Tribological Degradation Research Articles

Role of phenolic resin in the cryogenic tribological performance of impregnated graphite cooled by liquid nitrogen

In this study, tribological performance of phenolic resin-impregnated graphite in liquid nitrogen was tested, revealing that its cryogenic performance was worse than that of pure graphite, which conflicted with the observed application effects at room temperature. When the room-temperature environment was changed to liquid nitrogen, the wear resistance of pure graphite significantly improved. Therefore, the incorporation of phenolic resin was the fundamental factor determining the tribological degradation. Tribological and mechanical properties of phenolic resin were analyzed through cryogenic tests and molecular dynamics simulation. Brittleness of phenolic resin was further enhanced by the cooling effect of liquid nitrogen, leading to poorer cryogenic tribological performance of impregnated graphite. It is necessary to reconsider the application of phenolic resin-impregnated graphite for cryogenic environments.

Tribological characteristics and degradation mechanism of typical synthetic lubricants from room temperature to 300 ℃

In this study, the tribological characteristics of several synthetic lubricants—including poly alpha olefin (PAO), pentaerythritol ester (PET), perfluoropolyether (PFPE), ethyl siloxane fluid, chlorophenyl silicone oil (CPSO), and polydimethylsiloxane—were assessed from room temperature to 300 ℃. The results show that PAO 6 and PET exhibit exceptional lubrication properties at elevated temperatures. PAO 6, PET and ethyl siloxane fluid exhibits slight wear at high temperatures. Silicon oils, notably, tend to form Si aggregates at the Si3N4 and M50 (8Cr4Mo4V) wear interface. Among the silicone-based lubricants, ethyl siloxane fluids demonstrated the lowest wear rate, attributed to the generation of dense Si-O films at the wear interface that offer protective benefits. This work provides essential data support for the application of high-temperature lubricants.

Tribological and corrosive degradation of differently surface engineered 17-4 PH steel

In the present work, a high-velocity oxy-fuel (HVOF) thermal spray process was used to deposit ceramic coatings containing alumina (Al2O3)− 0.8 wt% ceria (CeO2)− 0.2 wt% reduced graphene oxide (rGO) on 17–4 PH steel. The results were compared with the nitrided 17–4 PH (N17–4 PH) steel. The mechanical characteristics of the bare substrate, nitrided substrate, and coating were evaluated regarding micro (Vickers) hardness, scratch hardness, nanoindentation, and high-temperature nanoindentation (300 °C). The tribological behavior of all the specimens mentioned earlier was studied in a universal mechanical tester in a ball on flat reciprocating wear test mode for different loads. Electrochemical responses regarding corrosion properties in 3.5 wt% aqueous salt solution were recorded and analyzed. The results showed that the ceramic coating performed better than the other two specimens regarding mechanical, tribological, and electrochemical properties. For example, the coating was nearly ten and six times more wear resistant than 17–4 PH steel and N17–4 PH steel, respectively, at 50 N load. The performance enhancement in the coating was ascribed to the coating hardness, dense microstructure, and introduction of rGO in the coatings, which participate in the tribological process. Further detailed analysis of the bare steel, ceramic coating, and the nitrided steel properties reveals that the nitriding process can be replaced with the proposed ceramic coating through the HVOF technique for tribological, corrosive, and extreme environmental applications for 17–4 PH steel.

The evolution of subsurface deformation and tribological degradation of a multiphase Fe-based hardfacing induced by sliding contact

Multiphase Fe-based hardfacing alloys, for example Tristelle 5183 Fe-21%Cr-10%Ni-7.5%Nb-5%Si-2%C in wt.%, are extensively used for tribological applications, including valves, bearings and drive mechanisms, where two surfaces are unavoidably subjected to loaded sliding contact within engineering systems. In this study, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterise, for the first time, the tribologically affected material induced by the self-mated sliding contact of HIPed Tristelle 5183. This provided novel insight into the deformation modes which permit the accumulation of the high levels of subsurface strain required for plasticity dominated (adhesive) wear in a commercial hardfacing. In the subsurface regions furthest from the sliding contact, plastic deformation is accommodated by deformation induced martensitic transformation to ϵ-martensite and α′-martensite, twinning, the generation of planar dislocation arrangements (generated by planar slip) and the generation of dislocation tangles. Closer to the sliding contact, the subsurface becomes unstable, and nanocrystallisation driven by grain boundary mediated deformation mechanisms and crystallographic slip completely engulf the near surface microstructure. It is postulated that nanocrystalisation within the subsurface is a needed in order to accommodate the extremely high strains required in order to permit tribological degradation via plasticity dominated wear. The extrusion of metallic slivers via plastic ratcheting generates ductile shear cracks governed by plastic strain, and the failure of these slivers generates plate/flake-like wear debris.

Corrosion of food grinding discs in gastro-intestinal environment

The need for food size reduction before consumption has led to the use of motorized grinding machine which operates on energized rubbing of two grooved cast-iron discs, and this unintentionally results in tribological degradation and corrosion of grinding discs into the ground food. The objective of this study was to carry out an assessment of corrosion susceptibility of grinding discs from different manufacturing methods in simulated gastro-intestinal environment. Six grinding discs from three states in Nigeria were selected for this study, based on manufacturing methods namely: rotary, cupola, and pit furnaces. Experimental techniques used for the study included: X-Ray Fluorescence spectroscope for determination of chemical composition and X-Ray Diffractometer was used for phase identification. Corrosion susceptibility of grinding discs on interaction with pseudo-body fluid was studied using potentiodynamic polarization scan and product analysis (gasometric) methods in simulated gastro-intestinal environment, typical of human stomach, as electrolyte. The electrolyte contained 2 g/L NaCl acidified to pH of 1.7 with HCl and regulated at 37 °C. Optical microscopy of the electrochemical samples was done for corrosion damage assessment. The key finding from the study was that all the grinding discs contain iron and silicon as dominant alloy elements, which existed predominantly as iron carbide and ferrosilicon phases. Corrosion of the discs in simulated gastric solution was well profound irrespective of the manufacturing method, though, with varying degree among the discs. The outcome of this study is applicable to food industries where cognitive measures may have to be taken on materials selection to minimise the risk of food contamination from materials corrosion.

Mechanical and Morphological Characteristics of Nickel, Chromium and Nitride-Based Coatings Formed via Electrodeposition and Magnetron Sputtering Techniques on Mild Steel. An Overview

Mild Steel (MS) is considered as the most widely employed engineering material, which is primarily being used in an automotive industry. Several parts including fuel system, outer and body panel, trims, chassis exhaust, along with many other parts are made up of MS. The driving force behind versatility of MS is its unique set of characteristics. However, the issues arise when its tribological degradation occur that creating problems in service conditions. The best solution for this problem is to coat the mild steel with transition metal-based nitride coatings such as, Ni and Cr. Insufficient Literature is available related to the mechanical performance of single/gradient layer (Ni, Cr) N ternary coating on mild steel substrate. Current review focuses on the characteristics of the coatings that are deposited through two different deposition techniques; electrodeposition and magnetron sputtering. The studied coatings materials are nitrides of nickel and chromium, deposited in several layers. Furthermore, the structural and mechanical properties of these coatings have been compared.

Modulating tribological properties and degradation rate in Hank's solution of Zn–Mn alloys electrodeposited on Mg with variable Mn content

Zn–Mn alloy coatings with small amounts of Mn (Zn-0.19 wt.% Mn, Zn-0.21 wt.% Mn, Zn-0.26 wt.% Mn and Zn-0.34 wt.% Mn) were formed by electrodeposition, onto pre-treated Mg substrates (Mgt) covered with a Zn film (Zn/Mgt). The chemical composition in depth profiles, morphological and structural characteristics of the Zn–Mn coatings on Zn/Mgt (labeled as Zn–Mn/(Zn/Mgt)) were analyzed using Glow Discharge Optical Emission Spectroscopy (GD-OES), Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDS), and X-ray diffraction (XRD). When the manganese content was greater than 0.19 wt.%, the results reveal the formation of two Zn–Mn phases: η-ZnMn and ζ-MnZn13; while the formation of the ζ-MnZn13 phase was favored by increasing the Mn content in the alloy. On the other hand, microhardness, wear resistance, and coefficient of friction significantly increase when coating Zn/Mgt substrate with the Zn–Mn alloy. The corrosion performance of this alloy was evaluated by potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The degradation rate in Hank's solutions of the pristine Mg substrate (0.29 mm yr−1) decreases due to the Zn–Mn coating. Furthermore, the degradation rate of Zn–Mn was further decreased from 0.051 to 0.022 mm yr−1, by varying the amount of Mn in the Zn–Mn alloy from 0.19 to 0.26 wt.% Mn, respectively. However, the rate of degradation increases up to 0.064 mm yr−1 at higher Mn content, Zn-0.34 wt.% Mn. Therefore, the microhardness, wear volume, and degradation rate of Zn–Mn/(Zn/Mg) in Hank's solution can be modulated by varying the Mn composition in the alloy.

Mechanical, Corrosive, and Tribological Degradation of Metal Coatings and Modified Metallic Surfaces

Mechanical, corrosive, and tribological degradation of metal and metal coatings is just one of the challenges faced by numerous industries [...]

Low energy proton irradiation tolerance of molybdenum disulfide lubricants

As the world’s space agencies look to long duration spaceflight beyond low earth orbit, engineering materials in deep space flight will endure galactic cosmic ray irradiation, of which 85% is protons. Characterization of proton irradiation damage near the threshold displacement energy is required to understand the mechanisms behind performance degradation and the fluence dependent effects of a thermalized spectrum on surface sensitive tribological characteristics. Here, tribological degradation of a space-grade molybdenum disulfide lubricant exposed to low energy (500 eV) protons is investigated as a function of fluence. A 21% increased coefficient of friction and 86% increase in wear rate is measured at 1020H/m2, and 170% increased CoF and 465% increased wear rate at 3·1023H/m2. Associated softening and decreased stiffness is measured by nanoindentation. X-ray photoelectron spectroscopy and Raman spectroscopy identify the mechanism of tribological degradation as being the preferential removal of sulfur leading to a disordered and reactive non-stoichiometric MoS2-x surface with compromised tribological properties. Missions beyond low-earth orbit will be required to withstand GCR radiation, and it is not suggested that the density of radiation damage sustained will be acutely detrimental to MoS2 lubricants. Still, research missions should plan to characterize the magnitude of radiation damage effects.

Effect of Vibration on Emergency Braking Tribological Behaviors of Brake Shoe of Deep Coal Mine Hoist

The effects of vibration on the emergency braking tribological behaviors of the brake shoe of a deep coal mine hoist were investigated in this study. The thermal, frictional and mechanical parameters of the brake shoe were obtained. The vibration characteristics of the brake shoe during emergency braking were investigated, employing multibody dynamics analysis. The effect of vibration on the emergency braking tribological behaviors (temperature and stress distributions) of brake interfaces was explored using the finite element method. The self-made tribo-brake test rig of a brake shoe was employed to reveal the friction deterioration behaviors of the brake shoe during emergency braking. The results show obvious vibrations of all brake shoes along the direction of positive braking pressure during emergency braking. The vibration causes increases in the equivalent Von Mises stress and temperature at the contact interfaces between the brake disc and the brake shoe as compared to the case of ignoring the vibration. Along the rotation direction of the brake disc, the equivalent stress and temperature of the brake disc surface present three overall rapid increases, as well as two slight decreases during emergency braking. As compared to cyclic emergency braking, continuous emergency braking exhibits more obvious tribological degradation of the brake shoe, attributed to enhanced vibration. The wear loss of the brake shoe increases with increasing emergency braking cycles and continuous emergency braking time.

Investigation of metal elements diffusion in Cr2O3 film and its effects on mechanical properties

Cr2O3 films were deposited on Inconel718 alloy substrate by using an arc ion planting system, and then annealed at 1000 °C in different atmospheres. The diffusion behavior of metallic elements from the substrate in different atmospheres and its effect on mechanical properties of the film were researched. The results show that Ti and Cr elements in the substrate would diffuse to Cr2O3 film surface when the films are annealed in argon, nitrogen and oxygen. A diffusion layer comprised of Cr and TiO2, which could attribute to the residual oxygen in furnace, formed on the surface of the argon-annealed film. In nitrogen atmosphere, Ti and Cr elements were nitrided to form Cr2N and TiN, and then they packed to form a diffusion layer on the film surface. Especially, a mesh-like heave comprised of Cr2O3 and Cr2Ti7O17 formed on the surface of the oxygen-annealed film. However, there is no element diffusion detected in the vacuum-annealed film, while lots of cracks formed on the film surface. Annealing in different atmospheres could improve the adherence strength obviously. The vacuum-annealed film maintains a high hardness, and possesses excellent tribological properties degradation. After argon and nitrogen annealing, the loose diffusion layers result in the hardness decreasing and tribological properties degradation. For the oxygen-annealed film, internal diffusion of oxygen decreases the surface hardness obviously. Moreover, although Cr2Ti7O17 lubricant formed on film surface, the loose surface structure deteriorates the tribological properties.

Tribological performance and degradation of 1‐n‐butyl‐1‐methylpyrrolidinium methylsulfate ionic liquid in glycerol as lubricant for steel‐steel sliding contacts

AbstractThe ionic liquid (IL) 1‐n‐butyl‐1‐methylpyrrolidinium methylsulfate was studied as additive for glycerol in steel‐steel contacts. The mixtures were evaluated in different IL concentrations with a reciprocating sliding tribometer in a ball‐on‐disc configuration under elastohydrodynamic and boundary conditions at room temperature and 100°C, respectively. At room temperature, friction and wear were mainly determined by the high viscosity of glycerol; hence, little differentiation was found. At 100°C, surface smoothening resulted in decrease of friction and wear with increase of IL concentration, which indicates corrosion as dominant part of the lubricating mechanism. A 0.6‐wt% IL turned out as best performing mixture regarding tribological behaviour and additive efficiency. Methylsulfate is reduced to sulphide when in contact with the steel surface. Methylsulfate reacts with glycerol to give glyceryl sulfate already during mixing as revealed by mass spectrometry. Acorrdingly, after triboexperiments, ions composed of sulfate, iron, and glycerol were identified.

Effect of interfacial voltage on tribological characteristics of polysilicon micro-contacts tested in ambient air under dynamic impact conditions

A polycrystalline silicon microtribometer was used to examine the evolution of tribological properties under dynamic mechanical impact and hot switching conditions. Changes in surface properties were tracked via periodic static adhesion tests. Surfaces experienced two distinct periods in the course of the dynamic lifetime—a run-in phase with little measurable surface modification and a degradation phase with significant surface modification and corresponding increases in the measured adhesion force. No statistically significant differences were found in either the run-in period length or the degradation rate between hot switching conditions and purely mechanical impacting. However, when combining these two parameters, it was discovered that longer run-in periods correspond to slower degradation rates for the mechanical switching but correspond to faster degradation rates for the hot switching. This can be attributed to the action of the surface hydrocarbons physisorbed from the ambient air. These hydrocarbons have high surface mobility because they are bound by weak van der Waals forces. Under hot switching conditions, mobility is enhanced by increasing surface temperature caused by electrical current flow through nano-asperities. Mobile hydrocarbons diffuse across the surface (driven by concentration gradients) to damaged areas resulting in a healing effect that is dominant in the hot switching tests. Results are interpreted in light of the principle tribological degradation and healing mechanisms and the experimental sources of these mechanisms.

Fabrication and Tribological Performance of Zr-Coated Carbide against 40Cr Hardened Steel.

In order to enhance the tribological performance of YT14 carbide, pure Zr coating was deposited on the substrate surface using a multi-arc ion plating method. The surface topography, adhesion strength, thickness, and micro-hardness of the Zr coating were tested. Dry sliding friction experiments against a 40Cr hardened steel ring were conducted with Zr-coated carbides and traditional ones. The average coefficients of friction were measured and compared. The wear characteristics of the samples were examined by scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDX). The test results indicated that the Zr coating deposited on the carbide surface exhibited excellent adhesive strength and lower hardness. The average friction coefficient of Zr coated carbide decreased by 20%–30% in comparison with that of the uncoated one. The Zr coated carbide could reduce the adhesive wear compared with the uncoated one, and the main tribological degradation mechanisms of the coating were abrasive wear, coating flaking and delamination.

Investigation of the tribological behaviour of WC/TiC based cermets in contact with Al2O3 alumina under high temperature

AbstractWC/TiC-based cermets are, generally, considered as potential alloys widely used in hot rolling industry because of their interesting properties, namely high resistance to wear and oxidation. This work was aimed at studying the tribological behaviour, at relatively high temperatur, of WC/TiC-based cermets prepared using the powder metallurgy procedure. Three WC/TiC-Co cermets were prepared with different titanium carbide (TiC) additions namely 5%, 10% and 15% [in weight percentage (wt.%)], and a tungsten carbide-cobalt (WC-Co) grade without TiC which was considered as a reference material, resulting in a total of four samples. Friction tests were carried out, at two different contact temperatures of 450°C and 650°C, using a tribometer and an alumina ball during 2 h 46 min with load and speed of 20 N and 0.5 m/s, respectively. The obtained friction coefficients indicate that WC/TiC-based grades are relatively stable compared to the reference grade which shows an unstable friction coefficient with many peaks. It was also found that wear rates decreased with increasing TiC content, but exhibited a noticeable increase with rising temperature. Moreover, and in order to characterise the tribological degradation, the wear tracks microstructure composed of 80% WC, 15% Co and 5% of TiC, were analysed using a scanning electron microscope (SEM) process. Consequently, an enhancement of the wear resistance at 650°C was observed, and oxides of various types rich in tungsten, cobalt and oxygen were identified through SEM/energy electron spectrometery (EDS) images.

Study on the Interaction between Talc and Perfluoropolyethers under Tribological Contact

Particle contamination at the head–disk interface (HDI) is a major concern for the long-term reliability of hard disk drives. In the current study, it is shown that, surprisingly, soft and lubricious talc particles have a significant damaging effect on the friction performance of media lubricants, nanometer-thick perfluoropolyethers. Thermogravimetric analysis (TGA) and the adsorption studies indicate that two mechanisms, Lewis acid–catalyzed decomposition and surface adsorption, are responsible for the observed tribological degradation. The potential impacts of the findings here on the design of next-generation media lubricant have been discussed.

Tribological Degradation of Head–Disk Interface in Hard Disk Drives Under Accelerated Wear Condition

To further increase the areal storage density of hard disk drive, one solution is to reduce the spacing between the magnetic head and disk to sub-1-nm regime. Such ultra-low spacing introduces great challenges to tribological reliability in the head-disk interface (HDI). Therefore, it is necessary to understand the characteristics and mechanisms of HDI degradation in the tribological condition. This paper investigates the degradation behaviors of HDI based on an accelerated wear experiment. Acoustic emission and thermal asperity sensors were used simultaneously to monitor the touch down dynamics before and after each cycle of the overdrive test to characterize the HDI degradation behaviors. Through analyzing the evolutions of HDI dynamic characteristics, the degradation mechanisms, including wear mechanism shift and HDI instability propagation were figured out.

A critical review on the tribological compatibility of automotive materials in palm biodiesel

Although the compatibility of biodiesel with the key components of automobile engine such as cylinder, pistons, piston rings, connecting rods, bearings, etc. have posed a big challenge to tribologists, they have yet to come up with a solution to reduce tribological degradation of different metals as well as the used fuel. Some efforts have already been given to understand the corrosion and wear of automotive materials in diesel and biodiesel. It was found that though biodiesel is more corrosive than diesel, it provides better lubricity in terms of wear and friction. This finding has led us to the conclusion that the combined effect of wear and corrosion on materials and the consequent effect on biodiesel degradation could be crucial and yet to be investigated. The present study also highlighted some other relevant factors which showed notable implications on wear and corrosion in biodiesel. Those factors including auto-oxidation, moisture absorption, change in fuel properties (e.g. TAN number, viscosity, density, etc.) are found to have important influence for understanding the science behind tribology in biodiesel.

The Effects of Environmental Water and Oxygen on the Temperature-Dependent Friction of Sputtered Molybdenum Disulfide

Molybdenum disulfide (MoS2) is well known for exceptional friction and wear properties in inert and high vacuum environments. However, these tribological properties degrade in humid and high temperature environments for reasons that are not fully understood. A prevailing hypothesis suggests that moisture and thermal energy facilitate oxidation, which increases the shear strength of the sliding interface. The purpose of this study is to elucidate the contributions of water, oxygen, and temperature to the tribological degradation of MoS2. Generally speaking, we found a minimum friction coefficient that occurred at a temperature we defined as the transition temperature. This transition temperature ranged from 100 to 250 °C and was a strong function of the MoS2 preparation and thermal sliding history. Below the transition temperature, friction increased with increased water, but was insensitive to oxygen. Above the transition, friction increased with increased oxygen, but decreased to a limited extent with increased water. These results are generally consistent with prior results, but clarify some inconsistencies in the literature discussions. Contrary to the prevailing hypothesis, the results suggest that water does not promote oxidation near room temperature, but directly interferes with lamellar shear through physical bonding. Increased temperatures drive off water and thereby reduce friction up to the transition temperature. The results suggest that oxidation causes increased friction with increased temperature above the transition temperature. The data also suggest that water helps mitigate high temperature oxidation by displacing the environmental oxygen or by preferentially adsorbing to the surface.

Tribological degradation of MoS2–Ti sputtered coating when exposed to elevated temperatures

The use of solid lubricants is an effective way to control friction and wear in applications where traditional lubricants such as oils and greases cannot be used. MoS2 is a popular solid lubricant which has been widely used in many applications, especially space applications in view of its good performance in vacuum. Recent developments in physical vapour deposition technology have led to the development of sputtered MoS2 films doped with different metals to improve their durability and reduce the detrimental effects of oxidation and humidity on their tribological performance. In this work, a MoS2–Ti coating deposited on a hot forming tool steel substrate has been studied at ambient and elevated temperatures. The objective was to investigate how the friction and durability of the MoS2–Ti coating are affected after exposure to elevated temperatures. The results have shown that low friction values of ∼0·02 were obtained at room temperature and low relative humidity of 25%. An increase in relative humidity to 40% led to an increase in friction by almost 100%. There was a very significant degradation in frictional characteristics as well as durability after the MoS2–Ti coating was exposed to 400°C. The wear of the counter surface also increased when sliding against the MoS2–Ti coating exposed to elevated temperatures. This has been attributed to interaction of the counterbody with hard abrasive molybdenum oxides formed on the MoS2–Ti coating due to exposure to elevated temperatures.