Formation Of Transfer Layer Research Articles

Improve wear resistance of C/C composites as artificial bone using diamond-like carbon coatings

In this study, diamond-like carbon (DLC) coatings and silicon-doped diamond-like (Si-DLC) coatings were prepared on the surface of C/C composites by a combination of plasma-enhanced chemical vapor deposition (PECVD) and magnetron sputtering processes. The film composition, microstructure and atomic bond structure were characterized using X-ray photoelectron spectroscopy, field-emission scanning electron microscopy and Raman spectroscopy. The mechanical properties and friction behavior related to the Si element were investigated using nanoindentation and HT-1000 high temperature friction and wear tester. The biocompatibility of the materials was also evaluated by the MG-63 proliferation test. The results indicate that Si elements were successfully incorporated into the DLC films, bonding with C and O atoms, which altered the thermal stability and microstructure of the coatings, reduced the internal stress of the films, and increased disorder. Compared to C/C composites, all coated layers exhibited lower coefficients of friction, with the formation of transfer layers and graphitization induced by friction contributing to the excellent tribological performance. Both coatings showed no cytotoxicity and demonstrated good biocompatibility. Both coatings are effective in reducing wear and chip losses in C/C composites when used as artificial bones. This work suggests that diamond-like carbon coated C/C composites can be excellent structural materials for human body in biomedical science.

Revealing wear mechanisms of coated shafts in low-speed journal bearings immersed in liquid Lead-Bismuth Eutectic (LBE)

This study investigates wear mechanisms of coated shafts in journal bearings within liquid lead-bismuth eutectic. Shafts were coated with TiAlN, a-C:H, multi-layer TiAlN with sputtered carbon, and chrome plating. Bearings made from sintered iron with carbon inclusions (DEVA 120 and DEVA 121) were tested in LBE at 200 °C and 50 rpm using a dedicated test rig. The a-C:H coatings failed due to tribofilm wear with DEVA 120, while TiAlN coatings failed from fatigue wear with DEVA 120 but succeeded with DEVA 121. Chrome-plated shafts experienced abrasive and adhesive wear with DEVA 121 but survived DEVA 120 due to transfer layer formation. The study highlights the need to understand wear mechanisms and material compatibility to develop durable coatings for harsh environments.

Enhanced high-temperature tribological performance of fluorinated tetrahedral amorphous carbon (ta-C:F) coatings in sliding applications

This study investigated the dry sliding behaviour of fluorinated tetrahedral amorphous carbon (ta-C:F) coatings against uncoated 52100 steel at temperatures ranging from 25 °C to 300 °C. The ta-C:F coatings demonstrated significant reductions in both the coefficient of friction(COF) during the running-in stage and at steady state, particularly within the temperature range of 25 °C to 200 °C, surpassing the performance of well-established a-C:H coatings. SEM analyses revealed the formation of transfer layers on the contact surface of 52100 steel when tested against ta-C:F coatings at temperatures up to 200 °C, while none were detected at temperatures ≥250 °C. Raman spectroscopy indicated a transition from sp3 to sp2 carbon structures in the carbonaceous transfer layers with increasing temperature, and XPS scans confirmed an increase in fluorine (F) concentration within these layers, correlating with reduced COF. The comparative analysis at 120 °C emphasized the intrinsic advantages of ta-C:F coatings in high-temperature applications, demonstrating a nearly 50% lower COF (0.08) when compared to traditional boundary-lubricated steel-to-steel sliding contacts. These findings have significant implications for enhancing the efficiency and durability of various mechanical systems, particularly in industries like automotive and manufacturing.

Improving the tribological performance of CFRPTFE at elevated temperature by sliding against Ti-TiCx/DLC film

Polytetrafluoroethylene (PTFE) has been widely used in industrial field for sealing parts. However, it is well known that PTFE is always subject to serious wear at high temperature (over 150 °C), which has become the main drawback limiting serve life of important equipment such as compressors. In this paper, a new solution is proposed for improving the wear resistance of carbon fibers-reinforced PTFE (CFRPTFE). Multilayer Ti-TiCx/DLC film is prepared and used as the counterface of CFRPTFE. Friction and wear tests at high temperature (200 °C and 250 °C) are carried out. The uncoated 17-4PH steel disks precisely polished by abrasive papers with different grain sizes are used as the reference counterface (SS80 and SS7000). It is found that by sliding against Ti-TiCx/DLC film, the tribological behaviors of CFRPTFE at high temperature can be improved. The friction coefficient between CFRPTFE and DLC under different test conditions can be kept in stable state. The wear rates of CFRPTFE reduce by 50%–70% compared to SS80, and reduction of 20%–40% can be observed when compared to SS7000. It can be found that graphitization transition at high temperature promotes the transfer layer formation and contributes to lower friction and lower wear compared to traditional processed counterface at high temperature. These significant improvements can prolong the lifetime of CFRPTFE moving parts used in high-temperature and heavy-load applications. Finally, engineering verification of the proposed friction pair is carried out in miniature oil-free high-pressure compressor.

Ultrasonic-Vibration-Superimposed Face Turning of Aluminium Matrix Composite Components for Enhancing Friction-Surface Preconditioning

Aluminium matrix composites (AMCs) represent an important group of high-performance materials. Due to their specific strength and a high thermal conductivity, these composites have been considered for the large-scale production of brake discs. However, preconditioning the friction surfaces is necessary to avoid severe wear of both the brake discs and the brake linings. This can be achieved through controlled friction against commercially available brake-lining materials and the formation of transfer or reactive layers (tribosurfaces). Homogeneous tribosurfaces allow for nearly wear-free brake systems under moderate brake conditions. In this work, preconditioning was carried out with a pin-on-disc tester, aiming for the fast creation of homogeneously formed and stable tribosurfaces. The influence of surface microedges perpendicular to the direction of friction on the machined AMC surfaces on the build-up speed and homogeneity of the tribosurfaces was investigated. The microedges were generated using ultrasonic-vibration-superimposed face turning. Thereby, the vibration direction corresponded to the direction of the passive force. For research purposes, the distance of the microedges was changed by varying the cutting speed and feed. The experiments were carried out using AMC disc specimens with a reinforcement content of a 35% volume proportion of silicon carbide particles. Machining was realised with CVD-diamond-tipped indexable inserts. The evaluation of the generated surfaces before and after preconditioning was achieved using 3D laser scanning microscopy and scanning electron microscopy. It was demonstrated that ultrasonic-vibration-superimposed face turning effectively generated microedges on the AMC surfaces. The results show that larger distances between the microedges enhanced the formation of stable tribosurfaces. Thus, the tribosystem’s steady state was reached quickly. Therefore, the benefits of AMC-friction-surface microstructuring on the generation of tribosurfaces under laboratory conditions were proven. These findings contribute to the development of high-performance AMC brake systems.

Investigation of mechanical and tribological performance of wood dust reinforced epoxy composite under dry, wet and heated contact condition

Abstract Natural fibers have received a lot of attention from academia as well as industry in the context of sustainable materials. Since they are more environmentally friendly than traditional synthetic materials, their physico-mechanical and frictional properties such as porosity, moisture absorption, high strength, modulus, toughness, and wear resistivity make them appropriate for a variety of industrialized applications where issues involving a significant quantity of dumping must be taken into account. The paper introduces an attempt to use epoxy-based composites reinforced with wood dust for various applications. The composites are prepared with various wood filler stacks (0, 2.5, 5, 7.5, 10, and 12.5 wt%) embedded with epoxy resin and subjected to tensile and flexural testing. The highest ultimate tensile strength achieved at 7.5 wt% wood dust support is 22 MPa, whereas the highest flexural modulus is 0.48 GPa at 12.5 wt% composites. The composite’s wear properties is examined under dry, wet, and heated contact conditions using a pin-on-disk (POD) machine. In dry condition, coefficient of friction (COF) varies from 0.10 to 0.38 whereas, in wet condition, the value of COF decreased by 70–83 %. In heated state, the COF is increased by up to 15 % when varying the temperature from 40 °C to 80 °C. The composite exhibits better wear behavior in the lower filler support than in the higher filler support due to the sturdy connection between the matrix and filler. On the other hand, the wet state’s tribological performance is superior to the dry and heated states. During surface morphology analysis, it is found that various voids, crack formation, wear debris, and thin transfer layer formation take place on the composite.

Experimental studies on the effect of application methods on the lubricant performance during serial production in automotive industry

Lubricant breakdown and galling phenomena are widely observed at the tooling surface during the stamping of aluminium components for the automotive industry, which compromise the formed surface quality and reduce tool-life. The lubricant performance has been found to be significantly influenced by its method of application. In the present research, a dedicated lubricant was evaluated by utilizing an advanced lab-scale friction testing system, TriboMate, and the effects of lubricant application method and lubricant quantity on the coefficient of friction evolution were investigated. It has been found that lubricant performance was significantly improved when the lubricant was applied on the hot workpiece blank, compared to the cold tooling surface, and when the lubricant quantity was increased. The gradual increase of friction evolution despite lubricant application on the workpiece blank was found to be due to the formation of an aluminium transfer layer at the tooling surface.

Tribocorrosion of TiC-based composites incorporating Ni and Co binders in saline solutions

Metallic binders impart necessary toughness to ceramic-metal composites, yet are vulnerable to corrosion and wear. Thus far, the tribocorrosion mechanism remains little understood, obstructing the design of durable composites for ocean drilling applications. Against this backdrop, we selected the TiC-based composites encompassing the Ni and Co binders having different standard electrode potentials as model systems, and studied their tribocorrosion behaviors with the aid of microscopic characterizations and first-principles calculations. Results showed that the TiC-Ni system maintained lower corrosion current densities at the pure corrosion condition, due to the reduced tendency of galvanic corrosion. Such system also realized lower coefficient of friction (COF) and wear losses at the pure wear condition, benefiting from the reduced adhesion at the sliding interfaces as well as the improved composite fracture toughness. Under corrosion-wear interactions, however, the TiC-Co system revealed alleviated material losses, as the rapid build-up of oxide tribolayers enhanced the surface hardness and facilitated the transfer layer formation. Thus, contrary to the intuition that corrosion-resistant binders should be beneficial to the tribocorrosion resistance, the current work highlighted the binder's ability to generate surface layers that helped to resist corrosion-accelerated wear, a point that needs to be emphasized in future development of robust composite materials.

Fretting wear resistance of amorphous/amorphous (AlCrFeNi)N/TiN high entropy nitride nanolaminates

The application of amorphous high entropy ceramics as wear-resistant materials is limited due to their inherent brittleness at room temperature and strain softening during deformation. In order to overcome this limitation, we constructed amorphous/amorphous (AlCrFeNi)N/TiN nanolaminates with varying modulation period thickness by introducing a second amorphous phase through reactive radio frequency (RF) magnetron sputtering, along with corresponding monolithic amorphous films. Microstructure, mechanical properties, and tribological behaviors of the films were characterized wear in detail. Fretting wear results show that the nanolaminates with an average modulation period of 6 nm exhibited a wear rate of 2.8 times lower than that of the (AlCrFeNi)N film and 8.4 times lower than that of the TiN film. Further analysis using FIB-TEM revealed that the enhanced wear resistance of (AlCrFeNi)N/TiN nanolaminates was attributed to the high-density heterointerfaces. These interfaces inhibited the initiation and propagation of mature shear bands and acted as barriers to stress distribution. Additionally, the oxide composite layer at the interface demonstrated a synergistic effect through a mechanically induced tribo-chemical reaction, resulting in slight plastic deformation. For the amorphous (AlCrFeNi)N film, moderate wear resistance was achieved through the formation of transfer layer at the interface. For the amorphous TiN film, the dimensional stability of the film deteriorates due to the significant strain softening that occurs during deformation. This study deepens our understanding of the friction mechanisms involved in amorphous high entropy ceramics, offering valuable insights for the design of high damage-resistant materials.

Fabrication of Visible Light Sensitive Electrospun TiO2 Nanofibers Using Squaric Acid for Photocatalytic Application

Degradation of organic pollutants using photocatalysts has gained utmost importance, due to the increasing environmental pollution. Despite various attempts to improve the photocatalytic efficiency of well-known photocatalysts such as titanium dioxide (TiO2), by making them visible light active, various issues need to be resolved. In this work, attempts have been made to improve the visible light absorption capacities of the electrospun TiO2 nanofibers by modification using squaric acid (SqA). An interfacial charge transfer complex is formed by the condensation reaction between the hydroxyl groups on the surface of the TiO2 nanofibers and the SqA ligand. Various characterizations confirmed that the modification using SqA had led to the formation of the interfacial charge transfer layer, without affecting the crystallinity or morphology of the TiO2 nanofibers. The modified TiO2 nanofibers showed sensitivity to visible light with red shift in the optical absorption. It exhibited an improved photocatalytic efficiency of 85% against the degradation of tetracycline, compared with 60% for unmodified TiO2 nanofibers. It also showed an increased rate of degradation of 0.21 mg/L/min, when compared with the 0.13 mg/L/min of unmodified TiO2 nanofibers.

Investigation of the microstructure and mechanical properties of borosilicate reinforced magnesium nano composites

In the current investigation, nano borosilicate of varying weight proportions was used to strengthen AZ91D magnesium alloy. The squeeze casting process was used to create the material, and its microstructure and mechanical characteristics were analyzed to determine its suitability for functional applications. Using SEM and ASTM standards, morphology and mechanical properties were analyzed. Morphological studies indicate that reinforcing particles are evenly distributed throughout the matrix alloy's regions. Morphological studies illustrates that the nBS was uniformly distributed in AZ91D alloy without forming residual pore. The hardness (21 %) and tensile properties (26 %) of synthesized nano composites was improved due to reduction in grain size and higher dislocation density in comparison with monolithic alloy. Owing to the strong interfacial bonding strength and the dispersion strengthening the compressive strength of magnesium nano composites increased (24 %). As a result of improvements in the load bearing capacities of the reinforcing particles as well as the formation of transfer layers between the matrix and the reinforcement particles wear resistance significantly improved (25 %).

Frictional performance of C/C–SiC materials at high loads: The role of composition and third-body

Ceramic matrix composites like carbon fiber-reinforced silicon carbon (C/C–SiC) are brake materials for applications at high thermo-mechanical loads. This study investigates the influence of three C/C–SiC pad materials with different compositions on frictional performance. For this purpose, the ceramic pad materials were tested against a steel disk on a dynamometer at brake pressures from 20 to 60 MPa. A large effect due to the different Si and SiC contents of the three pad materials on the frictional behavior was expected. Although the wear rates differed from 40 to 140 mm3/MJ, only marginal differences were found for the coefficient of friction. Hence, additional tests to interrupt and sequence the brake procedure revealed the formation of an intermediate metallic transfer layer from the steel disk on the ceramic pads. The formation and disappearance of this third-body, which was not found in start-complete-stop testing, and the consequences for the frictional properties are discussed.

Tribological Performance of Laser Shock Peened Cold Spray Additive Manufactured 316L Stainless Steel

Abstract In recent years, cold spray additive manufacturing (CSAM) has become an attractive technology for surface modification and protection. However, due to the intrinsic porous nature of CSAM coatings, they suffer from rapid material degradation due to premature brittle fracturing induced by tribological interactions. In this work, laser shock peening (LSP) was utilized as a post-processing technology to mitigate the surface porosity and augment the surface characteristics of CSAM 316L stainless steel (SS). Due to the synergistic influence of severe plastic deformation and rapid surface heating, the surface porosities were effectively healed, thus reducing the surface roughness. Combined with the surface-strengthening effects of LSP, the frictional resistance and transfer layer formation on the CSAM LSP surfaces were reduced. The underlying mechanisms for these findings were discussed by correlating the atomic, microstructural, and physical features of the LSP surfaces. Based on these findings, it can be suggested that LSP is indeed a useful technique to control the surface characteristics of CSAM 316L SS coatings.

Current-carrying wear characteristics of Al-Cu alloys against stainless steel

The wear characteristics of Al-Cu alloy against stainless steel were investigated on the equipment with current applied across the sliding interface. The effects of Cu content (5% ∼ 15%) and current density on the wear surface morphology and wear rate of the alloy were discussed. The results show the wear rate of Al-Cu alloys generally increased with increasing current density and Cu content, revealing a negative relationship between hardness and current-carrying wear rate. It was found that a material transfer layer would be formed on the sliding surface of the stainless steel pin, which induced the adhesive wear of Al-Cu alloy samples and decreased the wear rate of the alloy. Al-Cu alloy with high Cu content had a slower formation of the material transfer layer.

Effect of magnetic field intensity on friction and wear of TiN- and TiCN-coated neodymium magnets

Numerous machinery components are constantly influenced by magnetic fields, mainly because of the environments in which they operate. In addition, these components show different friction and wear characteristics throughout their lifetime because of their operating conditions. Here, the tribological characteristics of magnetized materials were investigated. The magnet specimens consisted of a neodymium magnet, which is one of the strongest magnets, coated with TiN or TiCN. Sliding tests were conducted with a ball-on-disk-type tester. The tribological properties of magnetized samples were compared considering their different coating conditions. The wear amount was measured under constant load and cycle conditions. The measured wear amount was used to evaluate the specimens’ tribological characteristics. One of the important factors affecting the wear and friction properties is the magnetic flux density and the formation of an oxidative transfer layer under a magnetic field. Samples subjected to a magnetic field showed better wear resistance as a result of a magnetic effect that resulted in debris being oxidized at the rubbing interface, which reduced debris production. These results can be used to evaluate the reliability of mechanical components exposed to a magnetic field.

Investigation of tribological properties of polypropylene (PP)—Acrylonitrile butadiene styrene (ABS) blends reinforced with graphene nano-platelets (GNPs)

The tribological response of PP-ABS/GNPs nanocomposites fabricated via extrusion and injection molding with varying wt% GNPs fractions were examined under varying normal load and sliding speed wear test parameters. The specimens with 3% GNPs and 11% GNPs respectively exhibited the lowest and highest specific wear rates and COF under all test conditions. Increased load led to significantly reduced COF values, whereas increased sliding speed led to a slight reduction in COF by contributing to the formation of a continuous transfer layer. Addition of GNPs helped to retain the worn material on the contact surface and led to improved wear resistance up to the weight fraction of 3% after which non-homogeneous dispersion of GNPs occurred.

Microstructure, mechanical and high-temperature tribological properties of MoS2-Cr-Ag composite films

In the present work, MoS2-Cr-Ag composite films with various Ag content were synthesized by magnetron sputtering. The microstructure, mechanical and high-temperature tribological properties of as-prepared films were systematically investigated. The results indicated that MoS2-Cr-Ag composite films showed the preferred orientation of (002) crystal plane, which makes it have a dense structure. The maximum micro-hardness of MoS2-Cr-Ag composite films reached up to 309 HV, which was more than 4 times that of pure MoS2. The tribological properties of MoS2-Cr-Ag composite films at room temperature were evaluated. It was found that MoS2-Cr-Ag composite films presented significantly superior tribological properties than MoS2-Cr film at room temperature, which could be ascribed to the addition of Ag inhibits the oxidation of MoS2 and promotes the formation of a dense transfer layer on the surface of friction pair during the friction process. Furthermore, the tribological properties of MoS2-Cr-Ag composite films at 350 °C in air were also evaluated. It was also found that MoS2-Cr-Ag composite films presented superior tribological properties than MoS2-Cr film, which could be ascribed to the formation of Ag2Mo4O13 during the friction process at elevated temperature. In particular, MoS2-Cr-Ag composite film with 9.22 at. % Ag presented superior tribological properties at room temperature and at 350 °C high temperature. These results indicated that the appropriate amount of Cr and Ag co-doping can significantly improve the tribological properties of MoS2-based films at room temperature and 350 °C in air. It provided a design methodology to ameliorate the tribological properties of MoS2 film.

Friction behaviors and wear mechanisms of multi-filler reinforced epoxy composites under dry and wet conditions: Effects of loads, sliding speeds, temperatures, water lubrication

Polymer composites have been extensively used as marine engineering structures under extreme environmental conditions for their mechanical/thermal stability and special self-lubricating performance. In the present paper, the multi-fillers reinforced epoxy composites (MFREC) had been prepared and analyzed. The mechanical, thermal properties, friction behaviors and wear mechanisms of MFREC were systematically investigated. The research results showed that the increase (98.46%) of MFREC tensile toughness was mainly attributed to improvement of tensile strength (9.56%), tensile modulus (22.07%), and elongation at break (39.09%) due to multi-fillers reinforcement and its compatibility with the epoxy matrix. Then, increases in loads and temperatures reduced frictional coefficients at the expense of wear rate and line roughness of MFREC due to the change in contact state (from elastic to plastic state). Additionally, effects of sliding speeds and water lubrication on MFRCE were not obvious compared to loads and temperatures owing to the formation of transfer layer and lubrication of water film. Furthermore, among the several influencing factors studied for tribological changes, MFREC was the most sensitive to the load effect due to the higher shear force of applied-load steel-ball by a tangential displacement, temperature second, sliding speed third and water lubrication last because of the lubricating effect and heat dissipation function of water film.

Synthesis of self-grown nanostructured NiO via pulse ionization for binderless psuedocapacitor electrode

In air laser irradiation was carried out onto Ni sheet with ultra-short, pulsed laser for direct synthesis of NiO thin layer. The layer consisted of 3D nanostructures with excellent porosity and enhanced surface area for the fabrication of pseudo capacitive electrodes. Mainly laser parameters such as scan speed and frequency were analyzed. It was observed that at lower scan speed, excellent surface area was achievable which during microscopy, the morphology of the structure depicted a “broccoli” like structure. The oxidized layer forms because of series of events at ultra-short duration associated with laser-material interaction in ambient conditions such as energy transfer, heating, melting, evaporation, ionization, plasma formation, rapid quenching, and oxide layer formation. The obtained oxide layer consists of 3D self-standing nanostructure with the active material directly growing on the substrate without the requirement of binder. A combined contribution of pseudo capacitance due to surface rapid, redox reactions along with ion adsorption-desorption because of EDL's presence provided remarkable performance. With this fabrication approach, NiO, a battery active material demonstrated fast charge-discharge capabilities evident from galvanostatic charge-discharge test. Owing to the idea of one step direct synthesis and green fabrication process, the performance of the electrode was remarkable. An areal capacitance of 98.682 mF cm−2 and specific capacity of 59.209 mC cm−2 was achievable at a current density of 1 mA cm−2. This work promotes the idea of green synthesis of nano morphology and one step fabrication method.

Gradient Structure of the Transfer Layer in Friction Stir Welding Joints.

Despite a thirty-year history of friction stir welding, some basic aspects still remain unclear. In particular, questions arise about mass transfer and the formation of transfer layers. It is not clear why there are visible boundaries between the layers. The structure of the transfer layer has been studied very little. These issues are not considerably important from the viewpoint of obtaining high-quality welds, but they can help to a better understanding of the welding process. In this paper, the structural evolution in the transfer layer of 2024 aluminum alloy welds produced under various loads and with ultrasonic assistance is discussed. Structural studies revealed a gradient structure in the transfer layer. The grain size, the volume fraction and size of large intermetallic particles decrease towards the center of the layer, while the volume fraction of semi-coherent secondary particles increases. As a result, the microhardness is higher in the center of the transfer layer. A mass transfer mechanism is proposed based on the experimental results: the rotating tool transfers the material back layer by layer during welding; the contacting layers rub against each other and generate heat, due to which the structure at the layer boundary changes. With increasing axial force on the tool, the grain size also increases due to higher heat generation. Ultrasound has almost no effect on the grain structure, but it reduces the volume fraction and size of secondary particles and microhardness.