Transfer Film Research Articles

Effect of Argon Flow Rate on Tribological Properties of Rare Earth Ce Doped MoS2 Based Composite Coatings by Magnetron Sputtering

Exploring the doping components of the coating is of great significance for improving the tribological properties of the MoS2-based coating. The optimization of magnetron sputtering process parameters can also improve the coating quality. In this paper, the effects of working gas flow rate on the microstructure in a vacuum chamber, nano-hardness, and tribological properties of Ce-Ti/MoS2 coatings were studied using DC and RF unbalanced co-sputtering technology. It is found that the coating structure was coarse and porous when the Ar flow rate was excessive (70 sccm), significantly affecting the mechanical properties; there are pit defects on the surface of the coating when the flow rate is just minor (30 sccm), and the coating easily falls off during the friction process. When the flow rate is 40~60 sccm, the coating grows uniformly, the hardness reaches 7.85 GPa at 50 sccm, and the wear rate is only 4.42 × 10−7 mm3 N−1 m−1 at 60 sccm. The coating doped with Ce and Ti is an approximate amorphous structure. Under appropriate gas flow rate conditions, the friction induces a transfer film with a layered structure, and the MoS2 (002) crystal plane orientation is arranged in parallel at the edge of the wear debris, effectively reducing the shear force during sliding and reducing wear. Based on rare earth doping, this study improves the tribological properties by optimizing the working gas parameters, which plays a reference role in preparing high-quality MoS2-based coatings.

Sputter‐Deposited α‐MoO3 Interlayers for van der Waals Epitaxy and Film Transfer

AbstractIntegration of functional thin films onto flexible substrates is driven by the need to improve the performance and durability of flexible electronic devices. A van der Waals epitaxy technology that accomplishes the transfer of oxide or metal thin films via exfoliation or dissolution of sacrificial α‐MoO3 layers produced by sputtering is presented. The α‐MoO3 thin films, consisting of weakly bonded 2D layers, grow epitaxially on SrTiO3 (001) substrates, exhibiting mosaic domains rotated by 90°. Metallic Au films grown on the α‐MoO3 are transferred by mechanical exfoliation or by dissolving the α‐MoO3 in water at 45 °C. Spinel‐structured CoFe2O4 thin films grown on α‐MoO3 layers are easily transferred to flexible substrates via mechanical exfoliation, and the magnetic anisotropy of the transferred CoFe2O4 films is modulated by bending.

Electro-capillary peeling of thin films

Thin films are widely-used functional materials that have attracted much interest in academic and industrial applications. With thin films becoming micro/nanoscale, developing a simple and nondestructive peeling method for transferring and reusing the films remains a major challenge. Here, we develop an electro-capillary peeling strategy that achieves thin film detachment by driving liquid to percolate and spread into the bonding layer under electric fields, immensely reducing the deformation and strain of the film compared with traditional methods (reaching 86%). Our approach is evaluated via various applied voltages and films, showing active control characterizations and being appropriate for a broad range of films. Theoretically, electro-capillary peeling is achieved by utilizing the Maxwell stress to compete with the film’s adhesion stress and tension stress. This work shows the great potential of the electro-capillary peeling method to provide a simple way to transfer films and facilitates valid avenues for reusing soft materials.

Magneto-Thermo Heat Transfer of a Chemically Reactive and Viscous Dissipative Casson Nanofluid Thin Film Over an Unsteady Stretching Surface with Variable Thermal Conductivity

This paper addressed unsteady magnetohydrodynamic flow and heat transfer of an incompressible Casson nanofluid thin film past a stretching sheet by considering the features of thermal radiation, chemical reaction, and viscous dissipation. The problem is modeled mathematically, and the governing basic equations are brought into nonlinear ordinary differential equations by utilizing appropriate similarity transformations. Then the transformed equations are then solved numerically by using the bvp4c solver. The influences of pertinent physical variables are performed on velocity, temperature gradient, and nanoparticle concentration gradient profiles. It is seen that the profile of the nanoparticle concentration gradient enhances by increasing the values of the Schmidt number, whereas the opposite trends are observed by increasing the values of the thermophoresis parameter. It is also analyzed that by increasing the values of the thermophoresis parameter, there is an increase in the profiles of the temperature and concentration distributions. The computed results are obtained by giving main consideration to the convergence process and comparing them with the results existing in the literature.

Fabrication of polarity inverted LiNbO3/GaN channel waveguide by surface activated bonding for high-efficiency transverse quasi-phase-matched wavelength conversion

GaN is an attractive material for integrating optical quantum devices. Adding a large optical nonlinearity of MgO doped congruent LiNbO3 (MgO:CLN) to GaN will improve the efficiency of quantum light sources. In this work, we proposed transverse quasi-phase-matched wavelength conversion devices with waveguide core materials of MgO:CLN and GaN. The waveguide core is formed by an adhesion-free surface activated bonding (SAB). A high thin film transfer yield was achieved with a high bonding strength of 4 MPa by optimizing the bonding conditions and reducing the surface roughness of the GaN film to be 0.5 nm in a 100 × 100 μm2 area using chemical mechanical polishing. The MgO:CLN/GaN waveguide structure was successfully fabricated by MgO:CLN thin film transfer, lift-off and dry etching processes. This MgO:CLN/GaN adhesion-free SAB technique is expected to be applied to various devices, such as optical devices and electronic devices, to enhance their functionality.

Towards Controlled Transfer of (001) β-Ga2O3 to (0001) 4H-SiC Substrates

We demonstrate successful surface blistering of He-implanted (001) β-Ga2O3 substrates, bonding to (0001) 4H-SiC, and initial results towards large-area transfer of (001) β-Ga2O3 to 4H-SiC. Surface blistering of unbonded, implanted substrates is an important indication of successful exfoliation and transfer of films, which is achieved by initiating He bubble nucleation during a low temperature anneal followed by bubble growth at a high temperature anneal. Prior to annealing, implanted substrates were bonded to (0001) 4H-SiC at room temperature using a thin ~5 nm Ti interlayer. However, the β-Ga2O3 substrate did not wafer split from the bonded structure after annealing. Instead, small area transfers up to ~200 μm were achieved (~7% of the total bonded area transferred while the entire structure remained bonded). Further optimization of implant parameters is underway. These are promising results towards achieving large wafer-scale (001) β-Ga2O3 composite wafers suitable for β-Ga2O3 devices with efficient thermal management characteristics.

Tribological properties of friction pairs under double composite surface configuration with diamond film and laser texture

A composite model, which combined diamond thin film with surface microstructure, was designed on the surface of silicon carbide by picosecond laser and hot filament chemical vapor deposition. And the multifunctional friction and wear tester was used to study the tribological performance of the friction pair (silicon carbide-graphite) under oil-poor conditions to examine the tribological performance of the friction pair in terms of surface temperature rise and time-varying wear. The results show that the friction coefficient under the composite modeling of surface microstructure and diamond film reaches 0.009, and at the same time, the surface temperature of the composite modeling is only 61.2 ℃, which is 5.1% lower than that of only diamond film and 62.1% lower than that of no surface treatment, which indicates that the high frictional heat has caused a significant graphitization transition in the film. And the surface of the friction sub-surface with the lowest temperature (surface microstructure and diamond thin film composite modeling) kept the carbon content at more than 90% without the formation of Si-C bonding, which guaranteed the complete carbon friction transfer film; At the same time, the ID/IG ratio of the friction surface under the composite modeling of the surface microstructure and diamond film is about 0.06 at the abrasion mark, the ID/IG ratio of the diamond film only is about 0.33, and the ID/IG ratio of the friction surface without any surface treatment is about 1.37. Transient high temperatures lead to abrasion and localized spalling on the surface of friction pairs, causing graphite oxidation to become progressively more severe, thus transforming abrasive wear into adhesive wear. As a result, double composite surface configuration with diamond film and laser texture further reduced the transient temperature rise of the surface and improved the tribological performance of the friction pairs.

Enhanced ammonia/amines sensitivity at room temperature using plasma polymerized polyvinyl acetate-reduced graphene oxide composite film sensors

Amines and ammonia can harm the environment, even in small concentrations. Efficient amine sensors are required to monitor the quality of food and air. A growing number of industries need sensors that can recognize a particular gas. Here, we demonstrate composite films made of plasma polymerized vinyl acetate (PVAc) and reduced graphene oxide (rGO) to address the crucial issues of limited selectivity, long-term instability, and temperature instability in chemoresistive gas sensors. Change in resistance of the sensor was studied in presence of analyte gas. An inductively linked plasma polymerization setup prepares PVAc films under carefully calibrated deposition conditions. Several samples are analysed to determine the ideal PVAc to rGO ratio for the composite film. Compared to individual PVAc and rGO films, final samples have demonstrated a sensitivity to ammonia and amines up to 15 times higher. The sensitivity of measuring ammonia/amines ranges from 628 for trimethylamine to a maximum of 3389 for methylamine. The sensitivity of measuring ammonia is 1621, while the sensitivity of measuring dimethylamine is 2041. The redox reaction, charge transfer, and swelling of polymer films explain potential sensing processes. Ammonia/amine selectivity has been enhanced by up to 160 compared to other volatile organic compounds (VOCs) using PVAc-rGO composite films. Based on unique selectivity, these films may also successfully distinguish between ammonia and other amines. It is shown that fluctuations in temperature between 30 °C and 150 °C did not affect the sensitivity of PVAc-rGO films. These films remain sensitive for far longer than three months. As a result, composite films of PVAc-rGO may be used to fabricate exceptionally sensitive and reliable gas sensors for ammonia/amines environmental monitoring.

A new coated self-lubricating spherical plain bearing with high performance and excellent security

The low service performance and sudden failure characteristics of coated self-lubricating spherical plain bearings (SPBs) limit their engineering application prospects. In the current study, two new self-lubricating coatings types were applied to the bearing contact surfaces. The bearings were compared and investigated using life tests. Furthermore, the wear failure mechanism was investigated. The results show that self-lubricating coatings improved the service performance of the traditional bearings with manganese phosphate coating. Among them, double-sided coated bearings had the best service performance and life. More interestingly, the torque and temperature rise signal curves will show a notable signal downstage before the signal mutation stage. The large-area and complete mixed friction transfer film on the contact surfaces was the main reason for the signal downstage. Moreover, the failure mechanism changed from abrasive wear to adhesive wear and fatigue wear with the increment of load. This study results preliminarily verify the performance improvement of high-performance coatings and provide a theoretical reference for further breaking through the engineering application bottleneck of coated self-lubricating SPBs.

The Tribological Properties of Polyimide/Polyamide Imide/Epoxy Coating Filled by WS2 and ZnO Under Dry, Water, and Sediment Conditions

Three types of polyimide/polyamide imide/epoxy resin (PI/PAI/EP) coating materials filled with different amounts of WS2 and ZnO were designed, and the coatings were prepared on the surface of 1010 steel substrates using liquid spray coating technology. The mechanical and tribological characteristics of these coatings were investigated. The CoFs (coefficients of friction) of these coatings were lower than those of the copper alloy proposed to be replaced under dry sliding wear and water lubrication. The lowest CoF of 0.237 was achieved with 7.35 wt% WS2, and the highest CoF of 0.251 was observed for 4 wt% ZnO. However, the coating with 7.35 wt% WS2 had the lowest hardness and poorest load-bearing capacity under water lubrication. The coating with 4 wt % ZnO had the best load-bearing capacity and the lowest wear rate. The agglomeration of the coating on the substrate was influenced by the content of ZnO. The CoF of the coating was influenced by both the transfer film formed by WS2 and the amount of ZnO floating on the surface of the coating. The embedding of sand into the coating surface during friction increased the surface roughness, which led to an increase in the CoF.

Interface construction of micro/nano hierarchical structure to enhance the tribological performance of carbon fabric/phenolic composite

Carbon fabric (CF)/polymer composites are potential lubricating materials, which could be used for plane bearing lining, sliding guide rails, and other moving parts of advanced equipment. But the low bonding strength at the interface between the carbon fibers and the polymer matrix is a great challenge to developing high-performance CF/polymer composites. In this study, the CF is coated with an active transition layer using high-adhesion polydopamine (PDA) as an ideal plate for the TiO2 micro/nano hierarchical structure to construct CF-PDA-TiO2. This hierarchical structure is made of micro-bundles, each composed of numerous nanorods, and decorated on CF surface densely and uniformly. The interfacial combination of CF-PDA-TiO2 and phenolic resin (PF) shows excellent performance, and the interlaminar shear strength (ILSS) of CF-PDA-TiO2/PF is improved from 10.48 MPa to 37.22 MPa, attributed to the improved interfacial physicochemical interaction. Furthermore, the tribological performance of CF-PDA-TiO2/PF with size of Φ30 mm✕5 mm is characterized by sliding against 440C stainless steel ball with diameter of 8 mm using ball-on-disc sliding wear tester (MPX-3). The tribological results demonstrate that the friction coefficient and wear rate of CF-PDA-TiO2/PF are reduced by 37.91% and 77.6%, compared to CF/PF. Moreover, the CF-PDA-TiO2/PF maintains low friction coefficient and wear rate under high-load and high-speed sliding conditions. This is mainly because TiO2 nanorod bundles exhibit micro/nano multi-scale interfacial enhancement, promoting stress distribution and micro-cracks deflection etc. Moreover, TiO2 nanorod bundles could promote the formation of a uniform transfer film to decrease friction and wear. This work implies that interface construction of micro/nano hierarchical structure is a promising way to enhance the tribological performance of CF/polymer composites.

All‐Screen‐Coatable Photo‐Thermoelectric Imagers for Physical and Thermal Durability Enhancement

AbstractCarbon nanotube (CNT) film photo‐thermoelectric (PTE) imagers are suitable for non‐destructive inspection techniques owing to their functionalities. Simultaneously, their practical application remains a crucial bottleneck due to low yield handling in the device fabrication (e.g., disconnections between photo absorbent channels and readout electrodes). However, studies clarifying the above malfunction mechanism and associated dominant factors in device handling, such as specific fabrication or material selection steps, still need to be completed. To address this issue, this work introduces all‐screen‐coatable fabrication techniques for CNT film PTE imagers to enhance their physical and thermal durabilities. First, this work determined that the transfer of CNT films on supporting substrates dominantly governs the mechanical robustness of the channels and that thermal curing in the subsequent fabrication process is an essential factor in the yields of channel‐electrode connections. The proposed approach ensures a transfer‐free direct coating of the CNT film on diverse substrates and is sufficiently durable against thermal curing‐induced disconnections at the channel‐electrode interfaces. The screen‐coating technique is also available for whole device materials of solution‐processable CNT film PTE imagers, simplifying fabrication processes. All‐screen‐coatable CNT film PTE imagers synergize their inherent functional sensing and high‐yield operations toward versatile applications.

Effect of h-BN and Nano-SiO2 Fillers on the High-Temperature Tribological Properties of PEEK/PI-Based Composites

PEEK is being used increasingly often in seals, bushings, bearings, and other moving parts due to its excellent mechanical and tribological properties. Herein, PEEK-based composites were prepared using PI as the organic filler and h-BN and nano-SiO2 particles as the inorganic fillers. There was significant improvement in the tribological properties of PEEK at conditions above the glass transition temperature; the coefficient of friction of +20P/4B/4Si was stabilized at 0.06 at 200 °C and the wear rate was reduced by 60% compared to PEEK. The role played by the thermal conductivity of h-BN and the promotion of friction transfer film by nano-SiO2 in improving the tribological properties of PEEK is illustrated. The modified composites exhibited stable mechanical and tribological properties over a wide temperature range, which is instructive for instrumentation and testing applications in harsh environments.

Friction mechanism of DLC/MAO wear-resistant coatings with porous surface texture constructed in-situ by micro-arc oxidation

A porous textured DLC/MAO multilayer coating was constructed in-situ on Al alloy by depositing a diamond-like carbon (DLC) film onto a micro-arc oxidation (MAO) layer. The morphology, composition and tribological properties were investigated. The wear mechanism of the coating and the effect of load on wear were studied in detail under dry and oil-lubricated conditions. The results showed that DLC/MAO coating had excellent load-bearing capacity and wear resistance. The porous texture was generated in-situ on the aluminum alloy substrate by micro-arc oxidation technology, which played a mechanical interlocking effect in making the multi-layer coating tightly bonded. It can also capture wear debris to reduce abrasive wear under dry conditions while storing lubricating oil to supplement the lubricating film under oil-lubrication. DLC top film optimized the frictional resistance induced by the porous texture through graphitization and low-shear transfer film formation, reducing up to 70.7 % and 54.9 % in friction coefficient and wear track width under dry conditions. Under oil lubrication, the solid-liquid synergy between the graphitized layer and the liquid lubricating film can reduce the friction coefficient and wear track width by up to 20.9 % and 52.1 %. Hence, the combination of DLC top film and MAO tie layer realizes excellent anti-friction/wear and durability.

Biomimetic PVA-PVDF-based triboelectric nanogenerator with MXene doping for self-powered water sterilization

The harsh environment at sea level can reduce the harvesting efficiency of triboelectric nanogenerators (TENGs) for blue energy. Based on this, the doping ratio of MXene was optimized and was applied to enhance the moisture resistance, anti-fouling, wear resistance and dielectric properties of PVA triboelectrode. 8 wt% MXene doping provides more hydrogen bonding sites on PVA surface, thereby adsorbing more water molecules as electropositivity materials and improves its anti-fouling performance by forming hydration layer. Meanwhile, MXene increases the load capacity of hybrid transfer film and greatly improves the wear resistance of PVA film, and can form microcapacitor to improve its dielectric properties. In addition, biomimetic PVDF electrode was prepared by imitating the hydrophobic mechanism of leaves and significantly improved the anti-fouling and moisture resistance of PVDF. The Voc and Isc of TENG reached to 1056V and 36.6 μA at 95% humidity and improved by 2.37 times. The charge density and binding energy of PVA/MXene and PVA before and after adsorbed water molecule were calculated by DFT. Furthermore, the self-powered water sterilization system based on PVA/MXene-PVDF-based TENG achieved a sterilization rate of 98.99% at the flow rate of 2000 mL min−1, which was much higher than ordinary AC power (86.80%).

Extreme contact pressure-induced in-situ structural evolution of nanoclusters governing macroscopic superlubricity in a-C:H films

Though hydrogenated amorphous carbon (a-C:H) films can provide macroscale superlubricity states in vacuum, their self-lubricating behaviors are highly dependent on the applied loads. The mechanisms of loss of superlubricity under ultra-low or extremely high contact pressure remain unclear. In this work, the origin of load-sensitive superlubricity of a-C:H films was revealed based on spatially resolved structural analyses of the sliding interfaces. The results highlighted the key role of contact pressure-induced diversified nano-structural evolution of transfer films in controlling superlubricity. To achieve superlubricity, a sufficiently high contact pressure was required to trigger the structural evolution of transfer films from polymer-like disordered bonding network structure towards locally ordered, layered-like sp2 nanoclustering structures. Robust superlubricity can still be maintained under extremely high peak Hertz contact pressure up to 4.87 GPa, which is the highest value reported for macroscopic superlubricity in carbon-based materials. Nevertheless, excessively high contact pressure can cause an increase in the interfacial shear strength due to the pressure-induced generation of heterogeneous transfer films with thin, poor-hydrogenated, over-graphitized local regions embedded with enriched ironic sub-micro debris and nanoparticles, which inhibited further decrease of friction coefficient under extremely high contact pressure. These findings will enable more effective space applications of superlubricious a-C:H films under extreme conditions.

Influence of PTFE-Based Dry Lubricants on Friction and Wear Behavior in Dry Lubricated Steel–Bronze Contact

Abstract In this article, solid lubricants are investigated to examine their tribological performance in a dry lubricated steel–bronze contact. The examined solid lubricants are made of polyamide (PA) and irradiated polytetrafluoroethylene (PTFE), which are chemically bonded by reactive melt extrusion. For the tribological investigations, a block-twin-disc test rig, on the one hand, and a three-disc test rig, on the other hand, were used under ambient conditions, where the solid lubricant for lubricating the steel–bronze contact was released from a block or a disc. Results from the tribological investigations are presented here, showing the friction and wear behavior in a steel–bronze contact depending on the slide-to-roll ratio in the contact between the steel disc and the compound body. Furthermore, surface analytical investigations on the steel and bronze discs were carried out. These studies showed that the chemical bonding of 20 wt% of irradiated PTFE in PA12 improves the wear and friction behavior in steel–bronze contact significantly, due to the buildup of a transfer film of PTFE on the steel surface.

Influence of MoS2 coating treatment on the damage behaviour of the self-lubricating friction pair of spherical plain bearings

This study applied a MoS2 coating layer on the surface of 100Cr6 bearing steel balls through high-temperature sintering and tested and evaluated the modified friction pair. Compared to the unmodified friction pair, the MoS2 coating treatment significantly improved the self-lubricating property of the friction pair, reduced the friction coefficient of the friction pair by 0.05, maximum wear depth was reduced by 32% during the test cycle and prolonged the retention time of the PTFE transfer film at the friction interface. After modification, the wear mechanism of the friction pair changed from abrasive wear to fatigue wear and then to slight adhesive wear. Results indicate that MoS2 coating has great application prospects in improving the tribological properties and operational reliability of spherical plain bearings.

Phosphorus-based flame retardant acrylic pressure sensitive adhesives with superior peel strength and transfer characteristics

Acrylic pressure sensitive adhesives (PSAs) are widely utilized in various fields due to their excellent thermal, weather, and oil resistance. However, due to their flammability, they are vulnerable to fire, which brings a critical challenge for their application in various industries. Here, new phosphorus-based acrylic PSAs which show excellent flame retardancy are demonstrated, without sacrificing adhesion properties. By controlling the monomer composition based on five different monomers, we synthesized seven acrylic copolymers for PSAs, and investigated the correlation between monomer composition and adhesion characteristics in terms of peel strength and transfer characteristics. Among seven polymers, A5H5 which exhibits the highest peel strength (1117 gf/in.) and superior transfer characteristics (transfer area 8.30 %) is selected for further investigation. The phosphorous-based acrylic PSAs are prepared through addition of different amounts of dimethyl methylphosphonate in A5H5 polymeric matrix, and thoroughly investigated in terms of flame retardancy and adhesion characteristics in terms of peel strength and transfer characteristics. The phosphorus-based PSA (A5H5-D30) exhibited superior flame retardancy of V-0 rating under the UL-94 characterization method. Furthermore, the A5H5-D30 present excellent film transfer characteristic showing a transfer area of 0 % and residue of 0 wt% in air without massive decrease in peel strength (991 gf/in.).

Construction of ternary PEG200-based DESs lubrication systems via tailoring tribo-chemistry

Designing novel lubricants with easily customized structures, devisable compositions, and simple and economic synthesis over traditional lubricants is critical to fulfilling complex applications, prolonging machine lifetime, and saving energy. Deep eutectic solvents (DESs), which show tunable composition, adjustable structure, easy fabrication, and environmental friendliness, are promising candidates for variable and complicated lubricants applications. To promote the use of DESs as lubricants, a series of PEG200-based DESs with active heteroatoms were fabricated to tailor the tribological performance via tribo-chemistry. Thereinto, PEG200/boric acid (BA) DES shows optimal lubrication performance by forming tribo-chemical reaction film composited of B2O3, iron oxides, and FeOOH, and PEG200/thiourea (TU) DES displays abrasive wear-reducing property by producing FeS tribo-chemical film. Given the excellent abrasive wear-resistance of PEG200/TU DES and friction reduction of PEG200/BA DES, ternary PEG200/BA/TU DESs, composited of PEG200/TU DES and PEG200/BA DES, are first exploited. The ternary DESs possess superior wettability and thermal stability, which render them potential lubricants. Tribological tests of the ternary DESs demonstrate that synergistic lubrication is achieved by forming a transfer film consisting of FexBy, BN, B2O3, and FeS. Wherein FexBy, BN, and B2O3 increase load bearing of the film, and FeS mitigates severe abrasive wear. The proposed design philosophy of novel DESs as lubricants opens up a unique realm that is unattainable by traditional DESs lubrication mechanisms and provides a platform to design next-generation DESs lubrication systems.