Friction and Wear Behavior of AlMgB14–TiB2 Composite at Elevated Temperature

In this article, field-activated and pressure-assisted synthesis was employed to synthesize an ultra-hard, super-abrasive AlMgB₁₄–TiB₂ composite ceramic. The friction and wear performance of the AlMgB₁₄–TiB₂ composite were evaluated in ambient air at temperatures up to 800 °C by using a reciprocating ball-on-disk high-temperature tribometer. X-ray diffraction experiments were performed to study the crystal structure of worn surfaces of AlMgB₁₄–TiB₂ specimens at various temperatures. Scanning electron microscopy and energy dispersive analysis were used to examine the worn surface features and chemical composition of the AlMgB₁₄–TiB₂ composite, respectively. Results showed that the friction coefficient of the AlMgB₁₄–TiB₂ composite ranged from 0.45 to 0.55 below 300 °C, while the data obtained at 500 and 600 °C were about 0.65. The damage mechanism is transformed from mild abrasive damage at room temperature to adhesive wear at elevated temperature. In the case of 800 °C, the AlMgB₁₄–TiB₂ composite exhibited the lowest friction coefficient as the formation of a lubricious oxide film on the wear track.     

Ionic Liquids as Lubricants of Titanium–Steel Contact. Part 2: Friction, Wear and Surface Interactions at High Temperature

The tribological behaviour and surface interactions of titanium sliding against AISI 52100 steel have been studied at 200 and 300 °C in the presence of two commercial imidazolium room temperature ionic liquid (ILs): 1-octyl-3-methylimidazolium tetrafluoroborate (L108) and 1-hexyl-3-methylimidazolium hexafluorophosphate (LP106). L108 presents the higher thermal stability but gives higher friction coefficients and wear rates than LP106, with long running-in periods and high friction values, both at 200 and 300 °C. Friction and wear rates for LP106 are lower and decrease as the temperature increases from 25 to 200 °C. At 200 °C, LP106 shows a constant friction coefficient, without running-in, produces a mild wear on titanium and no surface damage on steel. LP106 fails at 300 °C, close to its degradation temperature, due to tribochemical decomposition through partial dissociation of the hexafluorophosphate anion, with formation of a phosphorus-rich layer on the steel ball, while the titanium wear track surface is heterogeneous, showing regions with the presence of fluoride and others with the presence of phosphate. When the steel ball is substituted for a ruby sphere under the same conditions at 300 °C, a low friction coefficient and mild wear is observed, due to the higher stability of the LP106 lubricant at the ruby–titanium interface. The friction coefficients, wear mechanisms and surface interactions have been studied by means of friction-distance records, SEM, EDX and XPS.     

Parametric study of abrasive wear of Co–CrC based flame sprayed coatings by Response Surface Methodology

Co base powder (EWAC1006 EE) was modified with the addition of 20%WC and the same was further modified by varying amounts of chromium carbide (0, 10 and 20 wt%) in order to develop three different coatings. Microstructure, elemental mapping XRD, porosity and hardness analysis of the three coatings was carried out. The effect of CrC concentration (C), load (L), abrasive size (A), sliding distance (S) and temperature (T) on abrasive wear of these flame sprayed coatings was investigated by Response Surface Methodology and an abrasive wear model was developed. A comparison of modeled and experimental results showed 5–9% error.     

Laser Surface Hardening of Frictional Pairs Made from Steel—Copper Pseudoalloy

The microstructure and microhardness of the surface layer of annular projections on disks of steel—copper powder pseudoalloy are investigated after laser heat treatment by a 1-kW fiber laser. The maximum microhardness of 1000 HV is attained within the martensite formed in pearlite colonies of the initial steel—copper pseudoalloy. The properties of the surface layer depend not only on the laser parameters but also on the surface geometry of the samples.     

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

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

The Effect of “Hot-Spot” Temperatures on the Unlubricated Wear of Steel

Experiments are described in which pins of low-alloy, medium-carbon steel are worn against disks of the same material under unlubricated sliding conditions. The friction and wear characteristics of this system are measured as functions of load and speed. The choice of loads and speeds was made in such a way as to obtain the entire range of “hot-spot” temperatures possible for the system. The results are then compared with those to be expected from a model of the wear process in which the wear at the contacting regions between the pin and the disk is closely associated with the oxidation of the metal in these regions. The temperature of oxidation is assumed to be the calculated “hot-spot” temperature. In order to make the results compatible with the proposed model, it is necessary to introduce a new parameter (having the dimensions of length) which is shown to increase steeply with increasing “hot-spot” temperature up to about 700 C. It then levels off, at about 10^?6 cm, for all hot-spot temperatures in excess of about 700 C. In this way, the hot-spot temperature is shown to be a very important variable in the wear of steel.     

Wear Performance Forecasting of Chopped Fiber–Reinforced Polymer Composites: A New Approach Using Dimensional Analysis

Solid particle erosion of polymer matrix composites is a complex process in which wear occurs from the target surface by impingement of rigid sand particles in an air medium. The rate of material removal (RMR), also referred to as the erosion rate, mainly depends on target material parameters and the erosion conditions such as impact angle, impact velocity, and erodent size. A new semi-empirical model for prediction of the erosion rate of polymer matrix composites has been developed using a dimensional analysis technique based on Buckingham's π theorem. The predictive model analytically rests upon parameters related to chopped glass fiber composites, erodent (target material properties), and operating variables that mainly affect the erosion process of chopped glass fiber–vinyl ester resin composites. The forecasting ability of the predictive model has been assessed and verified by experimental investigations for chopped glass fiber–reinforced vinyl ester resin (VGF) composites. Validation of the theoretical erosion rates obtained from the predictive model showed that they were in good agreement with the experimentally determined erosion rates, where the average error range was estimated to be ～10 to ～20%.     

Wear Resistance of Hardened Components Produced from Electrospark Cobalt–Chromium Powder by Additive Manufacturing

Russian Engineering Research - The wear resistance of hardened additive products is studied experimentally. The products are made from electrospark cobalt–chromium powder obtained in alcohol....     

Gas–Solid Erosive Wear of Biomimetic Pattern Surface Inspired from Plant

Gas–solid erosive wear is a phenomenon in which serious mechanical damage is caused by the impact of solid particles on a wall. In this study, we investigated the erosive wear characteristics and mechanism of biomimetic groove surfaces in gas–solid erosive wear. Orthogonal experimental results showed that the order of the factors that influenced the erosive wear of the biomimetic groove surface was morphology > space > feature size. The V-shaped groove surface exhibited the best erosive wear resistance over the smooth, square, and U-shaped groove surfaces. The surface microstrain calculated by X-ray diffraction lines was used to study the mechanism of erosive wear resistance enhancement of the biomimetic surface. The microstructure of the eroded surface was analyzed by scanning electron microscopy. The appearance of ribs on the biomimetic groove surface increased the erosive wear of the surface in a distal position with respect to the ribs themselves. This article shows more opportunities for bionic application in improving the anti-erosion performance of moving parts that work under dirt and sand particle environments.     

Eddy-Current Evaluation of Wear Resistance of Case-Hardened Chromium–Nickel 20KhN3A Steel

The paper considers feasibility of eddy-current evaluation of the wear resistance of the quenched and tempered (100–400°C) case-hardened 20KhN3A steel under conditions of abrasive wear and sliding friction. The effect of cold processing on the susceptibility of the eddy-current method to the wear resistance of a hardened layer has been studied. The effect of the carbon content in the martensite prior to tempering over the range of 0.3 to 0.9 mass % on eddy-current measurements is discussed.     

Dry Reciprocating Sliding Friction and Wear Response of WC–Ni Cemented Carbides

A number of WC–Ni based cemented carbide grades with distinctive binder contents were tested with the goal to evaluate their dry reciprocating sliding friction and wear behaviour against WC–6 wt.%Co cemented carbide using a Plint TE77 tribometer and distinctive normal contact loads. The generated wear tracks were analysed by scanning electron microscopy and quantified volumetrically using surface scanning topography. The experimental results revealed one WC–Ni grade with superior wear performance.     

Low Wear Steel Counterface Texture Design: A Case Study Using Micro-pits Texture and Alumina–PTFE Nanocomposite

Laser-induced surface micro-pits pattern has been successfully used under fluid lubrication to reduce friction and wear through mechanisms of enhanced hydrodynamic lubrication and fluid retention. Limited successes of friction and wear reduction using solid lubricant and textured surfaces have been reported in the literature, and there still lacks an efficient way of finding textures that produce desired tribological performances. This study evaluates the effect of counterface micro-pits texture on wear of a notable alumina–PTFE nanocomposite and uses the Taguchi method and “Simplex Method” to find the micro-pits parameters producing the lowest wear of the composite material. The optimum texture found yields a composite wear rate of 1 × 10^?7 mm³/Nm, a value identical to the material’s wear rate against untextured counterface. However, when slid against a freshly replaced composite pin, the existing transfer film on the optimum texture reduces composite’s wear volume at low wear transition by 90% and yields a steady-state wear rate of 3.9 × 10^?7 mm³/Nm. On the contrary, preexisting low wear transfer film on untextured counterface increases wear of the newly replaced pin by 10× and yields a wear rate of 4.4 × 10^?6 mm³/Nm. Results in this study suggest larger, shallower and sparser counterface pits are more favorable for debris entrapment, transfer film formation and wear reduction when slid against polymeric solid lubricants. It also raises new possibilities of self-adapting low wear counterface texture design that could potentially support low wear without requiring large amounts of run-in wear volume of bulk solid lubricants.     

Measuring Evolution of Transfer Film–Substrate Interface Using Low Wear Alumina PTFE

Tribology Letters - Severe adhesion, also referred to as galling, is a critical problem in press hardening, especially in stamping tools used for hot forming of Al–Si-coated ultra-high...     

Sliding Wear Behavior of HVOF-sprayed Cr3C2–NiCr/CeO2 Composite Coatings at Elevated Temperature up to 800 °C

Four types of Cr₃C₂–NiCr coatings containing different fractions of CeO₂ additive were deposited using high velocity oxy-fuel spraying. Hardness tester, X-ray diffractometer, contact surface profiler, and scanning electron microscope equipped with energy dispersive spectrometer were employed to characterize the microhardness, phase composition, surface roughness, and microstructure of as-sprayed coatings. At the same time, the friction and wear behavior of the as-sprayed coatings sliding against Si₃N₄ ball at room temperature and elevated temperature of 400 or 800 °C under unlubricated condition was evaluated using an oscillating friction and wear tester. The worn surfaces of the composite coatings and Si₃N₄ counterpart balls were analyzed by means of scanning electron microscopy, X-ray diffraction, and three dimensional non-contact surface profiler. The friction and wear mechanisms of the coatings with and without CeO₂ additive were comparatively discussed. Results show that the composite coatings doped with CeO₂ had better wear-resistance than that without CeO₂, and the coating containing 4 wt% CeO₂ showed the best wear-resistant property. The improved wear-resistant properties of the composite coatings doped with CeO₂ were attributed to the refined microstructure and improved mechanical properties induced by CeO₂.     

Surface Modification of Machine Parts Made of Iron–Carbon Alloys Operating under Conditions of Friction and Wear

The article has described a promising oxyalloying technique for the surface modification of machine parts made of iron–carbon alloys that operate under conditions of friction and wear. The new method has been implemented via the surface impregnation of steel and cast-iron parts with superheated steam of aqueous solutions of salts containing chemically active alloying elements. A multilayer coating formed on the surfaces of parts as a result of this treatment increases their performance characteristics, which has been confirmed by the integrated research.     

Surface Characterization and Erosion–Corrosion Behavior of Q235 Steel in Dynamic Flow

The study aims at investigating the surface evolution and erosion–corrosion behavior of Q235 steel during erosion–corrosion process in various dynamic flows. For the purpose, true flow fields with the average flow velocities of 0.4 and 0.8 m/s and impact angles of 0°, 30° and 90° to the sample surface were successfully measured by particle image velocimetry. The topography of erosion–corrosion surface was observed by laser scanning confocal microscopy. The evolution of localized corrosion pattern is found to be determined by impact angle, i.e., round or elliptical corrosion pit corresponds to impact angle of 90° and ribbon-like corrosion pit corresponds to 0°. The deeper corrosion pits were observed at impact angle of 30° than those at the other two impact angles owing to combined effects of shear and normal stresses. Electrochemical impedance spectroscopy of samples shows smaller radiuses of capacitive loops at velocity of 0.8 m/s than those at 0.4 m/s. Equivalent circuit analysis implies unstable surface state of sample in dynamic flow. Above results indicate that the flow velocity and impact angle play the key role in the erosion–corrosion behavior of Q235 steel.     

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

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

Wear–Corrosion Resistance of DLC/CoCrMo System for Medical Implants with Different Surface Finishing

The field of medical implants in the human body is a growing area with diverse tribological aspects. This application field has its own specific characteristics, dominated by stringent quality requirements due to the human suffering and sometimes life-threatening consequences of a surface failing to fulfil its required function. Combined wear–corrosion tests could provide more complete information about the implant behaviour in the aggressive body environment than separate wear and corrosion testing. Combined wear–corrosion experiments were performed using a reciprocating ball-on-plate apparatus equipped with an electrochemical cell. Untreated CoCrMo alloy samples as well as diamond-like carbon (DLC) coated samples were used as plate. The DLC coatings were tested with three different surface finishes: as-deposited, polished with diamond and brushed. All DLC coated samples with and without mechanical finishing had lower corrosion activity under wear–corrosion conditions and also smaller wear tracks when compared with the CoCrMo alloy. The current density for the coated alloy was about two orders of magnitude lower on average (10^?5 vs. 10^?3 A cm^?2) and had a final coefficient of friction of only 50% of the uncoated metal (0.15 vs. 0.3). The brushed DLC showed the lowest current density and its behaviour was better than polished DLC and DLC as-deposited up to a potential of +0.93 V.     

Characterization of Microscale Wear in a Polysilicon-Based MEMS Device Using AFM and PEEM–NEXAFS Spectromicroscopy

Mechanisms of microscale wear in silicon-based microelectromechanical systems (MEMS) are elucidated by studying a polysilicon nanotractor, a device specifically designed to conduct friction and wear tests under controlled conditions. Photoelectron emission microscopy (PEEM) was combined with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and atomic force microscopy (AFM) to quantitatively probe chemical changes and structural modification, respectively, in the wear track of the nanotractor. The ability of PEEM–NEXAFS to spatially map chemical variations in the near-surface region of samples at high lateral spatial resolution is unparalleled and therefore ideally suited for this study. The results show that it is possible to detect microscopic chemical changes using PEEM–NEXAFS, specifically, oxidation at the sliding interface of a MEMS device. We observe that wear induces oxidation of the polysilicon at the immediate contact interface, and the spectra are consistent with those from amorphous SiO₂. The oxidation is correlated with gouging and debris build-up in the wear track, as measured by AFM and scanning electron microscopy (SEM).     

The Microstructure and Wear Characteristics of Cu–Fe Matrix Friction Material with Addition of SiC

The Cu–Fe matrix continuous braking friction materials using SiC as abrasive were fabricated by powder metallurgy technique, and the effect of content and size of SiC were investigated. The tribological properties of friction materials sliding against AISI 1045 steel ring were carried out on a block-on-ring tester at different loads and sliding speeds. The strengthening effect of nano-SiC (55 nm) was superior to that of micro-SiC (70 μm) of the tribological properties for friction materials. The friction coefficients of friction materials increased with increasing nano-SiC content. However, the wear rates decreased with increasing nano-SiC content and then increased when the content of nano-SiC particle exceeded 10 wt%. The specimen contained 10% nano-SiC had the best tribological properties at different testing conditions.