Wear Rate Values Research Articles

Evaluation of the influences of wax content on the tribological and mechanical performance of polytetrafluoroethylene-blended polyamide

In this study, the influences of wax content on the tribological and mechanical performance of nylon-polytetrafluoroethylene blend were evaluated. Wear tests were carried out using nylon 6 + 10% polytetrafluoroethylene + wax pins on AISI 316 L disc material. The wax percentages in the blend are 2%, 4% and 6% by weight. Tests were carried out at room temperature with applied loads of 50–100 N and sliding speeds of 0.4–1.6 m/s. These conditions are equvilent to a combined pressure and speed factor values of 0.141–5.664 MPa m/s. Although the results showed a slight drop in mechanical properties, the friction coefficients and the wear rates of nylon blend were significantly reduced by the addition of wax filler. The friction coefficient was reduced from 0.29 to 0.13 and the reduction in the wear rate was up to 73%. Furthermore, the results also showed that the change in pressure and speed factor values did not have a significant influence on the specific wear rate values. Finally, micrographs of the the worn surfaces showed the presence of transfer film, deformation and adhesive wear mechanisms.

Wear mechanism of CrN/NbN superlattice coating sliding against various counterbodies

Wear properties of CrN/NbN superlattice coating deposited on the WC-12Co substrate was investigated while using 100Cr6 steel, SiC and Al2O3 ball as counterbodies for friction pairs. The value of friction coefficient and wear rate was lowest at ~0.01 and 2.6×10−7mm3/Nm, respectively, when coating slides against Al2O3 ball. In contrast, friction coefficient and wear rate were increased while sliding with steel and SiC ball. The deviation in friction coefficient was described by mechanical and chemical properties of these balls. Hardness of Al2O3 and SiC ball was comparable but significant deviation in friction coefficient was observed. That is related to oxidation resistance of these balls which is high for Al2O3 compared to SiC ball as evident by Raman analysis of the wear track. However, hardness and oxidation resistance were low for steel ball which shows oxidational wear mechanism.

A parametric study of electrical discharge machining process parameters on machining of cast Al/B4C metal matrix nanocomposites

Aluminium metal matrix nanocomposite reinforced with 0.5 wt% B4C nanoparticles was prepared by a novel ultrasonic cavitation method. The metal matrix nanocomposite was studied microscopically to ascertain the uniform distribution and the degree of dispersion of the B4C nanoparticles within the aluminium metal matrix. Electrical discharge machining was employed to machine the metal matrix nanocomposite with copper electrode by adopting response surface methodology using face-centred central composite design technique. This method has been applied to investigate the influence of process parameters and their interactions. Furthermore, a mathematical model has been formulated in order to study the machining characteristics. It has been observed that pulse current was found to be the most important factor that affects the characteristics of all the three output parameters such as material removal rate, electrode wear rate and surface roughness. The pulse current and pulse on time have statistical significance on both electrode wear rate and surface roughness. Higher pulse off time lowers the electrode wear rate value, whereas both pulse current and pulse on time increase the electrode wear rate. Similarly, surface roughness also increases with increase in pulse current and pulse on time. From the analyses, the optimum combination of the parameters has been identified for the metal matrix nanocomposite. The results obtained from the confirmation experiments were compared with the experimental results and found that errors are in the acceptable range.

Wear Behaviour of Plasma Paste Boronized of AISI 8620 Steel with Borax and B2O3 Paste Mixtures

In the present study, AISI 8620 steel was plasma paste boronized (PPB) by using paste mixtures with different borax and B2O3 percentages. The PPB process was carried out in a DC plasma system at 973, 1023 and 1073 K for 5 h in a gas mixture with 70% H2–30% Ar under a constant pressure of 103 Pa (10 mbar). The thickness of boride layers ranged from 15.9 to 53.6 μm depending on the temperature and process time. The hardness of the borides formed on the surface of the steel substrate and unborided steel substrate were 1648–1924 HV0.05 and 226 HV0.05, respectively. X-ray diffraction analysis of the boride layers on the surface of the samples were obtained for FeB and Fe2B phases. The wear tests on the steel were performed by using a ball-on-disc test device at room temperature with applied load of 10 N and with a shear velocity of 0.2 m/s. Wear test results showed that the highest value of wear rate was observed in the unborided sample while the lowest wear rate was observed in the PPB samples with 30% borax + 70% B4C paste at 1073 K for 5 h.

Tribological performance of polymer composites used in electrical engineering applications

Sliding wear performance of 20% mica-filled polyamide 6 (PA6 + 20% mica) and 20% short glass fibre-reinforced polysulphone (PSU + 20 GFR) polymer composites used in electrical applications were investigated using a pin-on-disc wear test apparatus. Two different disc materials were used in this study. These are AISI 316 L stainless steel and 30% glass fibre-reinforced polyphenylenesulphide (PPS + 30%GFR) polymer composite. Wear test was carried out at 10, 20 and 30 N applied load values and 0·5 m/s sliding speed and at ambient temperature and humidity. Different combinations of rubbing surfaces were examined and friction coefficient and specific wear rate values were obtained and compared. For two material combinations used in this investigation, the coefficient of friction shows insignificant sensitivity to applied load values and large sensitivity to material combinations. For specific wear rate, PA6 + 20% mica composite has shown insensitivity to change in load, speed and materials combination while PSU + 20% glass fibre composite has shown high sensitivity to the change in load and material combinations. The friction coefficient of PA6 + 20% mica and PSU + 20 glass fibre rubbing against the AISI 4140 steel disc is between 0·35 and 0·40. In rubbing against PPS + 30% glass fibre their values were between 0·25 and 0·30. Specific wear rate for PA6 + 20% mica and PSU + 20% glass fibre composites are in the order of 10 − 13 to 10 − 14 m2/N. Finally, the wear mechanisms are a combination of adhesive and abrasive wear processes. In terms of application, especially in electrical systems, a substantial contribution was provided to extend switch life. Thus, besides robustness, this also ensured safety for the system and the users against undesirable situations.

Effect of electrical current on the tribological behavior of the Cu-WS2-G composites in air and vacuum

As the traditional graphite-based composites cannot meet the requirement of rapid developing modern industry, novel sliding electrical contact materials with high self-lubricating performance in multiple environments are eagerly required. Herein a copper-based composite with WS2 and graphite as solid lubricant are fabricated by powder metallurgy hot-pressed method. The friction and wear behaviors of the composites with and without current are investigated under the condition with sliding velocity of 10 m/s and normal load of 2.5 N/cm2 in both air and vacuum. Morphologies of the worn surfaces are observed by optical microscope and compositions of the lubricating films are analyzed by XPS. Surface profile curves and roughness of the worn surfaces are obtained by 2205 surface profiler. The results of wear tests show that the friction coefficient and wear volume loss of the composites with current are greater than that without current in both air and vacuum due to the adverse effects of electrical current which damaged the lubricating film partially and roughed the worn surfaces. XPS results demonstrate that the lubricating film formed in air is composed of oxides of Cu, WS2, elemental S and graphite, while the lubricating film formed in vacuum is composed of Cu, WS2 and graphite. Because of the synergetic lubricating action of oxides of Cu, WS2 and graphite, the composites show low friction coefficient and wear volume loss in air condition. Owing to the fact that graphite loses its lubricity which makes WS2 become the only lubricant, severe adhesive and abrasive wear occur and result in a high value of wear rate in vacuum condition. The formation of the lubricating film on the contact interface between the brush and ring is one of the factors which can greatly affect the wear performance of the brushes. The low contact voltage drop of the composites in vacuum condition is attributed to the high content of Cu in the surface film. This study fabricated a kind of new sliding electrical contact self-lubricating composite with dual-lubricant which can work well in both air and vacuum environments and provides a comprehensive analysis on the lubrication mechanisms of the composite.

UV or AO Irradiation Effects on the Tribological Properties of the Talc/GF/PI Composites

The development of polyimide (PI) composites, particularly for use in aerospace and tribological applications, has gained importance over the past decades. However, there have been scarce studies on the ultraviolet (UV) or atomic oxygen (AO) irradiation characteristics of the polyimide composites, the understanding of which may aid in expanding its application in space environment. To study the irradiated effects of UV and AO on the tribological behaviour of the PI composites, glass fibers (GF)-reinforced PI composites filled with Talc were irradiated by UV or AO in a ground based simulation system. Glass fibers (GF) reinforced PI composites filled with talc were fabricated by means of a hot press molding technique. The volume contents of the talc (10, 20, 30 %) were chosen to study the effects of filler content on the tribological behavior of the composites, while the proportion of the glass fiber was kept at 15 vol %. To contrast the different effects of UV and AO irradiation on the tribological properties of the composites, experiments without irradiation and after UV or AO irradiation were conducted. The specimens of the composites were irradiated with UV for a period of 4h, while AO irradiation chosen for 6h. Dynamic mechanical analysis (DMA) and thermal gravimetric analysis (TGA) measurements were conducted. The friction and wear behaviors of the composites, rotating against GCr15 steel balls, were investigated on a ball-on-disk test rig. at room temperature and at a rotating speed of 0.1256 m/s and a load of 1N. Experimental results revealed that the composites exhibited high modulus and wear rate values with increasing talc content, but low coefficients of friction (COF). After AO irradiation, the COF of the composites increased, but UV irradiation had no obvious effect on the tribological property of the composites. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) study of the composite surface showed that the chemical composition of the surface changed after UV irradiation because of the photooxidation and rough surface or even mountain-like structures were formed after AO erosion. The experiments indicated that the different space environments had an important effect on the tribological properties of the polymer composites. It is expected that this study may help expand the application of the polyimide composites in the field of space.

Poly(methyl methacrylate)/carbonated hydroxyapatite composite applied as coating on ultra high molecular weight polyethylene

Poly(methyl methacrylate)/carbonated hydroxyapatite (PMMA/CHA) composite in the form of solution for its application as coating on ultra high molecular weight polyethylene (UHMWPE) substrate was studied. The coating has been prepared by mixing the carbonated hydroxyapatite in situ with the poly(methyl methacrylate) polymerization. The carbonated hydroxyapatite (CHA) was prepared by a conventional method. Fourier transformed infrared spectroscopy (FTIR) technique was used to study the hydroxyapatite synthesis and composite coating. The characterization of coating thickness was performed by light microscopy whereas the surface morphology was characterized by scanning electron microscopy (SEM) finding out a rough coating with a thickness of 29μm. We have performed a pin-on-disk test to investigate the wear and friction behavior of the PMMA/CHA coating in dry conditions with loads ranging from 2 to 10N; the same methodology was applied to test the UHMWPE substrates for comparatives studies. We also estimate the wear rate values of PMMA/CHA coating at each load, which are found to be ranging from k=3.75×10−5 to 8.13×10−5mm3/Nm. Additionally, the adhesion strength value between PMMA/CHA coating and UHMWPE substrate was 0.89MPa.

Tribological characterization of TiCN coatings deposited by two crossed laser ablation plasma beams

The simultaneous laser ablation of two targets (graphite and titanium) in an Ar-N2 gas mixture was carried out to deposit thin films of the ternary compound TiCN at room temperature. The base conditions used to produce the TiN without carbon were taken from our previous studies. The experimental conditions for the ablation of the carbon target were varied so that the carbon content in the films could be changed depending on the carbon ion energy. The control of the experimental conditions was carried out using a Langmuir planar probe which permitted the determination of the mean kinetic ion energy. The maximum hardness value of 35 GPa, was obtained with a carbon ion energy of about 250 eV, which corresponds to a film with 5 at% carbon content. In order to perform tribological and scratch tests, two types of substrate were used: nitrided AISI 316 stainless steel and AISI 316 stainless steel previously coated with a thin titanium layer (∼50 nm). Values of the wear rate in the range of 1.39×10−6 to 7.45×10−5 mm3 N−1 m−1, friction coefficient from 0.21 to 0.28 and adhesion from scratch test measurements up to 80 N for final critical load, were obtained.

The effect of the addition of aramid fibers on tribological properties of the polyimide after ultraviolet or atomic oxygen irradiation

The aramid fibers reinforced polyimide composites were fabricated by means of a hot-press molding technique. The mechanical and tribological behaviors of the reinforced composites were studied. The friction and wear properties of the composites, rotating against a GCr15 steel ball, were investigated on a ball-on-disc test rig. To contrast the effects of the ultraviolet radiation and atomic oxygen, experiments without radiation or after ultraviolet or atomic oxygen radiation were conducted. Experimental results revealed that 20% aramid fiber reinforced polyimide exhibited higher modulus. However, the coefficient of friction decreased with the increase of the aramid fiber content. The composites had a lower wear rate value after atomic oxygen radiation. Microstructure of worn surface of the tested composites was inspected by scanning electron microscopy, and X-ray photoelectron spectroscopy study of the composite surface showed that the chemical composition of the surface changed after ultraviolet or atomic oxygen radiation because of the oxidation.

Polyamide 6/Polyurethane/Graphite Composites Prepared by Anionic Polymerization Process. II. Friction and Wear

Polyamide 6-polyurethane (PA6-PU) block copolymers filled with graphite particles were prepared by anionic polymerization process. The friction and wear experiments were conducted using a UMT-3 machine with the chromium steel ball sliding on surface of the composites at high sliding speeds of 500rpm, 1000rpm and 1500rpm and loads of 78.5N and 157N. With adding of graphite, coefficient of friction and wear rate values of the composites decreased firstly, and then increased. And the influence of the applied load and sliding speed on tribological properties of the composites was explored in this study. The results showed coefficient of friction and wear rate values increased with the increasing of load. Coefficient of friction decreased and wear rate values increased with increasing of sliding speed. Microstructure of wear surface of the tested composites was inspected by scanning electronic microscope(SEM) and wear mechanism of the composites was studied.

Reciprocal dry sliding wear behaviour of B4Cp reinforced aluminium alloy matrix composites

In the present work, AlSi9Cu3Mg alloy matrix composites reinforced with 15 and 19vol% B4Cp were produced by squeeze casting route at 850°C under low vacuum. Titanium-containing flux (K2TiF6) was used to promote the wetting between B4C and liquid aluminium metal. It was found, from the microstructural observations, that the wetting improved by the formation of a thin Ti-rich reaction layer. In order to investigate the wear properties, the samples were subjected to reciprocating wear tests against AISI 4140 pin under dry sliding conditions. The effect of B4C volume fraction, sliding velocity, applied load and sliding distance on reciprocal dry wear behaviour of composites was studied using general full factorial experimental design. The effects of factors and interactions on the coefficient of friction (COF) and the wear rate values of both composite specimens and counter materials were studied. Worn surfaces and wear debris were characterised using field emission gun scanning electron microscope (FEG-SEM), Energy Dispersive X-Ray Spectroscopy (EDS), optical microscope (OM) and X-Ray diffraction (XRD). From microstructural investigations, wear mechanism was suggested as a combination of adhesive, abrasive, and delamination wear.

Effects of glass-to-rubber transition of thermosetting resin matrix on the friction and wear properties of friction materials

The present study is to examine the effects of glass-to-rubber transition of resin matrix on the friction and wear characteristics of friction materials, in relation to different types of thermosetting resins. Dynamic mechanical thermal analysis and friction test results revealed that glass-to-rubber transition of thermosetting resins influenced significantly the friction and wear behavior of the composite materials. There was a significant increasing tendency in friction coefficient and wear rate values for all composites when braking temperatures increased to 200 or 250°C, accompanying the resin matrix converted from glassy state to rubbery state.

Tax policy developments, donor inflows and economic growth in Malawi

In this investigation the friction and wear performance of GUR 1020 medical grade ultra-high molecular weight polyethylene (UHMWPE) polymer under dry sliding, distilled water and egg albumen lubrication conditions were evaluated. The sliding experiments were carried out on a pin-on-disc tribometer. The contact configuration used was a polymer pin on a rotating AISI 304L stainless steel disc. Wear tests were carried out for 30 min duration at room temperature with 50, 100 and 150 N applied load values and at 0.50, 1.0 and 2.0 m/s sliding speeds condition. The results show that the coefficient of friction for GUR 1020 medical grade UHMWPE polymer is more significantly influenced by applied load and sliding speed values under dry sliding condition rather than lubricant media condition. Furthermore, the coefficient of friction and specific wear rate increases with the increase in applied load and speed values. This increase is much pronounced under dry sliding condition. Moreover, for the range of load and speed values of this study the specific wear rate using egg albumen lubricant registered lower values than that of the distilled water lubricant and the dry conditions. Finally, the specific wear rate values for GUR 1020 medical grade UHMWPE polymer under dry, water lubricant and egg albumen lubricant conditions are at the levels of 8x10-14, 1.4x10-14 and 0.5x10-14m2/N respectively. Key words: Medical Grade UHMWPE, tribology, distilled water, wear.

Influence of the hard segment content on the mechanical and tribological properties of the polyurethane modified by hydroxyl‐terminated polydimethylsiloxane under different lubricated conditions

AbstractTwo kinds of polyurethane (PU) composites with different hard segment content modified by a high molecular weight hydroxyl‐terminated polydimethylsiloxane (HTPDMS) were prepared. The effect of the hard segment content on the mechanical and tribological properties of the PU composites was studied. Tensile strength of the PU composites increased with the increasing of the hard segment content. The friction and wear experiments were tested on a MRH‐3 model ring‐on‐block test rig at different sliding speeds and loads under different lubricated conditions. Experimental results revealed that the coefficient of friction (COF) and the wear rate value of the PU composites decreased with increasing hard segment content and the COF of the PU composites under dry friction was higher than that under water and sea water lubrication. Scanning electron microscopy (SEM) investigations showed that the worn surfaces of the PU under water and sea water lubrication were smoother than that under dry friction. Besides, the wear rate value of the PU composites under water and sea water lubrication was smaller than that under dry friction. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Production and properties of Cu/Cr2O3 nano-composites

Cu/Cr2O3 nano-composites have high potential for structural and electrical applications in which enhanced mechanical characteristics are required. In this research, nano-composite specimens containing different amounts of Cr2O3, with Cr content of 1–3wt.%, were produced by in-situ oxidation of Cu–Cr alloyed powders during sintering. X-ray diffraction test was carried out to analyze the progress of mechanical alloying and detection of probable Cr2O3 particles formed due to internal oxidation during sintering. The morphology of milled powders was examined using scanning electron microscopy (SEM).Physical and mechanical property results of nano-composite specimens indicate the density, specific electrical resistivity, hardness and wear rate values alternation with amount of Cr2O3 in Cu matrix, which in turn is related to specimen Cr content.

Preparation and tribological properties of chitosan/hydroxyapatite composite coatings applied on ultra high molecular weight polyethylene substrate

We prepared a chitosan/hydroxyapatite composite as coating on ultra–high-molecular-weight polyethylene substrates. The hydroxyapatite was prepared by a precipitation method obtaining particles with nanometer sizes with needle and spherical morphologies. The coating was prepared by a mixture of hydroxyapatite and lower molecular weight chitosan. Fourier transformed infrared spectroscopy technique was used to study the hydroxyapatite synthesis and composite coating. The chitosan/hydroxyapatite coating has been compared with a pure chitosan coating on ultra–high-molecular-weight polyethylene substrate in order to study the influence of hydroxyapatite incorporation. The characterization of coating thickness was performed by light microscopy, whereas the surface morphology was characterized by scanning electron microscopy. A ball-on-disc tribometer, employing a 6-mm diameter tungsten carbide ball, was run as a test method to investigate tribological behaviors of the chitosan/hydroxyapatite and chitosan coatings in dry conditions. It was found that the friction coefficients of the chitosan/hydroxyapatite coating have lower values than chitosan coating. The chitosan/hydroxyapatite coating exhibited lower wear rate values than the chitosan coating. The incorporation of hydroxyapatite nanoparticles into chitosan increased the coating thickness from 20 µm to 37 µm. We have found a composite hardness of 9.1 HV and 6.4 HV for the chitosan and chitosan/hydroxyapatite coating, respectively.

Tribological behaviour of laser coated thermoplastic polyurethane sliders used in lift installations

This paper presents the effect of a polyamide coating on the tribological behaviour of thermoplastic polyurethane guide shoes used in lift installations. Polyamide coatings with a good bonding and low porosity were obtained by laser deposition. The tribological performance of the coatings has been evaluated during labscale testing, accelerated prototype testing and prototype testing under real conditions. The energy consumption of the lift installation and the wear rate in dry and lubricated conditions was evaluated. It was shown that in real working conditions, it is possible to obtain energy consumption and wear rate values under dry conditions using polyamide laser deposited sliders that are similar to the current solution using untreated TPU sliders with full lubrication.

Friction coefficient and wear rate of polymer and composite materials at different sliding speeds

In the present study, variation of friction coefficient and wear rate with sliding speed is investigated experimentally when stainless steel 304 (SS 304) pin slides on different types of composite and polymer materials such as cloth reinforced ebonite (commercially known as gear fibre), glass fibre reinforced plastic (glass fibre), nylon and polytetrafluoroethylene (PTFE). To do so, a pin on disc apparatus is designed and fabricated. Experiments are carried out at sliding speed 1, 2, 3 m/s, normal load 15 N and relative humidity 70%. In general, friction coefficient and wear rate increase with the increase in sliding speed for all the tested materials. At identical conditions, the values of friction coefficient of nylon and wear rate of PTFE are highest among the tested materials. On the other hand, the lowest values of friction coefficient and wear rate are different for different materials depending on the sliding speed.

The Effect of Gas Flow Rate on the Thin Film Deposition Rate on Carbon Steel Using Thermal CVD

Solid thin films have been deposited on carbon steel substrates in a chemical vapor deposition (CVD) reactor where natural gas, mostly methane (CH4), was used as a precursor gas. The effect of gas flow rate on the thin film deposition rate has been investigated experimentally. The effect of gap between activation heater and substrate on the deposition rate has also been observed. To do so, a hot filament thermal chemical vapor deposition unit is used. The flow rate of natural gas varies from 0.5 to 2 l/min at normal temperature and pressure (NTP) and the gap between activation heater and substrate varies from 4 to 6.5 mm. Results show that the deposition rate on carbon steel increases with the increase of gas flow rate. It is also seen that deposition rate increases with the decrease of gap between activation heater and substrate within the observed range. These results are analyzed by dimensional analysis to correlate the deposition rate with gas flow rate, surface roughness and film thickness. In addition, friction coefficient and wear rate of carbon steel sliding against SS 304 under different normal loads are also investigated before and after deposition. The obtained results reveal that in general, the values of friction coefficient and wear rate are lower after deposition than that of before deposition.