Polyetheretherketone (PEEK) is a high-performance thermoplastic widely used in orthopaedic and biomedical applications due to its excellent mechanical properties, biocompatibility, and suitability for additive manufacturing. However, its relatively poor friction and wear resistance limits its use in long-term, load-bearing implants. This study investigates the effect of hexagonal boron nitride (hBN) and silicon nitride (Si3N4) reinforcements on the mechanical and tribological performance of 3D-printed PEEK composites fabricated via melt blending and fused filament fabrication (FFF). The composites exhibited uniform filler dispersion, good printability, and tensile properties comparable to neat PEEK, along with maintained thermal stability. Under impact loading, reinforced samples showed enhanced energy absorption and a transition from complete fracture to hinge-type incomplete fracture, indicating improved resistance to crack propagation. Tribological evaluation under simulated joint conditions revealed that hBN-reinforced PEEK reduced friction (∼20%) and wear (∼50%), whereas Si3N4-reinforced PEEK increased friction (∼40%) and caused noticeable damage to the cobalt–chromium (CoCr) counter surface. These findings highlight the potential of hBN as an effective reinforcement for improving the tribological performance of 3D-printed PEEK composites, while also revealing limitations associated with Si3N4.

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.

Tribocorrosion studies have primarily focused on hard-on-hard articulations, with limited research on metal-on-polymer (MoP) configurations despite their clinical relevance. This study investigates the tribocorrosion behaviour of cobalt-chromium (CoCr) alloy against 3D-printed polyetheretherketone (PEEK), conventionally manufactured PEEK, and ultrahigh molecular weight polyethylene (UHMWPE), with UHMWPE as the reference material. Tests were conducted using a reciprocating tribometer under open circuit and potentiostatic conditions in phosphate buffered saline (PBS) and bovine calf serum, with in-situ electrochemical monitoring. The results demonstrated that the presence of serum significantly decreased the charge transfer of the CoCr surface, hence decreasing electrochemical degradation when compared to PBS lubrication. The manufacturing methods for PEEK resulted in different surface characteristics, leading to variations in tribocorrosion behaviour; however, polishing to achieve homogeneous roughness minimized these differences. Furthermore, CoCr exhibited significantly higher charge transfer when slid against all tested PEEKs compared with UHMWPE (at least two-fold higher), suggesting that a PEEK-CoCr tribocouple results in an increase of tribocorrosion and a greater potential for metal ion release than a UHMWPE-CoCr tribocouple.

The impact of cryogenic cyclic aging on the thermal, mechanical, and tribological properties of polyetheretherketone (PEEK) and its composites was investigated to reveal the mechanisms and factors affecting the durability of high-performance materials under prolonged exposure to extreme environments. Cryogenic cyclic aging involved twelve cycles, each consisting of 6-day aging in liquid nitrogen (−196 °C) and 1-day in oven at 40 °C in normal ambient (relative humidity ∼30 %), mimicking operational conditions of cryogenic systems. Tribological tests were conducted using a ball-on-disk configuration with a stainless steel (SS 316L) ball counterface. Tests were performed at 25 °C in air and high vacuum (10⁻⁵ Pa). The thermal stability of the materials was slightly affected. Thermal stresses developed during aging led to polymer embrittlement. Fracture toughness decreased by approximately 22 % after cyclic aging. Abrasive wear increased significantly for unreinforced PEEK, while PEEK composites showed a rise in adhesive wear with prolonged aging. In air, the wear rate increase reached 510 %, whereas in vacuum, some compositions exhibited a wear rate reduction of up to 56 %.

The strive to reduce harmful emissions from transport has resulted in an increased emphasis on minimising friction in lubricated contacting components to improve the energy efficiency of automotive engines. In this sense, it is of particular interest to investigate whether a synergistic tribological performance could be achieved by combining two or more friction modifier additives with nanoparticles. This study conducts a comprehensive investigation into the tribological characteristics of lubricant formulations enriched with nanodiamonds (NDs), combined with organic (Glycerol Monooleate, GMO) and inorganic (molybdenum dithiocarbamate, MoDTC) friction modifiers and a low-concentration anti-wear additive (Zinc dialkyl dithio-phosphate, ZDDP). The interaction between NDs and MoDTC has been evaluated using reciprocal sliding tests at two different temperatures. The outcomes of the tribological experiments revealed that the interaction of NDs and MoDTC can enhance the friction and wear performance of steel pairs. However, this enhanced performance is shown to highly depend on other additives present in the lubricant mixture. Analysis of wear scars using High-Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM) and Raman spectroscopy reveals that when NDs are fully entrapped into the formed tribofilm that contains the MoDTC-derived MoS2 layer, the lowest friction coefficient can be achieved.

The current pre-clinical testing standards for total hip replacements (THRs), ISO standards, use simplified loading waveforms that do not fully replicate real-world biomechanics. These standards provide a benchmark of data that may not accurately predict in vivo wear, necessitating the evaluation of physiologically relevant loading conditions. Previous studies have incorporated activities of daily living (ADLs) such as walking, jogging and stair negotiation into wear simulations. However, these studies primarily used simplified adaptations that increased axial forces and applied accelerated sinusoidal waveforms, rather than fully replicating the complex kinematics experienced by THR patients. To address this gap, this study applied patient-derived ADL profiles—jogging and stair negotiation—using a three-station hip simulator, obtained through 3D motion analysis of total hip arthroplasty patients, processed via a musculoskeletal multibody modelling approach to derive realistic hip contact forces (HCFs). The results indicate that jogging significantly increased wear rates compared to the ISO walking gait waveform, with wear increasing from 15.24 ± 0.55 to 28.68 ± 0.87 mm3/Mc. Additionally, wear was highly sensitive to changes in lubricant protein concentration, with an increase from 17 g/L to 30 g/L reducing wear by over 60%. Contrary to predictive models, stair descent resulted in higher volumetric wear (8.62 ± 0.43 mm3/0.5 Mc) compared to stair ascent (4.15 ± 0.31 mm3/0.5 Mc), despite both profiles having similar peak torques. These findings underscore the limitations of current ISO standards in replicating physiologically relevant wear patterns. The application of patient-specific loading profiles highlights the need to integrate ADLs into pre-clinical testing protocols, ensuring a more accurate assessment of implant performance and longevity.

The tribological interaction of cutting tool while drilling of carbon fiber reinforced plastic and titanium stacks (CFRP-Ti stacks) involves complex and rapid variation in wear mechanism due to disparate material characteristics. The abrasive CFRP and adherent titanium pose distinct thrust forces and torque along with complex wear mechanism, resulting in rapid tool wear. To improve tool durability and performance, Diamond-like Carbon (DLC) coatings are applied. However, traditional tribotest are incapable to mimic continuous contact renewal against multi-material stacks drilling. Here, for first time cross-cylinder tribotest against multi-material workpiece cylinder of [CFRP-Ti]n stacks is employed to imitate wear mechanism of DLC coatings for drilling/machining of CFRP-Ti stacks. The tribological analysis of different DLC coatings was performed against CFRP-Ti stacks and its individual constituents. The results showed cyclic variation in coefficient of friction (COF) against CFRP-Ti workpiece with aggressive wear action and complex tribological response, relatively unique and comparable to real drilling process. In comparison, the DLC-Bn coating showed best wear resistance with ∼1.5–2.5 times durability when tested against Ti6Al4V and CFRP workpiece. Additionally, the results demonstrated the effectiveness of DLC-Bn coatings in mitigating variation to the sub-surface morphology of WC-Co substrate against CFRP-Ti workpiece.

The sustainable utilization of polymers depends on efficient recycling and the ability to retain their critical physical properties for further processing. In this study, high-density polyethylene (HDPE) nanocomposite properties were enhanced by the integration of carbon dots (CDs), in terms of processability and optical traceability during recycling. HDPE composites with varying CDs loadings were prepared to assess their effects on optical and mechanical properties over three consecutive recycling cycles. The composite containing 0.5 wt% CDs demonstrated a 17% increase in tensile strength after recycling, with a maximum strain of 11%, significantly outperforming the neat HDPE while preserving its crystalline structure. Additionally, incorporating 0.1 wt% CDs reduced the wear rate by up to 98%, highlighting a substantial improvement in durability. Improved processability of the recycled material was confirmed by producing 3D-printed specimens at each CDs concentration. Notably, composites containing 0.1 wt% CDs exhibited excellent printability even after three recycling cycles. CDs have also been utilized as luminescence tracers. This study revealed that the quenching of the blue phosphorescence associated to the carbonyl groups of the polymer backbone was highly dependent on the CDs content. Importantly, nanocomposites with 0.1 wt% CDs exhibited progressive luminescence changes corresponding to the number of recycling cycles, enabling quick and reliable traceability and sorting using standard mobile phone cameras. These findings are highly promising, paving the way for rapid, automated, and scalable HDPE recycling. This innovation offers significant potential for advancing the circular economy of HDPE and enhancing the sustainability of polymer materials.

This study investigates the effect of test-environment, temperature, and cryogenic aging in liquid nitrogen for 5 months on mechanical and tribological performance of polyimide (PI) and PI composites. Tribological tests were conducted at 25 °C in air, and at both 25 °C and −100 °C in a high vacuum (10-5 Pa) environment. Impact of cryogenic aging, testing condition on PI-based materials varied depending on the polymer structure and composition. Cryogenic aging led to embrittlement, increasing the coefficient of friction and wear rate up to 77 % and 165 %, respectively. Some polyimides exhibited the lowest coefficient of friction (0.04) in vacuum at 25 °C, while the temperature reduction to −100 oC in vacuum generally decreased the tribological performance, increased contact stresses and abrasive wear of the materials.

Spurred by the growing trend towards sustainability and use of green material alternatives, Carbon Fiber Reinforced Polymer paired with Titanium alloys (CFRP-Ti stacks) are employed in aerospace industry for their high strength-to-weight ratio and good galvanic corrosion resistance. However, production of holes for bolt or rivet connections, imperative for components assembly depicts unmatched difficulties in their machinability due to superior mechanical characteristics and distinct nature of stack components, causing rapid tool wear and compromised hole quality. In this work, in-depth tool wear analysis of Diamond-like-Carbon (DLC) coated drills were analysed periodically to evaluate tool wear growth and associated wear mechanism while drilling of CFRP-Ti stacks. Qualitative analysis was performed after drilling set number of holes by two DLC coated drills (DLC-Ar and DLC-Bn), and results compared with uncoated solid carbide (WC) drills tested under similar dry machining conditions. The wear progress was observed by SEM and EDX; and for extensive wear mechanism investigation, Focused Ion Beam (FIB) cross-sections were analysed. Moreover, morphological examination of etched drills after drilling experiment was performed to observe active cutting regions for overall damage extent, gain insight about coating reminiscences and underlying wear mechanism. The results demonstrate that DLC-Bn drill showed best performance with reduced thrust forces and torque, reduced wear of cutting edges and no fracture/chipping of drill corner compared to DLC-Ar and WC drill. Although, DLC-Ar drill does alleviate corner chipping but suffer premature coating failure, undergoes intense tribo-chemical wear, excessive removal of carbide grains and generation of highest thrust forces compared to WC drill.