Search Results (235)

This study aims to investigate the outcomes of carbonaceous products, derived from the decomposition of the components of vehicular brake materials, under high-temperature wear tests. Pin-on-disc (PoD) wear tests were conducted by using cast iron discs against pins made of commercially available low-steel friction material. Tests were carried out at different temperatures: 155 °C, 200 °C, 250 °C, and 300 °C. The characterization of the sliding plateaus on worn pin surfaces was based on X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. It was noted that at temperatures above 200 °C, the thermal degradation of the inorganic resin, used as a material binder, occurs. An interesting observation was recorded at 300 °C; the brake pin material’s friction curve showed higher stability despite having an excessive wear rate. However, the brake pin’s specific wear coefficient was higher at this temperature than was observed in the other friction tests. A detailed study of the friction plateaus on the worn-out pins at 300 °C revealed that the decomposed carbon resin product, i.e., the distorted graphite, was widespread over the surface of the pin. Lubricant stabilization can be expected, as established by the observed values of the coefficient of friction (CoF), retaining values within the 0.4–0.6 range, even at high temperatures. Other friction material components may have contributed to the formation of this ubiquitous carbonaceous interface film. Full article

In this study, the wear behavior of AA7075/silicon carbide/fly ash hybrid surface composites processed with a clean and green friction stir processing technique was investigated. The microstructure of the composites was investigated to determine the particle dispersion. Wear tests using a pin-on-disc tribometer were conducted, and wear tracks and debris analyses were conducted using scanning electron microscopic imaging, EDX, and mapping. The wear rate of the composites was higher in the case of the composites with agglomerated zones, which led to the loose SiC/fly ash particles pulling out during the action of dry sliding. However, on the other hand, the wear resistance was improved in the composites with uniformly distributed SiC/fly ash particles. The hard SiC/fly ash particles acted as optimized load-bearing asperities and induced more wear resistance during the action of dry sliding against the mating plate, which was made of mild steel. In the case of the well-dispersed composites, the wear mechanisms shifted from fretting fatigue and adhesion to abrasion. The presence of a high Fe content in the wear debris was confirmed in the most wear-resistant composite sample, S-20, which was produced with the following parameters: tool rotation (w) of 1000 rpm, tool traverse (v) of 40 mm/min, hybrid ratio (HR) of 75:25, and a volume percentage of reinforcements (vol.%) of 8. Full article

Metal matrix composites (MMCs) reinforced with Copper Oxide (CuO) and Aluminum (Al) 6061 (Al6061) alloys are being studied to determine their mechanical, physical, and dry sliding wear properties. The liquid metallurgical stir casting method with ultrasonication was employed for fabricating Al6061-CuO microparticle-reinforced composite specimens by incorporating 2–6 weight percent (wt.%) CuO particles into the matrix. Physical, mechanical, and dry sliding wear properties were investigated in Al6061-CuO MMCs, adopting ASTM standards. The experimental results show that adding CuO to an Al6061 alloy increases its density by 7.54%, hardness by 45.78%, and tensile strength by 35.02%, reducing percentage elongation by 40.03%. Dry wear measurements on a pin-on-disc apparatus show that Al6061-CuO MMCs outperform the Al6061 alloy in wear resistance. Al6061-CuO MMCs’ strength has been predicted using many strengthening mechanism models and its elastic modulus through several models. The strengthening of Al6061-CuO MMCs is predominantly influenced by thermal mismatch, more so than by Hall–Petch, Orowan strengthening, and load transfer mechanisms. As the CuO content in the composite increases, the strengthening effects due to dislocation interactions between the matrix and reinforcement particles, the coefficient of thermal expansion (CTE) difference, grain refinement, and load transfer consistently improve. The Al6061-CuO MMCs were also examined using an optical microscope (OM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) before and after fracture and wear tests. The investigation shows that an Al6061-CuO composite material with increased CuO reinforcement showed higher mechanical and tribological characteristics. Full article

The literature analysis did not indicate any studies on fluorination tests of carbon nanocomposite coatings doped with transition metals in a form of nanocrystalline metal carbide in amorphous carbon matrix (nc-MeC/a-C). As a model coating to investigate the effect of fluorination in a tetrafluoromethane (CF₄) atmosphere, a nanocomposite carbon coating doped with chromium-forming nanocrystals of chromium carbides in a-C matrix (nc-CrC/a-C) produced by magnetron sputtering from graphite targets and using a Pulse-DC type medium frequency power supply was chosen. After the deposition of the gradient chromium carbonitride (CrCN) adhesive sublayer, the fluorination of the main coating was conducted in a reactive mode in an (Ar + CF₄) atmosphere at various CF₄ content. It was observed that the presence of CF₄ in the atmosphere resulted in a reduced amount of chromium carbides formed in favor of chromium fluorides. Thus far, this is an observation that seems unnoticed by the carbon coatings researchers. Fluorine was assumed to bond much more readily to carbon than to chromium, due to the stability of tetrafluoromethane (CF₄). The opposite seems to be true. The mechanical properties (nano-hardness and Young’s modulus) and tribological properties in the ‘pin-on-disc’ friction pair are presented, along with the analysis of bonds occurring between chromium, carbon, and fluorine by means of X-ray photoelectron spectroscopy (XPS). Full article

The present work epitomises extracting the graphite (Gr) solid lubricant from the corn stover. The extracted Gr was incorporated as reinforcement in the A356 alloy (Al-7Si), and the effect of the Gr particles on the mechanical and tribological properties was investigated. In spite of this, the input process parameters for the dry sliding wear test at room temperature against the EN31 steel disc were optimised through ANOVA analysis. The fabricated A359—X wt% (X = 0, 2.5, 5, 7.5) composite through bottom pouring stir casting techniques was analysed microstructurally by using XRD and FESEM analysis. The micro Brinell hardness and tensile strength were investigated per ASTME10 and ASTME8M standards. A wear test was performed for the composite pins against the EN31 steel disc according to ASTM G99 specifications. The XRD analysis results depict the presence of carbon (C), aluminium (Al), and silicon (Si) in all the wt% of the Gr reinforcement. However, along with the elements, the Al₂Mg peak was confirmed for the A356—7.5 wt% Gr composite and the corresponding cluster element was confirmed in FESEM analysis. The maximum micro Brinell hardness of 92 BHN and U.T.S of 123 MPa and % elongation of 7.11 was attained at 5 wt% Gr reinforcement due to uniform Gr dispersion in the A356 alloy. Based on the ANOVA analysis, the optimal process parameters were obtained at 20 N applied load, 1 m/s sliding velocity, and 1000 m sliding distance for the optimal wear rate of 0.0052386 g/km and 0.364 COF. Full article

To improve the wear resistance of the Ti60 alloy, laser cladding was used to obtain a composite coating containing a high-entropy (Ti_0.2Zr_0.2Mo_0.2Ta_0.2Nb_0.2)B₂ boride phase, with Ti, Zr, Mo, Ta, Nb, and B powders as the raw materials. The microstructure and wear characteristics of the coating were studied using XRD, SEM, EDS, and the pin-on-disc friction wear technique. The results show that the coating mainly consists of six phases: (Ti_0.2Zr_0.2Mo_0.2Ta_0.2Nb_0.2)B₂, ZrB₂, TiB, TiZr, Ti_1.83 Zr_0.17, and Ti_0.67Zr_0.67Nb_0.67. The average microhardness of the coating was 1062.9 HV_0.1 due to the occurrence of the high-entropy, high-hardness (Ti_0.2Zr_0.2Mo_0.2Ta_0.2Nb_0.2)B₂ boride phase, which was about 2.9 times that of the Ti60 alloy substrate. The coating significantly improved the wear resistance of the Ti60 alloy substrate, and the mass wear rate was about 1/11 that of the Ti60 alloy substrate. The main types of wear affecting the coating were abrasive, adhesive, and oxidation wear, while the main wear affecting the Ti60 alloy matrix was abrasive wear, accompanied by a small amount of adhesive and oxidation wear. Full article

Polymer additive manufacturing has advanced from prototyping to producing essential parts with improved precision and versatility. Despite challenges like surface finish and wear resistance, new materials and metallic reinforcements in polymers have expanded its applications, enabling stronger, more durable parts for demanding industries like aerospace and structural engineering. This research investigates the tribological behaviour of FFF surfaces by integrating copper and aluminium reinforcement particles into a PLA (polylactic acid) matrix. Pin-on-disc tests were conducted to evaluate friction coefficients and wear rates. Statistical analysis was performed to study the correlation of the main process variables. The results confirmed that reinforced materials offer interesting characteristics despite their complex use, with the roughness of the fabricated parts increasing by more than 300%. This leads to an increase in the coefficient of friction, which is related to the variation in the material’s mechanical properties, as the hardness increases by more than 75% for materials reinforced with Al. Despite this, their performance is more stable, and the volume of material lost due to wear is reduced by half. These results highlight the potential of reinforced polymers to improve the performance and durability of components manufactured through additive processes. Full article

For space missions to either the Moon or Mars, protecting mechanical moving parts from the abrasive effects of prevailing surface dust is crucial. This paper compares the abrasive effects of two lunar and two Martian simulant regoliths using special pin-on-disc tests on a stainless steel/polytetrafluoroethylene (PTFE) sealing material pair. Due to the regolith particles entering the contact zone, a three-body abrasion mechanism took place. We found that friction coefficients stabilised between 0.2 and 0.4 for all simulants. Wear curves, surface roughness measurements, and microscopic images all suggest a significantly lower abrasion effect of the Martian regoliths than that of the lunar ones. It applies not only to steel surfaces but also to the PTFE pins. The dominant abrasive micro-mechanism of the disc surface is micro-ploughing in the case of all tests, while the transformation of the counterface is mixed. The surface of pin material is plastically transformed through micro-ploughing, while the material is removed through micro-cutting due to the slide over hard soil particles. Full article

Zirconium-based alloys are highly regarded by the research community for their exceptional corrosion resistance, thermal stability, and mechanical properties. In our work, we investigated two newly developed alloys, Zr_42.42Cu_41.18Al_9.35Ag_7.05 and Zr_46.81Cu_35.44Al_10.09Ag_7.66, in the form of ingots and ribbons. In the course of our investigation, we conducted a comprehensive structural and thermal analysis. In addition, an examination of the corrosion activity encompassing electrochemical studies and an analysis of the corrosion mechanisms was carried out. To further evaluate the performance of the materials, tests of their mechanical properties were performed, including microhardness and resistance to abrasive wear. Structural analysis showed that both alloys studied had a multiphase, crystalline structure with intermetallic phases. The samples in the form of ribbons showed improved corrosion resistance compared to that of the ingots. The ingot containing a higher content of copper Zr_42.42Cu_41.18Al_9.35Ag_7.05 was characterized by better corrosion resistance, while showing lower average hardness and a higher degree of abrasive wear based on SEM observations after pin-on-disc tests. Full article

Vanadis 8 steel is a tool steel manufactured by powder metallurgic processing. Its main alloy elements are V, Cr and Mo. By implementing an experimental design with five factors—all of them are related to the thermal processing of this steel and with ionic nitriding—the effects of said factors on adhesive wear resistance and corrosion resistance were studied. For this purpose, Pin-on-Disc wear tests and lineal polarization resistance tests were carried out using an aqueous solution with 3.5% NaCl by weight. The main aim was to increase this steel use in more aggressive environmental conditions, such as in coastal environments. By means of XRD, the percentage of retained austenite was determined, and by SEM-EDX, the microstructure was revealed. The conclusion is that adhesive wear resistance is improved if thermal processing parameters are at such levels that increase austenite destabilization and reduce retained austenite content. This means to destabilize austenite at 1180 °C during 1 h, with oil quenching, tempering at 520 °C during 2 h and ionic nitriding at 520 °C during 2 h. Corrosion resistance is highly improved with ionic nitriding. At the same time, to compensate for the negative effect on corrosion resistance of a high density of primary and secondary carbides, it is essential to carry out the ionic nitriding treatment. The harmful effect of electrochemical microcells that appear in the carbide/matrix interface is compensated by the passivating effect generated by the nitrided surface. Full article

To meet the demand for energy-efficient and, at the same time, durable, functional components, the improvement of tribological behavior is playing an increasingly important role. One approach to reducing friction in lubricated tribological systems is the microtexturing of the surfaces tailored to the application, but in most cases, this leads to increased manufacturing costs and thus often makes their use in industry more difficult. In this work, we, therefore, present an approach for an efficient design and fully integrated production process using a cam tappet as an example. For the used cam tappet contact, we first determined the optimal texture geometries using two differently complex EHL (elastohydrodynamic lubrication) simulation models. Based on these, textured tappets were manufactured in a combined manner using sheet-bulk metal-forming and deposition with a diamond-like-carbon (DLC) coating for additional wear protection without further post-processing of the coating. We show that the simulation approach used has a rather subordinate influence on the optimization result. The combined forming of components with textured surfaces is limited by the local material flow, the resulting texture distortion, and tool wear. However, a targeted process design can help to exploit the potential of single-stage forming. The applied DLC coating has good adhesion and can completely prevent wear in subsequent reciprocal pin-on-disc tests, while the friction in the run-in behavior is initially higher due to the soothing effects of the coating. The experiments also show a tendency for shallow textures to exhibit lower friction compared to deeper ones, which corresponds to the expectations from the simulation. Full article

This paper studied the tribological behaviour of parts manufactured using fused filament fabrication (FFF) technology with PETG (polyethylene terephthalate glycol) coated with IGUS tribological filaments. The research focuses on analysing how these multi-material parts behave under different loads. The objective of this study is to evaluate the wear resistance and friction coefficient of parts coated with different thicknesses of IGUS material. The methodology employs pin-on-disc (PoD) tribological tests to measure behaviour under various load conditions and coating thicknesses. The results indicate that increasing the coating thickness improves surface stability and reduces roughness, although it does not significantly affect the average friction coefficient. This research concludes that coating thickness has a moderate impact on surface quality and that the applied load significantly influences the depth and width of the wear groove. This contribution is valuable for the field of additive manufacturing as it provides a better understanding of how to optimise the tribological properties of parts manufactured using FFF, which is crucial for industrial applications where wear and friction are critical factors. The practical application includes the potential improvement of components in the automotive and aerospace industries. Full article

Total hip arthroplasty (THA) is a surgical procedure for patients with pain and difficulty walking due to hip osteoarthritis. In primary THA, the acetabulum and femoral head are replaced by a prosthesis where the modular femoral head and inner liner of the acetabulum form the bearing surface. The most popular bearing surface used in the United States, metal-on-polyethylene, consists of a cobalt–chromium molybdenum (CoCrMo) alloy femoral head that articulates with a polyethylene acetabular liner, typically made of highly cross-linked polyethylene. While successful in most cases, THA sometimes fails, commonly from aseptic loosening due to the wear debris of polyethylene. Fine-particle shot peening (FPSP) is a simple method for enhancing the mechanical properties and surface properties of metal, including reducing friction and enhancing the lubrication properties of the metal surface. In this study, we applied FPSP to the CoCr in the femoral head of a hip prosthesis to improve its surface properties and conducted experiments with pin-on-disc tribometers using CoCr as a pin and highly cross-linked polyethylene as a disc to mimic the THA implant. The results show that FPSP significantly enhances the tribological properties of the CoCr surface, including lubrication; decreases the friction coefficient; and decreases the polyethylene wear volume. Full article

Modern engine bearing materials encounter the challenge of functioning under conditions of mixed lubrication, low viscosity oils, downsizing, start–stop engines, potentially leading to metal-to-metal contact and, subsequently, premature bearing failure. In this work, two types of polymer overlays were applied to the bearing surface to compensate for extreme conditions, such as excessive loads and mixed lubrication. Two different polymer overlays, created through a curing process on a conventional engine bearing surface with an approximate thickness of 13 µm, were investigated for their friction and wear resistances under a 30 N load using a pin-on-disc setup. The results indicate that the newly developed polymer overlay (NDP, PAI-based coating) surface has a coefficient of friction (COF) of 0.155 and a wear volume loss of 0.010 cm³. In contrast, the currently used polymer overlay (CPO) in this field shows higher values with a COF of 0.378 and a wear volume loss of 0.024 cm³, which is significantly greater than that of the NDP. It was found that, in addition to accurately selecting the ratios of solid lubricants, polymer resins, and wear-resistant hard particle additives (metal powders, metal oxides, carbides, etc.) within the polymer coating, the effective presence of a transfer film providing low friction on the counter surface also played a crucial role. Full article

DIN 16MnCr5 is commonly used in mechanical engineering contact applications such as gears, joint parts, shafts, gear wheels, camshafts, bolts, pins, and cardan joints, among others. This study examined the microstructural and mechanical properties and tribological behavior of different surface treatments applied to DIN 16MnCr5 steel. The samples were hardened at 870 °C for 15 min and then quenched in water. The surface conditions evaluated were as follows: quenched and tempered DIN 16MnCr5 steel samples without surface treatments (control group), quenched and tempered DIN 16MnCr5 steel samples with gas-nitriding at 560 °C for 6 h, quenched and tempered DIN 16MnCr5 steel samples with pack boriding at 950 °C for 4 h, and quenched and tempered DIN 16MnCr5 steel samples with duplex gas-nitriding and pack boriding. Microstructure characterization was carried out using metallographic techniques, optical microscopy, scanning electron microscopy with energy-dispersive spectroscopy, and X-ray diffraction. The mechanical properties were assessed through microhardness and elastic modulus tests using nanoindentation. The tribological behavior was evaluated using pin-on-disc tests following the ASTM G99-17 standard procedure under dry sliding conditions. The results indicated that the surface treated with duplex gas-nitriding and pack boriding exhibited the highest wear resistance and a reduced coefficient of friction due to improved mechanical properties, leading to increased hardness and elastic modulus. Full article