Recent Progress on Wear-Resistant Materials: Designs, Properties, and Applications

Machine Learning-Based Design of Superhard High-Entropy Nitride Coatings

Limited by the inefficiency of the conventional trial-and-error method and the boundless compositional design space of high-entropy alloys (HEAs), accelerating the discovery of superior-performing high-entropy nitride (HEN) coatings remains a formidable challenge. Herein, the superhard HEN coatings were designed and prepared using the rapidly developing data-driven model machine learning (ML). A database containing hardness and different features of HEN coatings was established and categorized into four subsets covering the information on composition, composition-physical descriptors, composition-technique parameters, and composition-physical descriptors-technique parameters. Feature engineering was employed to reduce dimensionality and interpret the impact of features on the evolution of hardness. Both root mean squared error (RMSE) and decision coefficient (R2) were applied to assess the predictive accuracy of ML models with different subsets, proportions of test set, and algorithms. The model with best predicted performance was used to explore superhard HEN coatings in a predefined virtual space. Among the generated 5-/6-/7-/8-component (excluding N) systems, the coating possessing highest hardness was individually selected for further preparation. Four newly prepared coatings achieved the superhard level with an average prediction error of 7.83%. The morphology, chemical composition, structure, and hardness of the newly prepared coatings were discussed. The nanocrystal-amorphous nanocomposite structure of the novel AlCrNbSiTiN coating with the highest hardness of 45.77 GPa was revealed. The results demonstrated that ML can effectively guide the design and composition optimization of superb-performance protective HEN coatings.

Carbon Dots with Spatially-Mediated-N/S-Co-Doping Enabling One-Year Stable Lubricant with Oil Leakage Detection Capability

The dispersion stability of nano-lubricating additives is crucial for the shelf life of lubricant and its practical applications. Nitrogen-sulfur co-doped carbon dots (N,S@CDs) via a one-step hydrothermal method with nitropyrene and thiourea as raw materials are hereby presented. The N and S elements are selectively distributed throughout the entire carbon skeleton with a doping amount of 22.6 at%. The as-synthesized N,S@CDs exhibit excellent dispersion stability in PEG200 and maintain stability for over one year. The experiment results indicate that N,S@CDs significantly improve the anti-wear and friction reduction properties of PEG200, while the friction coefficient is reduced from 0.25 to 0.09 with 1.5 wt% N,S@CDs addition, and the wear volume, depth, and width are reduced by 68%, 52%, and 57%, respectively. The good lubrication performance is attributed to N,S@CDs excellent dispersion stability, enhanced filling and polishing effects, and complex tribochemical reactions caused by heteroatom doping to form a stable protective film on the worn surface. Furthermore, the as-prepared N,S@CDs exhibit intrinsic fluorescence intensity in PEG200 with the photoluminescence quantum yield (PLQY) of 12.5% and remain fluorescent stable during the long-term friction process, therefore the N,S@CDs have a potential application prospect in non-destructive detection of oil leakage via fluorescence labeling method.

Low-frequency conductivity of low wear high-entropy alloys

High-entropy alloys (HEAs) provide new research avenues for alloy combinations in the periodic table, opening numerous possibilities in novel-alloy applications. However, their electrical characteristics have been relatively underexplored. The challenge in establishing an HEA electrical conductivity model lies in the changes in electronic characteristics caused by lattice distortion and complexity of nanostructures. Here we show a low-frequency electrical conductivity model for the Nb-Mo-Ta-W HEA system. The cocktail effect is found to explain trends in electrical-conductivity changes in HEAs, while the magnitude of the reduction is understood by the calculated plasma frequency, free electron density, and measured relaxation time by terahertz spectroscopy. As a result, the refractory HEA Nb15Mo35Ta15W35 thin film exhibits both high hardness and excellent conductivity. This combination of Nb15Mo35Ta15W35 makes it suitable for applications in atomic force microscopy probe coating, significantly improving their wear resistance and atomic-scale image resolution.

Macroscale Superlubricity on Nanoscale Graphene Moiré Structure-Assembled Surface via Counterface Hydrogen Modulation

Interlayer incommensurateness slippage is an excellent pathway to realize superlubricity of van der Waals materials; however, it is instable and heavily depends on twisted angle and super-smooth substrate which pose great challenges for the practical application of superlubricity. Here, macroscale superlubricity (0.001) is reported on countless nanoscale graphene moiré structure (GMS)-assembled surface via counterface hydrogen (H) modulation. The GMS-assembled surface is formed on grinding balls via sphere-triggered strain engineering. By the H modulation of counterface diamond-like carbon (25 at.% H), the wear of GMS-assembled surface is significantly reduced and a steadily superlubric sliding interface between them is achieved, based on assembly face charge depletion and H-induced assembly edge weakening. Furthermore, the superlubricity between GMS-assembled and DLC25 surfaces holds true in wide ranges of normal load (7-11 N), sliding velocity (0.5-27 cm -1s), contact area (0.4×104-3.7×104 µm2), and contact pressure (0.19-1.82 GPa). Atomistic simulations confirm the preferential formation of GMS on a sphere, and demonstrate the superlubricity on GMS-assembled surface via counterface H modulation. The results provide an efficient tribo-pairing strategy to achieve robust superlubricity, which is of significance for the engineering application of superlubricity.

Structural, mechanical, wear and anticorrosive properties of CrSiCN coatings used for industrial woodworking applications

The woodworking applications are a fast-growing field that aims to create advanced coatings with superior wear resistance, reduced friction, and robust corrosion protection. Chromium silicon carbonitride (CrSiCN) coatings have emerged as a promising solution that offers a unique combination of properties ideal for various industrial applications. The C/N ratio significantly influences the coatings' mechanical and tribological properties. By optimizing the C/N ratio, this research aims to reveal new insights for CrSiCN coatings, enhancing their application in environments that require durability, efficiency, and longevity. In this paper, the effect of the C/N ratio on the structural, mechanical, and corrosion resistance of CrSiCN coatings deposited by cathodic arc evaporation on different steel substrates was studied. The main purpose was to enhance the mechanical and anticorrosion properties of the CrSiCN coatings and to select the optimum parameters for the deposition of layers with superior properties. The results showed that the final properties can be tailored by choosing specific deposition conditions. In this case, the C/N ratio proved to be critical since coatings with higher carbon content presented enhanced corrosion resistance, being able to withstand operating conditions similar to real-life.

A Review on the Effect of Metal Oxide Nanoparticles on Tribological Properties of Biolubricants

This review provides a comprehensive and accessible literature review on the integration of nanoparticles into biolubricants to enhance wear and friction regulation, thus improving the overall lubricated system performance. Nanotechnology has significantly impacted various industries, particularly in lubrication. Nanobiolubricants offer promising avenues for enhancing tribological properties. This review focuses on oxide nanoparticles, such as zinc oxide (ZnO), aluminum oxide (Al2O3), copper oxide (CuO), titanium dioxide (TiO2), zirconium dioxide (ZrO2), and graphene oxide (GO) nanoparticles, for their ability to enhance lubricant performance. The impact of nanoparticle concentration on biolubricant properties, including viscosity, viscosity index, flash point temperature, and pour point temperature, is analyzed. The review also addresses potential obstacles and limitations in nanoparticle incorporation, aiming to propose effective strategies for maximizing their benefits. The findings underscore the potential of nanobiolubricants to improve operational efficiency and component lifespan. This review aims to provide valuable insights for researchers, engineers, and professionals in exploring and leveraging nanotechnology's potential in the lubrication industry. This review paper explores the basics of tribology along with its significance, green principles, mechanisms, and energy savings because of friction, wear, and lubrication. Condition monitoring techniques are also explored to achieve brief knowledge about maintaining reliability and safety of the industrial components. Recent advances in tribology including superconductivity, biotribology, high-temperature tribology, tribological simulation, hybrid polymer composite's tribology, and cryogenic tribology are investigated, which gives a thorough idea about the subject.

Assessing the reinforced molecular/mechanical behaviors of GOs@Mo-MOFs films deposited via electrophoresis onto microdevices: Experimental and theoretical perspectives

One of the primary hurdles in microdevice fabrication lies in ascertaining the most impactful tactics for adapting metal surfaces. Through a one-pot tackle and distinct mechanochemical reactions evoked by 15 min aqueous wet sand-milling (SM-15), we successfully grafted Mo-based metal-organic frameworks (Mo-MOFs) onto graphene oxides (GOs). Following this, a convenient and readily scalable methodology of electrophoretic deposition was implemented to create controllable thickness of SM-15 GOs@Mo-MOFs lubricating films, achieving considerable enhancements of 143% and 91% in hardness and Young's modulus, respectively, when compared to those of SM-15 Mo-MOFs. The successful synthesis of SM-15 GOs@Mo-MOFs was corroborated using strategies such as x-ray diffraction, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy. Analyses using the micro-tribotester indicated that the new film exhibited a lowest friction coefficient of roughly 0.5 when imposed with a load of 5 N and sliding speed of 8 mm/s. In addition, the optical profiler nano-indentation in situ scanning probe microscope revealed that SM-15 GOs@Mo-MOFs films had smaller and shallower scratches and grooves compared to SM-15 Mo-MOFs ones. The calculated results of key descriptors (EHOMO, ELUMO, ΔE, etc.) in density functional theory quantitatively disclosed the interaction mechanisms between GOs@Mo-MOFs molecules and microdevices. We first scrutinized the innate properties of molecule adsorption energy and frictional mechanical behaviors using synergetic cross-scale simulations, such as Monte Carlo and finite element methods. The expectation was that this process would motivate a valuable technique for shielding in the thriving micromanufacturing.

Chitosan-Based Structural Color Films for Humidity Sensing with Antiviral Effect

This scientific investigation emphasizes the essential integration of nature's influence in crafting multifunctional surfaces with bio-inspired designs for enhanced functionality and environmental advantages. The study introduces an innovative approach, merging color decoration, humidity sensing, and antiviral properties into a unified surface using chitosan, an organo-biological polymer, to create cost-effective multilayered films through sol-gel deposition and UV photoinduced deposition of metal nanoparticles. The resulting chitosan films showcase diverse structural colors and demonstrate significant antiviral efficiency, with a 50% and 85% virus inhibition rate within a rapid 20 min reaction, validated through fluorescence cell expression and real-time qPCR (polymerase chain reaction) assays. Silver-deposited chitosan films further enhance antiviral activity, achieving remarkable 91% and 95% inhibition in independent assays. These films exhibit humidity-responsive color modifications across a 25-90% relative humidity range, enabling real-time monitoring validated through simulation studies. The proposed three-in-one functional surface can have versatile applications in surface decoration, medicine, air conditioning, and the food industry. It can serve as a real-time humidity sensor for indoor and outdoor surfaces, find use in biomedical devices for continuous humidity monitoring, and offer antiviral protection for frequently handled devices and tools. The customizable colors enhance visual appeal, making it a comprehensive solution for diverse applications.

Recent advances in computational design of structural multi-principal element alloys

Multi-principal element alloys (MPEAs) have gained extensive interest for structural applications owing to their excellent strength, fracture toughness, wear resistance, creep resistance, and fatigue resistance. In this review, recent progress in the computational design of MPEAs for structural applications is outlined. This includes the scientific advancements achieved through computational methods in the field of structural MPEAs, how new methodologies have emerged due to the needs of complex alloy systems, and adaptations to the existing tools to address emerging problems in the field. We discuss advances in atomistic simulation methods, including structure generation algorithms, element-resolved local lattice distortion, chemical short-range order, local slip resistance, and radiation tolerance, along with experimental comparisons. A detailed discussion on interatomic potentials is included, with a focus on various machine learning-based fitting methods. The application of data science and machine learning for identifying and discovering MPEAs with desirable mechanical performance is summarized and presented.

Metal-Driven Autoantifriction Function of Artificial Hip Joint

The service life of an artificial hip joint is limited to 10-15 years, which is not ideal for young patients. To extend the lifespan of these prostheses, the coefficient of friction and wear resistance of metallic femoral heads must be improved. In this study, a Cu-doped titanium nitride (TiNX -Cu) film with "autoantifriction" properties is deposited on a CoCrMo alloy via magnetron sputtering. When delivered in a protein-containing lubricating medium, the Cu in TiNX -Cu quickly and consistently binds to the protein molecules in the microenvironment, resulting in the formation of a stable protein layer. The proteins adsorbed on the TiNX -Cu surface decompose into hydrocarbon fragments owing to the shear stress between the Al2 O3 /TiNX -Cu tribopair. The synergistic effect of the catalysis of Cu and shear stress between the Al2 O3 /TiNX -Cu tribopair transforms these fragments into graphite-like carbon tribofilms with an antifriction property. These tribofilms can simultaneously reduce the friction coefficient of the Al2 O3 /TiNX -Cu tribopair and enhance the wear resistance of the TiNX -Cu film. Based on these findings, it is believed that the autoantifriction film can drive the generation of antifriction tribofilms for lubricating and increasing the wear resistance of prosthetic devices, thereby prolonging their lifespan.

Velocity-Dependent Friction of Graphene at Electrical Contact Interfaces

Graphene has enormous potential as a solid lubricant at sliding electrical contact interfaces of micro-/nanoelectromechanical systems that suffer severe wear. Understanding the velocity-dependent friction of graphene under different applied voltages contributes to the application of graphene in sliding electrical contact scenarios. The friction of graphene, measured by conductive atomic force microscopy, under low applied voltage increases logarithmically with sliding velocity─the same as when no voltage is applied but at a faster rate of increase. The variation of friction was explained by the thermally activated Prandtl-Tomlinson model with increased potential barrier and temperature because of the applied voltage. An opposite trend in which friction decreases with sliding velocity is observed under high applied voltage. Topography, adhesion measurements, and SEM characterization demonstrate the wear of the tip. Moreover, the tip wears more severely at low sliding velocity compared to a high sliding velocity. It was interpreted that the excessive Joule heat at the electrical contact interface under high applied voltage weakens the mechanical properties of the tip, resulting in wear and high friction. The increase in the sliding velocity could accelerate the Joule heat transfer and reduce wear and friction. The studies provide beneficial guidelines for the design of graphene-lubricated sliding electrical contact interfaces.

MXene/graphene oxide nanocomposites for friction and wear reduction of rough steel surfaces

Development of solid lubricant materials that render reliable performance in ambient conditions, are amenable to industrial size and design complexities, and work on engineered surfaces is reported. These coatings are composed of Ti3C2Tx-Graphene Oxide blends, spray-coated onto bearing steel surfaces. The tribological assessment was carried out in ambient environmental conditions and high contact pressures in a ball-on-disc experimental set-up. The evaluation yielded that the use of Ti3C2Tx-Graphene-Oxide coatings led to substantial reduction in friction down to 0.065 (at 1 GPa contact pressure and 100 mm/s) in comparison to the uncoated of single-component-coated surfaces, surpassing the state-of-the-art. The coatings also provided excellent protection against wear loss of the substrate and counter-face. The results were explained based on the observations from Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and nanoindentation measurements. In operando formation of a dense, hard and stiff, dangling-bond-saturated tribolayer was observed to be the reason for the sustained lubricity even at high test loads and sliding speeds. This report presents the holistic exploration and correlation of structure-property-processing pertaining to the advancement of solid lubrication science.

Tribology of Copper Metal Matrix Composites Reinforced with Fluorinated Graphene Oxide Nanosheets: Implications for Solid Lubricants in Mechanical Switches

The potential for the use of copper coatings on steel switching mechanisms is abundant owing to the high conductivities and corrosion resistance that they impart on the engineered assemblies. However, applications of these coatings on such moving parts are limited due to their poor tribological properties; tendencies to generate high friction and susceptibility to degradative wear. In this study, we have fabricated a fluorinated graphene oxide-copper metal matrix composite (FGO-CMMC) on an AISI 52100 bearing steel substrate by a simple electrodeposition process in water. The FGO-CMMC coatings exhibited excellent lubrication performance under pin-on-disk (PoD) tribological sliding at 1N load, which reduced CoF by 63 and 69%, compared to the GO-CMMC and pure copper coatings that were also prepared. Furthermore, FGO-CMMC achieved low friction and low wear at higher sliding loads. The lubrication enhancement of the FGO-CMMCs is attributed to the tribochemical reaction of FGO with the AISI 52100 steel counterface initiated by the sliding load. The formation of an asymmetric tribofilm structure on the sliding track is critical; the performance of the FGO/Cu tribofilm formed in the track is boosted by the continued fluorination of the counterface surface during PoD sliding, passivating the tribosystem from adhesion-driven breakdown. The FGO-CMMC and GO-CMMC coatings also provide increased corrosion protection reaching 94.2 and 91.6% compared to the bare steel substrate, allowing for the preservation of the long-term low-friction performance of the coating. Other influences include the improved interlaminar shear strength of the FGO-containing composite. The excellent lubrication performance of the copper matrix composite coatings facilitated by FGO incorporation makes it a promising solid lubricant candidate for use in mechanical engineering applications.

Achieving Diamond-Like Wear in Ta-Rich Metallic Glasses

Most metals and alloys suffer from high friction and wear due to their low hardness and lack of self-lubrication. Although plenty of strategies have been proposed, it is still a long-standing challenge to achieve diamond-like wear in metals. Metallic glasses (MGs) are supposed to possess low coefficient of friction (COF) because of their high hardness and fast surface mobility. However, their wear rate is larger than that of diamond-like materials. Here, this work reports the discovery of Ta-rich MGs that exhibit diamond-like wear. This work develops an indentation approach for high-throughput characterization of crack resistance. By employing deep indentation loading, this work is able to efficiently identify the alloys that exhibit better plasticity and crack resistance according to the differences of indent morphology. With high temperature stability, high hardness, improved plasticity, and crack resistance, the discovered Ta-based MGs exhibit diamond-like tribological properties, featured by COF as low as ≈0.05 for diamond ball test and ≈0.15 for steel ball test, and specific wear rate of only ≈10^-7 mm³ N^{- 1} m^-1 . The discovery approach and the discovered MGs exemplifie the promise to substantially reduce friction and wear of metals and may unleash the potential of MGs in tribological applications.

Prospective applications of two-dimensional materials beyond laboratory frontiers: A review

The development of nanotechnology has been advancing for decades and gained acceleration in the 21st century. Two-dimensional (2D) materials are widely available, giving them a wide range of material platforms for technological study and the advancement of atomic-level applications. The design and application of 2D materials are discussed in this review. In order to evaluate the performance of 2D materials, which might lead to greater applications benefiting the electrical and electronics sectors as well as society, the future paradigm of 2D materials needs to be visualized. The development of 2D hybrid materials with better characteristics that will help industry and society at large is anticipated to result from intensive research in 2D materials. This enhanced evaluation might open new opportunities for the synthesis of 2D materials and the creation of devices that are more effective than traditional ones in various sectors of application.

LCF and HCF of Short Carbon Fibers Reinforced AE42 Mg Alloy

Lightweight magnesium alloys and magnesium matrix composites have recently become more widespread for high-efficiency applications, including automobile, aerospace, defense, and electronic industries. Cast magnesium and magnesium matrix composites are applied in many highly moving and rotating parts, these parts can suffer from fatigue loading and are consequently subjected to fatigue failure. Reversed tensile-compression low-cycle fatigue (LCF) and high-cycle fatigue (HCF) of short fibers reinforced and unreinforced AE42 have been studied at temperatures of 20 °C, 150 °C, and 250 °C. To select suitable fatigue testing conditions, tensile tests have been carried out on AE42 and the composite material AE42-C at temperatures of up to 300 °C. The Wohler curves σ_a (N_F) have shown that the fatigue strength of the reinforced AE42-C in the HCF range was double that of unreinforced AE42. In the LCF range at certain strain amplitudes, the fatigue life of the composite materials is much less than that of the matrix alloys, this is due to the low ductility of this composite material. Furthermore, a slight temperature influence up to 150 °C has been established on the fatigue behavior of the AE42-C. The fatigue life curves Δε_total (N_F) were described using the Basquin and Manson-Coffin approaches. Fracture surface investigations showed a mixed mode of serration fatigue pattern on the matrix and carbon fibers fracturing and debonding from the matrix alloy.

Synthesis, Microstructure Investigation, Mechanical and Tribological Behaviour of the AA5083-WC Composite

In this study, AA5083-WC composites were developed by ball milling followed by hot consolidation. The microstructures of the developed composites were investigated using XRD, SEM, EDX, and EBSD. The developed composites exhibited a homogeneous dispersion of WC particulates in the AA5083 matrix without any interactions at the matrix/reinforcement interface. The results confirmed the development of a refined equiaxed grain structure of AA5083-WC composites where the EBSD results revealed an average grain size of 4.38 µm and 3.32 µm for AA5083-6%WC (AW-6) and AA5083-12%WC (AW-12) composites, respectively. The results showed that incorporating WC particulates in the AA5083 alloy matrix significantly improved the compressive stress-strain behaviour and considerably enhanced the resistance to wear and friction. The AA5083-12%WC (AW-12) composite displayed the maximum strength and the highest resistance to wear and friction, whereas the as-milled AA5083 alloy (AW-0) exhibited the lowest strength and the least resistance to wear and friction. The AA5083-12%WC (AW-12) composite exhibited the optimum mechanical and tribological behaviour of the developed composites, making it a promising candidate for tribological applications.

Hydrophilic Surface Modification of Amorphous Hydrogenated Carbon Nanocomposite Films via Atmospheric Oxygen Plasma Treatment

Herein we investigated hydrophilic surface modification of SiO_x containing amorphous hydrogenated carbon nanocomposite films (DLC:SiO_x) via the use of atmospheric oxygen plasma treatment. The modified films exhibited effective hydrophilic properties with complete surface wetting. More detailed water droplet contact angle (CA) measurements revealed that oxygen plasma treated DLC:SiO_x films maintained good wetting properties with CA of up to 28 ± 1° after 20 days of aging in ambient air at room temperature. This treatment process also increased surface root mean square roughness from 0.27 nm to 1.26 nm. Analysis of the surface chemical states suggested that the hydrophilic behavior of DLC:SiO_x treated with oxygen plasma is attributed to surface enrichment with C-O-C, SiO₂, and Si-Si chemical bonds as well as significant removal of hydrophobic Si-CH_x functional groups. The latter functional groups are prone to restoration and are mainly responsible for the increase in CA with aging. Possible applications of the modified DLC:SiO_x nanocomposite films could include biocompatible coatings for biomedical applications, antifogging coatings for optical components, and protective coatings to prevent against corrosion and wear.

Hydrogen-Enhanced Catalytic Conversion of Amorphous Carbon to Graphene for Achieving Superlubricity

The solid-state conversion of amorphous carbon into graphene is extremely difficult, but it can be achieved in the friction experiments that induce macroscale superlubricity. However, the underlying conversion mechanisms remain elusive. Here, the friction experiments with Cu nanoparticles and (non-hydrogen (H) or H) a-C in vacuum, show the H-induced conversion of mechanical to chemical wear, resulting in the a-C's tribosoftening and nanofragmentating that produce hydrocarbon nanoclusters or molecules. It is such exactly hydrocarbon species that yield graphene at hydrogen-rich a-C friction interface, through reaction of them with Cu nanoparticles. In comparison, graphene isn't formed at Cu/non-H a-C friction interface. Atomistic simulations reveal the hydrogen-enhanced tribochemical decomposition of a-C and demonstrate the energetically favorable graphitization transformation of hydrocarbons on Cu substrates. The findings are of importance to achieve solid-state transformation between different carbon allotropes and provide a good strategy to synthesize other graphitic encapsulated catalysts with doped elements.

Surface Mechanical Properties and Topological Characteristics of Thermoplastic Copolyesters after Precisely Controlled Abrasion

Due to the high probability of surface-to-surface contact of materials during routine applications, surface abrasion remains one of the most challenging factors governing the long-term performance of polymeric materials due to their broad range of tunable mechanical properties, as well as the varied conditions of abrasion (regarding, e.g., rate, load, and contact area). While this concept is empirically mature, a fundamental understanding of mechanical abrasion regarding thermoplastics remains lacking even though polymer abrasion can inadvertently lead to the formation of nano-/microplastics. In the present study, we introduce the concept of precision polymer abrasion (PPA) in conjunction with nanoindentation to elucidate the extent to which controlled wear is experienced by three chemically related thermoplastics under systematically varied abrasion conditions. While depth profiling of one polymer reveals a probe-dependent change in modulus, complementary results from positron annihilation lifetime spectroscopy confirm that the polymer density changes measurably, but not appreciably, with depth over the depth range explored. After a single PPA pass, the surface moduli of the polymers noticeably increase, whereas the corresponding increase in hardness is modest. The dependence of wear volume on the number of PPA passes is observed to reach limiting values for two of the thermoplastics, and application of an empirical model to the data yields estimates of these values for all three thermoplastics. These results suggest that the metrics commonly employed to describe the surface abrasion of polymers requires careful consideration of a host of underlying factors.

Evidence of Tribological Adaptation Controlled by Tribosynthesis of FeWO4 on an WC-Reinforced Electron Beam M2 Steel Coating Rubbed against a HSS Disk in a Range of Sliding Speeds

In the present work, the tribological experiments on sliding the electron beam composite M2+WC coating have been carried out with characterization of the sample microstructures and phases both before and after the testing using metallography, SEM, EDS, and XRD. The sliding in the speed range 0.8-3.6 m/s resulted in simultaneous reduction in both wear rate and coefficient of friction with the sliding speed. Investigations showed that such a tribological adaptation was due to the tribochemical generation of lubricative FeWO₄ and Fe₂WO₆ mixed oxides and the generation of a mechanically mixed composite layer on the worn surfaces that consisted of carbide fragments, an oxidized metal matrix, and was lubricated by in-situ formed mixed iron-tungsten oxides.

Self-Lubricating Effect of WC/Y–TZP–Al2O3 Hybrid Ceramic–Matrix Composites with Dispersed Hadfield Steel Particles during High-Speed Sliding against an HSS Disk

WC/Y–TZP–Al2O3 hybrid ceramic–matrix composites (CMCs) with dispersed Hadfield steel particles were sintered and then tested at sliding speeds in the range of 7–37 m/s and contact pressure 5 MPa. Fast and low-temperature sinter-forging allowed obtaining micron-sized WC grains, submicron-sized alumina-reinforced yttria partially stabilized polycrystalline tetragonal zirconia (Y–TZP–Al2O3), and evenly distributed Hadfield steel grains. Such a microstructure provided new hybrid characteristics combining high hardness with high fracture toughness and tribological adaptation. The CMCs demonstrated low friction and high wear resistance that were better than those demonstrated by other composite materials such as, for example, MAX-phase composites, zirconia-base ceramics, ZrB2-SiC ceramics, and metal matrix WC–(Fe–Mn–C) composites. These good tribological characteristics were obtained due to the in situ mechanochemical formation of iron tungstates FeWO4 and Fe2WO6 on the worn surfaces of composite samples. These mixed oxides were included in multilayer subsurface structures that provided the self-lubricating and self-healing effects in high-speed sliding because of their easy shear and quasi-viscous behavior.

Nanoarchitected Tough Biological Composites from Assembled Chitinous Scaffolds

ConspectusOver hundreds of millions of years, organisms have derived specific sets of traits in response to common selection pressures that serve as guideposts for optimal biological designs. A prime example is the evolution of toughened structures in disparate lineages within plants, invertebrates, and vertebrates. Extremely tough structures can function much like armor, battering rams, or reinforcements that enhance the ability of organisms to win competitions, find mates, acquire food, escape predation, and withstand high winds or turbulent flow. From an engineering perspective, biological solutions are intriguing because they must work in a multifunctional context. An organism rarely can be optimally designed for only one function or one environmental condition. Some of these natural systems have developed well-orchestrated strategies, exemplified in the biological tissues of numerous animal and plant species, to synthesize and construct materials from a limited selection of available starting materials. The resulting structures display multiscale architectures with incredible fidelity and often exhibit properties that are similar, and frequently superior, to mechanical properties exhibited by many engineered materials. These biological systems have accomplished this feat through the demonstrated ability to tune size, morphology, crystallinity, phase, and orientation of minerals under benign processing conditions (i.e., near-neutral pH, room temperature, etc.) by establishing controlled synthesis and hierarchical 3D assembly of nano- to microscaled building blocks. These systems utilize organic-inorganic interactions and carefully controlled microenvironments that enable kinetic control during the synthesis of inorganic structures. This controlled synthesis and assembly requires orchestration of mineral transport and nucleation. The underlying organic framework, often consisting of polysaccharides and polypeptides, in these composites is critical in the spatial and temporal regulation of these processes. In fact, the organic framework is used not only to provide transport networks for mineral precursors to nucleation sites but also to precisely guide the formation and phase development of minerals and significantly improve the mechanical performance of otherwise brittle materials.Over the past 15 years, we have focused on a few of these extreme performing organisms, (Wang , Adv. Funct. Mater. 2013, 23, 2908; Weaver , Science 2012, 336, 1275; Huang , Nat. Mater. 2020, 19, 1236; Rivera , Nature 2020, 586, 543) investigating not only their ultrastructural features and mechanical properties but in some cases, how these assembled structures are mineralized. In specific instances, comparative analyses of multiscale structures have pinpointed which design principles have arisen convergently; when more than one evolutionary path arrives at the same solution, we have a good indication that it is the best solution. This is required for survival under extreme conditions. Indeed, we have found that there are specific architectural features that provide an advantage toward survival by enabling the ability to feed effectively or to survive against predatory attacks. In this Account, we describe 3 specific design features, nanorods, helicoids, and nanoparticles, as well as the interfaces in fiber-reinforced biological composites. We not only highlight their roles in the specific organisms but also describe how controlled syntheses and hierarchical assembly using organic (i.e., often chitinous) scaffolds lead to these integrated macroscale structures. Beyond this, we provide insight into multifunctionality: how nature leverages these existing structures to potentially add an additional dimension toward their utility and describe their translation to biomimetic materials used for engineering applications.

Self-Lubricating Effect of FeWO4 Tribologically Synthesized from WC-(Fe-Mn-C) Composite during High-Speed Sliding against a HSS Disk

WC-(Fe-Mn-C) composites with γ-iron and γ + α’ matrices were sintered and then tested at sliding speeds in the range 7–37 m/s. The coefficient of friction was exponentially reduced as a function of sliding speed reaching its minimum at 37 m/s. This behavior was provided by the mechanochemical formation of iron tungstate FeWO4 on the worn surfaces of composite samples. The lubricating effect of iron tungstate did not, however, allow for a reduction in wear. The worn surface was represented by a 3–10 μm-thickness tribological layer composed of fine WC and iron particles cemented by FeWO4. This layer provided the self-lubricating effect in high-speed (high-temperature) sliding because of its easy shear and quasi-viscous behavior. The underlying 25–65 μm of thickness layer was composed of only heat-affected WC and recrystallized iron grains.

Macroscale Robust Superlubricity on Metallic NbB2

Robust superlubricity (RSL), defined by concurrent superlow friction and wear, holds great promise for reducing material and energy loss in vast industrial and technological operations. Despite recent advances, challenges remain in finding materials that exhibit RSL on macrolength and time scales and possess vigorous electrical conduction ability. Here, the discovery of RSL is reported on hydrated NbB₂ films that exhibit vanishingly small coefficient of friction (0.001-0.006) and superlow wear rate (≈10^-17 m³ N^-1 m^-1 ) on large length scales reaching millimeter range and prolonged time scales lasting through extensive loading durations. Moreover, the measured low resistivity (≈10^-6 Ω m) of the synthesized NbB₂ film indicates ample capability for electrical conduction, extending macroscale RSL to hitherto largely untapped metallic materials. Pertinent microscopic mechanisms are elucidated by deciphering the intricate load-driven chemical reactions that generate and sustain the observed superlubricating state and assessing the strong stress responses under diverse strains that produce the superior durability.

A Modelling Study of the Correlation between the Layer Obtained by Selective Transfer and the Dislocations Movement at the Friction Surfaces Limit

The selective transfer phenomenon (STP) is based on physico-chemical processes occurring in the contact area of a friction pair, with an element from a copper alloy and allows the metallic transfer of particles of micro/nanometric size, forming a thin superficial tribologically performing layer under energy and relative motion conditions. During the formation of the layer, its crystalline network has an excess of defects and this makes the dislocations to come to the surface. The layer thickness is small, porous, and with comparable dimensions to those of the tensions field of the dislocations. This paper presents a review and analysis of the STP based on dislocations movement to establish and know the tensions field influence, the energy (about 0.25 J/m), and the linear tension of dislocations (~2.42 × 10−9 N) at the contact surfaces zone of a friction pair, by which we can ensure a low wear state (~4.16 × 10−5–2.16 × 10−4 g/min), and a reduced friction coefficient (~0.014–0.034). Therefore, the purpose of the paper is to analyze the STP based on the dislocations movement because is proves the existence (presence), importance, and utility of the dislocations, respectively, the dislocations movements during the conditions’ selective transfer, at the limit of the friction surfaces, under the action of a tensions field, whose components are determined analytically by modelling, together with energy and the linear tension. Also, the layer formed through STP has the property of ensuring during the deformation process an agglomeration of dislocations (structural defects) which protects it from destruction, and therefore, a self-regulation of the equilibrium processes, disturbed during the friction process, to maintain the friction and wear of the friction pairs within reduced limits.

Dual-Phase Nanocomposite TiB2/MoS1.7B0.3: An Excellent Ultralow Friction and Ultralow Wear Self-Lubricating Material

Proper lubrication is essential to the reliable and efficient operation of mechanical systems ranging from the industrial to the nanoscale. Self-lubricating materials that can self-generate and sustain concurrent ultralow friction and ultralow wear in harsh environments open up a unique realm that is unattainable by traditional external lubrication mechanisms, but developing such extraordinary materials has been a long-standing grand challenge. Here, we devise an unconventional strategy to construct a dual-phase nanocomposite (DPNC) that comprises a wear-resistant phase (TiB₂) and an internal lubricant source (MoS_1.7B_0.3). Tribological tests demonstrate simultaneous ultralow friction coefficient (∼0.03) and ultralow wear rate (∼10^-10 mm³·N^-1·m^-1) of the synthesized DPNC specimen in ambient environments; these superb properties remain intact after the specimen has been annealed at 400 °C in air. First-principles energetic and stress-strain calculations elucidate atomistic mechanisms underpinning DPNC TiB₂/MoS_1.7B_0.3 as an ultimate self-lubricating material. This accomplishment solves the classic lubricity-durability tradeoff dilemma, enabling advances to meet the most challenging lubrication needs.

Influence of Austempering of As-Cast Medium Carbon High-Silicon Steel on Wear Resistance

The aim of this study was to evaluate the effect of austempering compared to quenching and low-temperature tempering on wear resistance of an as-cast medium carbon high-silicon steel intended for rock breaking. Austempering was done by isothermal holding at 270, 300 and 350 °C in molten salt baths, while quenching was done in water. The austempering treatments resulted in microstructural combinations of bainite and martensite. The isothermal holding at 270 °C resulted in bainite and self-tempered martensite, while isothermal holdings at 300 and 350 °C resulted in bainite and untempered martensite. The two quench and temper treatments resulted in tempered martensite. In general austempering resulted in lower hardness values when compared to quenching and tempering but higher impact toughness. The wear resistance was best for quenching and low temperature tempering, followed by austempering at 270 °C, but at slightly lower hardness and 25% higher impact toughness. The other two austempering treatments resulted in worse wear resistance.

Investigations on the Influence of Annealing on Microstructure and Mechanical Properties of Electrodeposited Ni-Mo and Ni-Mo-W Alloy Coatings

Ni-Mo and Ni-Mo-W coatings were electrodeposited on a stainless steel sheet, and then were annealed at 200, 400, and 600 °C. The effect of annealing heat treatment on the microstructure of Ni-Mo and Ni-Mo-W electrodepositions, their nano-hardness, and tribological properties were investigated. It was revealed that the average crystalline are refined and phase separation are promoted with formation of Mo-W related intermetallic precipitates at temperature exceed 400 °C on account of the co-existence of Mo-W elements within Ni-Mo-W coatings. Annealing heat treatment leads to hardening, and the hardness and elastic module increase significantly. The grain boundary (GB) relaxation and hard precipitated intermetallic particles are responsible for the annealing-induced hardening for ≤400 °C annealed and 600 °C annealed Ni-Mo-W coatings, respectively. In addition, both adhesive wear and abrasive wear are observed for coatings, and abrasive wear becomes predominant when annealing temperature up to 600 °C. The wear resistance of coatings is improved eventually by formation of a mixture of lubricated oxides upon annealing at 600 °C and the enhancement of H/E ratio for ≤400 °C annealed Ni-Mo-W coatings.

On Improving Wear Resistance of Cr-Al-N Coatings Using Dynamic Glancing Angle DC Magnetron Sputtering

The development of alternatives for wear protection in surface engineering can be responsible for a significant decrease in energy waste as a large amount of the energy produced in the world is lost due to tribological contact. Dynamic Glancing Angle Deposition has been recently evaluated as a route to produce coatings with improved wear performance. In this technique, the substrate oscillates along with a determined range in front of the sputtering target during the growth of the film. In this study, five oscillatory ranges (0, ±5°, ±10°, ±15°, ±20°) were probed to manufacture nanostructured Cr-Al-N coatings using direct current magnetron sputtering, and their impact was investigated on the grain morphology, phase formation, chemical composition, and performance of the coatings. FEG-SEM revealed the formation of multilayer-like architecture across the grains of the coatings. The deposition rate and hardness improved, and a more than 2-fold decrease in the material loss was observed in a comparison between the stationary-deposited conventional coating and the sample produced under ±10° oscillatory range. This indicated the potential use of this technique in future surface engineering applications.

The Effect of Surface Topography Feature Size Density and Distribution on the Results of a Data Processing and Parameters Calculation with a Comparison of Regular Methods

In this paper, the influence of occurrence of surface texture features on the values of surface topography parameters calculated after the application of various data processing techniques was presented. Different types of surface topographies were considered, as follows: cylinder liners, some with additionally burnished dimples, turned, ground, milled, laser-textured, composite, ceramic, or isotropic in general. The effects of feature size on the areal form removal, noise suppressions, or end-effect reducing in surface texture measurements were studied. The variations of the ISO 25178 standard surface topography parameters were taken into consideration in detail. It was assumed that some of the feature sizes, distributions, and densities have a substantial impact on the values of surface topography parameters calculated after applications of regular (commonly used) algorithms and procedures, defined as basic operations, provided for raw surface texture data obtained directly from the measurement process. In the end, some of the practical applications for receiving the relevant values of surface topography parameters were proposed.