wear mechanism of the composites at room temperature. At elevated temperature, the formation and effective spreading of Ba _x Sr_1−x SO₄ (x = 0.25, 0.5, 0.75) lubricating films during sliding play an important role in the reduction of the friction and wear.