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Hydrogenated diamond‐like carbon (H‐DLC) films are limited by their poor thermal stability, which significantly affects the tribological applications and needs improvement. Accordingly, nanodiamond (ND) and hexagonal boron nitride (h‐BN) are used to address this issue. When the H‐DLC surface is deposited using ND+h‐BN mixture with mass ratio of 1:1 and a concentration of 0.1 mg mL−1 and vacuum‐heated at 200 °C and 1 × 10−5 Pa, a superlow friction coefficient of 0.0015 can be obtained, with a reduction of 98.33% as compared to pure H‐DLC. Correspondingly, the wear rates of wear scar and wear track decreased by 81.95% and 24.83%, respectively. High vacuum thermal treatment can purify the adsorbed species on the surfaces of ND and h‐BN, and produce newly‐exposed dangling bonds. Simultaneously, new bonds of C‐N are formed between ND and h‐BN, and the nanoparticles adhere together to form a polymer‐like structure under friction. Furthermore, the ND can support h‐BN and reduce its agglomeration. Under the action of tribochemical reaction, the layer spacing of hexagonal boron nitride is increased to obtain a better shear slip. The combination of these factors resulted in ultra‐low friction. This study paved the way for developing functional anti‐friction additives for durable and high‐performance lubrication. [ABSTRACT FROM AUTHOR]

22MnB5 boron steel, an Ultra High Strength Steel (UHSS), is celebrated for its exceptional strength and wear resistance, making it highly valuable in automotive and other industries where lightweight materials are essential. Its superior wear resistance also makes it suitable for use in cutting tools. This study aimed to evaluate the performance of 22MnB5 boron steel as a turning insert for metal machining, specifically in relation to cutting speed and cutting environments. The 22MnB5 boron steel blanks were laser-cut into round shapes with a thickness of 2.6 mm and a diameter of 12 mm, following the RNGN 120300 standard. Machining tests were performed on AA 6061 aluminum alloy under both dry and wet conditions, with cutting speeds ranging from 100 to 450 m/min. The outcomes highlighted that 22MnB5 boron steel is effective for machining AA 6061, with tool wear stabilizing between 200 and 350 m/min. Tool wear ranged from 0.15 to 0.27 mm in dry conditions and was reduced to 0.08-0.18 mm in wet conditions. At lower speeds, built-up edges were the predominant wear mechanism, while at higher speeds, adhesive wear in the form of a tribolayer was more pronounced. These findings highlight the potential of 22MnB5 boron steel for efficient machining, particularly under wet conditions, offering valuable insights into improving tool life and reducing production costs. [ABSTRACT FROM AUTHOR]

Compositions of ashless thiophosphoric and thiocarbamine compounds were studied as a tribologically active additive. Studies of the anti-wear properties of compositions in both fresh and oxidized oil samples in comparison with the effectiveness of a similar functional effect of a traditional additive, zinc dialkyldithiophosphate, were carried out on a tribometer that implements the wear process of conjugated pairs under sliding friction conditions simulating the boundary lubrication mode. The results of tribotests of mixtures of these compositions with metal-containing detergents of various chemical nature in a solution of synthetic lubricating oil as model variants of the composition of engine oils are presented. The synergism of the action of the ammonium salt composition of dialkyldithiophosphoric acid and methylene bis-dibutyldithio-carbamate, which provides a reduced content of sulfate ash and phosphorus, factors of environmental safety of the use of oils, is noted. [ABSTRACT FROM AUTHOR]

Solid lubrication is an excellent option to reduce friction and wear in dry sliding conditions, as well as a secondary source of protection in fluid-lubricated systems. Considering the most widely used solid lubricants, carbon-based lubricants are among the most versatile for tribological use. The reasons for this include their availability and their innate ability to adopt various nanostructures. The crystalline ordering of carbon has been identified as the main factor governing its tribological behavior. This work presents and discusses the most significant findings from an ongoing research program aimed at developing carbon-based solid lubricants. In this sense, several carbon-based materials with diverse levels of nanostructural order have been studied: three-dimensional (3D) crystalline graphite (GR); novel carbide-derived two-dimensional (2D) turbostratic carbon (CDC) produced from Fe–SiC (GSF) and B4C–Cr3C2 (GBC) solid-state reactions; NH3 plasma-functionalized multilayer graphene (MLG); in situ fluorinated diamond-like carbon (DLC) (isfDLC); vertically aligned carbon nanotube (CNT) films. Initially, we present a brief description of the processing route for obtaining these materials, followed by their microstructural characterization and a synthesis of the most relevant aspects of tribological evaluation. Dry sliding tests in reciprocating motion were employed with different tribo-pair geometries, specimens and counter-body materials, varied surface topography, and diverse routes to add solid lubricants to the contact (vacuum impregnation of sintered steels, drop-casting, self-lubricating composites and vertically aligned films). The results provide a holistic view of the nature of the tribolayers formed by these materials. Finally, a new micro-Raman (µRaman) analysis technique for quantifying the point and line defects of the carbon present in tribolayers is used to correlate the lubrication and degradation mechanism of carbonaceous solid lubricants with their initial nanostructure and testing conditions. This technique provides new insights into the nature of tribolayers produced by carbon-based solid lubricants.

The formation of tribolayers may play significant influences on fretting wear. At elevated temperature, the adhesion among wear debris and the increased diffusion rate facilitate the formation of tribolayers. However, the intensification of oxidation at elevated temperature and the low diffusion rate in oxides may play an adverse role. The present study aims to investigate the role of temperature in tribolayers in fretting wear using a γ-TiAl alloy. Scanning electron microscope, energy dispersive spectrometer, Raman spectrometer, transmission electron microscope and nanoindentation were utilized to investigate the wear debris, tribolayers, and wear scars. The fretting tests showed that, compared with that at room temperature (RT) and 350 °C, significant reduction in wear rate and decrease in the fluctuation of friction coefficient occurred at 550 and 750 °C. It was further revealed that when temperature raised from room temperature (RT) to 750 °C, the oxidation of the wear debris increased slightly and the diffusion coefficients increased prominently, which facilities the formation of well tribo-sintered tribolayers. The well tribo-sintered tribolayers presented homogenous structure, nanocrystalline grains with excellent mechanical properties, and resulted in the improvement in the fretting wear resistance of the γ-TiAl alloy at 550 and 750 °C. [ABSTRACT FROM AUTHOR]

Abstract The formation of tribolayers may play significant influences on fretting wear. At elevated temperature, the adhesion among wear debris and the increased diffusion rate facilitate the formation of tribolayers. However, the intensification of oxidation at elevated temperature and the low diffusion rate in oxides may play an adverse role. The present study aims to investigate the role of temperature in tribolayers in fretting wear using a γ-TiAl alloy. Scanning electron microscope, energy dispersive spectrometer, Raman spectrometer, transmission electron microscope and nanoindentation were utilized to investigate the wear debris, tribolayers, and wear scars. The fretting tests showed that, compared with that at room temperature (RT) and 350 °C, significant reduction in wear rate and decrease in the fluctuation of friction coefficient occurred at 550 and 750 °C. It was further revealed that when temperature raised from room temperature (RT) to 750 °C, the oxidation of the wear debris increased slightly and the diffusion coefficients increased prominently, which facilities the formation of well tribo-sintered tribolayers. The well tribo-sintered tribolayers presented homogenous structure, nanocrystalline grains with excellent mechanical properties, and resulted in the improvement in the fretting wear resistance of the γ-TiAl alloy at 550 and 750 °C.

The tribological properties of γ-TiAl alloys under sliding condition have been well established, but the mechanisms for fretting wear, especially at elevated temperature, remain to be further clarified. In the present study, the tribological behaviors and mechanisms of a γ-TiAl alloy were investigated under an elevated temperature fretting condition. The wear scars, debris, and tribolayers were studied with scanning electron microscope, energy dispersive spectrometer, and Raman spectrometer. The structural and mechanical properties of the tribolayers were investigated utilizing transmission electron microscope and nanoindentation tests. The results demonstrated that the severe adhesive wear, delamination, and abrasive wear in the early stage of fretting resulted in high wear rate of the γ-TiAl alloy. As fretting progresses, the formation of tribolayers with nanograins and excellent mechanical properties improved the fretting wear resistance of the γ-TiAl alloy. Due to the protective effect of the adhesively transferred γ-TiAl, the wear rate of the nickel-based superalloy counterpart was significantly lower. [ABSTRACT FROM AUTHOR]

In this paper, the tribological behavior of Cu-SiO2 composite against 1045 steel was studied. Based on the characterization of worn surface, worn subsurface and wear debris in morphology and composition, the friction layer effects on the tribological behavior of coupled materials and the wear mechanism were discussed. Abrasive wear and adhesive wear are the dominant mechanisms at the 0.56 m/s–1.12 m/s condition. Delamination wear and oxidation wear are the dominant wear mechanisms at the 1.68 m/s–2.24 m/s condition. Plastic and thermal deformation cause the evolution in morphology and structure of the tribolayer of Cu-SiO2. There is a certain correlation between the friction coefficient and the variation in friction temperature during sliding wear of Cu-SiO2 and 1045 steels. The addition of SiO2 induces the accumulation of frictional heat at the friction interface, which leads to an increase in the average temperature of the contact surface and transfer. [ABSTRACT FROM AUTHOR]

Carbon-based solid lubricants are excellent options to reduce friction and wear, especially with the carbon capability to adopt different allotropes forms. On the macroscale, these materials are sheared on the contact along with debris and contaminants to form tribolayers that govern the tribosystem performance. Using a recently developed advanced Raman analysis on the tribolayers, it was possible to quantify the contact-induced defects in the crystalline structure of a wide range of allotropes of carbon-based solid lubricants, from graphite and carbide-derived carbon particles to multi-layer graphene and carbon nanotubes. In addition, these materials were tested under various dry sliding conditions, with different geometries, topographies, and solid-lubricant application strategies. Regardless of the initial tribosystem conditions and allotrope level of atomic ordering, there is a remarkable trend of increasing the point and line defects density until a specific saturation limit in the same order of magnitude for all the materials tested. [ABSTRACT FROM AUTHOR]

Abstract Carbon-based solid lubricants are excellent options to reduce friction and wear, especially with the carbon capability to adopt different allotropes forms. On the macroscale, these materials are sheared on the contact along with debris and contaminants to form tribolayers that govern the tribosystem performance. Using a recently developed advanced Raman analysis on the tribolayers, it was possible to quantify the contact-induced defects in the crystalline structure of a wide range of allotropes of carbon-based solid lubricants, from graphite and carbide-derived carbon particles to multi-layer graphene and carbon nanotubes. In addition, these materials were tested under various dry sliding conditions, with different geometries, topographies, and solid-lubricant application strategies. Regardless of the initial tribosystem conditions and allotrope level of atomic ordering, there is a remarkable trend of increasing the point and line defects density until a specific saturation limit in the same order of magnitude for all the materials tested.

The evolution of pearlite into an amorphous wrapped nanolamellar heterostructure (AWNH) within the tribolayer is an important process for the formation and stabilization of a nanocomposite self-lubricating surface. Here, experimental characterizations were performed to show that an AWNH was an intermediate product of transformation of pearlite to oxide nanoparticles and played a supporting role as a self-lubricating layer of the substrate. Furthermore, the molecular dynamics simulation method was used to analyze the wear properties and load-bearing capacities of four different microstructures to reveal the unique AWNH deformation mechanism and its effect on the self-lubrication behavior. The results showed that the AWNH exhibited a low friction and good wear resistance, which could be ascribed to its high hardness, high plasticity, and outstanding interface deformation coordination ability. The shear bands were restricted by the nanolamellar structure, and the shear transition zone that formed at the interfaces caused the plastic deformation to be uniformly distributed, which provided favorable conditions for supporting the self-lubricating layer. The results of this study provide theoretical guidance for analyzing the deformation mechanisms and tribological behaviors of AWNHs and help to optimize self-lubricating material design.

Gradient nanograin (GNG) metals possess outstanding resistance to sliding friction and wear. The tribolayer plays a major role in the wear performance of metals. However, the current understanding of the tribolayer in GNG metals is still limited. In particular, some GNG metals show low wear resistance under high contact stress. Here, we investigate the wear behavior of coarse grain (CG) and GNG Ti–6Al–4V alloys and its impact on the wear resistance by sliding contact experiments in combination with finite element modeling. We have found wear-induced the oxidation tribolayer with amorphous structures in GNG Ti–6Al–4V alloy for the first and its impact on wear behavior. It is found that the wear damage mainly occurs in the oxidation tribolayer with amorphous structures, which can generate micro-cracks in Ti–6Al–4V alloy. The wear behavior, including wear resistance, wear micro-cracks, and subsurface structural transformations, is stress-dependent, which can be divided into two distinct regimes-elastic and plastic. Coarse grains (CGs) can form the oxidation tribolayer with amorphous structures in elastic and plastic regimes. Compared to CGs, gradient nanograins (GNGs) can suppress the formation of the oxidation tribolayer with amorphous structures and have higher wear resistance in elastic regime, while GNGs form the oxidation tribolayer with amorphous structures more quickly and have lower wear resistance in plastic regime. This work forges the links between stress-dependent subsurface structural transformations and wear resistance for GNGs, and may provide guidance for the wear application of GNG metals.

The work is devoted to the study of the tribological properties of functional coatings based on the FeO oxide matrix, additionally doped with boron oxide B2O3 and zirconium dioxide ZrO2. The coatings are obtained by highly concentrated short-pulse laser processing of powder compositions previously applied to metal surfaces. The resulting coatings are subject to wear tests under conditions of dry sliding friction with fixation of the friction coefficient, depending on the applied load and the composition of the powder composition. The results give an idea of the degree of change in the coefficient of friction of coatings depending on the powder compositions, as well as their alloying. It has been confirmed that additional alloying with boron oxide has a positive effect on the tribological performance of the coating; in particular, the introduction of 4% boron oxide reduces the coefficient of dry sliding friction to a unique 0.09–0.10. At the same time, a more stable scuffing resistance of friction surfaces is observed, confirmed by studies of surface roughness after testing. A feature of the tribological behavior of the coatings under study is the excessively high temperature background of the tests, reaching 300°C. High temperature and the presence of oxide structures are a catalyst for the formation of stable tribological structures between the rubbing surfaces. The nature of the tribostructures is self-organizing in a "glaze" type and has the property of recovery under friction conditions. After the formation of tribostructures in the friction zone, a significant decrease in temperature and an abrupt decrease in the friction coefficient are observed. With an increase in the amount of boron oxide, the friction coefficient does not decrease so significantly and the minimum value of the dry friction coefficient corresponds to 0.14–0.15, which is caused by a decrease in the cohesive strength of the coating. [ABSTRACT FROM AUTHOR]

Owing to high strength and good biocompatibility, Mg–Zn binary alloys have attracted significant attention as a potential candidate for producing human implants. However due to the formation casting defects and dendritic structure, these alloys show poor mechanical and wear performances. Alloying and applying severe plastic deformation methods are suggested as two techniques for modifying and improving the above properties. In this study, dry-sliding wear and friction behaviors of the Mg–0.5Zn (MZ) alloy were enhanced by micro-alloying with Zr (0.25 wt%) and applying multi-pass friction stir processing (FSP) technique. Adding Zr reduced the average grain size (AGS) from 1.5 ± 0.3 mm in the MZ sample to about 510 ± 50 μm through the formation of evenly distributed Zr-rich particles with the chemical composition of Mg: 8.84, Zn: 0.75, and Zr: 90.41 A% in the structure. Furthermore, the attendance of thermostable Zr particles stimulated the dynamic recrystallization (DRX) during FSP and reduced the AGS to less than ≈2 μm after the 3rd FSP pass. This substantial grain refinement along with the casting defects reduction, and the fragmentation and redistribution of Zr particles enhanced the hardness and tensile properties of the substrate. Thus, the improved substrate in the FSPed samples, increased the stability of the formed tribolayer on the worn surfaces and changed the wear mechanisms from severe adhesive/delamination in the MZ alloy to mild abrasive/adhesive in the FSPed Zr-modified samples. Therefore, in the optimal condition (3-pass FSPed Mg–0.5Zn–0.25Zr sample), the hardness and total elongation percentage (EL%) increased by 55% and 648% while the mass loss and average friction coefficient (AFC) were reduced by 54% and 39%, respectively, compared to the as-cast Mg–0.5Zn alloy (under a load of 30 N).

Hard and wear-resistant coatings created utilizing physical vapor deposition (PVD) techniques are extensively used in extreme tribological applications. The friction and wear behavior of coatings vary significantly with temperature, indicating that advanced coating concepts are essential for prolonged load-bearing applications. Many coating concepts have recently been explored in this area, including multicomponent, multilayer, gradient coatings; high entropy alloy (HEA) nitride; and functionally modified coatings. In this review, we highlighted the most significant findings from ongoing research to comprehend crucial coating properties and design aspects. To obtain enhanced tribological properties, the microstructure, composition, residual stress, hardness, and HT oxidation resistance are tuned through doping or addition of appropriate materials at an optimized level into the primary coatings. Such improvements are achieved by optimizing PVD process parameters such as input power, partial pressure, reactive gas flow rates, substrate bias, and temperature. The incorporation of ideal amounts of Si, Cr, Mo, W, Ag, and Cu into ternary and quaternary coatings, as well as unique multilayer designs, considerably increases the tribological performance of the coatings. Recent discoveries show that not only mechanical hardness and fracture toughness govern wear resistance, but also that oxidation at HT plays a significant role in the lubrication or wear failure of coatings. The tribo-induced metal oxides and/or Magnéli phases concentrated in the tribolayer are the key governing factors of friction and wear behavior at high temperatures. This review includes detailed insights into the advancements in wear resistance as well as various failure mechanisms associated with temperature changes.

Copper impregnated carbon/carbon composite (Cu-C/C composite) was fabricated for novel sliding collector material by weaving carbon fiber, heat treatment and Cu alloy impregnation. The effects of counterpart materials (Fe ball and Cu ball) on friction and wear behaviors were investigated and compared with the result of carbon contact strip used in high-speed railway. Morphology, chemical composition, phase and structure of wear surface and tribolayer were characterized to clarify tribological mechanisms. The results show that friction coefficient follows the order: Cu-C/C composite/Cu ball > carbon contact strip/Fe ball > Cu-C/C composite/Fe ball > carbon contact strip/Cu ball. The carbon crystalline of wear surface appears preferred orientation along the sliding orientation, which is benefit for boundary lubrication. When the counterpart material is Fe ball, Cu-C/C composite is superior to pure carbon strip in mechanical strength, electrical conductivity, wear resistance and friction performance. [ABSTRACT FROM AUTHOR]

The behavior of four phosphate ester additives with varying levels of phosphorus concentrations (very high, high, medium, and low) was examined through the course of drilling a Ti-6Al-4V titanium alloy at a constant metal removal rate (4.2 mm3/s). Cutting fluid (CF) additives were evaluated using torque, specific cutting energy (SEC), and tool wear. The drilling conditions employed had a significant influence on the performance of the phosphate ester additives. At 0.105 m/s and 0.188 m/s, the phosphate ester with very high phosphorous levels possessed the lowest SCE and torque values. The high-phosphorous-level phosphate ester displayed enhanced drilling performance at 0.293 m/s. At 0.419 m/s, the SCE and torque performance of the medium-phosphorous-level phosphate ester was preferable. The drilling performance of the phosphorus esters was observed to be related to the working mechanisms of the additives, which, in turn, was associated with the formation of a phosphorus-rich tribolayer and an organophosphate tribolayer on the cutting blade. [ABSTRACT FROM AUTHOR]

The content, distribution and size of retained austenite (RA) affect its mechanical stability in carburized layers. The stability of RA plays a decisive role in cold work hardening and strain-induced martensitic transformation during sliding friction; these changes determine wear resistance. In this study, a database was established based on laser confocal metallographic images of carburized layers on 23CrNi3MoA steel after different carburizing treatments. Eight algorithms were used to identify and calculate the amounts of RA in the carburized layers. The tribolayers and wear on the surfaces that underwent three carburizing processes, P13, P15, and P17, were characterized and tested. The results showed that the U-Net algorithm with an attention module and drop block regularization was the most suitable for the database. Predictions of the RA contents of surfaces after P13, P15, and P17 treatments were 19.9%, 28.1%, and 40.1%, respectively. The errors of the predictions compared with experimental results were within 5%. The surface carburized by the P15 process contained moderate amounts of RA and had the best wear resistance because the friction strain induced the formation of nanolamellar structures and the transformation of RA to martensite. The results of this study support the use of deep learning to identify and calculate the amounts of RA in carburized layers and optimize carburizing processes of mild steel.

Wear behavior of three different AA6061-0.5 wt% CNT composites fabricated using different dispersion techniques by stir-squeeze-casting have been studied against a steel ball counter body. The uniform CNT distribution in composites fabricated by dropping pellets of Al-powder and CNT (PD composite) yields the lowest coefficient of friction (COF) and specific wear rate (SWR) for both the composite material and the counter body. Both COF and SWR increase as the load increases from 5 N to 10 N, but drop as the load increases further to 15 N. Even at 150 °C, the presence of CNTs improved the tribological performance of AA6061. A detailed study of CNT morphologies on the worn surface and Raman spectroscopy indicate their beneficial role as a solid lubricant to reduce COF and material loss during wear. • Wear behavior of Al-CNT composite strongly affected by CNT dispersion in Al melt. • The COF and SWR of pellet drop composites (PD) were 68 % and 77 % lower than AA6061. • At 150 °C, PD composite is more wear resistance than AA6061 even at higher load. • Stability of tribolayer determines the wear behavior of the composites. • Raman Peak shift and I D /I G ratio indicate structural change of CNTs due to wear. [ABSTRACT FROM AUTHOR]

Doping with non-metal element is effective to improve the porous morphology and enhance the mechanical and tribological properties of transition metal dichalcogenides (TMDs) based film. However, the mechanical properties of TMDs based film with single additive should be enhanced further for better wear resistance. In this work, B/N dual-doping was used to further enhance the deformation resistance and toughness of MoS 2 based films deposited by magnetron sputtering, while the effect of B/N dopants on the structure, mechanical and tribological properties has been investigated. Mo-S-B-N film with B content of 20.91 at. % and N content of 18.13 at. % consists of MoS 2 and amorphous nitride/boride, in which B/N dual doping film forms a higher ordered MoS 2 lamellar structure compared to B doping film. With a hardness of 11.6 ± 0.9 GPa and improved toughness, the film achieves a low wear rate and average friction coefficient is achieved. Comparing B/N dual doping film to B doping film, the stable formation of tribolayer with more strengthened deformation resistance results in the steady friction and the improved wear resistance, while the limited TMDs reorientation leads to the slight increase of friction coefficient. • B/N dual-doping was proposed to prepare the reinforced MoS 2 based sputtered films. • The amorphization of MoS 2 attributed to excessive B dopants were suppressed by N addition. • Wear mechanism of B/N dual-doping MoS 2 based films are investigated by AFM and chemical component analysis on wear track. [ABSTRACT FROM AUTHOR]

In this paper, the tribological behavior of Cu-SiO2 composite against 1045 steel was studied. Based on the characterization of worn surface, worn subsurface and wear debris in morphology and composition, the friction layer effects on the tribological behavior of coupled materials and the wear mechanism were discussed. Abrasive wear and adhesive wear are the dominant mechanisms at the 0.56 m/s–1.12 m/s condition. Delamination wear and oxidation wear are the dominant wear mechanisms at the 1.68 m/s–2.24 m/s condition. Plastic and thermal deformation cause the evolution in morphology and structure of the tribolayer of Cu-SiO2. There is a certain correlation between the friction coefficient and the variation in friction temperature during sliding wear of Cu-SiO2 and 1045 steels. The addition of SiO2 induces the accumulation of frictional heat at the friction interface, which leads to an increase in the average temperature of the contact surface and transfer.

Al–Sn–Si alloys have been widely used as bearing alloys in automotive engines. In those alloys, β(Sn) phase serves as the solid lubricant and Si particles are used to improve the hardness, fatigue resistance as well as seizure resistance. With the development of machinery, bearing alloys with higher load-carrying capacity and better tribological properties are demanded to meet the application under severe conditions. Adding appropriate Mg to the Al–Sn–Si alloy can effectively optimize the tribological properties. In this paper, the microstructure, mechanical properties and tribological properties of the Al–12Sn–4Si-xMg (x = 0, 0.5, 1, 1.5, all in wt.%) alloys were studied. The Al–12Sn–4Si-1.5 Mg alloy had the smallest grain size and more uniform microstructure than other specimens. The Al–12Sn–4Si-1.5 Mg alloy showed significantly better wear resistance than the Al–12Sn–4Si alloy at 2 N–70 N. The volume wear rates and friction coefficients at 15 N–70 N were lower than those at 2 N–8 N. The evolution of volume wear rate and friction coefficient with load was related to the evolution of tribolayer with load. The wear mechanism of the alloys was mainly oxidation wear, adhesive wear and fatigue wear, accompanied with abrasive wear.

Hard and wear-resistant coatings created utilizing physical vapor deposition (PVD) techniques are extensively used in extreme tribological applications. The friction and wear behavior of coatings vary significantly with temperature, indicating that advanced coating concepts are essential for prolonged load-bearing applications. Many coating concepts have recently been explored in this area, including multicomponent, multilayer, gradient coatings; high entropy alloy (HEA) nitride; and functionally modified coatings. In this review, we highlighted the most significant findings from ongoing research to comprehend crucial coating properties and design aspects. To obtain enhanced tribological properties, the microstructure, composition, residual stress, hardness, and HT oxidation resistance are tuned through doping or addition of appropriate materials at an optimized level into the primary coatings. Such improvements are achieved by optimizing PVD process parameters such as input power, partial pressure, reactive gas flow rates, substrate bias, and temperature. The incorporation of ideal amounts of Si, Cr, Mo, W, Ag, and Cu into ternary and quaternary coatings, as well as unique multilayer designs, considerably increases the tribological performance of the coatings. Recent discoveries show that not only mechanical hardness and fracture toughness govern wear resistance, but also that oxidation at HT plays a significant role in the lubrication or wear failure of coatings. The tribo-induced metal oxides and/or Magnéli phases concentrated in the tribolayer are the key governing factors of friction and wear behavior at high temperatures. This review includes detailed insights into the advancements in wear resistance as well as various failure mechanisms associated with temperature changes. [ABSTRACT FROM AUTHOR]

The behavior of four phosphate ester additives with varying levels of phosphorus concentrations (very high, high, medium, and low) was examined through the course of drilling a Ti-6Al-4V titanium alloy at a constant metal removal rate (4.2 mm3/s). Cutting fluid (CF) additives were evaluated using torque, specific cutting energy (SEC), and tool wear. The drilling conditions employed had a significant influence on the performance of the phosphate ester additives. At 0.105 m/s and 0.188 m/s, the phosphate ester with very high phosphorous levels possessed the lowest SCE and torque values. The high-phosphorous-level phosphate ester displayed enhanced drilling performance at 0.293 m/s. At 0.419 m/s, the SCE and torque performance of the medium-phosphorous-level phosphate ester was preferable. The drilling performance of the phosphorus esters was observed to be related to the working mechanisms of the additives, which, in turn, was associated with the formation of a phosphorus-rich tribolayer and an organophosphate tribolayer on the cutting blade.

The application of Ion Beam Analysis with a focussed ion beam to the field of tribology, especially solid lubricant coatings that do not need liquid lubricants, is described. As model systems, tetrahedrally-amorphous carbon coatings (ta-C) after friction contact with 100Cr6 steel in high vacuum and with brass in ambient atmosphere were selected. With the appropriate combination of He and H ion beams and techniques like Rutherford Backscattering Spectrometry and Particle Induced X-ray Emission, detailed information was obtained about the laterally- and depth-resolved element composition in the wear tracks and counter body wear scars, leading to insights in the friction induced transformation processes between a solid coating and a counter body, including material loss of the coating and material transfer between the coating and counter body that are correlated with the friction experiments. [ABSTRACT FROM AUTHOR]

Abstract The use of high strength aluminium alloys, such as 6XXX and 7XXX series, is continuously increasing for automotive applications in view of their good strength-to-weight ratio. Their formability at room temperature is limited and they are thus often formed at high temperatures to enable production of complex geometries. Critical challenges during hot forming of aluminium are the occurrence of severe adhesion and material transfer onto the forming tools. This negatively affects the tool life and the quality of the produced parts. In general, the main mechanisms involved in the occurrence of material transfer of aluminium alloys at high temperature are still not clearly understood. Therefore, this study is focussed on understanding of the friction and wear behaviour during interaction of Al6016 alloy and three different tool steels in as-received and polished state. The tribotests were carried out under dry and lubricated conditions, with two distinct lubricants, using a reciprocating friction and wear tester. The worn surfaces were analysed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results showed a high dependence of friction and wear behaviour on the tool steel roughness as well as on the stability of the lubricant films. Tribolayers were found to develop in the contact zone and their capacity to improve the tribological behaviour is seen to be drastically impacted by the surface roughness of the tool steel. When the tribolayers failed, severe adhesion took place and led to high and unstable friction as well as material transfer to the tool steel.

Dry sliding of AISI 1020 steel samples against a hardened steel counterbody under electric current was carried out according to the "pin-on-ring" scheme. It was found that the surface layer was plastically deformed in sliding with a current density of higher than 80 A/cm2. This led to the formation of a tribolayer, and the thickness of the tribolayer reached 20 μm as the current density increased to 280 A/cm2, when catastrophic wear began. At the same time, an increase in the average contact temperature was observed, which was found by using five thermocouples, placed on the sample axis, as well as using the infrared thermography method. It was established that the average steel/steel contact temperature does not exceed 400°C under the current density of 200–600 A/cm2 in the contact. Sliding under a current density lower than 80 A/cm2 did not lead to noticeable plastic deformation of the surface layer, the tribolayer was absent, and the wear was close to zero. It was shown that the plastic deformation of the tribolayer led to the formation of two sectors on the sliding surface of the AISI 1020 steel sample. One of the sectors showed signs of deformation according to the viscous fluid mechanism without visible signs of adhesion. Traces of adhesion and plastic displacement by asperities of the counterbody were visible on another sector of the friction surface. The electrical conductivity of the contact decreased but did not reach zero in the mode of catastrophic wear. The contact temperature did not reach 400°C. The impossibility of a noticeable increase in the contact temperature is associated with a strong heat removal due to high wear intensity. Therefore, it can be assumed that setting external impact (high ambient temperature, pressure, current density, etc.), leading to an increase in the contact temperature to 350–400°C, will necessarily cause catastrophic wear of steel or other metals. [ABSTRACT FROM AUTHOR]

Tribological behaviour of Ti–6Al–4V alloy sliding against WC-Co was evaluated by employing WS2 nanoparticles blended in a cutting fluid used for machining of this alloy. Pin-on disk tests were carried out under boundary-lubricated condition using a cutting fluid (70% water and 30% oil) blended with WS2 nanoparticles (CF + WS2). When a cutting fluid with ≥ 0.5 wt.% WS2 was used, the COF of the tribosystem was reduced compared to CF + 0%WS2. The lowest COF of 0.05 was obtained when 1.0 wt.% WS2 was used. Low and stable COF values were accompanied by the formation of a tribolayer incorporating WS2 and WO3 on the WC-Co surfaces. During orthogonal machining of Ti–6Al–4V using CF + 1.0%WS2, a tribolayer with the similar composition was formed on the cutting edge of the WC-Co tool and the average cutting force was reduced by 35% compared to cutting with CF + 0%WS2. Machining with CF + 1.0%WS2 produced thinner chips. Other improvements in machining performance attained using CF + 1.0%WS2 included reduction of adhesive wear on the tool and a lower roughness of the machined surface. [ABSTRACT FROM AUTHOR]

This study investigates the role of sliding counterbodies, which significantly affect the wear properties and friction of nanocrystalline diamond (NCD) film. The bearing steel balls exhibit a high friction coefficient of 0.12, whereas a ceramic ball of Si3N4 achieves an ultralow friction coefficient of 0.06. The evolution of different friction coefficients with different counterbodies is associated with the formation of a tribolayer at the sliding interface. The decreased friction coefficient in NCD films sliding against Si3N4 ball is likely linked to the occurrence of lubricating nanostructures, especially the silica‐like oxide compounds and graphite‐like carbon phases. The findings of this study may provide new avenues for the design and development of wear‐resistant and environment‐friendly hard carbon films. [ABSTRACT FROM AUTHOR]

The deformation and structural evolution characteristics of cementite in tribolayers significantly impact the friction and wear properties of pearlitic steels. However, the mechanism and size dependency of cementite amorphization remain unclear. Herein, the focused ion beam (FIB) lift-out technique was used to prepare transmission electron microscopy (TEM) samples of tribolayers formed during dry sliding of pearlitic steel. The microstructure of and elemental distributions in the tribolayers were characterized. Furthermore, molecular dynamics (MD) simulations were employed to analyze the behavior of dislocation slip systems in ferrite that extended toward cementite and induced amorphization. The results indicated that cementite amorphization occurred prior to dissolution within the tribolayer. Dislocation slips at the phase interface resulted in C diffusion and cementite amorphization. The transformation of cementite was size dependent. Thin lamellae transformed into amorphous lamellae, while local deformation and shear bands formed in thick lamellae. These research findings could contribute to rational design of cementite and to control of its structural evolution behavior within a tribolayer, thereby enhancing the wear resistance of a material. • Dislocation slip at the phase interface results in diffusion of C and amorphization of cementite in a tribolayer. • The amorphization process is size dependent, with 5 nm being the size that most easily forms amorphous materials. • Thin lamellae transform into amorphous lamellae, while local deformation and shear bands form in relatively thick lamellae. [ABSTRACT FROM AUTHOR]

This research aims to fabricate Cu-10Sn-5Ni /10wt%TiC functionally graded composite (Øout100 X Øin70 X 100 mm) through horizontal centrifuge cast technique and to study its tribo-mechanical characteristics. Microstructural observation revealed higher percentile of reinforcement particles at inner wall zone compared to middle and outer zones. Vicker’s micro hardness tests revealed proportional increase of hardness along the radial wall towards inner periphery. Inner (7-15 mm) zone had higher tensile strength (291 MPa) compared to outer (1-7 mm) zone (236 MPa). Non-lubricated tribology experiments were performed at inner, middle and outer region of composite using pin-on-disc tribometer under a wide range of loads, sliding distances and sliding velocities. From the wear experiment results, it was observed that inner region had minimal wear due to rich particle presence. Scanning Electron Microscopy on worn specimen at low and high wear parametric conditions exhibited features like delamination, ploughing, micro cutting, particle pull-out, plastic deformation with flaky wear debris and thin film formation.

The current work focuses on enhancing wear resistance due to the presence of reinforcements and the effect of ageing treatment on hybrid composites of Al6061-SiC+B4C. By varying weight percentage, two kinds of reinforcements, viz. silicon carbide and boron carbide, were prepared for hybrid composites by the liquid state process known as the method of stir casting. The solutionising temperature of 550 °C for 2 hours and ageing temperature of 100-200°C at different time intervals were used for both Al6061 alloy and its composites during heat treatment. Microstructural and mechanical characterisation were carried out using a standard testing procedure. Compared to Al6061 matrix alloy, artificially peak aged composites show 100-140% improvement in hardness due to harder reinforcements and precipitation of solute rich secondary phases during ageing treatment. Overall, an 80-100% increase in wear resistance observed during peak ageing of hybrid composites. Analysis of Al6061 matrix alloy wear out surface shows extensive grooving and ploughing of the surface with the matrix material smear at many spots. The presence of tribolayer in Al6061-SiC+B4C composites shows a smoother surface than the Al6061 matrix alloy, which results in an excellent lubrication effect during an improvement in wear resistance. The wear surface of base aluminium alloy doesn't show the existence of iron in the tribolayer. The research work is significant in forming a thermally activated wear-resistant metallic tribolayer with good tribological properties. [ABSTRACT FROM AUTHOR]

Here, new insight into amorphization induced by deformation at ferrite-cementite nanointerfaces in a tribolayer is put forward, and an atomistic investigation into interfacial effects on amorphization is carried out using molecular dynamics (MD) simulations and spherical aberration-corrected high-resolution TEM (HRTEM) characterization. Nanoamorphous particles mix with oxide particles attached to the wear surface, which provide a lubrication state during dry sliding friction of pearlite steels. HRTEM images and energy-dispersive X-ray spectroscopy (EDS) maps show alternating ferrite-amorphous-ferrite lamellar features in the tribolayer. MD simulation results show that ferrite-cementite nanointerfaces with the Bagaryatskii orientation play important roles in the above amorphization, which can be exposited by the deformation response between the ferrite and cementite being inconsistent. A high density of dislocation defects destroys the ferrite-cementite interfaces to create an amorphous nucleation region, and after nucleation, the amorphization will expand into the cementite. This study lays the theoretical basis for revealing the mechanism of cementite amorphization in the tribolayer and will provide new ideas for designing and manufacturing amorphous self-lubricating films or solid materials.

The use of high strength aluminium alloys, such as 6XXX and 7XXX series, is continuously increasing for automotive applications in view of their good strength-to-weight ratio. Their formability at room temperature is limited and they are thus often formed at high temperatures to enable production of complex geometries. Critical challenges during hot forming of aluminium are the occurrence of severe adhesion and material transfer onto the forming tools. This negatively affects the tool life and the quality of the produced parts. In general, the main mechanisms involved in the occurrence of material transfer of aluminium alloys at high temperature are still not clearly understood. Therefore, this study is focussed on understanding of the friction and wear behaviour during interaction of Al6016 alloy and three different tool steels in as-received and polished state. The tribotests were carried out under dry and lubricated conditions, with two distinct lubricants, using a reciprocating friction and wear tester. The worn surfaces were analysed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results showed a high dependence of friction and wear behaviour on the tool steel roughness as well as on the stability of the lubricant films. Tribolayers were found to develop in the contact zone and their capacity to improve the tribological behaviour is seen to be drastically impacted by the surface roughness of the tool steel. When the tribolayers failed, severe adhesion took place and led to high and unstable friction as well as material transfer to the tool steel. [ABSTRACT FROM AUTHOR]

Relationships between tribological properties of Ti-6Al-4V and the machining behaviour of the same alloy drilled by a WC-Co cutting tool using minimum quantity lubrication (MQL) were studied. The tribological behaviour of Ti-6Al-4V sliding against WC-Co was evaluated by determining the changes in the coefficient of friction (COF) using cutting fluids employed in MQL and flooded drilling tests. When pin-on-disk tests were carried out under the boundary lubricated condition, the MQL fluid (MQLF) provided a low COF of 0.16 at 25 ℃ and 0.24 at 250 ℃. The observed low COFs were attributed to formation of a tribolayer on the WC-Co counterfaces. A high COF of 0.45 observed at 300 ℃ indicated that the tribolayer was no longer stable. Application of conventional water-based cutting fluid (CF) also resulted in a low COF of 0.26 at 25 ℃ but the COF rose to 0.32 at 100 ℃. During drilling tests, MQLF was supplied at a rate of 80 ml/h using an external MQL system. The average drilling torque was reduced by 35% compared to CF as a result of the formation of tribolayer on the cutting edge of the tool as well as on the drilled hole surfaces, as the cutting temperature remained <250 ℃. According to Raman and X-ray photoelectron spectroscopy (XPS) analyses, the tribolayer on the drilled hole surface was formed as a result of degradation of additives in the MQL. The presence of phosphate- and sulfate-based anti-wear components in the tribolayer proved to be beneficial in preventing metal-metal contacts during drilling and provided a low COF. The low COF between tool-workpiece contact resulted in a low and uniform torque response throughout the drilling cycles and prevention of built-up edge (BUE) formation, leading to an improved surface finish. [ABSTRACT FROM AUTHOR]

In order to improve drilling performance of Inconel 718 alloy, a cutting fluid (CF) consisting of 70% water and 30% vegetable oil blended with graphene nanoplatelets was used. Sliding of Inconel 718 workpiece using WC-Co drills with CF containing 54 × 10−5 wt% graphene (GCF) reduced the coefficient of friction (COF) between the tool and workpiece surfaces from 0.16 to 0.08 and resulted in the formation of tribolayers. The maximum drilling torque of 6 Nm for CF was reduced to 2 Nm using GCF. Additionally, arithmetic mean height (Sa) of drilled surfaces decreased from 8 to 4 μm and a reduction in the amount of material transferred from the Inconel 718 to the cutting edge of the drill was observed. The drilling temperature decreased from 150 to 100 °C using GCF during the process. Subsurface plastic deformation that occurred at the drilled surfaces of Inconel 718 was examined by cross-sectional optical microscopy which revealed that both the depth of deformation zone and the magnitude of subsurface strains were lower compared with flooded drilling. Therefore, graphene added in small quantities to the cutting fluid can provide an energy efficient method for drilling of Inconel 718. Graphical abstract [ABSTRACT FROM AUTHOR]

In this research, AZ31 Mg alloy was reinforced with varying wt.% of SiC doped reduced graphene oxide(r-GO). Tribological behaviour of the developed MMC was investigated by varying the control factors viz. sliding velocity, sliding distance and applied load. Results revealed that addition of reinforcement has improved the wear resistance of developed Metal Matrix Composite (MMC). Amongst the samples, MMC made of 20 wt.% SiC doped r-GO showcased minimal wear rate and as well it is the optimal doping percentage for r-GO nanosheets. Any further addition of SiC into r-GO exhibited higher wear rate. Occurrence of delamination and abrasion wear mechanism was clearly evident from the worn out surface morphology of the developed MMC. [ABSTRACT FROM AUTHOR]

This research aims to fabricate Cu-10Sn-5Ni/10wt%TiC functionally graded composite (Øout100 X Øin70 X 100 mm) through horizontal centrifuge cast technique and to study its tribo-mechanical characteristics. Microstructural observation revealed higher percentile of reinforcement particles at inner wall zone compared to middle and outer zones. Vicker's micro hardness tests revealed proportional increase of hardness along the radial wall towards inner periphery. Inner (7-15 mm) zone had higher tensile strength (291 MPa) compared to outer (1-7 mm) zone (236 MPa). Non-lubricated tribology experiments were performed at inner, middle and outer region of composite using pin-on-disc tribometer under a wide range of loads, sliding distances and sliding velocities. From the wear experiment results, it was observed that inner region had minimal wear due to rich particle presence. Scanning Electron Microscopy on worn specimen at low and high wear parametric conditions exhibited features like delamination, ploughing, micro cutting, particle pull-out, plastic deformation with flaky wear debris and thin film formation. [ABSTRACT FROM AUTHOR]

The tribological properties of Nickel-based composites containing Ti3SiC2 and Ag2W2O7 fabricated by spark plasma sintering against Si3N4 balls were investigated using a ball-on-disk tribometer from room temperature to 600 °C. The tribolayers formed on the friction surface and their effects on the tribological properties of composites at different temperatures were discussed based on the worn surface characterization. The results show that Ag2W2O7 is decomposed into metallic silver and CrWO4 during the high-temperature fabrication process. The composite with the addition of 20 wt% Ti3SiC2 and 5 wt% Ag2W2O7 exhibits a friction coefficient of 0.33–0.49 and a wear rate of 7.07×10−5–9.89×10−5 mm3/(Nm) over a wide temperature range from room temperature to 600 °C. The excellent tribological properties at a wide temperature range are attributed to the formation of a glaze layer at low temperature and a tribooxide layer at high temperature, which can provide a low shearing strength for the synergistic effects of Ag and tribooxides. [ABSTRACT FROM AUTHOR]

Abstract In the work, Mo element is used to adjust composition and distribution of the lubricating phase of the self-lubricant Ti(C, N)-based cermets. Ring-block wear test of self-mate pairs is conducted. The microstructure and wear behavior evolution of the cermets are investigated. The results indicate by adjusting the content of Mo, the distribution of graphite on the surface of the self-lubricant cermets changes. With the increase of Mo content, the volume of graphite decrease, and the undissolved Mo increase. During self-mate pair sliding wear, the tribolayer transform from graphite to graphite+MoOx and then to MoOx. The cermets with 4 wt%. Mo show the best tribological properties, which shows a smooth and dense composite tribolayer formed mainly by graphite and MoOx. Highlights • Mo element is used to adjust distribution of the lubricating phase. • Tribolayer transform from graphite to graphite + MoOx and then to MoOx induced by Mo. • Cermets-4 wt%Mo show the best tribological properties caused by a smooth and dense graphite+ MoOx composite tribolayer [ABSTRACT FROM AUTHOR]

In this study, natural attapulgite (ATP) mineral powder was implanted into an in-situ synthesized TiB/Ti composite by the SPS method using Ti-Al-B-attapulgite raw powders to improve the tribological properties. The introduction of ATP improved the microstructure, mechanical properties, and tribological performance of the in-situ TiB-reinforced titanium matrix composite. The addition of 1 wt.% ATP powder has refined both the grain structure of the matrix and the size of the in-situ TiB, leading to the increase of 39.3% in matrix nanohardness and 31.4% in microhardness of the composite. During the friction process, dehydration reactions, group recombination, and tribochemical reactions occurred in the ATP minerals dispersed in the rubbing contact area of the composite, inducing the formation of a tribolayer with a smooth nanocrystalline film. The tribolayer is mainly composed of titanium oxides (TiO, TiO 2 , and Ti 2 O 3), iron oxides (FeO, Fe 2 O 3 , and Fe 3 O 4), ternary compounds (Al 18 B 4 O 33 and Al 2 Ti 7 O 15), oxide ceramics (Al 2 O 3 and SiO 2), solid lubricating phases (graphite and attapulgite), iron, and enstatite (MgSiO 3). The nanocrystalline structure composed of FeO, Fe 2 O 3 , and TiO, as well as the strengthening effect of hard phases such as SiO 2 , MgSiO 3 , Al 2 O 3 , Al 18 B 4 O 33 , and Al 2 Ti 7 O 15 , endowed the tribolayer with a high hardness, good plasticity, and toughness. The exceptional mechanical properties and dispersed solid lubrication phases of the tribolayer resulted in the excellent tribological properties of the ATP-TiB/Ti composite. • In-situ TiB/Ti composite doping with attapulgite was prepared by SPS method. • Doping of attapulgite improved microstructure, mechanical/ tribological properties. • Compact tribolayer with nanocrystalline structure formed on worn surface. • High H / E and H 3/ E 2 of the tribolayer led to good tribological properties. [ABSTRACT FROM AUTHOR]

The morphology, dimensions and chemical composition of tribolayers strongly depend on the pressures and temperatures acting on the contact. They are formed by reactions between surfaces in contact with each other as well as with the atmosphere, lubricants and possible contaminants. In this paper, the influence of test time (180, 500, 1000 and 2500 h) on the formation and characteristics of tribolayers in pairs of DLC-stainless steel that were tested under an atmosphere of refrigerant gas R134a and without lubricating oil was analyzed. The characterization was performed using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) (morphology and chemical composition) and white light interferometry (thickness). The tribolayer thicknesses ranged from 100 to 500 nm, and they were composed of elements originating from mutual transfers between the tribological pairs, as well as oxides that were more pronounced on the stainless steel surface. The results show that the tribolayers are chemically stable, maintaining the same composition over time, and their thicknesses remained constant after 1000 h of testing.