Tribochemical Wear Research Articles

Environment-dependent tribochemical reaction and wear mechanisms of Diamond-like carbon: A reactive molecular dynamics study

Diamond-like carbon (DLC) is widely utilized in various fields as a promising solid lubricating material. However, the lubricity and wear behaviors of DLC are highly sensitive to the environment, and the relevant mechanisms are hidden by complex tribochemical reactions at the friction interface. In this study, we performed reactive molecular dynamics (RMD) simulations of DLC to clarify the wear mechanisms in various environments (vacuum, water, and oxygen environments). Two types of tribochemical reaction-induced wear were observed: chemical wear induced by the triboemission of CxHy and CxHyOz compounds and mechanical wear induced by the formation of interfacial C–C bonds. Moreover, the results revealed that the environment affects the tribological behavior of DLC primarily through its impact on the surface chemical state, that is, the quantity and type of surface terminations. In terms of the number of surface terminations, the more surface terminations there are, the more chemical wear and less mechanical wear they cause. In particular, oxygen-containing terminations (e.g., C–OH and C=O) are more resistant than H terminations to interfacial bond formation and mechanical wear. The present work provides important insights into the wear mechanisms of DLC, aiding in the reduction of DLC wear by controlling the environment.

Wear study of additively manufactured repair material for R260 grade rails

Additive Manufacturing (AM) has been considered as a promising method for repairing rails and extending their service life. In this work, the wear rates of twin-disc specimens produced through laser additive manufacturing against ER7 material are studied applying creepages from 0.4 % to 2.6 %. The approved E11018-G electrode material is atomised and fully cladded into twin-disc rail specimens by Laser Powder Directed Energy Deposition. After the weight loss tests at 1400 MPa, experimental results are fitted with the theoretical adhesion curve modifying FASTSIM coefficients. This adhesion curve is employed to numerically calculate the slip contact area of each test. A non-linear correlation has been found and defined between wear and the slip area including the non-linear zone. This relationship is identified for tribochemical wear for low creepages and delaminative wear for middle and high creepages by surface and metallographic characterisation. The obtained results allow to predict the wear of the additively manufactured E11018-G repair material under wheel-rail contact conditions when the slip area is known.

New insights on the mechanism of tribochemical interaction-induced wear of H-terminated Si(110)

Reactive molecular dynamics simulations are employed to reveal the atomic-level mechanisms of tribochemical interaction-induced wear of H-terminated Si(110) in humid environment. The result shows that with interfacial water increasing, the surface wear first increases and then decreases under 2.5 GPa, while always decreases under 4.0 GPa. Four different Si atomic removal mechanisms are revealed, i.e., the stretching effect of interfacial bridge bonds, the weakening effect of H adsorption, the strain effect of O intrusion, and the pure shearing effect of a-SiO2 tip, and their occurrences show the same normal pressure and interfacial water amount dependence as the surface wear. The analysis on the prerequisite for their occurrences shows that the corresponding interfacial tribochemical interactions are first facilitated and then suppressed under 2.5 GPa, while suppressed under 4.0 GPa, which is the origin of the different normal pressure and interfacial water amount dependence of the surface wear. Moreover, it is found that a-SiO2 surface can provide H, O, or Si atoms to participate in the interfacial tribochemical interactions, and has an absolutely dominant role in the material removal of Si(110)-H compared with interfacial water, but its role is gradually suppressed by the increased interfacial water. This work sheds new and deeper lights on the mechanism for the effect of tribochemical interactions on the Si material removal in chemical mechanical polishing.

Elucidating tribochemical reaction mechanisms: insights into tribofilm formation from hydrocarbon adsorbates coupled with tribochemical substrate wear

The molecules with higher tribochemical reactivity exhibited smaller activation volume, implying that less mechanical energy was required to initiate tribochemical reactions.

Corrosion and wear interplay: Tribo-electrochemical evaluation of NiTiNOL60 alloy in sulfuric acid

The combined corrosion and wear behaviour of NiTiNOL60 alloy is important in various engineering applications. While previous studies have explored its performance in artificial seawater environments, limited information exists regarding its tribocorrosion characteristics in acidic conditions. This paper investigates the synergistic interaction between sliding wear and electrochemical processes for NiTiNOL60 alloy in a sulfuric acid environment, employing experimental procedures compliant with ASTM standards. Microscopic analysis confirms the alloy's Ni-rich composition, featuring a dense network of B2 NiTi + Ni4Ti3 cubic and rhombohedral crystal matrix structures. Our research and results reveal that material degradation during tribocorrosion arises from the combined effects of sliding wear and electrochemical reactions. Consequently, multiple wear mechanisms influenced by tribochemical wear are observed, with delamination and micro-cracks being notably prominent under higher applied loads due to surface tensile stress and contact pressure, leading to crack propagation perpendicular to the sliding direction. These findings have practical implications for optimising the performance and durability of NiTiNOL60 alloy in acidic environments, offering valuable insights for load-bearing engineering applications.

Mechanical property analysis and tribological response optimization of SiC and MoS2 reinforced hybrid aluminum functionally graded composite through Taguchi's DOE

Pistons and cylinder liners in automotive engines often experience wear, requiring mechanical and tribological characteristics that are not attainable with conventional metals and alloys. This study explores the viability of an Al11Si2CuFe functionally graded composite, produced through centrifugal casting, reinforced with 5 wt% SiC and 3 wt% MoS2 for these applications. Microstructural and tribo-mechanical characteristics were investigated, and wear properties were statistically analyzed using Taguchi's method, considering parameters such as sliding distance (750–1750 m), load (10−30N), and sliding velocity (1–3 m/s). Microstructural analysis revealed a gradient reinforcing particle distribution and particle clusters, alongside θ-Al2Cu phase formation confirmed through transmission electron microscopy. Mechanical property examination of the outer layers indicated an improvement of 17.3 and 27.34 % in tensile strength and micro-hardness, respectively, over the inner layers owing to the centrifugal force, increased dislocation density, and effective bridging effect between the reinforcing particles and matrix. Wear studies identified applied load as the influential parameter, with optimal wear occurring at 10 N, 750 m, and 2 m/s, as confirmed through analysis of variance studies. Worn surface analyses revealed abrasion, fatigue, and tribo-chemical wear regimes, characterized by the formation of wear tracks, particle pull-outs, delamination layers, mechanically mixed and oxide layers.

Atomic-scale insights into the tribochemical wear of diamond on quartz surfaces

A detailed understanding of diamond wear is crucial due to its use in high-performance cutting tools. Despite being a much harder material, diamond shows appreciable wear when cutting silicon dioxides due to a tribochemical mechanism. Here, we use nonequilibrium molecular dynamics simulations with a reactive force field to investigate the wear of single-crystal diamond tips sliding on α-quartz surfaces. Atom-by-atom attrition of carbon atoms is initiated by the formation of C-O interfacial bonds, followed by C-C cleavage, and either diffusion into the substrate or further oxidation to form CO2 molecules. Water molecules dissociate to form hydroxyl groups, which passivates the surfaces and reduces interfacial bonding and wear. At low loads, the initial wear rate increases exponentially with temperature and normal stress, consistent with stress-augmented thermally activated wear models. At higher loads, the initial wear rate becomes less sensitive to the normal stress, eventually plateauing towards a constant value. This behaviour can be described using the multibond wear model. After long sliding distances, wear also occurs through cluster detachment via tail fracture. Here, wear becomes approximately proportional to the sliding distance and normal load, consistent with the Archard model. The normalised wear rates from the simulations are within the experimentally-measured range.

Wear of cemented carbide tools in a copper alloy forging process - Verification of a new lab test

Cemented carbide tools are commonly used in both shearing and forging processes associated to zipper production. In the actual production, the tool life is often limited by wear after many millions of repeated contacts with copper alloys. A series of previous investigations has shown that the wear of the tools is tribochemical for both shearing and forging, however with different features. The mechanisms causing this wear are not well understood.To gain deeper insights into the active wear mechanisms during the copper alloy forging process, a new tribotester was proposed and developed. By this tester, a cemented carbide cylinder is repeatedly put in sliding contact with a rotating copper alloy cylinder in a crossed cylinders arrangement. The test was interrupted at selected intervals so that the cemented carbide cylinder could be repeatedly evaluated by SEM and EDS. It was revealed that the characteristic wear of actual tools, tribochemical smooth wear in common, and preferential removal of Co binder and partially Zn rich transfer for the forging tool, can be reproduced by this tribotester.

Lubricity of chelated orthoborate-phosphonium ionic liquids on tetrahedral amorphous carbon and steel surfaces

In boundary lubrication, formation of tribofilms and subsequent friction and wear properties are strongly influenced by lubricant affinity to the lubricating surfaces. Ionic liquids (ILs), which are composed of ions, are expected to provide enhanced surface affinity compared to molecular liquids. This is also of interest for non-ferrous surfaces such as diamond-like carbon (DLC) coatings. DLC technology is widely utilised for sliding components, but DLC performance with conventional lubricants does not always fulfil the requirements. In this study, we compare lubricating performance of two non–halogenated ILs with a common cation, trihexyl(tetradecyl)phosphonium, but different anions, bis(oxalato)borate and bis(mandelato)borate, in the steel/steel and steel/DLC contacts. The tribofilms formed and their lubrication mechanism are investigated using a wide range of surface analysis techniques: Atomic Force Microscopy (AFM), nano-indentation, SEM-EDX and X-ray Photoelectron Spectroscopy (XPS). It is demonstrated that both ILs exhibited better lubricating performance than PAO oils of similar viscosity. It is also shown that the lubricating performance is controlled by the chemical stability of ILs, surface hardness and topography. The phosphonium bis(oxalato)borate IL exhibited excellent lubricity but its performance was adversely affected by the rough and very hard DLC surface that disrupted a delicate balance between the rates of tribofilm formation and removal. A higher chemical stability of the phosphonium bis(mandelato)borate IL facilitated formation of a non-sacrificial ionic tribofilm that reduced friction to a lower extent than the phosphonium bis(oxalato)borate IL but without accelerated tribochemical wear. The results demonstrate the potential for controlling lubrication properties by tuning functional groups of anion structure and subsequent chemical reactivity of ILs with lubricated surfaces.

B2-structured Fe3Al alloy manufactured by laser powder bed fusion: Processing, microstructure and mechanical performance

Prealloyed Fe3Al was successfully manufactured by laser powder bed fusion. The best set of process parameters led to parts with a relative density of 99.5 %, a surface roughness, Sa, of 31.5 ± 5.6 μm and a hardness of 319 ± 14 HV0.1. Its microstructure as well as its mechanical properties at room and high temperatures were analyzed. The results of the chemical composition showed minor variations in aluminum content oscillating between 21 and 28 at.% along the melt pool. Additionally, elongated grains were observed to grow parallel to the building direction, as well as the development of a weak {001} texture along the building direction. The mechanical properties were influenced by the temperature. Compression tests showed a loss in strength with the increase in temperature, from a yield strength of 621 ± 40 MPa at room temperature to 89 ± 20 MPa at 650 °C. Reciprocating sliding wear tests showed that fragmentation of the intermetallic at room temperature occurs, whereas plastic deformation dominated at higher temperatures. For all temperatures, tribochemical wear was also present due to the oxidation of wear debris.

A two-stage approach to Ni-P-SiC coatings and their friction against SiC in water

Inspired by the low friction of self-mated SiC in water, a two-stage technique is proposed to deposit Ni-P-SiC coating with a high particle content to achieve low friction against SiC in water. The process comprises the electrophoretic deposition of SiC particles layer on a mild steel substrate followed by the electroless plating of NiP coating. The effects of SiC content on the surface appearance, phase structure and cohesive strength were studied. Much attention was paid on the friction behavior of the coatings in water. Experiment results show that compared with the traditional electroless plating method, the two-stage technique can enhance the implanted SiC particle content effectively. Notable, with the increasing of SiC content, the friction coefficient decreases correspondingly and the lowest friction coefficient of 0.015 can be achieved for the Ni-P-SiC coatings with the highest SiC particle content. The major surface degradation mode is abrasive wear during running-in then tribochemical wear dominates at the low friction stage.

How moisture driven mechanochemistry stabilizes transfer film adhesion and cohesion in ultralow wear PTFE composite

Prior studies suggest mechanical interlocking, preferential adhesion of polar polymers, and PTFE tribochemistry all contribute to the wear reduction in polar polymer-filled PTFE composites; whereas their relations remain poorly understood. This study aims to decouple the relevant mechanisms by investigating wear and tribofilm environmental sensitivities of a 5 wt% polyamide-imide (PAI) filled PTFE composite. The results highlight (1) strong correlation between a carboxylate-salt-rich transfer film and ultralow wear, and (2) a tribochemical interface gradient that discourages transfer film removal. We proposed that PTFE tribochemistry induces ultralow wear by significantly increasing (1) transfer film adhesion through a virtuous cycle of tribochemical accumulation and wear reduction and (2) transfer film cohesion by promoting a surface energy interface gradient beneficial to low wear.

Influence of mechanical properties of coating and substrate on wear performance of HDLC and TiN-coated AISI 5140 alloy steel

This paper investigates the mechanical and wears resistance properties of AISI 5140 alloy steel coated with thin films of hydrogenated diamond-like carbon (HDLC) and titanium nitride (TiN). HDLC and TiN films were sputtered onto AISI 5140 alloy steel samples using the magnetron sputtering technique. In addition to coatings, the metallic substrates were also evaluated for hardness and wear resistance. The findings on wear losses, patterns, and wear trace widths were determined after the wear tests. In tribological tests, a variety of wear patterns were observed on both thin film coatings. The primary wear mechanisms of TiN coatings were found to be tribochemical wear, substrate material loss, and wear debris. However, the HDLC coating experienced wear due to ploughing action, with minor patches of the thin film being removed from the underlying material, but scanning electron microscopy observations showed no detectable wear. Using Raman spectroscopy, the structural properties of HDLC were analyzed, and the findings were compared to those of wear patterns. The results showed that the coating significantly improved the wear resistance of the AISI 5140 alloy steel and that the TiN-coated AISI 5140 alloy steel sample was more comparable to wear than the HDLC-coated AISI 5140 alloy steel sample. It is also shown that, as compared to an uncoated metallic substrate, the resilience of thin film coated components is a key factor impacting component life.

Effect of fuel contamination on tribological properties of flex-fuel engines lubricating oils

Engines that allow the use of any percentage of alcohol and gasoline are flex-fuel engines. These motors face significant tribological challenges that seem to be associated with inadequate lubrication and severe tribochemical wear. The present work aimed to understand flex-fuel engines’ lubrication, friction better, and wear phenomena. Therefore, the authors analyzed the effects of adding percentages of fuels (ethanol and gasoline) to synthetic oil, evaluating the tribological performance of these lubricants. The lubricants were tested in an HFRR (High Frequency Reciprocating Rig) in order to measure the lubricity, friction, and wear between surfaces in relative motion under load. During the test, the coefficient of friction (COF) was evaluated, as well as the wear characterization via SEM/EDS and AFM. The results showed that the contamination of the lubricant with the fuels studied in this work decreased its lubrication capacity. This effect was more pronounced for higher proportions of ethanol once it promoted a tribocorrosion on the surface.

Tribo-chemical wear of various 3d-transition metals against DLC: Influence of tribo-oxidation and low-shear transferred layer

Diamond-like carbon (DLC) is a promising solid lubricant owing to its excellent anti-friction and wear-resistance characteristics. However, the high hardness of DLC causes two-body abrasion to its counterpart, which generally are ferrous and brass metals having a relatively low hardness, resulting in severe wear of counterpart. Therefore, it is required to solve the wear-imbalance issue, leading to noise and vibration in tribo-system. In this study, we aimed to investigate the wear behavior of counterparts sliding against DLC. We used four-3d-transition metals (Ti, Fe, Ni, and Cu) as the counterpart of DLC, based on the chemical properties for carbon and oxygen, i.e., the activation energy of oxidation and work of separation with carbon. Our finding is suggested that the wear of transition metals was governed by oxidative wear rather than mechanical wear (e.g., adhesive wear and abrasive wear). Moreover, their oxidative wear was prevented by carbon-containing tribofilm, which is transferred from DLC continuously. It revealed that severe oxidational wear was caused in copper and iron, because of their chemical properties.

Tribological behaviour of PTFE composites: Interplay between reinforcement type and counterface material

In this paper, we studied the sliding wear behaviour of polytetrafluoroethylene (PTFE)-based composites under conditions relevant to rotary seals. We specifically aimed to investigate the interactions between different particle-based reinforcements (lamellar or spheroidal bronze particles, PEEK particles) and different counterfaces (uncoated or Cr2O3-coated stainless steel), building upon our own previous work on fibre reinforced-composites to make up for the paucity of literature papers on the role of counterfaces. Pin-on-disc tests were performed under different load and speed conditions using spherical-tipped composite pins against coated or uncoated stainless steel discs to mimic the (initially) non-conformal, unidirectional sliding contact of lip seals. Though all composites attained a steady-state regime controlled by a tribochemical wear mechanism, namely tribofilm formation, there were significant differences among the tribofilms produced by different tribo-systems. Systems that released fine, oxidized metal debris (bronze-filled PTFE and/or uncoated counterpart) developed >1 μm thick, continuous tribofilms on both mating surfaces. Thickness and continuity of the tribofilm decreased with a non-wearable Cr2O3-coated counterpart and/or PEEK as a filler. The tribofilm was conducive to lower steady-state friction, but not lower wear, against stainless steel, whereas all performances (friction coefficient, specific wear rate) were levelled out with a Cr2O3-coated counterface.

Tribological characteristics and mechanism of nitrile butadiene rubber coated with typical liquid lubricants

When marine stern shafts operate under low speed and heavy load conditions, the metal shaft and water-lubricated bearing will be in a state of boundary lubrication or even dry friction. Poor lubrication can cause severe wear and friction-induced vibration, endangering the stealth performance of underwater vehicles. In this study, several typical liquid lubricants, including liquid paraffin, tung oil (TO), dimethyl silicone oil (DSO), ionic liquid (IL), and hexamethylene diisocyanate (HDI) were selected as the surface coatings for nitrile butadiene rubber (NBR). Using a tribological test machine with a high-precision vibration acceleration sensor, as well as scanning electron microscopy (SEM) and other techniques, the tribological performance and mechanisms of the NBR samples coated with different lubricants were studied under various working conditions. The results showed that the liquid lubricant significantly reduced the coefficient of friction of the NBR at high rotational speeds by over 92.2%. The sample coated with HDI showed obvious tribochemical wear, and coating with the rest of the liquid lubricants decreased the specific wear rate of NBR. According to the friction-induced vibration signals, we found that an increase in loading aggravated friction-induced vibrations, and the vibrational energy was mainly concentrated in the low frequency range. The liquid paraffin and TO coatings barely changed the vibration characteristics of the NBR, while the other three lubricants produced more friction-induced self-oscillations. In conclusion, compared to the other liquid lubricants, TO exhibited the best tribological performance. The finding of this study further our understanding of the friction and vibration behaviours of polymer materials, providing a reliable basis for designing composite materials with good lubrication and vibration damping performance.

Role of Interfacial Bonding in Tribochemical Wear.

Tribochemical wear of contact materials is an important issue in science and engineering. Understanding the mechanisms of tribochemical wear at an atomic scale is favorable to avoid device failure, improve the durability of materials, and even achieve ultra-precision manufacturing. Hence, this article reviews some of the latest developments of tribochemical wear of typical materials at micro/nano-scale that are commonly used as solid lubricants, tribo-elements, or structural materials of the micro-electromechanical devices, focusing on their universal mechanisms based on the studies from experiments and numerical simulations. Particular focus is given to the fact that the friction-induced formation of interfacial bonding plays a critical role in the wear of frictional systems at the atomic scale.

The enhancement of individual friction and corrosion properties of CrSiN coatings by Mo doping in seawater

A series of CrSiN coating with various Mo contents were fabricated on Ti6Al4V alloys using a closed unbalanced magnetron sputtering system and their tribological and electrochemical behaviors were investigated. The results of friction tests suggested that oxidation behaviors of Mo element in the prepared coatings promoted the wear mechanism transforming to tribochemical wear, and the more Mo doping enhanced the tribological performance and presented the lowest wear rates of 2.27 × 10 −7 mm 3 /N.m and 8.12 × 10 −8 mm 3 /N.m for tribopairs of Cr( Mo )SiN/Al 2 O 3 and Cr( Mo )SiN/Si 3 N 4 , respectively. Besides, the corrosion product of MoO 3 reduced the corrosion rate of CrMoSiN coatings, CrMoSiN coating showed the low corrosion rate of 0.58 × 10 −3 mm/yr indicated that the passive behaviors of Mo element improved the corrosion resistance, and provided a good protection to Ti6Al4V alloys in seawater. • Cr( Mo )SiN coatings were successfully fabricated using the unbalance magnetron sputtering system. • The oxidization behaviors of Mo element decreased the friction coefficient. • The wear mechanism would be transformed to tribochemical wear with an increase in the Mo content. • The more Mo element doping enhanced tribological performance of CrMoSiN coating in seawater. • The corrosion rate and current density were slowed down due to the passive behaviors of Mo element on coating's surface.

Improving abrasive wear resistance of Si3N4 ceramics with self-matching through tungsten induced tribochemical wear

Si3N4 ceramics with 0 vol% and 5 vol% tungsten particles were fabricated by gas pressure sintering. Commercial Si3N4 ceramic balls were used as the tribo-pair to test the influence of the tungsten particles on the wear resistance of Si3N4 ceramics. The tungsten particles in the samples were exfoliated and oxidized during the rubbing process. The tungsten oxide was uniformly doped into the wear debris, which turned the harmful exfoliated abrasives into a useful tribo-film. Compared with the monolithic Si3N4 ceramic, the abrasive wear of Si3N4 ceramics with introducing tungsten particles was almost eliminated, and the oxidative wear and surface fatigue were also reduced. The specific wear rate was reduced by more than an order of magnitude, from 4.70 × 10−6 mm3 N−1·m−1 to 3.78 × 10−7 mm3 N−1·m−1.