Counterface Disc Research Articles

Tribological characterisation of 6061 aluminium alloy reinforced with submicron alumina particle under solid lubrication at room temperature

The tribological behaviour of aluminium (Al) 6061 alloy reinforced with 20% submicron (0.7 µm) alumina (Al2O3) particles has been investigated at room temperature under solid lubricated conditions of graphite and molybdenum disulphide (MoS2). Pin-on-disc wear tests were carried out at various stresses, with the composite pin sliding against an AISI 4041 steel counterface disc. At room temperature and under low and moderate loads, graphite proved to be effective in reducing wear rate by a factor of 6 and coefficient of friction from 0.50 ± 0.01 to 0.20 ± 0.01. Under MoS2 lubrication, the wear rate and coefficient of friction were significantly reduced at all tested loads (5 to 110 N), indicating that MoS2 is an effective lubricant in reducing wear rate by a factor of 40 and coefficient of friction from 0.50 ± 0.01 to 0.06 ± 0.01 for the composite at all loads.

Tribological Behaviour of MoS2 and Graphite Reinforced Aluminium Matrix Composites

Tribological behaviour of MoS2 and graphite reinforced aluminium matrix composites were investigated in this research. In the current scenario, applications in which either metal based alloys or composites are used, requires lubrication to avoid friction. In such cases, self-lubricating materials based aluminium composites can be fabricated to exhibit better tribological properties. These materials can be fabricated by reinforcing self-lubricating materials like graphite (Gr), molybdenum disulphide (MoS2) and so on within the aluminium matrix. In this tribological study, two different solid lubricants (Gr and MoS2) were taken at equal proportions to fabricate aluminium matrix composites individually through stir casting method. Pin on Disc apparatus was utilized to record the rate of wear of the composite specimen by considering the process parameters like sliding distance, load and counter-face disc hardness. Experiments were designed by Taguchi’s approach and analyzed by means of response values and analysis of variance (ANOVA). Results depicted that graphite based aluminium alloy composites possessed better wear resistance than MoS2 reinforced aluminium alloy composites.

Effect of vacuum annealing treatment on dry sliding wear behavior of TiC/Ti-1100-0.5Nb composite under different operating temperatures

Dry sliding wear tests at 25 °C and 500 °C were performed for TiC/Ti-1100-0.5Nb composites on the quenched and tempered GCr15 steel counter-face disks in this work. Meanwhile, the TiC/Ti-1100-0.5Nb composites were treated at the annealing temperature of 1050 °C, 1100 °C, 1150 °C, respectively. Results demonstrate that the TiC quantity and α-laths spacing increase with the increase of annealing temperature. The composites have better high temperature wear properties. The composites under 1100 °C vacuum annealing treatment possess the best wear performance, which benefited from the coordination of granular TiC particles dispersion strengthening and the solid solution strengthening of carbon atoms. The wear mechanism of the composite changes from the adhesive and abrasive wears at room temperature to oxidative mild wear at 500 °C. The formation of nano Fe2O3 and TiO2 oxide particles on worn surface plays a protective role during the wear process, which improved the high temperature wear properties.

Effect of Expanded Graphite on the Tribological Behavior of Tin–Bronze Fiber Brushes Sliding against Brass

Fiber brushes with expanded graphite (EG) as a lubricant were successfully prepared. Compression properties of brushes filled with unbent fibers and bent fibers with different packing fractions were compared. Moreover, the friction and wear behaviors of the brushes with the same fiber packing fractions (17.5 vol%) but different EG volume contents were investigated. The effect of EG content on the tribological behavior of the fiber brush was analyzed according to the microstructure, debris, and worn surface of the brush and counterface disc. Results showed that both the elastic constant and compression strength of the brushes filled with bent fibers increased with an increase in packing fraction. Brushes filled with 17.5 vol% bent fibers had similar compression strength (2.69 MPa) but a lower elastic constant (150 N/mm) compared to the brush filled with 17.5 vol% unbent fibers (2.62 MPa and 425 N/mm). The friction coefficients and wear rates of the brushes decreased from 1.02 and 1.6 × 10−5 mm3/Nm to 0.25 and 0.28 × 10−5 mm3/Nm as the EG increased to a critical value (23.7 vol%). The worn surface and wear debris demonstrate that the wear mechanism of tin–bronze fiber brushes with EG sliding against brass discs transforms from adhesive wear to abrasive wear due to the formation of an EG lubricating film.

TRIBOLOGICAL CHARACTERISTICS OF ELECTROLESS Ni–B–Mo COATINGS AT DIFFERENT OPERATING TEMPERATURES

Electroless nickel coatings containing Mo possess higher thermal stability in comparison with the binary alloy variants. In a quest to achieve enhanced thermal stability of Ni–B coatings, Mo is incorporated to obtain a ternary Ni–B–Mo coating. The coatings are deposited on AISI 1040 steel and characterized using energy dispersive X-ray (EDX) analysis, X-ray diffraction method and scanning electron microscope. The coatings are observed to lie in the mid-B range with amorphous structure in as-deposited condition. On heat treatment, precipitation of crystalline Ni and its borides is observed. The typical cauliflower-like surface morphology of the deposits could be observed in scanning electron micrographs. Microhardness measurements reveal the enhanced thermal stability of Ni–B–Mo coatings. Tribological behavior of Ni–B–Mo coatings at room and elevated temperatures (100∘C, 300∘C and 500∘C) is observed on a pin-on-disc type tribo-tester by varying the applied normal load (10–50[Formula: see text]N) and rotational speed of the counterface disc (60–100[Formula: see text]rpm). The purpose of the present work is to observe the tribological behavior and associated tribo-mechanisms at different temperatures under dry sliding condition. In general, the wear of the coatings increases with an increase in applied normal load and speed at room temperature, 100∘C and 300∘C. At 500∘C, the wear increases with load but with speed it first increases up to 80[Formula: see text]rpm and then decreases. The COF does not show a similar behavior like the wear with varying load and speed at different temperatures. Instead, it is controlled by the accompanying wear mechanisms, formation of oxide debris and oxide layers of Ni and Mo. The worn surface of the coatings is examined using scanning electron microscope and EDX analysis. Back scattered images of wear tracks of Ni–B–Mo coatings at the highest levels of load (50[Formula: see text]N) and speed (100[Formula: see text]rpm) at different temperatures further reveal the oxide formation and tribochemical reactions.

Wear Behavior and Mechanism of CoCrMo Alloy Fabricated by Powder Metallurgy Route

This research is devoted to study the wear behavior and mechanism of CoCrMo alloy due to the uitilization of the alloy in application mainly exposed to wear. Samples fabricated by powder metallurgy route compacted under (1000MPa) and sintered at (1200ºC) in the argon atmosphere. Wear test type pin-on-disc was performed under dry sliding condition over steel counterface disc. For the first group of wear tests four vertically loads (10,15,20 and 25) N were applied at fixed sliding speed (1.476) m.s−1, time (15 min) and sliding distance (1329m). The second group of tests were conducted at fixed applied load (25) N for (60 min) interrupted to four equal intervals and at the same above sliding speed. The worn surface of the tested samples and formed wear debris particles were investigated and analyzed with aid of SEM and SEM-Mapping facilities. The results showed that the wear rate increased by increasing the applied load and a transition from mild wear to severe wear was occurred at (20 N) for fixed sliding time (15min). The maximum measured wear rate was (39.72×10−7) mm3.mm−1 at the highest applied load. While for the second group the wear rate was decreased when the sliding time exceeded 30 min. The main wear mechanism was adhesive type detected by material transfer, with lower abrasive type which is revealed from the existence of fine grooves. Oxidation and plastic deformation features are also observed.

A critical comparison of dynamometer data with pin-on-disc data for the same two friction material pairs – A case study

Friction and wear behavior of brake materials is often investigated using Pin-on-Disc (PoD) or dynamometer tests. Dynamometer tests reproduce the real braking conditions since they are carried out on real parts. whereas PoD tests are carried out using small pins, under constant sliding velocity and contact pressure. In the present technical note, the friction and wear behavior of two commercial friction materials, a low-met and a non-asbestos organic (NAO) material, dry sliding against a pearlitic cast iron counterface disc was investigated. The PoD tests were carried out at room temperature and at 300 °C; the dynamometer tests were conducted simulating urban braking conditions. The experimental data were compared and the main wear mechanisms were identified. The wear mechanisms observed with the PoD at room temperature turned out to be similar to those observed with the dynamometer tests. On the other hand, the PoD tests carried out at 300 °C revealed particular features in the friction layer that were not detected in the dynamometric tests. As far as the tribological data are concerned, the average friction coefficients recorded during the dynamometric tests were similar to the values recorded in the PoD tests, whereas the wear coefficients were one order of magnitude lower, most probably due to the limited area of contact of the pins.

A preliminary investigation on the use of the pin-on-disc test to simulate off-brake friction and wear characteristics of friction materials

During off-brake driving, some unwanted contact between the brake pads and the rotating discs may occur, thus inducing inefficient fuel usage and additional environmental pollution. This paper addresses the frictional behavior of 5 commercial low-met and NAO friction materials dry sliding against a cast iron counterface disc, under low contact pressures, typical of off-brake driving. In the investigated conditions, kinetic and static coefficient of frictions (COFs) were found to be independent from the contact pressure. The static COFs were all found to be around 0.2, whereas the kinetic COFs were found to be higher in the low-met materials with respect to the NAO materials and they were found to be roughly independent from the contact pressure. The results were explained with reference to the adhesive theory of friction, highlighting the paramount role of the Fe-oxides embedded in the friction layer.

Pin-on-disc study of a friction material dry sliding against HVOF coated discs at room temperature and 300 °C

The tribological behavior of a commercial semi-metallic friction material dry sliding against an uncoated cast iron disc and HVOF coated discs at room temperature and at 300 °C has been investigated. Two types of coatings were investigated, based on Cr3C2-NiCr and WC-CoCr systems. The tests were carried out using a pin-on-disc apparatus. The characteristics of the friction layer that forms on the worn surfaces of the friction material (the pin) and on the counterface disc were analyzed and correlated with the friction and wear behavior of the couplings. At room temperature, quite a long initial stage was observed, required to form a compact friction layer and to achieve a constant average friction coefficient. At 300 °C, steady-state conditions are attained almost from the beginning of the test. The wear rates of the friction materials are mild at room temperature and close to severe at 300 °C because of the thermal softening of the friction material. The wear rates of the coated discs are always negligible, since the contact temperature is not sufficiently high to induce a softening or an oxidative damage of the coatings. Although referring to rather simplified testing conditions, the results obtained in this study provide useful indications on the possibility of using HVOF coatings in braking systems to reduce not only their wear but also, most importantly, the release of particulate matter in the environment.

Dry sliding of a low steel friction material against cast iron at different loads: Characterization of the friction layer and wear debris

Pin-on-disc testing was used to investigate the sliding behavior and the wear products of a low-steel friction material against a cast iron disc at different applied loads, to investigate the effect of the temperature rise induced by frictional heating. The testing rig was operated in a clean chamber with a purified incoming air flux. The outgoing flux carries the wear particles to an impactor that counted and sorted them by average diameter and weight. At increasing applied loads, corresponding to a proportional increase of the pin-disc contact temperature, the coverage of both the pin and disc surface by a friction layer was found to increase too. The relevant X-Ray diffraction patterns revealed the presence of a large amount of graphite and different compounds originating from the friction material and from the counterface disc, mainly iron oxides, as concerns this latter. After the test at the lowest investigated load, i.e., 1kg, the disc worn surface exhibited abrasive grooves and a discontinuous friction layer mainly made of compacted iron oxide particles. After the test at higher loads, i.e., 5 and 7kg, the disc surface was covered by a compact friction layer. As concerns the friction layer on the pins, most of the ingredients from the friction material were detected, in association with the iron oxides from the disc. These results can be interpreted in terms of the temperature stability range of the phenolic resin used as a binder of the friction material. The characterization of the collected airborne wear debris showed that the particles produced by the low temperature (i.e., low load) test were mostly equiaxed; whereas those produced by the high temperature (i.e., high loads) tests, predominantly displayed a plate-like morphology. The mechanisms of their formation in relation to the characteristics of the friction layers are illustrated and discussed.

Influence of micro- and nanofiller contents on friction and wear behavior of epoxy composites

AbstractIn this study, the influence of micro- and nanofiller contents on the tribological performance of epoxy composites was studied. The fillers are micro-Al2O3, micro-TiO2, and micro-fly ash and nano-Al2O3, nano-TiO2, and nanoclay fillers. The microfillers were added to the epoxy by 10%, 20%, and 30% by weight. The nanofillers were added to the epoxy by 2.5%, 5%, and 10%. Friction and wear tests were conducted using the pin-on-disc arrangement. Tribo elements consisted of polymer pin and DIN 1.2344 steel counterface disc. A load value of 15 N, a sliding speed of 0.4 m/s, a sliding distance of 2000 m, and dry atmospheric conditions were applied to test conditions. The results show that the friction coefficients and the specific wear rates of the nanofilled composites increase as the filler content increases. For microfiller-filled epoxy composites, these values decrease as filler content increases. The tribological performance of epoxy composites is enhanced by the addition of microfillers, and the higher enhancement is reached with the addition of 30% fly ash filler. Finally, the pin and disc worn surface images show the presence of adhesive and some abrasive wear mechanisms.

Role of the friction layer in the high-temperature pin-on-disc study of a brake material

The tribological behavior of a commercial brake pad material, wear tested under dry sliding conditions against a cast iron counterface disc with a pin-on-disc apparatus, was investigated. Wear tests were conducted at the following disc temperatures: 25°C, 170°C, 200°C, 250°C, 300°C and 350°C. Above 170°C a transition from mild to severe wear was observed. At 25°C and 170°C, the friction layer on the pin surface consists of primary and compacted secondary plateaus. At 200°C and above, a progressive reduction of the pin surface coverage by the secondary plateaus, that are barely present after the 350°C test, is observed. Wear tracks on the discs derive from wear fragments due to the tribo-oxidation of the disc itself and from the wearing out of the pin material. The observed tribological behavior is very much influenced by the thermal degradation of the phenolic binder of the friction material, confirmed by thermogravimetric analyses, conducted on purpose on the pin material. Raman spectroscopy indicated the presence of carbonaceous products on the high temperature worn out pin surface. Although referring to rather extreme and simplified sliding conditions, the results obtained in this study provide useful indications on the role of the thermal stability of the organic component.

Comparative Study of Effect of Cryogenics Heat Treatment and Case Hardening on the Wear Property of 20MnCr5

This research is limited to study of wear resistance of 20MnCr5 (SAE 5120) alloy steel hardened by Carburizing and Cryogenics, which has wide application in industries like gears, shafts, bearings, pins etc. Cryogenics is used as a supplement treatment that is performed after carburizing. The abrasive wear study is performed on pin-on-disc tribotester. The counterface disc was kept same for both the heat treatments (carburizing and cryogenics). Sliding velocity of 0.8 m/s, 1.6 m/s, 2.4 m/s, Sliding Distance of 1200 m, 1400 m, 1600 m and Load of 3 kg, 4 kg and 5 kg were used to evaluate the wear resistance.

Dry Sliding Wear Behavior of a High-Mn Austenitic Twinning Induced Plasticity (TWIP) Steel Microalloyed with Ti

ABSTRACTHigh-Mn austenitic twinning induced plasticity (TWIP) steels are the object of intense worldwide scientific study due to the promising combination of strength and ductility of these alloys. Mechanical behavior of this family of new generation steels has been extensively studied recently. However, limited information regarding their tribological properties is available in the literature. The aim of this research work is to study the wear behavior of a high-Mn austenitic Fe–20Mn–1.5Si–1.5Al–0.4C TWIP steel microalloyed with Ti. The wear behavior was evaluated under dry sliding condition by the ‘‘pin-on-ring’’ method. For this purpose, solution-treated samples were worn for 10 km against a counterface disc made of hardened AISI M2 steel, under loads of 52, 103 and 154 N, and at speeds of 0.20, 0.60 and 0.86 m/s. The wear resistance was evaluated from the average wear rate. Wear debris and worn surfaces were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (SEM-EDS). The Ti addition to TWIP steel slightly improved the wear resistance particularly at a speed of 0.86 m/s and at loads of 52 and 103 N. Results show that the wear resistance increases with increasing sliding speed. This is attributed to the formation of an oxide layer acting as a protective layer against wear, which suggests that the main wear mechanism for the studied TWIP steel under these conditions is oxidative.

Sliding Friction and Wear Characteristics of Grade 410 Martensitic Stainless Steel

Present work aimed at investigating the friction and wear of martensitic stainless steel of grade 410. This steel is used in nuclear industry for various moving components due to its high strength and moderate corrosion resistance. Properties of this material depend upon the heat treatment to which subjected to. The wear tests by sliding were performed on a pin on disk apparatus whose pin is in normalized and tempered condition. The counter face disc was machined from EN24 steel of high hardness in nature. The AISI 410 stainless steel wear rates were evaluated using Pin-on Disc Tribometer at various load and sliding speed. The worn pins were investigated by using scanning electron microscopy and surface profilometer.

Sliding wear behavior of a high-Mn austenitic twinning induced plasticity (TWIP) steel microalloyed with Nb

High-Mn austenitic twinning induced plasticity (TWIP) steels are the object of intense worldwide scientific study due to the promising combination of strength and ductility of these alloys. Mechanical behavior of this family of new steels generation has been extensively studied recently; however, limited information regarding their tribologycal properties is available in the literature. The aim of this research work is to study the wear behavior of a high-Mn austenitic Fe–22Mn–1.5Si–1.5Al–0.4C TWIP steel and to compare it with a Nb-microalloyed one. The wear behavior was evaluated under dry sliding condition by the “pin-on-ring” method. As-solution treated condition samples were worn for 10km against a counterface disc made of hardened AISI M2 steel, under loads of 52, 103 and 154N, and at speeds of 0.20 and 0.86m/s. The friction coefficient was monitored during the test, and the wear resistance was evaluated from the average wear rate. The as-solution treated TWIP steels were characterized by optical microscopy (LOM), X-ray diffraction (XRD) and Vickers hardness test. Wear debris and worn surfaces were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (SEM–EDS) and XRD. Results show that the studied TWIP steels exhibit reasonably low friction coefficient, and that wear resistance increases with increasing sliding speed. This is attributed to the formation of an oxide layer. The Nb addition to TWIP steel slightly improved the wear resistance particularly at the load of 103N and at a speed of 0.20m/s.

The lubrication of poly(etheretherketone) by an aqueous solution of nattokinase

Poly(etheretherketone) (PEEK) is a high strength and high temperature engineering polymer. However, its tribological performance is not very good in its pure form unless fillers or fibers are added to form composites. As polymers are often used for applications where traditional oil based lubrication may become an issue, water-based lubrication is desirable. This paper explores the lubrication performance of a natural fibrinolytic enzyme, nattokinase, found in fermented soybean (natto) in the aqueous solution. Pins of PEEK were slid against a steel disk in a pin-on-disk tester with the aqueous lubrication. The counterface disk material was a tool steel (Ra=0.37μm). Tests were conducted at a rotational speed of 100rpm and a normal load of 80N. For comparison, tests were also conducted in NaCl solution. Nattokinase aqueous solution provides a coefficient of friction of 0.2 between PEEK and steel as compared to 0.3–0.35 for dry condition. The specific wear rates of PEEK for dry, deionized water, NaCl solution and aqueous nattokinase solution conditions were 10.5×10−6, 51.6×10−6, 228×10−6 and 8.8×10−6mm3/Nm, respectively. The fibrinolytic nattokinase enzyme provides lubricity with alkalinity reducing corrosion and eventually reducing wear.

Wear Characteristic of Al-Based Metal Matrix Composites Used for Heavy Duty Brake Pad Applications

Wear study of metal matrix composites used as friction material is one of the most important parameter for determining the brake performance. The present investigations relates to the development of Aluminum powder based brake pads; where the back plates are also made of Aluminum based powders respectively. Thus it is aimed to fabricate net-shape Aluminium powder based brake pads in a single forming operation with better characteristics (low wear, low temperature rise, stable coefficient of friction) employing a newly developed technology namely “Hot Powder Preform Forging” technique. Three Aluminum based friction composites which are designated as ALM 01, ALM 02 & ALM 03 were formulated. The dry wear test is carried out using a pin-on-disc tribo-tester at constant sliding speed of 9 ms-1 under a load of 50 N. The counter face disc is made of heat treated grey cast iron. During the test, the cumulative wear (gm), Coefficient of friction, temperature rise (oC) and noise level (dB) were recorded. The effect of load at constant speed on sliding wear, frictional characteristic of aluminum based MMC (rotor / drum) in dry condition is studied. On the basis of initial laboratory tests like density, Hardness, wear test, the samples were qualified for sub-scale dynamometer test at Rejected Take Off condition. Optical microscope was used to investigate the microstructure of metal matrix friction composites surfaces. The results revealed that coefficient of friction was more stable. The Cumulative wear (gm) was low with rise in temperature. It was also observed that distribution of ingredients in matrix was fine and homogeneous.

ANN-Based Wear Performance Prediction for Plasma Nitrided Ti6Al4V Alloy

Abstract Surface modification of a Ti6Al4V titanium alloy was made by the plasma nitriding process. Plasma nitriding was performed in a constant gas mixture of 20% H2–80% N2 at temperatures between 700 and 1000° C and process times between 2 and 15 h. Samples nitrided at different treatment times and temperatures were subjected to the dry sliding wear test using the pin-on-disc set up under 80N normal load with rotational speed of counter face disc of 0.8 m/s at room conditions. An artificial neural network (ANN) model of was developed for prediction of wear performance of the plasma nitrided Ti6Al4V alloy. The inputs of the ANN model were processing times and temperatures, diffusion layer thickness, Ti2N thickness, TiN thickness and hardness. The output of the ANN model was wear loss. The model is based on the multilayer backpropagation neural technique. The ANN was trained with a comprehensive dataset collected from experimental conditions and results of authors. The model can be used for the prediction of wear properties of Ti6Al4V alloys nitrided at different parameters. The ANN model demonstrated the best statistical performance with the experimental results.

Effect of Aluminum Nitride Addition on Dry Wear Properties of Al-11%Si Alloy Prepared by Stir Casting Process

Dry wear properties of aluminum nitride (AlN) reinforced aluminum-11% silicon alloy (Al-11%Si) was studied using a pin-on-disc configuration wear tester. Different weight percentages of AlN (0 – 10 wt.%) powder were added to the Al-Si alloy, melt and stir cast via bottom pour technique to form composites of Al-Si alloy/AlN. The dry sliding wear test were performed at a room temperature (27°C), under 25N and 70N load with fixed velocity of 1ms-1 and sliding distance between 1 to 5 km. The addition of 10 wt% of AlN improved wear resistance of Al-Si alloy by 72% and 130% indicated by volume loss for 25N and 70N load respectively. Mixed-wear mechanism of delamination, adhesion and abrasion was observed for the composite when applied loads were 25N and 70N while delaminating mechanism was dominance for Al-Si matrix alloy. Both Al-Si alloy with and without AlN reinforced found with FE element from counter-face disk that shows material transfer was significant.