Microstructure and Wear Behavior of a Manganese Bronze Bearing Material under Unlubricated Conditions

In an attempt to collect information about the tribological performance of copper-based bearings, the friction and wear behaviors of C86300 manganese bronze were investigated. The characteristics of the base material were determined by structural and mechanical investigations. Then, dry sliding pin-on-disc wear tests were performed against an AISI 52100 steel counterface. After the wear tests, the worn surfaces of the pins and wear debris were studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. In addition, light optical microscopy and microhardness measurements were performed for examination of the steel counterfaces and worn pin subsurface layers. With increasing normal load, the wear rate of commercial C86300 alloy (containing 0.6 wt% Si) decreased initially and then began to increase. After reaching a maximum wear rate at the load of about 60 N, the wear rate decreased again with a further increase in the normal load. However, the wear rate of this C86300 alloy mainly decreased with increasing sliding speed. Adhesive and abrasive wear were the dominant wear mechanisms under the designed conditions.     

Reciprocating Sliding Wear Behavior of 60NiTi As Compared to 440C Steel under Lubricated and Unlubricated Conditions

ABSTRACT

60NiTi is a hard (～60 HRC) and highly corrosion-resistant intermetallic with a relatively low elastic modulus (～100 GPa). In addition, this alloy exhibits a high compressive strength (～2,500 MPa) and a high elastic compressive strain of over 5%. These attributes make this alloy an attractive candidate to be employed in structural and mechanical component applications. However, sliding wear behavior of this intermetallic has not yet been studied in a systematic way. In this study, lubricated and unlubricated reciprocating sliding wear behavior of 60NiTi is compared to 440 C steel as a conventional bearing and wear-resistant alloy. Results of experiments carried out under different loads show that 60NiTi, despite having a higher hardness, exhibits a significantly inferior wear behavior under dry conditions in comparison to 440 C steel. These unexpected results indicate that 60NiTi does not follow conventional wear theories where the wear of materials has an inverse relationship to their hardness. On the other hand, under lubricated conditions with castor oil and a synthetic gear oil, 60NiTi exhibits low specific wear rates. These results exhibit the importance of proper lubrication in sliding mode applications where 60NiTi is exploited as a wear-resistant alloy.     

Tribological Characterisation of Graphene Oxide as Lubricant Additive on Hypereutectic Al-25Si/Steel Tribopair

The performance of a lubricant greatly depends on the additives it involves. However, recently used additives produce severe pollution when they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide (GO) is considered to be environmentally friendly. The scope of this study is to explore the fundamental tribological behavior of graphene, the first existing 2D material, and evaluate its performance as a lubricant additive. The friction and wear behavior of 0.5 wt% concentrations of GO particles in ethanol and SAE20W50 engine oil on a hypereutectic Al-25Si alloy disc against steel ball was studied at 5 N load. GO as an additive reduced the wear coefficient by 60–80% with 30 Hz frequency for 120 m sliding distance. The minimum value of the coefficient of friction (0.057) was found with SAE20W50 + 0.5 wt% GO. A possible explanation for these results is that the graphene layers act as a 2D nanomaterial and form a conformal protective film on the sliding contact interfaces and easily shear off due to weak Van der Waal's forces and drastically reduce the wear. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Raman spectroscopy were used for characterization of GO and wear scars.     

Tribological Behavior of Aluminum Hybrid Composites Studied by Application of Factorial Techniques

This article analyzes the influence of graphite reinforcement, load, sliding speed, and sliding distance on tribological behavior of A356 aluminum matrix composites reinforced with silicon carbide and graphite using the full-factorial design. The wear rates of A356/10SiC composite material and A356/10SiC/1Gr and A356/10SiC/3Gr hybrid composites have been analyzed. The composites were obtained by a modified compocasting procedure. Tribological tests were performed on a block-on-disc tribometer without lubrication. The testing included sliding speeds of 0.25 and 1.0 m/s, normal loads of 10 and 20 N, and sliding distances of 300 and 900 m. The analysis of the obtained results was performed using the full-factorial method based on the signal-to-noise (S/N) ratio. The effects of load, sliding speed, weight percentage of graphite reinforcement, and sliding distance on the wear rate are 38.99, 17.87, 13.95, and 11.25%, respectively. The best tribological characteristics were exhibited by the A356/10SiC/1Gr hybrid aluminum composite.     

Wear Behavior of Magnesium Alloy AZ91 Hybrid Composite Materials

The influence of hybrid reinforcements including silicon carbide and graphite particles with a size 37–50 μm on the wear characteristics of AZ91 magnesium alloy was studied. The dry sliding wear test was conducted using a pin-on-disc wear testing machine in the load range of 20 to 80 N at different sliding velocities in the range of 1.047 to 2.618 m/s. The results show that the wear resistance of composites was much better than that of the base matrix material under the test conditions. At a speed of 1.047 m/s and load of 40 N, the wear rate (mm³/km) of the unreinforced alloy was 6.3, which reduced to 3.8 in the case of 3% reinforced composite. The antiwear ability of magnesium alloy composite was found to improve substantially with the increase in silicon carbide and graphite content from 1 to 3% by weight and the wear rate was found to decrease considerably. At a speed of 1.047 m/s and load of 80 N, the wear rate (mm³/km) reduced from 11.8 to 9.1 when the reinforcement content increased from 1 to 3%. However in both the unreinforced alloy and reinforced composite, the wear rate increased with the increase in load and sliding velocity. An increase in the applied load increases the wear severity by changing the wear mechanism from abrasion to particle cracking-induced delamination. The worn surface morphologies of the composite containing 3% reinforcement by weight for the sliding velocity of 1.047 m/s were examined using scanning electron microscopy. Different wear mechanisms, namely, abrasion, oxidation, and delamination, have been observed.     

Effects of sliding velocity and normal load on friction and wear characteristics of multi-layered diamond-like carbon (DLC) coating prepared by reactive sputtering

Friction and wear tests were performed to investigate effects of sliding velocity and normal load on tribological characteristics of a multi-layered diamond-like carbon (DLC) coating for machine elements. The DLC coatings which consist of sequentially deposited gradient Cr/CrN, W-doped DLC (a-C:H:W) and DLC (a-C:H) layers were formed on carburized SCM 415 Cr–Mo steel disks using a reactive sputtering system. The tests against AISI 52100 steel balls were performed under various sliding velocities (0.0625, 0.125, 0.25, 0.5, 1 and 2 m/s) and normal loads (6.1, 20.7 and 49.0 N) in ambient air (relative humidity=26±2%, temperature=18±2 °C). Each test was conducted for 20 km sliding distance without lubricating oil. The results show that friction coefficients decrease with the increase in sliding velocity and normal load. Wear rates of both surfaces decrease with the increase in normal load. The increase in sliding velocity leads initially to the increase in wear rates up to the maximum value. Then, they decrease, as the sliding velocity increases above specific value that corresponds to the maximum wear rate. Through surface observation and analysis, it is confirmed that formation of transfer layers and graphitized degree of wear surfaces of DLC coatings mainly affect its tribological characteristics.     

Effect of temperature on friction and wear of prehardened tool steel during sliding against 22MnB5 steel

Abstract

Mechanical components in tribological systems exposed to elevated temperatures are gaining increased attention since more and more systems are designed to operate under extreme conditions. In hot metal forming, the effect of temperature on friction and wear is especially important since it is directly related to process economy (tool wear) and quality of the produced parts (friction between tool and workpiece). This study is therefore focused on fundamental understanding pertaining to the tribological characteristics of prehardened hot work tool steel during sliding against 22MnB5 boron steel. The tribological tests were carried out using a high temperature reciprocating sliding friction and wear tester under a normal load of 31 N (corresponding to a contact pressure of 10 MPa), a sliding speed of 0·2 m s^?1 and temperatures ranging from 40°C to 800°C. It was found that friction coefficient and specific wear rate decreased at elevated temperature because of formation of compacted wear debris layers on the surfaces.     

Effect of Compressive Deformation on Wear Property of Extruded ZK60 Magnesium Alloy

The present study investigates the dry sliding wear behavior of precompressed ZK60 alloy using a ball-on-disc wear test machine under normal loads of 20 and 40N at a sliding speed of 0.5m s^?1 for a constant sliding distance of 1,500m. Microstructures and worn surfaces were characterized by optical microscopy and scanning electron microscopy. Microhardness measurements were taken to evaluate mechanical properties. Results showed that both the microhardness and wear resistance of uncompressived alloy can be improved with precompression. This is attributed to the grain refinement via subdivision of twin lamellae generated by compressive deformation. Furthermore, the worn surface studies showed a mixed type of wear mechanisms: oxidative and delamination wear took place under higher applied loads.     

Effect of Sliding Speed and Applied Load on Dry Sliding Tribological Performance of TiAl Matrix Self-lubricating Composites

More durable, low-friction self-lubricating materials in modern industry are greatly needed for tribological systems. The current paper presents the tribological performance of TiAl matrix self-lubricating composites (TSC) containing MoS₂, hexagonal BN and Ti₃SiC₂ designated as MhT against GCr15 steel counterface under several sliding speeds from 0.2 to 0.8 m s^?1 and applied loads from 6 to 12 N. The results suggested that MhT played an important role in decreasing friction coefficients and wear rates. The covering percentage of transfer layers on worn surfaces varied with the changing of sliding speeds and applied loads, hence resulting in the distinct friction and wear characteristics of TSC. TSC containing 10 wt% MhT exhibited the best excellent tribological performance at 10 N–0.8 m s^?1, which could be due to the formation of the best compaction and largest coverage of transfer layer on the worn surfaces.     

Wear Behavior of Cooling Slope Rheocast A356 Al Alloy

In the present study, the dry sliding wear behavior of rheocast A356 Al alloys, cast using a cooling slope, as well as gravity cast A356 Al alloy have been investigated at a low sliding speed of 1 ms^?1, against a hardened EN 31 disk at different loads. The wear mechanism involves microcutting–abrasion and adhesion at lower load for all of the alloys studied in the present work. On the other hand, at higher load, mainly adhesive wear along with oxide formation is observed for gravity cast A356 Al alloy and rheocast A356 Al alloy, cast using a 45° slope angle. Unlike other alloys, 60° slope rheocast A356 Al alloy is found to undergo mainly abrasive wear at higher load. Accordingly, the rheocast sample, cast using a 60° cooling slope, exhibits a remarkably lower wear rate at higher load compared to gravity cast and 45° slope rheocast samples. This is attributed to the dominance of abrasive wear at higher load in the case of rheocast A356 Al alloy cast using a 60° slope. The presence of finer and more spherical primary Al grain morphology is found to resist adhesive wear in case of 60° cooling slope processed rheocast alloy and thereby delay the transition of the wear regime from normal wear to severe wear.     

Wear Characteristics of Traditional Manganese Phosphate and Composite hBN Coatings

In this study, the tribological properties of traditional manganese phosphate coatings and composite hBN coatings

composed of nano-hexagonal boron nitride (hBN) in layered manganese phosphate crystals on AISI 1040 steel were investigated. Wear tests were carried out under controlled temperature and humidity using ball-on-disc tribometers for samples that were either submerged in oil or retaining oil on their surfaces at a sliding speed of 2.5 cm/s with loads of 1, 3, 5, and 10 N and sliding distances of 40, 80, 100, and 120 m. The surface profiles before and after the tests were used to characterize the wear. The surfaces of the coated samples were examined using scanning electron microscopy (SEM). The coefficients of friction and wear rates of the coated samples were also measured. The average wear rates of the composite hBN-coated samples were significantly lower than those of the traditional manganese phosphate–coated samples for each of the loading conditions for the oil submersion and retained oil tests. The coefficient of friction (COF) values for the traditional manganese phosphate–coated samples did not change significantly with increasing load. The COF values for the composite hBN coated–samples decreased with increasing load in the oil submersion test.     

Friction and Wear Behavior of Irradiated Polyethylene Sliding Against a Rough Steel Surface

The aim of this study was to evaluate the tribological behavior of polyethylene crosslinked by gamma radiation sliding against a steel surface. Two high-density polyethylenes were irradiated to a total dose in the range of 2?20 Mrad under vacuum and at room temperature. After irradiation, the materials were annealed at 423 K and then cooled slowly to room temperature. The same thermal treatment was applied to the non-irradiated polymer. The wear behavior of the polymers was determined under controlled ambient temperature of 298 and 333 K using a homemade tribometer. Sheet-shaped specimens were loaded against the surface of a steel disc with different normal loads to generate nominal contact pressures in the range of 0.25–1.5 MPa. The tests were performed under dry conditions using a disc rotation to produce an average sliding speed of 0.6 m/s and during a period of time to provide an average sliding distance of 1,080 m. The wear rate was obtained as the mass loss by the sample divided by the sliding distance, and the friction coefficient was determined by measuring the friction force. The results indicate that the wear rate increases with load in the case of non-irradiated polyethylene and low-dose irradiated polymers, while the wear rate reaches a maximum value with the load in the case of the irradiated samples with high doses. The samples irradiated with a dose of 10 Mrad showed the lowest wear. The coefficient of friction (COF) increases slightly with the load in all the cases. Most irradiated polymers show higher COF than the non-irradiated material when compared at a given load. The results show that the irradiation dose applied to the polyethylenes produced no noticeable effect on the COF values when a comparison was made at a given applied load.     

Wear behaviour of AE42+20% saffil Mg-MMC

The wear behaviour of AE42 magnesium alloy and AE42+20% saffil short fibre composite is investigated in dry sliding condition using a pin-on-disc set-up in the load range of 5–40 N with sliding speeds of 0.838, 1.676 and 2.513 m/s for a constant sliding distance of 2.5 km. In case of both the alloy and the composite wear rate increases with increasing loads and the wear rate of the composite is lower at lower loads. At all sliding speeds, a crossover in wear rate is observed with the increase in load, i.e., above a certain load the wear rate of the composite becomes greater than that of the alloy, and the crossover shifts to lower loads with increase in the sliding speed. Severe sub-surface plastic deformation and fibre breakage are found to be the dominant mechanism for the unreinforced alloy and the composite, respectively.     

Stick–Slip Friction of Stainless Steel in Sodium Dodecyl Sulfate Aqueous Solution in the Boundary Lubrication Regime

The service life of a diesel fuel injector is highly affected by the tribological properties of the fuel. This study aims to investigate the friction and wear behaviors of emulsified bio-oil (EBO), which is a very promising alternative fuel for engines. Sliding wear tests were performed with a ball-on-disk tribometer using a GCr15 steel ball and a flat specimen as a counterpart. In these tests, the total sliding distance was 500 m, the load ranged from 10 to 20 N, and the oscillation frequency ranged from 30 to 50 Hz. Experimental results showed that EBO had better tribological properties than diesel oil and crude bio-oil. Contact load and oscillation frequency significantly influenced friction coefficient, wear volume, and wear damage pattern. The friction coefficient decreased with an increase in load and increased with an increase in oscillation frequency. Furthermore, the wear volume slightly increased with an increase in load or oscillation frequency. The damage mechanism is attributed to adhesive wear under low load and to abrasive wear under high load. The transition in the wear mechanism is related to the adsorption of the molecules in the EBO, the microstructural contact surface, and the mechanical actions.     

Tribological Behavior of WC-12Co Air Plasma–Sprayed Coating at Elevated Temperatures

The friction and wear performance of WC-12Co air plasma–sprayed (APS) coating at temperatures of 25–650°C under loads of 8 and 28 N in at atmospheric environment have been studied by a ball-on-disc tribometer. The effect of temperature and load on the tribological behavior of WC-Co coating was investigated. The results show that under a load of 8 N, the wear volume of the coating increases at 250°C due to the coating splat delamination and then it gradually decreases at 350–500°C. The friction could promote the formation of double oxide (CoWO₄), which is beneficial to reduce friction and wear. At higher temperatures, the wear volume increases again due to the removal of oxides. Under a load of 28 N, the wear volume of the coating increases enormously at 250°C due to the serious splat delamination. At 350°C, the load promotes double oxide formation, resulting in an early decrease in the coefficient of friction and a rapid reduction in wear volume. Although the wear volume decreases at 350–500°C, it is 10-fold higher than that under a load of 8 N. Above 500°C, the differences of the wear volumes of coatings under the two loads become less obvious, and similar trends also appear for the coefficients of friction. The synergistic effect between the load and temperature on the friction and wear mechanism of WC-12Co APS coating is discussed.     

Effect of cryogenic treatment on the tribological behaviour of H11 hot die steel dry sliding against D3 steel

The tribological behaviour, hardness and microstructural characteristics of vacuum and cryogenically treated AISI H11 steel at varied soaking temperature (?154 and ?184 °C) for specific time period (6, 21 and 36 h) have been examined in this research work. The influence of selected parameters on the tribological behaviour have been studied at five levels of varying sliding velocities (0.628–1.885 m/s) and normal loads (60–140 N) through block–on–ring dry sliding wear test against hardened and tempered AISI D3 tool steel (counter face). The experiments are designed based on full factorial response surface methodology. The responses (wear rate, average coefficient of friction and maximum contact temperature) are analyzed based on plotted graphs. The results reveal that 21 h at ?184 °C for H11steel is the optimal soak time to have the lowest wear rate. The sliding speed influences the wear rate more in comparison to load. Wear debris have shape of metallic plate. Carbide particles appeared to delaminate from the sample surface due to subsurface cracks and plastic deformation. The augmentation of apparent and bulk hardness number and wear resistance ascribed to the increase in number of fine globular secondary carbide and improved morphology of matrix microstructure of cryogenic-treated sample. It is also observed that cryogenic treatment reduces the retained austenite content to near zero.     

Effects of Aging Treatments on the High-Temperature Wear Behavior of 60Nitinol Alloy

This study was undertaken to investigate the effect of heat treatments on the high-temperature wear behavior of 60Nitinol. The samples were hot-worked, aged at two temperatures of 400 and 700°C for 1 h and then water quenched. The microstructure of the alloys was investigated by scanning electron microscopy and X-ray diffraction. Sliding wear tests were performed at two temperatures of 25 and 200°C using three types of 60Nitinol disks: hot-worked, aged at 400°C, and aged at 700°C. All wear tests were performed at a speed of 0.3 m/s under a normal load of 60 N for a total sliding distance of 1,000 m using WC-Co pins sliding against 60Nitinol disks. The worn surfaces and microstructure of the subsurfaces were studied by scanning electron microscopy. Compression and hardness tests were also performed to characterize the mechanical properties of the alloys. The highest fracture strain and lowest hardness were obtained for the sample aged at 700°C that contained Ni₃Ti₂ precipitants. This sample also showed the maximum wear resistance at a wear testing temperature of 200°C. This was attributed to the formation of a more compact and stable tribological layer on the worn surface of the softer sample.     

Tribological properties of flame sprayed Fe–Ni–RE alloy coatings under reciprocating sliding

Fe–Ni–RE self-fluxing alloy powders were flame sprayed onto 1045 carbon steel. The tribological properties of Fe–Ni–RE alloy coatings under dry sliding against SAE52100 steel at ambient conditions were studied on an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. Effects of load and sliding speed on tribological properties of the Fe–Ni–RE coatings were investigated. The worn surfaces of the Fe–Ni–RE alloy coatings were examined with a scanning electron microscopy(SEM) and an energy-dispersive spectroscopy(EDS). It was found that the Fe–Ni–RE alloy coatings had better wear resistance than the SAE52100 steel. An adhered oxide debris layer was formed on the worn surface in friction. Area of the friction layer varied with variety of sliding speed, but did not vary with load. The oxide layer contributed to decreased wear, but increased friction. Wear rate of the material increased with the load, but dramatically decreased at first and then slightly decreased the sliding speed. The friction coefficient of the material was 0.40-0.58, and decreased slightly with the load, but increased with sliding speed at first, and then tended to be a constant value. Wear mechanism of the coatings was oxidation wear and a large amount of counterpart material was transferred to the coatings.     

Tribological Performance of Boronized,Nitrided, and Normalized AISI 4140 Steel against Hydrogenated Diamond-Like Carbon-Coated AISI D2 Steel

In the current work, AISI 4140 steel was pack-boronized at 950°C for 3 h and gas-nitrided at 550°C for 72 h. All specimens used in this work were prepared from the same steel bar. A 3-µm-thick diamond-like carbon (DLC) coating (a-C:H) was deposited on the AISI D2 high-carbon, high-chromium, cold-worked tool steel by a plasma-assisted chemical vapor deposition technique. Normalized, boronized, and nitrided steel pins were tested against DLC-coated AISI D2 steel at various normal loads (15, 30, 60, and 80 N) for 1,000 and 3,000 m sliding distance in ambient air. Specific wear rate of all pins decreased with increasing load, and a similar trend was observed for the coefficient of friction (COF). Microscopic and energy-dispersive spectroscopic (EDS) analysis confirmed the role of the transfer layer for a low COF with increasing load. At all loads, the specific wear rate of boronized pins was lower than that of the nitrided and normalized pin specimens. Boronized pins showed a specific wear rate in the range of 0.27 × 10^?8 to 0.44 × 10^?8 mm³/Nm and the COF was about 0.1.     

Tribological Behavior of Composites Based on ZA-27 Alloy Reinforced with Graphite Particles

The objective of this investigation is to assess the influence of graphite reinforcement on tribological behavior of ZA-27 alloy. The composite with 2 wt% of graphite particles was produced by the compocasting procedure. Tribological properties of unreinforced alloy and composite were studied, using block-on-disk tribometer, under dry and lubricated sliding conditions at different specific loads and sliding speeds. The worn surfaces of the samples were examined by the scanning electron microscopy (SEM). The obtained results revealed that ZA-27/graphite composite specimens exhibited significantly lower wear rate and coefficient of friction than the matrix alloy specimens in all the combinations of applied loads (F _n ) and sliding speeds (v) in dry and lubricated tests. The positive tribological effects of graphite reinforcement of ZA-27 in dry sliding tests were provided by the tribo-induced graphite film on the contact surface of composite. In test conditions, characterized by the small graphite content and modest sliding speeds and applied loads, nonuniform tribo-induced graphite films were formed leading to the increase of the friction coefficient and wear rate, with increase of the sliding speed and applied load. In conditions of lubricated sliding, the very fine graphite particles formed in the contact interface mix with the lubricating oil forming the emulsion with improved tribological characteristics. Smeared graphite decreased the negative influence of F _n on tribological response of composites, what is manifested by the mild regime of the boundary lubrication, as well as by realization of the mixed lubrication at lower values of the v/F _n ratio, with respect to the matrix alloy.