Friction and Wear Performance of Carbon Nanotubes Reinforced Co-Based Atmospheric Plasma-Sprayed Coatings

Fabrication and characterization of TiB2-TiC-Co wear-resistant coatings on AZ91D magnesium alloy

Wear rates (μgm/s) versus rotor speed for carbon samples sliding against smooth and wavy copper rotors (250 μm thick copper sheets were attached to smooth and wavy steel and polycarbonate backings) were identical at some speeds, but at other speeds wear rates for the wavy rotors were almost half those of the smooth rotors. Slider vibrations (periodic, with period set by rotation) perpendicular to the sliding surface were measured and Fourier analyzed. Comparison of vibration spectral amplitudes to spectral amplitudes derived from surface profiles identified vibration modes dynamically enhanced by surface waviness on the wavy rotor. At speeds where wear rates on the wavy rotor were most reduced, amplitudes of certain modes in the vibration spectrum were most enhanced. For all these cases, the product of mode number times speed was nearly constant, suggesting resonance. Contact forces and contact voltage drop (due to a mA current flowing from slider to rotor) were measured and plotted versus time during all experiments. Friction coefficients rapidly varied between 0.1 and 0.4, but averaged 0.2. Traces of friction coefficient versus time for both wavy and smooth rotors were similar, even when wear rates plunged on the wavy rotor. There were no large jumps in the contact voltage drop data, suggesting that the slider never disconnected from any of the rotors. Photoelastic visualizations (Bryant and Lin, 1993) of slider-rotor interfaces revealed concentrated contact on the smooth rotors, but none on the wavy rotors. The absence (induced by vibration) of concentrated contact may have caused differences in wear rates. Appreciable reductions (up to 50 percent) in wear rate are possible by adding small surface waves to a rotor that induce micro-vibrations of the slider-spring-rotor contact system. The effect appears most pronounced at resonance.

Tribological characteristic of atmospheric plasma sprayed NiAl coatings with addition of nanostructured MoO3/Bi2O3 binary oxides as high temperature lubricant

Composite coatings using mixed alloy matrices reinforced with carbon-based solid lubricants as feedstock materials were prepared by atmospheric plasma spraying. The aim of the present study was to investigate the tribological characteristics of such coatings exploring potential benefits of CNTs as nano-additive to reduce friction and wear, improving lubrication conditions during operation in tribosystems, such as piston ring – cylinder liner systems. The chemical composition of feedstock materials and the thermal spray parameters during coatings deposition are correlated to friction coefficient and wear rate using pin-on-disk measurements. The developed coatings hybrid behaviour is studied. Co-based cermet as well as metal alloy anti-wear performance along with the promoted lubrication conditions during operation is revealed. The dependence of the developed coatings quality and performance on the characteristics of the feedstock powder is thoroughly discussed.

Tribological performance of thermally sprayed cermet coatings containing solid lubricants

Ultrahigh molecular weight polyethylene (UHMWPE) modified polyester-cotton composites were developed and studied for friction and sliding wear behaviour at different applied loads and UHMWPE concentrations. Sliding wear tests were conducted by using pin-on-disc apparatus. Composites in the form of the pin were tested against EN-24 steel disc. The specific wear rate of polyester reduced on reinforcement of cotton and on addition of UHMWPE. The coefficient of friction of polyester resin increased on cotton reinforcement and reduced significantly on addition of UHMWPE in cotton polyester composite. The composites exhibited reductions in specific wear rate against the normal load in the specimens those containing 7.41 or higher volume percent of UHMWPE. The significant reduction in wear rate of UHMWPE modified polyester-cotton composite has been discussed with the help of SEM observations of worn surfaces and coefficient of friction. The addition of 14.19 vol.% UHMWPE in polyester resin brought down the value of μ to nearly half to that of polyester resin and 1/3rd of cotton polyester composite.

Optimization of tribological characteristics in cryo-treated plastic/graphene oxide modified CFRP via ANN-based predictive modeling for aerospace applications

Tribological performance of Al2O3–SiO2/PAG composite nanolubricants for application in air-conditioning compressor

This current study deals with the tribological property of piston rings of cast iron coated with (CrC)X+(Mo+Fe)+NiCrX alloy with plasma spray coatings. The sample coating was prepared in increasing CrC composition from 10% to 50% in the interval of 10% by keeping Mo+Fe composition constant for each test sample. The coefficient of friction and wear rate of the deposited coating was studied with constant load and varying CrC%. With the increase of CrC%, the coefficient of friction decreases at load 50 N, 60 N, and 70 N. The wear rate also decreased with increasing CrC% at each load. For the investigation of Tribological property of coating, Pin-on-Disc tribometer was used. Coating morphology was characterised by SEM, EDS & XRD. It was found that a coating with 30% CrC had a drastic reduction in specific wear rate.

Paper-based friction materials containing four different graphite particle sizes were prepared using the wet paper-making process. The effects of graphite particle size on friction performance such as friction torque curves, dynamic friction coefficient, static friction coefficient and wear rate were studied by using an inertia friction tester. Meanwhile, the sensitivity of friction coefficient to braking pressure and rotating speed was also investigated. Worn surfaces of samples were analyzed by using scanning electron microscope. The results show that with graph- ite particle size decreasing, braking time increases and torque curves become more stable, while friction coefficient and wear rate decrease. The dynamic friction coefficient declines as braking pressure and rotating speed increase. Samples with proper particle size exhibit more stable friction coefficient in the continuous braking process. Lubri- cating film is formed to lower wear rate in the worn surface as the graphite particles size decreases.

doi:10.3329/jme.v37i0.826Â

Tribological behaviour of laser textured Ti3AlV 2.5V alloy under simulated body fluid

Investigation of agricultural waste and ZrB2 nanoparticles with reinforcement in aluminum alloy matrix

Friction film has an important influence on the tribological properties of C/C-SiC composites, which is closely related to its composition. In this study, exogenous third bodies in the form of powders of graphite, SiC, SiO2 and a mix of graphite, SiC, and SiO2 powders were added to the friction surface of the C/C-SiC composites under a constant speed. By comparing the change in the coefficient of friction (COF) and the wear rate of the C/C-SiC composites before and after addition of exogenous third bodies, the influence of each component on the tribological properties of the C/C-SiC composites and its mechanism were proposed. The graphite third body had a solid lubrication effect, with the average COF bellowing 0.344 and a 24% reduction in wear rate after addition. With the addition of SiC and SiO2 third body, the average COF was greater than 0.550 and 0.441, and the wear rate increased by 128.4% and 25.1%, respectively. SiO2 with a stronger pinning effect, promoted the formation of friction film and ultimately resulted in a smaller increase in average COF and wear rate. With the addition of the multi-component third bodies, the first platform containing SiO2 and SiC was formed, which resulted in a reduction in sharpness and being prone to refinement. Meanwhile, the large first platform accelerates the formation of friction film. Furthermore, while the first platform exceeded to the bearing capacity, SiC and SiO2 started to decompose, and redistributed in the friction film, which cause the instantaneous COF tended to stable with a low wear rate.

The production of self-lubricating composites containing second phase particles is one of the most promising choices for controlling friction and wear in energy efficient modern systems. Initially, we present a new microstructural model/processing route able to produce a homogeneous dispersion of in situ generated, discrete, solid lubricant particles in the volume of sintered composites. The high mechanical and tribological performances of the composites are a result of the combination of matrix mechanical properties and structural parameters, such as the degree of continuity of the metallic matrix, the nature, the amount, and the lubricant particle size and shape which determine the mean free path between solid lubricant particles and the active area covered by each lubricant particles. This new route was achieved by in situ formation of graphite nodules due to the dissociation of a precursor (SiC particles) mixed with metallic matrix powders during the feedstock preparation. Thermal debinding and sintering were performed in a single thermal cycle using a plasma-assisted debinding and sintering (PADS) process. Nodules of graphite (size ≤20 μm) presenting a nanostructured stacking of graphite foils with thickness of a few nanometers were obtained. Micro-Raman spectroscopy indicated that the graphite nodules are composed of a so-called turbostratic 2D graphite which has highly misaligned graphene planes separated by large interlamellae distance. The large interplanar distance and misalignment among the graphene foils has been confirmed by transmission electron microscopy and is, probably, the origin of the remarkably low dry friction coefficient (0.06). The effects of precursor content (0 to 5 wt% SiC) and of sintering temperature (1100 °C, 1150 °C and 1200 °C) on tribolayer durability and average friction coefficient in the lubricious regime (μ < 0.2) are presented and discussed. In addition, the effect of the metallic matrix composition (Fe-C; Fe-C-Ni; Fe-C-Ni-Mo) is presented. Friction coefficient decreased and durability drastically increased with the amount of graphite formed during sintering, whereas friction coefficient was little affected by sintering temperature. However, the durability of the tribolayer was greatly increased when lower sintering temperatures were used. The addition of alloying elements considerably reduced wear rate and friction of specimens and counter-bodies. Friction coefficient values as low as 0.04 were obtained for the Fe-C-Ni-Mo composites. We also analyzed the effect of precursor content and of sintering temperature on the tribological behavior under constant normal load sliding tests. Again, the presence of graphite nodules significantly reduced the friction coefficients and wear rates, whereas the sintering temperature hardly affected these parameters. The results were compared with those caused by other forms of graphite (nodules in nodular cast iron and powder graphite) and were discussed in terms of the crystalline structure of the analyzed graphite using micro-Raman spectroscopy. Chemical analyses of the wear scars using scanning electron microscopy (SEM – EDX) and Auger electron spectroscopy (AES) showed a tribolayer that was composed predominantly of carbon and oxygen. This tribolayer is removed and restored during sliding and is continuously replenished with graphite. Finally, the strong effect of surface finishing is presented and discussed.