Search Results (253)

This research study aims to evaluate the wear and corrosive behaviour of aluminum 6061 alloy hybrid metal matrix composites after reinforcing them with graphene (0.5, 1 wt.%) and boron carbide (6 wt.%) at varying weight percentages. The hybrid composites were processed through ball milling and powder compaction, followed by a microwave sintering process, and T6 temper heat treatment was carried out to improve the properties. The properties were evaluated and analyzed using FE-SEM, Pin-on-Disc tribometer, surface roughness, salt spray test, and electrochemical tests. The results were evaluated prior to and subsequent to the T6 heat-treatment conditions. The T6 tempered sample S1 (Al6061-0.5% Gr-6% B₄C) exhibits a wear rate of 0.00107 mm³/Nm at 10 N and 0.00127 mm³/Nm at 20 N for 0.5 m/s sliding velocity. When the sliding velocity is 1 m/s, the wear rate is 0.00137 mm³/Nm at 10 N and 0.00187 mm³/Nm at 20 N load conditions. From the Tafel polarization results, the as-fabricated (F) condition demonstrates an Ecorr of −0.789 and an Icorr of 3.592 µA/cm² and a corrosion rate of 0.039 mm/year. Transitioning to the T6 condition further decreases Icorr to 2.514 µA/cm², Ecorr value of −0.814, and the corrosion rate to 0.027 mm/year. The results show that an increase in the addition of graphene wt.% from 0.5 to 1 to the Al 6061 alloy matrix deteriorated the wear and corrosive properties of the hybrid matrix composites. Full article

Excessive friction at the wheel–rail contact can limit the lifespan of the wheels and rails. Meanwhile, insufficient friction can lead to increased braking distance, risking safety. Top-of-Rail (TOR) products are recognised for their potential to achieve intermediate friction levels at the wheel–rail contact and mitigate wear damages. However, the impact of these products on the airborne wear particles emitted from wheel–rail contact is not thoroughly evaluated. High particle concentration levels, particularly on underground train platforms, raise respiratory and cardiovascular health concerns. This research employs a pin-on-disc to study the effect of laboratory (environmentally acceptable) and commercial TOR products on friction, retentivity, wear, and airborne particle emissions at the wheel–rail interface. The results indicated that TOR products with higher retentivity offered a wider interval of desired intermediate friction levels. The TOR products significantly reduced particle emissions compared to the dry condition. TOR products can, therefore, be promising in controlling friction and mitigating wear and particle emissions at the wheel–rail interface. However, to achieve the benefits of these products, it is essential to tailor their chemical composition carefully. Full article

Friction surfacing (FS) is a solid-state process for depositing metallurgically bonded coatings for corrosion and wear protection. It is particularly attractive for depositing coatings in materials that are difficult to fusion deposit. Stellite 6 is one such material, which is widely used as a protective coating on steel structures to combat wear and corrosion. In the current study, Stellite 6 was successfully friction-surfaced on low carbon steel plates without using any preheating. The microstructures and wear behavior of Stellite 6 coatings produced using FS were comparatively investigated with those produced using the plasma transferred arc (PTA) process. The PTA coatings showed a cast microstructure consisting of γ-dendrites and an inter-dendritic carbide network. On the other hand, the FS coatings showed a wrought microstructure with dynamically recrystallized grains and fine, uniformly distributed carbide particles. The FS coatings also showed uniform composition across the coating thickness and were undiluted, while the PTA coatings showed significant dilution as well as strong local variations in chemistry. The FS coatings exhibited a 22% increase in hardness (550 HV) compared to the PTA coatings (450 HV). Pin-on-disc dry sliding wear tests showed that the FS coatings (1.205 mm³) were more wear resistant compared to the PTA coatings (6.005 mm³), highlighting their superior mechanical performance. This study uniquely demonstrates the feasibility of depositing Stellite 6 coatings using FS without the need for preheating or post-deposition heat treatments, while achieving superior microstructural refinement, hardness, and wear resistance compared to conventional PTA coatings. Full article

The potential of laser-based powder bed fusion (L-PBF) technology for producing functional components relies on its capability of maintaining or even improving the mechanical properties of the processed material. This improvement is associated with the microstructure resulting from the high thermal gradient and fast cooling rate. However, this microstructural advantage may be counterbalanced by the lack of full density, which could be tolerated to a certain degree for applications such as biomedical implants and medical equipment. In this study, medical-grade 316L stainless steel specimens with porosities ranging from 1.7 to 9.1% were additively manufactured by L-PBF using different combinations of laser power and scanning speeds. Tribological properties were evaluated by pin-on-disc testing in dry conditions against a silicon nitride test body and analyzed in the context of microstructural characterization by optical and electron microscopy. The results reveal that higher porosity allows for a diminishing wear rate, which is explained by the capacity of the pores to retain wear debris related with the three-body abrasion. This research provides practical insights into the design of medical wear-resistant components, thereby enhancing our understanding of the potential of L-PBF in the fields of materials science and biomedical engineering. Full article

In this paper, the abrasive effects of lunar simulant regoliths (LHS-1, LMS-1) have been investigated. Sealing performance of different sealant pin materials on stainless steel has been tested by the pin-on-disc method. Pin materials included block types such as pure polytetrafluoroethylene (PTFE), composite PTFE, as well as braided PTFE and hybrid-composite braided PTFE. Tribological properties were evaluated based on measured friction, wear, surface roughness and scanning electron micrographs. Most significant differences were observed in the sealing effect of the pins between the braided and the block-type pin materials. The stainless steel/pin pairs showed significantly higher (0.4–0.5) friction coefficients for the braided pins than the block ones (0.2–0.3), while there was not a significant difference in the abrasive effect of the different lunar regoliths. Although significant wear of the steel part occurred only with the block-type pins, this disadvantage was apparent in comparison with the braided pins. The abrasive particles caused deformation and eventually complete disintegration of the braided pins. Both the coefficient of friction and the wear could be estimated by a multiple linear regression model, in which different regolith size was the dominant independent parameter for the various pins. Full article

Machining titanium alloys, particularly Ti6Al4V, pose significant challenges in manufacturing engineering. The combination of high strength and low thermal conductivity makes Ti6Al4V a particularly difficult material to machine. One of these difficulties is the rapid wear and short tool life of cutting tools, which substantially increases manufacturing costs. To address this issue, the texturing of cutting tools, especially using laser-based techniques, has garnered significant attention due to its potential to enhance the tribological performance of textured surfaces. In this paper, by means of a groove design applied to a tungsten carbide (WC) disc by laser surface texturing (LST), its behavior and wear have been evaluated after subjecting it to tribological pin-on-flat tests by confronting it with Ti6Al4V pins with different reciprocating times (250 s, 500 s, 750 s and 1000 s) in lubricated and dry conditions. In addition, these same tests have been replicated without textures for comparison. Through conducting this research, we expect to gain new insights into texturing processes and their influence on friction and sliding behavior under lubricated conditions. Additionally, the study aims to evaluate how lubricant retention capacity varies to reduce friction and wear across different testing durations. The results show better behavior with textures, reaching a higher rate of volume loss in the titanium pins. The main conclusions obtained after these tests are that textures offer a better performance in tests up to 800 s. In addition, after this time, the lubricant begins to lose its properties, becoming an abrasive paste. Full article

High-strength nickel–chromium steel (20Cr2Ni4A) is typically used in bearing applications. Alternating magnetic field treatment, which is based on the use of a magnetiser, and which is fast and cost-effective in comparison to conventional processes, was applied to the material to improve its wear resistance. The results of pin-on-disc wear testing using a AISI 52100 alloy counter pin revealed a decrease in the specific wear rate of the treated samples by 58% and a reduction in the value of the coefficient of friction by 28%. X-ray diffraction analysis showed a small increase in the amount of martensite and higher surface compressive residual stresses by 28% leading to improved hardness. The observed changes were not induced thermally. The volume expansion by the formation of martensite was achieved at near room temperature and led to a further increase in compressive residual stresses. The significance of this study is that the improvement in the properties was achieved at a current density value that was two orders of magnitude higher than the threshold for phase transformation and dislocation movement. The reasons for the effect of the alternating magnetic field treatment on the friction and wear properties are discussed in terms of the contribution of the magnetic field to the austenite-to-martensite phase transformation and the interaction between the magnetic domain walls and dislocations. Full article

The effects of microstructure and mechanical properties on the wear resistance of B₄C-TiB₂ ceramic composite were studied. The composite was hot pressed from a B₄C-TiO₂ precursor at a temperature range of 1800 and 1850 °C. Both the relative density and amount of TiB₂ secondary phase of the B₄C-TiB₂ composite increased with the amount of TiO₂ sintering additive in B₄C-TiO₂ precursor. The hardness of the composite increased with a secondary phase portion up to 29.8 vol.% TiB₂. However, the positive effect of TiB₂ secondary phase on the fracture toughness of B₄C-TiB₂ composite was measured in the complete experimental range, with the highest average attained value of 7.51 MPa·m^1/2. The wear resistance of B₄C-TiB₂ composite increased with both the hardness and fracture toughness. The best wear resistance was achieved with the composite with a higher hardness value of 29.74 GPa. This sample consisted of 29.8 vol.% TiB₂ secondary phase and reached a fracture toughness value of 6.91 MPa·m^1/2. The fracture-induced mechanical wear of B₄C-TiB₂ composite was the main wear mechanism during the pin-on-disc wear test. Transgranular fracture with pullout of the surface and micro-crack formation in the direction perpendicular to the wear direction was observed on the worn surfaces. Full article

Titanium alloy is widely used as a biomaterial due to its strength, lightweight nature, and corrosion resistance. Despite its strength and lightweight nature, its low wear resistance limits its uses in prosthetic components. Laser surface texturing (LST) was used to improve the wear resistance of titanium alloys by creating textured surfaces before applying protective coatings. A biocompatible TiN composite protective coating was applied using physical vapour deposition (PVD) with a thickness of 4 µm. Response surface methodology (RSM) was used to predict the tribological properties by varying input parameters such as material type (TI, T2, T3, and T4), load in N, and sliding velocity in m/s. A pin-on-disc tribometer was used to conduct a unidirectional sliding wear test based on the RSM design. Tribological properties were studied to determine the impact of laser texturing on the bonding strength of the coating. As a result, material type T4 exhibits an improved coefficient of friction and specific wear resistance under varying sliding velocity and load conditions compared to other material types. The study was further supported by an ANSYS simulation, which revealed stress reduction affecting the coefficient of friction and, consequently, wear. The textured surface topography, wear mechanisms, and coating compositions were examined using scanning electron microscopy. Full article

The aim of this investigation was to examine how CeO₂ powder influences the performance of WC + Ni60 composite powder. Various cladding layers of WC + Ni60, incorporating differing mass fractions of CeO₂, were created on the surface of Q235 steel utilizing laser cladding technology. To analyze the microscopic structure of the resulting cladding layer, scanning electron microscopy was employed. Additionally, the abrasion and corrosion resistance properties were assessed through experimentation with a pin-and-disc friction and wear tester and an electrochemical workstation, respectively. The results of the study showed that when the mass fraction of CeO₂ was 1%, the grain on the surface of the coating was refined, the carbide formation was reduced, and the uniformity of the cladding layer was the best. In terms of corrosion resistance, the coating with 1% CeO₂ had a self-corrosion potential of 0.07 V and a self-corrosion current density of 1.82 × 10⁻⁵ A·cm⁻², showing the best corrosion resistance, and the coating self-corrosion potential was higher than that of the coating and substrate without CeO₂. In terms of abrasion resistance, coatings with 1% CeO₂ had a lower coefficient of friction (0.47) and a smaller wear rate 0.034 mm³, and the wear amount was only 23.5% of that of coatings without CeO₂, resulting in the best wear resistance. In conclusion, coatings containing 1% CeO₂ exhibit the minimal coefficient of friction and the lowest wear rates, while simultaneously providing optimal corrosion resistance. Full article

A FeCrMoNiCuBSiC metallic glass coating was designed and then deposited by the high-velocity oxygen fuel (HVOF) spraying technique. X-ray diffraction, a scanning electron microscope, and a microhardness tester were applied to characterize the phase, microstructure, and mechanical properties of the coating. The amorphous phase was the main phase in the coating, and crystal phases were almost undetectable in the XRD results. The coating had a dense structure (the porosity was 1.47 ± 0.32%) and high Vickers microhardness (848 ± 22 HV_0.3). The wear behavior of the coatings sliding against WC-Co was studied with a pin-on-disc wear test system and was compared with that of 316L stainless steel. The coating improved the wear resistance of the steel by around 7–9 times at different sliding speeds. As the sliding speed was increased, the wear loss rate of the steel obviously increased, yet the loss rate of the coating decreased first and then increased. This happened because the contact flash temperature induced by friction increases with the sliding speed, which results in oxidative behavior and crystallization events in the coating. The dominating wear mechanism of the coating is fatigue wear combined with oxidative wear. Full article

This paper presents an analysis of four clutch disc friction materials (from different manufacturers) used in manual transmissions. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were employed for the microstructural and chemical characterisation of the friction materials. To reveal the tribological properties of the selected clutch discs, three measurements of the friction coefficient between the material and the cast iron disc were conducted. The findings were employed to construct an artificial neural network using Easy NN software (V 14), with the objective of optimising the friction material. The chemical composition of the friction materials was employed as the input data, whereas the minimum, maximum, and average values of the friction coefficient, as well as the temperature generated during friction, were utilised as the output data. To assess the efficacy of the neural network, the correlation between the importance of input data and their sensitivity to output data was examined. It was determined that the model with three hidden layers exhibited a notable correlation between the six most influential chemical elements and their sensitivity. Based on this neural model, the chemical composition of the friction disc materials was optimised using the “Query” mode, aiming to minimise discrepancies in friction coefficients and temperature development. Full article

Polymer seals are utilized in various engineering applications to prevent leakage and contamination. The study investigates the wear and friction behavior of PTFE-based dynamic rotary seals, targeting their usage in space applications. Pin-on-disc dry sliding wear tests were performed with 0.5 MPa contact pressure and 0.2 m/s sliding velocity combining different lip seal (PTFE, PTFE+GF+MoS₂), packing (PTFE, PTFE+Aramid fiber+solid lubricant) and shaft materials (34CrNiMo6, PEEK) involving third-body lunar (LHS-1) and Martian regolith (MGS-1) simulants. To understand the different influences of extraterrestrial regolith simulants compared to commonly encountered abrasives on Earth, quartz sand was selected as a reference. Quartz soil resulted in lower wear rates but a similar coefficient of friction to other regoliths. In the case of lip seals, testing with LHS-1 on PEEK and testing with MGS-1 on steel resulted in the most severe wear. Post-mortem surface analysis revealed the effect of external abrasive particles on the wear process and the transfer layer formation. The surface analysis confirmed that both lunar and Martian regolith simulants resulted in significant embedded particles. Based on the wear performance results, the lip seals performed better, but installation with an external packing could further aid the tribosystem. Full article

Magnetic fraction isolated from steel furnace slag was tested as a component of Cu-free friction composites. The friction–wear performance and production of wear particles during their testing using a pin-on-disc tester against a cast iron disc were evaluated. To compare the effect of the magnetic fraction on the parameters studied, the composite with alumina and the composite with original steel furnace slag were also prepared and tested. All composites showed a comparable friction coefficient. The composite with original steel furnace slag, and the composite with a magnetic fraction showed higher wear resistance compared to the composite containing alumina. The positive effect of the magnetic fraction on the extent of the emission of wear particles was observed and explained by the decreased aggressiveness of this composite to the cast iron disc. The influence of the phase composition of the steel furnace slag and the magnetic fraction on the friction film formation was also indicated, and its effect on the production of wear particles was proposed. Full article

In various applications, dry friction could induce vibrations. A well-known example is frictional braking systems in ground transportation vehicles involving a sliding contact between a rotating and a stationary part. In such scenarios, the emission of high-intensity noise, commonly known as squeal, can present human health risks based on the noise’s intensity, frequency, and occurrences. Despite the importance of squeal in the context of advancing urbanization, the parameters determining its occurrence remain uncertain due to the complexity of the involved phenomena. This study aims to identify a relevant operando indicator for predicting squeal occurrences. To this end, a pin-on-disc test rig was developed to replicate various contact conditions found in road profiles and investigate resulting squealing. Each test involves a multimodal instrumentation, complemented by surface observations. It is illustrated that the enhanced thermal indicator identified is relevant because it is sensitive to the thermomechanical and tribological phenomena involved in squealing. Full article