The vast renewable energy potential of the oceans remains largely untapped, not due to a lack of energy conversion concepts, but because the moving components of wave, tidal, and current energy systems experience premature failure under the ocean's aggressive tribological environment. This review dissects the coupled (multi-mode) phenomena of friction, wear, lubrication, corrosion, erosion, and biofouling that collectively dictate the reliability of marine energy converters. Moving beyond isolated failure analyses, it establishes a system-level framework that links component function, motion kinematics, and degradation pathways under real oceanic conditions. The synthesis reveals how mechanical stresses, and environmental agents coevolve to form self-reinforcing degradation loops, where corrosion debris, cavitation, and microbial colonization accelerate wear and frictional loss in ways conventional testing cannot replicate. By consolidating these insights, the study formulates the fundamental, unanswered questions that define the frontiers of ocean tribology such as how third-body dynamics, transient electrochemistry, and surface-adherent biofilms interact at the interface to control material durability. Addressing these gaps is pivotal to transforming tribology from an afterthought to a central design principle, enabling durable, predictable, and economically viable marine energy systems.

Additive manufacturing (3D printing) of engineered living materials (ELMs) enables the spatial patterning of cells within three-dimensional (3D) polymer matrices. However, a critical barrier to deploying ELMs is the lack of universal and reliable strategies to contain cells within 3D printed matrices. While synthetic biology renders cell-specific containment, a materials-centric approach can provide a cell-agnostic biocontainment platform. Therefore, this study presents a hydrogel-based additive manufacturing strategy to fabricate ELMs with physicochemical biocontainment. The 3D printed ELMs are fabricated by copolymerizing Pluronic F127-bisurethane methacrylate (F127-BUM) with methacrylic acid (MAA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). Varying concentrations of these comonomers allow modulation of the ELM functionalities, namely, biocompatibility or antimicrobial properties. In particular, MAA-containing ELMs enable tunable biocontainment of the yeast Saccharomyces cerevisiae after immersion in 70 vol.% ethanol, leading to the formation of a time-dependent cell-free zone. The resulting yeast-laden ELMs enhance cell retention up to 300% (98 ± 12 h) and provide an average 38% fermentation increase compared to ELMs composed of only F127-BUM. In conclusion, this hydrogel-based spatiotemporal control strategy improves cell retention and metabolic activity performance in 3D-printed ELMs. These capabilities are promising for several applications, including 3D printed bioreactors and living therapeutic materials.

Net-zero by 2050 demands scalable renewables. Ocean wave/tidal energy, though denser than solar and wind, remains at low TRL. A pivotal barrier is the material durability and performance of ocean (hydraulic) rod linear bearings that remain key components of WECs including point absorbers. This study presents a comparative mechanical, thermal, and tribological evaluation of eight commercial and newly developed self-lubricating bearing materials, including thermoplastics, thermosets, elastomers, and a bronze-based alloy, under unlubricated conditions. The materials incorporate diverse reinforcement architectures, including short fibers, woven and continuous fiber fabrics, and solid lubricant particulate fillers. Tribological testing was conducted under an 18 hrs long-duration dry reciprocating pin-on-flat configuration at 0.02-0.1 m/s under 250 N load. Friction behavior, wear rates, and surface degradation were recorded. Post-test analyses using SEM, FTIR, and 3D surface profilometry revealed distinct wear mechanisms and transfer film behavior. Wear maps integrating friction, wear rate, and a normalized multi-parameter performance index reveal sliding-speed-dependent tribological transitions and enable ranking of marine composites. The findings establish a foundational understanding for bearing failure mechanisms, predictive design and material selection in ocean tribological systems.

As EV systems evolve, higher demands are placed on the reliability and sustainability of tribological components operating under combined mechanical and electrical stresses. Electrical damage arises when stray currents pass through bearing contacts, leading to electrical arcing, pitting, and surface degradation of rolling elements and raceways. DLC coatings, due to their low friction characteristics and inherent dielectric properties, are promising for electrically stressed environments. However, their tribological behavior under direct electrical stimulation remains insufficiently understood, especially in DLC/steel contacts. This study investigates the effect of applied direct current (0-2 A) on the dry sliding behavior of hydrogenated-DLC (H-DLC), tetrahedral amorphous carbon DLC (H-free DLC), and uncoated steel against a steel ball in ball-on-disk tribometer under ambient conditions. HDLC exhibited ultralow coefficient of friction (COF approximate to 0.05) and minimal wear at low current (0.1 A), attributed to the formation of a hydrogen-assisted graphitic tribolayer. In contrast, H-free DLC and steel showed comparable or increasing friction and wear with rising current. At currents >= 1 A, all materials experienced tribolayer breakdown with oxidation and surface degradation. These findings demonstrate that electric current can act as a tribo-chemical activation mechanism, with the response being strongly dependent on the coating material properties and structure.

Bone diseases lead to an increasing demand for implants to treat long bone defects and for load-bearing applications. Osteoporosis care and accidental injuries are major contributors to this rising need. Our research aims to demonstrate innovative material systems and methods for preparing implants that can be used in regenerative medicine. We hypothesize that by combining titanium alloys (Ti6Al4V) with hydroxyapatite (Hap), we can enhance biocompatibility and tribo-mechanical performance, which are critical for the longevity of Ti-based surgical implants. Additionally, we investigate the application of laser surface treatments to expose the underlying porosity, thereby enhancing cell transport and promoting cell growth. In this study, we investigate the effects of two fabrication techniques—Spark Plasma Sintering (SPS) and powder metallurgy (PM)—on the properties of laser-textured Ti64/Hap biocomposites. Our findings demonstrate that the selected processing route significantly influences the microstructure, tribological performance, and surface properties of these materials. An X-ray diffraction (XRD) analysis corroborates our results from incubation studies in simulated body fluids, highlighting the impact of phase transformations during sintering on the chemical properties of Ti-Hap composites. Additionally, while laser surface texturing was found to slightly increase the friction coefficient, it markedly enhanced the wear resistance, particularly for the PM and SPS Ti + 5%Hap composites.

Reinforcement with superhard ceramic additives protects material against the progressive loss of matrix under conditions of high abrasion and/or impact typical of drilling tools, ceramic nozzles, dry machining, and cutting tools. In this work, dense (>99 %) Al2O3 ceramic with and without 10 vol% cBN composites utilizing different sizes and/or Ti/Ni surface-coated cBN particles with different strength were fabricated by Spark Plasma Sintering (SPS). Sintering behavior, effect of additive on microstructure, mechanical properties of the composites and their erosive wear were thoroughly studied. Optimal sintering conditions were identified as 1350 degrees C, 100 MPa, and 5 min, producing composites with superior density (>99 %) and microstructural cohesion in pure alumina and composite reinforced with the cBN particles. Composites reinforced with Ni+Ti-coated cBN particles (88-105 mu m, 200 MPa) exhibited the best performance, with a hardness of 17.71 GPa, fracture toughness of 5.25 MPam(1)/(2), Young's modulus (E) of 350 GPa, with the minimum total work of 3.04 N.mm during indentation, and the lowest erosion rate (1.2 mm(3)/kg). Furthermore, the findings depict that slight deviations in sintering conditions led to significant variations in densification, and particle-matrix bonding, which in turn influenced the composite's resistance to erosive wear.

EV motors and machine elements operate at higher speeds, generate significant heat and noise (vibration), and subject lubricants (bearings) to multiple degrading factors, requiring thermal stability, wear protection, mitigating wear mechanisms like pitting and scuffing, and low electrical conductivity to prevent arcing damage to bearings. This study evaluates the tribological performance of four types of greases—PUEs, PUPao, PUEth (polyurea-based), and LiPAO (lithium–calcium complex-based)—to determine their suitability for electric motor bearings. Key performance metrics include tribological properties, electrical resistivity, leakage, bearing noise, and wear behavior. A four-ball wear test ranks the greases by scar diameter as PUPao < PUEs < PUEth < LiPAO, while the coefficient of friction is observed in the range of 0.15–0.18, with LiPAO exhibiting the lowest friction. Electrical resistivity tests reveal that PUEs grease has the lowest resistivity. Electrical leakage tests, conducted with a voltage differential across bearings, assess pitting damage, with PUEth and LiPAO showing evidence of surface pitting. Optical microscopy and scanning electron microscopy analysis is carried out to examine the pitting. In bearing noise tests, PUEs demonstrates the lowest noise levels, whereas LiPAO produces the highest. Visual and microscopic examination of the greases further characterizes their lubricating properties. Based on overall performance, the greases are ranked in suitability for electric motor applications as PUEs > PUPao > PUEth > LiPAO. The findings highlight the critical need for selecting appropriate grease formulations to ensure optimal bearing performance under varying operational conditions.

Additively manufactured complex geometries from copper alloys with high thermal and mechanical properties have drawn the attention of researchers. The present contribution explores the additive manufacturing (AM) of copper-based alloys from powder particles intended for heat sink and heat exchange applications. Selective laser melting (SLM) parameters featuring low laser beam power (160 W), moderate scanning speed (320 mm/s), and high energy density (200 J/mm3) were employed to fabricate dense components from CuSn10 particles. The present work deal with structural analysis and precision investigation of microfabrication, particularly in Struts, Tubes, and Fins. Mechanical properties (compression and hardness) for Strut structure, differential pressure evaluations for Tube structure, and analyses of thermal and electrical conductivities for Fin structure were investigated. The results showed an improvement in strength compared to those of pure copper, facilitating ease of AM. The obtained results affirm the feasibility of AM, demonstrating the successful creation of complex and combined solid-porous structures using SLM process from Cu alloys. A comprehensive structural investigation and characterization of the Cu-Sn alloy is presented here, aiming to establish a standardized approach for analysing Cu alloys. The results indicate that small-scaled structures fabricated via CuSn10 alloy exhibits a thermal conductivity of 34.3 W & sdot;m-1 & sdot;K-1, an electrical conductivity of 4.72x106 S/m, a hardness of 119 HV-50, a uniform surface roughness of 6 mu m, and can withstand a force loading of 1 kN.

Gyroid lattice structures, inspired by the natural interconnectivity of human bone, show promise in bone tissue engineering (BTE). This study explores the mechanical properties, and failure mechanisms of selective laser melted (SLM) Gyroid Ti6Al4V lattice structures with varying unit cell rotation angles (RA) of 0∘ (G0), 30∘ (G30), and 60∘ (G60) around the x-axis. The study assesses their mechanical and energy absorption properties through quasi-static compression testing and elastoplastic finite element (FE) analysis. Despite similar relative densities for all designed lattices, the RA variation significantly impacts mechanical performance. G30 exhibits superior load-bearing capacity, with higher modulus of elasticity, yield strength, ultimate strength, and plateau stress. It also has the highest energy absorption capacity, while G60 shows the highest surface area (SA) and surface area-to-volume ratio (SA/VR). These findings highlight the potential of Gyroid lattices for bone replacements due to their tunable mechanical and biological responses.

The mining sector seeks innovation to enhance operational efficiency and prolong cutting tool life. This research investigates the impact of cryogenic treatment (CT) for 12, 24, and 36 h on tungsten carbide cutting bits used in mine machineries, focusing on its effects on cutting force, energy consumption, and tool wear during lab-scale linear rock cutting. Microstructural analysis and hardness testing follow CT, revealing improvements in hardness, the formation of new compounds, and the presence of eta carbides. Analysis of linear rock cutting experiments shows that longer holding periods under CT lead to reduced cutting force, energy consumption, and tool wear. Comparing CT 24 to untreated bit at a cutting speed of 200 m/s, CT 24 demonstrates reduction in specific energy by 39.35 %, 41.13 %, and 29.39% at depth of cut (DoC) of 2 mm, 4 mm, and 6 mm, respectively. Additionally, CT 24 exhibits significantly lower wear rates (79.24 %, 85.44%, and 85.01 %) compared to UT bits at the same cutting speed. Microstructural analysis identifies multiple wear mechanisms in both treated and untreated worn tools. To optimize the cutting process for mining efficiency, grey relational analysis and Pythonbased non-dominant sorting are employed. Grey relational analysis identifies 24-h CT, a cutting speed of 200 m/ s, and a 2 mm depth of cut as optimal. Non-dominant sorting suggests 24-h CT, a cutting speed of 200 m/s, and 2-4 mm cut depth for optimal results. Pareto solutions indicate specific energy ranging from 14.96 to 9.20 kWh/ m3 and wear rates ranging from 0.33 to 0.39 x 10-4 cm3/cm. Insights from this study offer valuable guidance for the mining industry to enhance cutting tool efficiency and promote environmentally sustainable mining practices.

Tungsten and cobalt are included in the European Union’s list of critical raw materials (CRM). The share of WC-Co-based cutting tools is slowly decreasing, but they still account for a major share, and efficient recycling technology has to be developed. Different technologies are present but most of them have drawbacks such as contamination by the material of crushing equipment, excessive energy consumption, use of dangerous chemicals that need to be disposed (also causing health issues to workers), dramatic reduction of mechanical properties of the recycled powder, etc. The recycling of WC-Co hardmetal (cermet) tools with the help of thermal shock of varied intensity and the number of treatments followed by an assessment of the resulting change in mechanical properties (microhardness), number of fragments, as well as the weight of samples, were done. The device allowing automated application of a pre-defined number of heating-cooling cycles (water and liquid nitrogen were used as a cooling medium) was produced, and applied. The diagrams indicating the optimal (number of cycles and temperatures) treatment regime providing the highest strength were obtained, and scanning electron microscope images are illustrating the recycling efficiency.

Friction, wear, and the consequent energy dissipation pose significant challenges in systems with moving components, spanning various domains, including nanoelectromechanical systems (NEMS/MEMS) and bio-MEMS (microrobots), hip prostheses (biomaterials), offshore wind and hydro turbines, space vehicles, solar mirrors for photovoltaics, triboelectric generators, etc. Nature-inspired bionic surfaces offer valuable examples of effective texturing strategies, encompassing various geometric and topological approaches tailored to mitigate frictional effects and related functionalities in various scenarios. By employing biomimetic surface modifications, for example, roughness tailoring, multifunctionality of the system can be generated to efficiently reduce friction and wear, enhance load-bearing capacity, improve self-adaptiveness in different environments, improve chemical interactions, facilitate biological interactions, etc. However, the full potential of bioinspired texturing remains untapped due to the limited mechanistic understanding of functional aspects in tribological/biotribological settings. The current review extends to surface engineering and provides a comprehensive and critical assessment of bioinspired texturing that exhibits sustainable synergy between tribology and biology. The successful evolving examples from nature for surface/tribological solutions that can efficiently solve complex tribological problems in both dry and lubricated contact situations are comprehensively discussed. The review encompasses four major wear conditions: sliding, solid-particle erosion, machining or cutting, and impact (energy absorbing). Furthermore, it explores how topographies and their design parameters can provide tailored responses (multifunctionality) under specified tribological conditions. Additionally, an interdisciplinary perspective on the future potential of bioinspired materials and structures with enhanced wear resistance is presented.

Magnesium (Mg) and graphene in alloy formulations are of paramount importance for lightweight engineering applications. In the present study, ZE10 Mg-alloy-based nanocomposites reinforced with graphene nanoplatelets (GNPs) having a thickness of 10–20 nm were fabricated via ultrasound-assisted stir casting. The effect of GNP contents (0.25, 0.5, and 1.0 wt.%) on the microstructure, Vickers hardness, and tensile properties of nanocomposites was investigated. Further, tribological studies were performed under a ball-on-disc sliding wear configuration against a bearing ball counterbody, at room and elevated temperatures of 100 °C and 200 °C, to comprehend temperature-induced wear mechanisms and friction evolution. It was revealed that the GNP addition resulted in grain coarsening and increased porosity rate of the Mg alloy. While the composites exhibited improved hardness by 20–35% at room temperature and 100 °C, a minor change was observed in their hardness and tensile yield strength values at 200 °C with respect to the GNP-free alloy. A notable improvement in lowering and stabilizing friction (coefficient of friction at 200 °C~0.25) and wear values was seen for the self-lubricating GNP-added composites at all sliding temperatures. The worn surface morphology indicated a simultaneous occurrence of abrasive and adhesive wear mode in all samples at room temperature and 100 °C, while delamination and smearing along with debris compaction (tribolayer protection) were the dominant mechanisms of wear at 200 °C. Inclusively, the results advocate steady frictional conditions, improved wear resistance, and favorable wear-protective mechanisms for the Mg alloy–GNP nanocomposites at room and elevated temperatures.

Self-lubricating coatings extend the efficient dry-operational life of cutting and forming tools. In the current work, millimeter-thick NiCrBSi coatings with 10 wt% metal sulfide i.e. Ni3S2, CuS, or Bi2S3 were fabricated on a stainless steel substrate by laser cladding (in-situ alloying). Thermodynamic modelling utilizing the calculation of phase diagrams method (CALPHAD) was performed to predict the phase evolution during laser melting. Electron microscopy methods combined with X-ray diffraction and Raman spectroscopy were used to elucidate the developed microstructure. The coatings were further subjected to reciprocating dry sliding wear against a martensitic steel ball counterbody using a ball-on-plate configuration at 0.1 m/s and 50 N (Hertz contact pressure 1.7 GPa). The tests were conducted at room temperature (20), 400, and 600 degrees C. The results demonstrate a selflubricating behavior of the sulfide coatings resulting in friction reduction by -60 % at room temperature and -40 % at 400 degrees C sliding, particularly for Bi2S3-added cladding, due to the prevalent existence of lubricious phases of chromium sulfide (CrxSy) along with others (NiBi, Bi) and leading to 'self-healing' phenomena. The results are reported in comparison to the unmodified NiCrBSi alloy.

In spite of the critical environmental impacts of mining and the associated geopolitical supply risk, the strategic importance of rare metal tungsten is escalated by rapid expansions in industrialization, particularly in the ongoing low-carbon/energy era, which requires technologies that allow an economic, social, and ecologically friendly tungsten recovery from primary and secondary resources. The current recycling practices of tungsten carbide (WC)-based scraps have been accepted as economically and partially environmentally beneficial and can promote tungsten closed-loop recycling; however, low functional recycling rates and significant metal losses at varied stages hinder the economic recovery of metals. The current review presents the global situation of tungsten and WC flow with a focus on various sustainable methods to recycle spent tungsten and related metals. A detailed discussion of establishing a highly resilient circular economy with sustainable development goals is highlighted by juxtaposing the philosophy of the circular economy, integrated sustainability, and the metal life cycle approach. The article also discusses Industry 5.0 trends, such as sustainable digitalization and twin transition, to overcome the barriers associated with achieving efficient circular recycling. It is shown that cross-disciplinary methodologies, the integration of diverse technologies (digital/green), and the incorporation of state-of-the-art recycling techniques open up the future potential in the recycling sector.

To increase the performance of the tool materials operating at high temperatures (HT), the protection of the surface from wear is usually needed. Conventional lubricants pose problems due to their degradation and harmful effects on human health; therefore, self-lubricating materials are of great importance. In the current work, self-lubricating NiCrSiB millimeter-thick composite coatings with the addition of solid lubricants Ag and MoS2 were fabricated on stainless steel substrates using laser metal deposition. Upon microstructural analysis, it was revealed that the addition of MoS2 resulted in a uniform distribution of Ag throughout the coating thickness owing to a unique phenomenon of silver encapsulation. Further, the coatings were subjected to sliding wear tests against an alumina counterbody at a load of 5 N, a speed of 0.1 m s(-1), and a distance of 500 m under a unidirectional condition in a ball-on-plate configuration. The tests were performed from 20 to 800 degrees C. The results show that self-lubricating composite coatings demonstrate an exceptional performance up to 800 degrees C. Significant friction (best at 800 degrees C-0.25) and wear (best at 600 degrees C-4.3 times less) reduction for Ag + MoS2 added coating is seen. It was revealed that the presence of CrxSy and Ag on the wear track delivered lubrication at temperatures <400 degrees C while, a glazed tribolayer rich in silver molybdate phase (along with CrxSy, MoO3) was an effective lubricant at 600 and 800 degrees C. The results are reported in comparison to the unmodified Ni-based alloy.

Selective laser melting (SLM) process is a promising additive manufacturing technique for the fabrication of 3D metallic components with complex geometries. When applied to a porous structure made of a low-alloyed copper, the results show a good producibility and malleability for structures made of CuNi2SiCr. On the other hand, powder metallurgy proposes spark plasma sintering (SPS) process to introduce diamond particles (resin -bonded micron-size and crystalline with 50 % coating) into a 3D-built copper structure to achieve fast and highly densified fabrication. The present work aims to achieve better positioning, consolidation and densification of the diamond particles at the desired location of the structure, which includes both the lattice and the bulk. This paper studies an additively manufactured diamond-reinforced copper structure developed for fabricating heatsinks by SLM and SPS. These metal-diamond hybrid composites can potentially be used for electro-thermal applications, refractory composites or bio/tribological applications. The demonstrated privileges include i) AM techniques using SLM with low laser power, ii) larger layer thicknesses with higher productivity and iii) rapid fabrication of porous structures with successively applying plasma sintering to fill them with hard materials like diamond particles.

This work reports on the spark plasma sintering (SPS) of self-propagating high-temperature-synthesis (SHS)-derived Ni-W and Ni-W-2wt%hBN (4:1 molar ratio of metals) powders. The synthesis was carried out from a mixture of NiO and WO3 using Mg + C combined reducers through a thermo-kinetic coupling approach. Experiments performed in the thermodynamically optimal area demonstrated the high sensitivity of combustion parameters and product phase composition to the amount of reducers and hBN powder. The powder precursors with and without the addition of hBN were consolidated using SPS at a temperature and pressure of 1300 °C and 50 MPa, respectively, followed by a thorough phase and microstructural characterization of the obtained specimens. SHS-derived powders comprised the nano-sized agglomerates and were characterized by a high sinterability. The specimens of >95% density were subjected to ball-on-plate dry sliding wear tests at a sliding speed of 0.1 ms−1 and a distance of 1000 m utilizing an alumina ball of 10 mm in diameter under a 15 N normal load. The tests were performed at a temperature of 800 °C. A significant improvement in wear behavior was demonstrated for SHS-processed composites in comparison with their counterparts produced via conventional high-energy ball milling technique owing to the phenomena of ‘micro-polishing’, cyclic ‘self-healing’ and fatigue. However, the decisive effect of hBN addition in imparting lubrication during an HT wear test was not confirmed.

The circular economy is emerging as green technology solution for polymer and composite industries. However, the use of circular economy as an industrial practice is still a global challenge. In this article, polypropylene-cotton hybrid composite was developed using different amounts of cotton fibre waste (0, 10, 30, 40 wt%). Scanning electron microscope (SEM), tribometer, Rockwell hardness tester and binocular microscope were used for investigations of composite surface, hardness and coefficient of friction (COF). The mean coefficient of friction values was 0.64, 0.75, 0.88 and 0.94 for pure propylene, 10, 30 and 40% of cotton reinforced composites, respectively. The scanning electron microscopy characterization of hybrid composite revealed the voids, porosity and asperities due to random fibres orientation. The Rockwell hardness value of composites was increased due to rise of fibre fraction. Based on the COF values, hardness and surface characterization, polypropylene-cotton reinforced hybrid composite could be used functionally for thermal and sound applications.

Understanding the complex nature of wear behavior of materials at high-temperature is of fundamental importance for several engineering applications, including metal processing (cutting, forming, forging), internal combustion engines, etc. At high temperatures (up to 1000 °C), the material removal is majorly governed by the changes in surface reactivity and wear mechanisms. The use of lubricants to minimize friction, wear and flash temperature to prevent seizing is a common approach in engine tribology. However, the degradation of conventional liquid-based lubricants at temperatures beyond 300 °C, in addition to its harmful effects on human and environmental health, is deeply concerning. Solid lubricants are a group of compounds exploiting the benefit of wear diminishing mechanisms over a wide range of operating temperatures. The materials incorporated with solid lubricants are herein called 'self-lubricating' materials. Moreover, the possibility to omit the use of conventional liquid-based lubricants is perceived. The objective of the present paper is to review the current state-of-the-art in solid-lubricating materials operating under dry wear conditions. By opening with a brief summary of the understanding of solid lubrication at a high temperature, the article initially describes the recent developments in the field. The mechanisms of formation and the nature of tribo-films (or layers) during high-temperature wear are discussed in detail. The trends and ways of further development of the solid-lubricating materials and their future evolutions are identified.