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A ball-on-plate wear test was employed to investigate the effectiveness of graphene (GP) nanoparticles dispersed in a synthetic-oil-based lubricant in reducing wear. The effect by area ratio of elliptically shaped dimple textures and elevated temperatures were also explored. Pure PAO4 based oil and a mixture of this oil with 0.01 wt% GP were compared as lubricants. At pit area ratio of 5%, GP-base oil effectively reduced friction and wear, especially at 60 and 100°C. Under pure PAO4 oil lubrication, the untextured surfaces gained low friction coefficients (COFs) and wear rates under 60 and 100°C. With increasing laser—texture area ratio, the COF and wear rate decreased at 25 and 150°C but increased at 60 and 100°C. Under the GP-based oil lubrication, the textured surface with 5% area ratio achieved the lowest COF among those of the area ratios tested at all test temperatures. Meanwhile, the textured surface with 20% area ratio obtained the highest COF among those of the area ratios. With the joint action of GP and texture, the textured surface with 10% area ratio exhibited the best anti-wear performance among all of the textured surfaces at all test temperatures. [ABSTRACT FROM AUTHOR]

Dual-rotary fretting (DRF) is a complex fretting wear mode combining torsional fretting with rotational fretting. Two different typical friction-induced convex topographies (Type I and Type II) in contact area were showed, which are under the control of torsional and rotational fretting components, respectively. To investigate their evolution characteristics and formation mechanism, the convex topographies were analyzed by SEM, XPS, a nano-hardness tester and surface profilometry, etc. The results show that the convex topographies significantly depended on the test parameters and environmental conditions. The initiation and propagation of fretting fatigue cracks were found related with the convex topography under the fretting wear. [ABSTRACT FROM AUTHOR]

Abstract: A torsional wear and friction simulator with a ball on flat polymer was developed to analyze the tribological behavior of hip joints. Wear tests of polymethyl methacrylate (PMMA) against GCr15 (AISI 52100) steel and PMMA molecules (both with diameters of 40mm) were conducted. Based on the analysis of frictional kinetics behaviors, and observations of three-dimensional (3D) profiles and SEM morphologies, the damage characteristics of PMMA were discussed in detail. With the increases of angular displacement amplitude, three types of torque/angular displacement amplitude (T–θ) curves (i.e., linear, parallelogram, and elliptical loops) were observed during the process of torsional fretting wear. In each of these loops, PMMA ran in a partial slip regime (PSR), mixed slip regime (MSR), and gross slip regime (SR), respectively. Compared to the PMMA/PMMA (P/P) counter-pairs, the boundary of the fretting regime of PMMA/GCr15 (P/G) counter-pairs shifted toward the direction of lower angular displacement amplitudes. The wear mechanisms of P/G counter-pairs included fatigue wear, oxidative wear, and adhesive wear; however, only abrasive wear was found for the P/P counter-pairs. [ABSTRACT FROM AUTHOR]

Abstract: Tests of LZ50 carbon steel against 52100 steel balls in ambient air (RH=60%) and in nitrogen were carried out on a controlled-atmosphere torsional fretting tribometer. The morphologies of worn scars were observed by a scanning electron microscopy (SEM), and the tribochemical behaviors of the contact zones were analyzed by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX). Curves of friction torques vs. torsional angular displacement amplitude (T–θ curves) were used to describe the kinetic behaviors of torsional fretting. According to the T–θ curves and damage morphologies, three fretting running regimes (partial slip regime, mixed regime, and gross slip regime) can be identified. Results indicated that the mixed and gross slip regimes shifted to higher angular displacement amplitudes in nitrogen, comparably to that in air. With an increase in the number of cycles, the curves of the friction torques can be divided into three stages: initial stage, climbing stage, and steady stage. The friction torque in nitrogen was much higher than in air, and the wear damage in nitrogen was also severer than that in air. The oxidative debris formed in air served as a lubricant and alleviated fretting wear. The torsional fretting wear mechanisms in the air were oxidative wear, delamination, and abrasive wear; however, the wear mechanisms in nitrogen were delamination and abrasive wear accompanied by a strong plastic flow due to the effect of tribo-oxidation being restrained. [Copyright &y& Elsevier]

Cam mechanism is widely applied in industry because it can help achieve various complex motions of the follower via the cam contour design. However, its performance is significantly affected by the wear condition. This study proposes a load distribution measurement instrument to assist the study on friction and wear regularities of oscillating follower cam mechanisms through obtaining the normal pressure (F) and friction force (Ff) distributions along the cam profile. In the instrument, F and Ff are automatically calculated via a MATLAB program based on the geometry and the measured rotary resistance torque and rotary angle of the cam. The latter two parameters are obtained through a static torque sensor and a rotary encoder built in servo motor in real time, respectively. An experimental test was conducted and the cam morphology after service was observed using scanning electron microscopy. Results show that the wear condition of the cam is significantly related to the corresponding F and Ff. Complex load parameters of oscillating follower cam mechanisms can be provided by this instrument, which is crucial in understanding the friction and wear behaviors of cams and finding the vulnerable position. [ABSTRACT FROM AUTHOR]

Sliding electrical contact exists in various electrical equipment. However, its performance is significantly affected by the sliding condition such as the load, electricity, and the surface state of friction pairs. In this study, a novel instrument is designed and constructed for high-frequency microforce electrical sliding friction testing. The new instrument provides a unique experimental platform that enables high-frequency reciprocating friction and microforce loading, and it has an innovative data collection system that includes a cantilever beam structure to measure the microforce. In this instrument, parameters (positive force, friction, displacement, and voltage of frictional pair) are obtained and monitored in real time. The steel sheet and nickel-plated steel wire were used as materials to conduct an experiment, and the steel sheet morphology after the experiment was observed using a light microscope. Results show that the voltage and positive load significantly influence the friction coefficient and friction wear, which is crucial in understanding friction and wear behaviors. [ABSTRACT FROM AUTHOR]

The tribologically transformed structure of the white etching layer (WEL) always appears with some cracks accompanying microstructural evolution under friction. This work investigated crack behavior with the existence of WEL on pearlitic steel after rolling-sliding friction tests. The WEL microstructure was characterized using scanning electron microscopy, nano-indentation, focused ion beam, and transmission electron microscopy. According optical images, the WEL zone could be divided into white and yellowish zones; cracks existed at the boundary separating these two zones. The deformation degree of the cementite structure caused color differences in optical images and inhomogeneous chemical composition distributions in the same WEL zone. For cracks initiated and propagated at the WEL colony boundary, crack holes remained unconnected along the plastic deformation line. • Crack initiation and propagation in white etching layer (WEL) are investigated. • Under rolling–sliding friction, WEL of cementite appears on pearlitic steel. • WEL contains two "phases" of dissolved versus nanoscale cementite. • Cementite form determines color of WEL under optical microscopy. [ABSTRACT FROM AUTHOR]

A multiple-layer graphene was prepared on steel surface to reduce friction and wear. A graphene-containing ethanol solution was dripped on the steel surface, and several layers of graphene flakes were deposited on the surface after ethanol evaporated. Tribological performance of graphene-contained surface (GCS) was induced by reciprocating ball against plate contact in different RH (0% (dry nitrogen), 30%, 60%, and 90%). Morphology and wear scar were analyzed by OM, 2D profile, SEM, Raman spectroscopy, and XPS. Results show that GCS can substantially reduce the wear and coefficient of friction (COF) in 60% relative humidity (RH). Low COF occurs due to graphene layer providing a small shear stress on the friction interface. Meanwhile, conditions of high RH and textured surface could make the low COF persist for a longer time. High moisture content can stabilize and protect the graphene C-network from damage due to water dissociative chemisorption with carbon dangling bonds, and the textured surface was attributed to release graphene layer stored in the dimple. [ABSTRACT FROM AUTHOR]

The Ti/TiN multi-layer film was prepared on the depleted uranium (DU) substrate by cathodic arc ion plating equipment. The character of multi-layer film was studied by SEM, XRD and AES, revealed that the surface was composed of small compact particle and the cross-section had a multi-layer structure. The fretting wear performance under different frequencies was performed by a MFT-6000 machine with a ball-on-plate configuration. The wear morphology was analyzed by white light interferometer, OM and SEM with an EDX. The result shows the Ti/TiN multi-layer film could greatly improve the fretting wear performance compared to the DU substrate. The fretting wear running and damaged behavior are strongly dependent on the film and test frequency. The fretting region of DU substrate and Ti/TiN multi-layer under low test frequency is gross slip. With the increase of test frequency, the fretting region of Ti/TiN multi-layer change from gross slip to mixed fretting, then to partial slip. [ABSTRACT FROM AUTHOR]