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.     

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.     

Effect of Pulsed Biasing on the Droplet Formation and the Properties of Cylindrical Cathodic Arc–Grown Erosion-Resistant TiN Coatings

For the past few decades, cathodic arc–grown erosion-resistant coatings have become very popular and are widely used in aerospace applications to significantly enhance the service life of compressor blades. Though the coatings improve life, the concentrations of defects and stressed areas on the surface dictate the end life of the component. Therefore, in the present study, an attempt was made to minimize the defect area fraction along with the residual stresses in cylindrical cathodic arc–grown mono- and multilayer TiN coatings by optimizing pulsed bias voltage parameters such as duty cycle and magnitude of bias voltage. The effect of pulsed biasing and coating configuration on the physical, mechanical, and erosion properties of the TiN coatings was studied systematically. Within the monolayer TiN coating, the samples grown at ?500 V pulsed bias and 40% duty cycle had the best properties with about 50% enhancement in erosion resistance. These coatings were also found to exhibit the lowest residual stress, good adhesion, and moderately higher hardness. Further, the TiN coatings grown in a multilayer configuration (TiN_E-450/TiN_E-350) had the best erosion resistance.     

Effect of Operating Conditions on Tribological Response of Al–Al Sliding Electrical Interface

Aluminum is widely used in electrical contacts due to its electrical properties and inexpensiveness when compared to copper. In this study, we investigate the influence of operating conditions like contact load (pressure), sliding speed, current, and surface roughness on the electrical and tribological behavior of the interface. The tests are conducted on a linear, pin-on-flat tribo-simulator specially designed to investigate electrical contacts under high contact pressures and high current densities. Control parameters include sliding speed, load, current, and surface roughness. The response of the interface is evaluated in the light of coefficient of friction, contact resistance, contact voltage, mass loss of pins, and interfacial temperature rise. As compared to sliding speed, load, and roughness, current is found to have the greatest influence on the various measured parameters. Under certain test conditions, the interface operates in a “voltage saturation” regime, wherein increase in current do not result in any increase in contact voltage. Within the voltage saturation regime the coefficient of friction tends to be lower, a result that is attributed to the higher temperatures associated with the higher voltage (and resulting material softening). Higher interfacial temperatures also appear to be responsible for the higher wear rates observed at higher current levels as well as lower coefficients of friction for smoother surfaces in the presence of current.     

Tribological performances of ZDDP and ashless triphenyl phosphorothionate (TPPT) as lubricant additives on Ti–N and Ti–Al–N coated steel surfaces

Abstract

In recent years, there has been much attention on the effects of lubricant additives on the friction and wear properties of surface coatings. However, little research has been conducted to investigate the influence of antiwear additives on the tribological performances of titanium nitride (Ti–N) and titanium aluminium nitride (Ti–Al–N) coatings. It has been reported that introducing aluminium into Ti–N coatings enhanced their oxidation resistance. In this study utilising a pin on cylinder tribometer, lubricants containing zinc dialkyl dithiophosphate (ZDDP) or a more environmentally friendly alternative, ashless triphenyl phosphorothionate (TPPT), were used. Experimental results revealed that ZDDP and TPPT helped to reduce wear on both coatings through the formation of a tribofilm, although it was also found that both additives increased the friction coefficient on both surfaces. Based on overall findings, this paper suggests the use of TPPT as a suitable ZDDP replacement for providing wear protection on Ti–N and Ti–Al–N coatings.     

Investigation of the Structure of Surface and Tribological Properties of Composition Coatings Based on Thermosetting Epoxy–Polyester Resins

Composition coatings based on the epoxy–polyester matrix and polydisperse particles of structured carbon have been investigated. The formulation of the mixed compositions has been optimized. The effect of filler particles on structure formation of the surface and tribotechnical characteristics of composition coatings has been shown.     

Correlation Between Mechanical Properties and Nanofriction of [Ti–Cr/Ti–Cr–N] n and [Ti–Al/Ti–Al–N] n Multilayers

In this work, thin films deposited by pulsed DC magnetron sputtering of [Ti–Al/Ti–Al–N] _n and [Ti–Cr/Ti–Cr–N] _n multilayers of nanometric periods were analyzed by AFM in contact mode to measure values of lateral and normal forces. From these measurements, the coefficient of friction (COF) of these materials in contact with the AFM tip was calculated. Measurements were made with three types of silicon tips, diamond-coated, Pt–Cr-coated, and bare silicon. Significant differences between the tip materials in contact with the samples, which affected the COF, were observed. The effect of the environmental layer of water covering the surface sample and the tip appears as the most important factor affecting the tribology behavior of the tip-sample contact. For diamond-coated and bare silicon tips there is an additional adherence force increasing the normal load. But for tips platinum–chromium-coated there is a repulsive force due to this water layer, which behaves as a lubricant layer before a threshold load.     

Using Methods of Analysis of Optical Images of Friction Surfaces of Ti–Al–N Based Coatings for Assessing Accumulation of Damage and Diagnostics of Failure in Tribological Tests

Russian Journal of Nondestructive Testing - The processes of damage accumulation and failure in thin ceramic coatings based on the Ti–Al–N system deposited on ductile steel and brittle...     

The Friction and Wear Properties of Ti–Al–Nb Intermetallics by Plasma Surface Alloying

Both plasma chromizing and carburization following plasma chromizing (duplex treatment) for Ti–Al–Nb alloy were performed, respectively, and the microstructure, dynamic ultra-microhardness, and elastic modulus of the alloying layer were determined. Using silicon nitride (Si₃N₄) balls as the counterface materials, dry sliding friction tests on the substrate, the chromized layer, and the duplex-treated layer were completed by ball-on-disk tribometer at room temperature. The results indicated that the duplex-treated layer was mainly composed of Cr₂₃C₆, Cr₂Nb, pure chromium, and carbon phases, while the chromized layer consisted of Al₈Cr₅ and Cr₂Nb phases. The ultra-microhardness of the duplex-treated layer was higher than that of the chromized layer, whereas the elastic modulus of the duplex-treated layer was lower than that of the chromized layer. The friction coefficient of the duplex-treated layer was about three times lower than that of the chromized layer, while the wear rate was one order of magnitude lower than that of the chromized layer.     

The Tribological Behavior of As-Sprayed Graphene Oxide–Tungsten Disulfide Hybrid Coatings

Abstract

The application of solid lubricants in the metal forming of aluminum alloys is imperative due to their potential for the reduction of both friction and aluminum adhesion. This study focuses on examining the potential application of hybrid graphene oxide–tungsten disulfide (GO/WS₂) coatings in the forming of aluminum alloys. A series of experiments with different GO/WS₂ concentrations (between 1:1 and 12:1) was conducted to investigate the effects of increasing GO concentration on the tribological performance of the coatings. The coefficient of friction (COF) was evaluated using pin-on-disc experiments. The durability of the coatings (the sliding distance prior to the initiation of coating failure) was also recorded. Subsequent surface characterization was performed from within the sliding tracks induced on the coated Al-Mg discs and the mechanisms responsible for friction and wear are discussed. The GO/WS₂ hybrid coatings provided low COF values (within the range of 0.18?0.27) and mitigated against aluminum adhesion before failure. An optimum GO/WS₂ ratio (6:1) was noted as providing the optimum combination of low friction and improved durability. The concentration of GO in the hybrid coatings influenced the friction performance and durability of coatings, which was related to the formation of tribolayers on the aluminum surface and wear-induced transfer layers on the counterface surface. The formation of the tribolayers was attributed to the mixture of fragmented WS₂ platelets, GO flakes, and carbon binder comprising the tribolayer.     

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.     

Effect of Micro-scale Y Addition on the Fracture Properties of Al–Cu–Mn Alloy

Rare earth (RE) elements have positive effects on Al alloy, while most research is focused on microstructure and mechanical properties. As important application indices, toughness and plasticity are properties that are sensitive to alloy fracture characteristics, and few research studies have characterized the fracture properties of Al–Cu–Mn alloy on RE elements. The effect of different contents of Y on the fracture properties of Al–Cu–Mn alloy is investigated. T6 heat treatment (solid solution and artificial aging treatment), optical microscope (OM), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) methods are applied to the alloy. Results showed that when Y element is present at 0.1%, the section of the as-cast alloy has smaller sized dimples and the fracture mode presents ductile features. Slight changes in hardness are also observed and maintained at about 60 HV. With increasing content of the RE element Y from 0.1 to 0.5%, the θ phase and Cu atoms in the matrix were reduced and most stopped at Grain boundaries (GBs). Micro-segregation and an enriched zone of Y near the GBs gradually increased. At the same time, the inter-metallic compound AlCuY is aggregated at grain junctions causing deterioration of the micro-structure and fracture properties of the alloy. After T6 treatment, the flatness of the fracture surface was lower than that of all the as-cast alloy showing lots of dimples and teared edges with a significant increase in hardness. When Y content was 0.1%, the strength and hardness of the alloy increased due to refinement of the grain strengthening effect. The content of Y elements segregated in the inter-dendritic zone and GBs is reduced. Plasticity and deformation compatibility also improved, making cracks difficult to form and merge with each other along adjacent grain junctions and providing an increased potential for ductile fracture. This paper proposes the addition of RE Y as an effective and prospective strategy to improve the fracture properties of the Al–Cu–Mn alloy and provide a meaningful reference in terms of improving overall performance.     

Effect of Sliding Speed on Surface Modification and Tribological Behavior of Copper–Graphite Composite

In practice, the sliding speed is an important parameter for materials applied in sliding condition. We have conducted an experimental study to explore the effect of sliding speed on friction and wear performance of a copper–graphite composite. The sliding tests were carried out over a wide range of speeds with a pin-on-disc configuration. The results show that there is a critical speed at which there is a transition of the friction and wear regimes of the composite. In addition, the formation of a lubricant layer on the contact surface (surface modification) determines the actual tribological performance of the composite. The wear mechanisms in different wear regimes are also discussed.     

Tribological Properties of Reactive Magnetron Sputtered V2O5 and VN–V2O5 Coatings

Next generation of advanced hard coatings for tribological applications should combine the advantages of hard wear resistant coatings with low-friction films. In this study, the tribological behaviour of vanadium pentoxide (V₂O₅) single-layer as well as VN–V₂O₅ bi-layer coatings was investigated in the temperature ranging between 25 and 600 °C. For VN–V₂O₅ bi-layer coatings, the V₂O₅ top-layers were deposited by dc and bipolar-pulsed dc reactive magnetron sputtering, where the V₂O₅ phase shows preferred growth orientation in (200) and (110), respectively. The V₂O₅ single-layer coatings were prepared by dc reactive magnetron sputtering with a substrate bias of −80 V which leads to a preferred (200) growth orientation. Tribological properties were evaluated using a ball-on-disc configuration in ambient air with alumina balls as counterpart. The structure of the as-deposited films and eventual changes after tribometer testing were identified using X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The friction coefficient of VN–V₂O₅ bi-layer coatings deposited in dc and pulsed dc mode decreases from room temperature to 600 °C, where the pulsed dc VN–V₂O₅ coatings have a significantly lower coefficient of friction over the whole testing temperatures reaching a value of 0.28 at 600 °C. Up to 400 °C, V₂O₅ single-layer coatings showed almost the same coefficient of friction as pulsed dc VN–V₂O₅ bi-layer coatings but reached a value of 0.15 at 600 °C. It seems that thermal activation of crystallographic slip systems is necessary for V₂O₅ films to show a low-friction effect.     

Effect of Plasma Nitriding Environment and Time on Plain Fatigue and Fretting Fatigue Behavior of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V fatigue test samples at 520°C in two environments (nitrogen and nitrogen–hydrogen mixture in a ratio of 3:1) for two time periods (4 and 18 h). Plain fatigue and fretting fatigue tests were conducted on unnitrided and plasma nitrided samples. Plasma nitriding degraded lives under both plain fatigue and fretting fatigue loadings. The samples nitrided in nitrogen exhibited superior lives compared with the samples nitrided in the nitrogen–hydrogen mixture, possibly due to the relatively higher hardness (and presumably lower toughness) of the nitrided layer of the samples nitrided in the nitrogen–hydrogen mixture environment. For those samples nitrided in the nitrogen–hydrogen mixture, those nitrided for 18 h exhibited superior lives compared with those nitrided for 4 h. This trend was observed for samples nitrided in nitrogen gas at lower stress levels only; the converse was true at higher stress levels of 550 MPa and 700 MPa under plain fatigue loading. However, under fretting fatigue loading, the plasma nitriding time did not influence the lives significantly.     

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.     

The Effect of Spherical Silica Powder on the Tribological Behavior of Phenolic Resin–Based Friction Materials

The friction and wear behavior of friction materials filled with irregular silica, spherical silica and surface-treated spherical silica particles is discussed in this paper. Compared to irregular silica, spherical silica powders improve the wear resistance, but decrease the friction coefficient. Surface-treated spherical silica powder is more effective in the improvement in the wear resistance, but with the similar friction coefficient of irregular silica-filled materials. This makes it possible to be used as friction-improving fillers in brake materials. Mechanisms for the improvement are also discussed in this paper.     

Effect of Bio-Lubricant and Biodiesel-Contaminated Lubricant on Tribological Behavior of Cylinder Liner–Piston Ring Combination

This article addresses the issue of friction and wear characteristics of diesel engine cylinder liner–piston ring combinations under different lubricating conditions using a pin-on-disc wear tribometer. The discs were made out of actual engine cylinder liner material using a casting process. Pins were made out of top compression ring material. The tests were conducted on a pin-on-disc tribometer for wear and friction characteristics of the cylinder liner and piston ring combination with diesel-contaminated rapeseed oil–based bio-lubricant, diesel-contaminated commercial synthetic lubrication oil (SAE 20W40), biodiesel-contaminated commercial synthetic lubrication oil (SAE 20W40), and used (150 h) commercial synthetic lubrication oil (SAE 20W40). Experimental results demonstrated that the rapeseed oil–based bio-lubricant and biodiesel-contaminated synthetic lubricant exhibited better performance in terms of wear, friction, and frictional force under similar operating conditions. Thus, usage of newly formulated bio-lubricant and biodiesel in the long run may have a positive impact on engine life.     

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.     

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.