PurposeFacilitating a paradigm shift in industrial maintenance from reactive run-to-fail tactics to a proactive, physics-based understanding of surface deterioration is the main goal of this research. This study aims to create a roadmap for the next generation of intelligent tribosystems by bridging the gap between advanced laboratory-grade imaging and the demanding needs of the factory floor. By substituting high-fidelity physical data for speculation, this shift aims to offer a deeper understanding of the basic nature of wear.Design/methodology/approachThe deliberate combination of two different sensing technologies forms the methodological foundation of this system. It synchronizes the 3D micro-topography data obtained by digital holographic microscopy (DHM) with high-frequency acoustic emission stress waves. To mathematically refine and quantify material displacement, edge-detection algorithms are applied to this dual-sensor data. This synchronized data is fed into machine learning models, which are continuously trained to differentiate between minute deviations that indicate the beginning of wear and healthy operational signatures to move toward automation.FindingsCertain wear mechanisms, like adhesive scuffing and abrasive gouging, which are frequently indistinguishable when using a single-sensor approach, can be isolated by combining acoustic and holographic data. Additionally, compared to traditional vibration analysis, the results show that machine learning models can considerably reduce the rate of false positives by using this high-fidelity dual-stream data. Before they become catastrophic failures, the system effectively records burst events, like microscopic crack formation, in real time.Research limitations/implicationsThis research may make conservative, time-based maintenance estimates obsolete, which is a significant implication. According to the study, actual physical conditions rather than arbitrary schedules will determine the service life of expensive components in the future. Although research emphasizes the successful transition from the lab to harsh realities, it suggests that the next frontier for sustainable manufacturing research is the scalability of such insitu monitoring.Practical implicationsThe practical application of this framework offers substantial benefits for industrial sustainability and cost management. By enabling operators to optimize lubrication cycles and extend the service life of expensive machinery, the system directly reduces waste and avoids costly downtime. The scalability of this insitu monitoring provides a viable path for factories to implement autonomous oversight, ensuring that maintenance is only performed when physically necessary, thereby maximizing both resource efficiency and mechanical reliability.Originality/valueThe creation of a comprehensive wear fingerprint by synchronizing temporal and spatial data is what makes this work unique. This framework uses the high-speed temporal resolution of acoustic signals in conjunction with the accuracy of DHM to provide a microscopic view of surface health, whereas conventional methods concentrate on macro-level vibrations. In the context of Industry 4.0, this constitutes a novel foundation for autonomous quality control and high-fidelity digital twins.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2025-0500/

Vibrations are concomitant to operational industrial mechanical systems and in long-term are a potential threat for faults such as misalignment, increased wear or even severe damage of the machine parts. One of the physical phenomena behind is vibrational resonance, in which several vibration modes are merging into a single preference one with the risk of unbalanced forces self-amplification. The prognosis of such states in real-life is challenging, especially for complex and/or big scale machines, while their stochastic nature may reduce the remaining lifetime, disrupt functionality and increase the running costs. Recent advances in computational analysis propose early detection or even short-term forecasting of such operational regimes, however limited number of works address active damping of those, which is of a high industrial expectation. This work enriches this field, proposing an architecture that analyses complex vibrational data and damps resonances in real-time. Our particular focus is chatter marks a specific type of surface damage caused by the exposure of the contact surface by resonance induced strong periodical forces. Abrupt formations of chatter marks are reproduced on a twin disk tribometer, where two rotational axes are driven by independent servo motors with a tight line contact between both. The resonance cancelation is provided by a closed loop control that changes the axis relative rotation speeds with an objective to minimize the resonance frequencies. The feedback is provided by a supervisory trained classifier that predicts the intensity of resonance frequencies as a function of axes rotation speed, utilizing a mode decomposition of the measured vibrations as input. Our study investigates the applicability of optimal control and Bayesian optimization for real-time failure frequencies damping. Experimental tests show that damping control increases the remaining lifetime of the parts, preventing their severe damage even during chatter marks occurrence. The presented framework is generic, applicable to a broader number of industrial machines and operation conditions and scalable in temporal domain.

Pin-on-Disc tribometers are widely used to investigate friction and wear under unidirectional sliding conditions. In conventional systems, the normal load is typically applied as dead weight and is assumed to remain constant during testing. However, disc runout, misalignment, and structural dynamics can induce significant normal force oscillations, limiting the meaningfulness of friction tests under ”constant load”, reproducibility and representativeness of the tribological experiment. This paper presents the development and experimental evaluation of active normal force control for an upgraded Pin-on-Disc tribometer equipped with a voice-coil motor. Following system identification, both a simplified second-order physical model and a seventh-order parametric model are derived and used for controller design. Several control concepts are implemented and compared, including classical PI/PID controllers, state-space controllers with prefilter, integrator and Smith-predictor extensions, model predictive control, and repetitive control. A key contribution is the development of an angle-based repetitive controller that operates synchronously with the disc position rather than time, enabling compensation of periodic disturbances even during rotational speed changes. Experimental ramp and trajectory tests up to 3000 rpm demonstrate that the combination of repetitive control and model predictive control provides the best overall performance. It substantially reduces parasitic force oscillations at constant target loads and enables accurate tracking of dynamic normal force trajectories up to high rotational speeds. The proposed approach transforms the tribometer from a passive load application system into an actively controlled tribological simulator capable of reproducing complex, position-dependent load profiles relevant to real-world applications such as gearboxes, brake systems, and hardware-in-the-loop test environments.

MXenes have emerged as promising solid lubricants due to their layered structure, tunable chemistry, and ability to form mechanically robust, wear-resistant tribo-films. However, most studies have focused on single-metal MXenes such as Ti3C2Tx, Ti3CNTx, or V2CTx, leaving multimetal MXenes largely unexplored. Here, we present a comprehensive tribological and mechanochemical evaluation of ordered double-transition metal Mo2TiC2Tx and Mo2Ti2C3Tx coatings under dry sliding in ambient conditions. Using nanoindentation mapping, X-ray photoelectron spectroscopy, Raman spectroscopy, and electron microscopy, we demonstrate that Mo2Ti2C3Tx tends to form dense, chemically stabilized, and mechanically robust tribo-layers thus maintaining a low and stable coefficient of friction (∼0.1) and wear rate (∼0.1 × 10-3 mm3/N·m) under a contact pressure of 0.55 GPa. These tribolayers exhibit improved mechanical properties (hardness ∼ 4.2 GPa; Young's modulus ∼ 103 GPa), along with increased carbide retention and reduced surface oxidation. In contrast, Mo2TiC2Tx coatings display a less favorable behavior, resulting in a higher COF (∼0.5), greater wear rate (∼1.3 × 10-3 mm3/N·m), and the formation of thinner, chemically degraded tribo-layers under comparable conditions. Mo2Ti2C3Tx exhibited the best tribological and mechanical performance under comparable conditions, clearly outperforming Ti3C2Tx, Ti3CNTx, and Mo2TiC2Tx. Our study introduces Mo-based MXenes as an emerging frontier in solid lubrication and the importance of MXene structure and composition in their tribo-layer evolution and stress accommodation mechanisms.

Pin-on-Disc (PoD) tribometers are standard instruments in tribological research, yet conventional designs utilizing dead weights often suffer from significant parasitic normal force oscillations. These inconsistencies are primarily induced by disc runout and inherent system resonances, which compromise measurement accuracy. This study presents a comprehensive hardware upgrade of a PoD tribometer by replacing the static loading unit with an active system based on an actively controlled voice-coil motor. The primary objective is to minimize undesirable system dynamics while enabling the application of complex, user-defined force trajectories. The redesign process utilizes structural topology optimization of the supporting frame to achieve a superior internal stiffness-to-mass ratio. Specifically, the moving mass is minimized while maintaining high structural stiffness to shift resonance frequencies out of the operating range of the PoD. A parallelogram guidance system utilizing leaf springs is implemented to provide lateral constraint with minimal vertical stiffness, effectively decoupling the moving assembly from the surrounding tribometer frame. Results demonstrate a 40 % mass reduction in the optimized frame and experiments show a shift of the first relevant internal natural frequency to more than 300 Hz, exceeding the maximum operating rotational speed by a factor of 6. Consequently, even without active control, normal force oscillations are reduced by up to a factor of 10 compared to the original construction. This modified setup establishes a robust mechanical foundation for the active force control and damping strategies for future PoD testing.

In triboexperiments, structural and chemical changes in a material that lead to wear and, subsequently, component failure, are usually investigated ex post, when wear patterns are already fully formed. Therefore, time-resolved in-situ analysis is crucial for an in-depth investigation of the evolution of these wear patterns to reveal the underlying mechanisms in the tribocontact that entail to material damage and failure. This paper introduces a compact tribometer setup especially designed for operation inside a standard-sized diffractometer for both, laboratory and synchrotron applications. This setup enables the in-situ investigation of friction-induced wear mechanisms, such as material transfer, structural changes and surface layer formation using X-ray diffraction (XRD) analysis at specific points in time and space during the experiment without the necessity of sample transfer, which were complementarily compared to electron backscatter diffraction (EBSD) measurements. First results obtained at the KMC-2 beamline at BESSY II are presented and compared to laboratory measurements of the same tribosystems. Steel on Ti experiments revealed a change in the preferential orientation of the Ti crystallites induced by a sliding steel pin immediately after a few cycles. In experiments with Al-on-Ti and brass-on-Cu configurations, a transfer of the softer pin material to the harder sample surface and the subsequent formation of a mixed oxide layer were observed. The presented setup provides a versatile tool for the in-situ investigation of dynamic near-surface changes in tribosystems with a wide range of applications, including material transfer, surface layer formation, structural changes as well as the evolution of residual stresses.

Two-dimensional materials have been extensively studied due to their superior electrical, thermal, optical and mechanical properties, while the latter creates an enormous potential in tribology, especially when utilized as solid lubricant coatings. However, their usage as solid lubricant coatings under applied conditions remains scarce and challenging due to a limited quality of the coatings/substrate interface and lack of adhesion, thus inducing excessive wear as well as increasing friction and compromising durability/reliability. To enhance the performance of 2D coatings and bridge the gap between lab-tests and applied conditions (real-world applications), it is crucial to improve their substrate adhesion, facilitating the transition from a potential to tangible usage of 2D materials in tribology. Therefore, our perspective aims at summarizing the primary factors influencing the coating/substrate interface and adhesion, which can be subdivided into physical and chemical approaches. After critically summarizing the existing state-of-the-art related to experimental approaches, the current understanding based on numerical simulations, from density functional theory to machine learning-assisted molecular dynamics, is holistically analysed to provides atomistic insights to predict and design adhesive 2D interfaces. Our article closes with a perspective outlook on how to further boost coating/substrate adhesion thus guiding research activities with the overall goal to take full advantage of the outstanding properties of 2D materials in solid lubrication enabling the reliable implementation of 2D coatings in demanding, real-world tribological environments.

To decrease humans' negative environmental impact, it is crucial to decrease friction and wear in mechanical systems. For this purpose, two-dimensional (2D) nanomaterials, such as MXenes, can be used as solid lubricants in harsh environments. MXenes have been mainly studied under laboratory conditions; however, the tribological performance of coated mechanical parts has not yet been sufficiently researched. Therefore, this work aims at evaluating the tribological potential of MXene and hybrid MXene/MoS2 coatings as solid lubricants in real journal bearings. Steel shafts were spray-coated with multilayer MXene Ti3C2Tx, MoS2, and a mixture of these two nanoparticles (hybrid coating). Afterward, a multiple-bearing wear tribometer was used to test the coated shafts against standard bronze journal bearings as counter bodies. The tests were conducted under different atmospheric humidities under low contact pressure conditions. Wear and chemical analyses provided insights into the tribological performance of the 2D coatings and shed light on the chemical composition of the wear track and the resulting tribofilm. The results showed a lower coefficient of friction and increased wear resistance for MoS2, Ti3C2Tx, and the hybrid coating compared to the uncoated reference materials, with MoS2 as the best performer. Overall, a decrease in atmospheric humidity improved the tribological performance of the coatings. Based on the results of the chemical analysis, stable tribofilms were formed for MoS2 and the hybrid coatings, whereas a full tribofilm for Ti3C2Tx was not achieved under the tested conditions.

To meet the demand for industrial production of calendering or rolling, it is necessary to detect the onset of chatter before chatter marks appear on the workpiece. Therefore, mode decomposition techniques (empirical, bivariate empirical, and variational) combined with machine learning (ML) are used to detect impending failures. Signals from acceleration sensors are decomposed into a discrete number of modes, isolating the high-frequency oscillations by identifying local minima and maxima. Feature sets (peak to peak, standard deviation, etc.) of true intrinsic mode functions are extracted for training an ML model to detect the vibration states followed by the prediction of chatter marks. This innovative prediction model based on mode decompositions and ML shows its feasibility for early chatter identification.

Black phosphorus (BP), a rather new 2D material, features excellent electronic, optical, and tribological properties, but its potential for solid lubrication is completely unexplored. Therefore, our paper aims at experimentally evaluating the solid lubrication performance of 2D black phosphorus (BP) in dependence of the coating thickness by performing tribological tests under ball-on-disc linear-reciprocating sliding in dry conditions. BP was spray-coated onto bearing steel discs, while the effect of the thickness was evaluated by fabricating two BP coatings, BP-thin and BP-thick. Our results demonstrate that BP coatings reduced friction compared to uncoated reference samples. However, only thicker BP coatings are capable to induce a stable, long-lasting four-fold friction reduction, which was mainly traced back to the formation of a stable tribofilm in the contact zone. Therefore, our study proves the potential of BP for solid lubrication purposes with the overall aim to kick-start and boost more research endeavours in this newly emerging field.

Under vacuum conditions, MoS2 is an excellent 2D solid lubricant with remarkable tribological properties. However, its beneficial performance rapidly deteriorates when wear occurs. Within this context, MXene nano-sheets provide a potential alternative to MoS2 due to their superior wear resistance verified under ambient conditions. However, their vacuum performance is completely unexplored. Therefore, this paper aims at scrutinizing the frictional and wear performance of multi-layer Ti3C2Tx and Ti3C2Tx/MoS2 hybrid coatings used as solid lubricants under vacuum by reciprocating sliding tests using a pin-on-disc vacuum tribometer having MoS2 coatings as reference. To understand the involved friction and wear mechanisms as well as to elucidate the involved tribolayer formation, the wear tracks were analysed post-mortem by scanning electron microscopy and X-ray photoelectron spectroscopy. Our results evidenced that multi-layer Ti3C2Tx are not a suitable solid lubricant under vacuum conditions (friction higher than MoS2 coatings). In contrast, MXene/MoS2 hybrid coatings outperformed the pure MoS2 coatings thus displaying the best tribological performance, experiencing low friction for the entire test duration and reduced wear. Therefore, MXene/MoS2 hybrid coatings proved immense potential as anti-friction and wear resistance coatings for future work and prospective space applications.

The adverse impact of particle adhesions and agglomerations on gas flow performance is a prominent concern in high volume extraction systems. The formation of severe skull deposits, involving agglomeration and adhesion processes, particularly at elevated operation temperatures, necessitates labor intensive and costly manual removal. Consequently, investigating conditions that promote increased skull generation and exploring mechanisms for spontaneous removal through crack formation and chipping are of great significance. This study comprehensively documents the operational conditions of an industrial extraction system, accom panied by elemental gas phase composition analyses. Additionally, the chemical compositions of agglomerated adhesion samples were assessed using X ray diffraction (XRD) and inductively coupled plasma optical emission spectroscopy (ICP OES), and their inner structure was examined through SEM. Subsequently, mechanisms leading to these build ups were simulated on laboratory scale by covering original wall surface samples with agglomeration powder screened for a defined particle size. In experiments conducted at various high temperatures ranging from 800 degrees C to 1200 degrees C, while varying the CaCO 3 content levels in the powders, a layered structure similar to the real system was successfully acquired. Moreover, under certain defined conditions and different atmospheres, crack formation, significantly impacting the chipping behavior of the skull formations from wall surfaces during application, was observed and the compressive strength was examined. Through our laboratory experiments, specific operating conditions within the calcination cycle were revealed, leading to a substantial enhancement of autonomous discharge of large particle-wall agglomerations. Based on these findings, we propose general process optimization steps to improve the overall performance of the extraction system, such as reduction of fine CaCO 3 particles and reduction of the gas flow temperature.

MXenes have gained notable attention in tribology due to their excellent wear resistance based on the formation of beneficial tribofilms. However, studies using MXenes as solid lubricants have mainly focused on multi-layer Ti3C2Tx coatings, while little is known about the tribological performance of MXene composites. Therefore, our study aims at scrutinizing and understanding the tribological behavior of MXenes and MXene composites as solid lubricants under reciprocating sliding conditions. Theoretical predictions regarding the resulting interlayer adhesion and coating-substrate adhesion helped to design the hybrid coatings. Multi-layer Ti3C2Tx, molybdenum disulfide (MoS2) and two hybrid coatings using Ti3C2Tx and MoS2 (random mixture and sandwich-like) were spray-coated onto steel substrates with a coating thickness of about 800 nm. Dry sliding tests using a steel ball as counter-body were carried out at room temperature. The coatings’ morphology and formed tribofilms were holistically characterized by scanning and transmission electron microscopy (SEM, TEM) as well as X-ray photoelectron spectroscopy (XPS). Our results demonstrate that both hybrid coatings notably reduce friction and wear, outperforming their respective pure coatings (Ti3C2Tx and MoS2). This is attributed to synergistic effects between Ti3C2Tx and MoS2, with adhesion forces appearing to be the governing mechanism in enhancing the formation of stable tribofilms. Numerical calculations validate our experimental results, verifying that hybrid coatings exhibit low interlayer friction and high adhesion to ferrous substrates. Consequently, our work reveals the potential of Ti3C2Tx/MoS2 hybrid coatings to further optimize friction and wear.

Under vacuum conditions, MoS2 is an excellent 2D solid lubricant with remarkable tribological properties. However, its beneficial performance rapidly deteriorates when wear occurs. Within this context, MXene nano-sheets provide a potential alternative to MoS2 due to their superior wear resistance verified under ambient conditions. However, their vacuum performance is completely unexplored. Therefore, this paper aims at scrutinizing the frictional and wear performance of multi-layer Ti3C2Tx and Ti3C2Tx/MoS2 hybrid coatings used as solid lubricants under vacuum by reciprocating sliding tests using a pin-on-disc vacuum tribometer having MoS2 coatings as reference. To understand the involved friction and wear mechanisms as well as to elucidate the involved tribolayer formation, the wear tracks were analysed post-mortem by scanning electron microscopy and X-ray photoelectron spectroscopy. Our results evidenced that multi-layer Ti3C2Tx are not a suitable solid lubricant under vacuum conditions (friction higher than MoS2 coatings). In contrast, MXene/MoS2 hybrid coatings outperformed the pure MoS2 coatings thus displaying the best tribological performance, experiencing low friction for the entire test duration and reduced wear. Therefore, MXene/MoS2 hybrid coatings proved immense potential as anti-friction and wear resistance coatings for future work and prospective space applications.

The contact between wheel and rail crucially affects the management of railways, since the vehicle dynamics, safety, and performance, for example, are all dependent on this. Therefore, in this contribution the load-dependence of nominal contact area – a broadly not considered aspect of the wheel-rail contacts within the literature – is addressed. We are applying an ultrasonic technique for the detection of the contact zone and an improved post-processing scheme for the measured ultrasonic reflection data. Accordingly, we found that the nominal contact area shows a power-law dependence on load which only on average is predicted by the elliptical Hertzian contact theory.

In high volume extraction systems adhesions and agglomerations of particles are detrimental to the gas flow throughput. Particle-wall adhesions can lead to severe skull formation, i.e. agglomeration of deposits, especially at high operation temperatures, which have to be manually removed at high effort and costs. Therefore, the conditions of increased build-up phases as well as conditions for spontaneous removal through crack formation and chipping are of major interest. To understand relevant mechanisms the operational conditions in an industrial extraction system were thoroughly documented including analyses of the elemental gas phase composition. Additionally, the chemical compositions of agglomerated adhesion samples were investigated by means of XRD and ICP-OES as well as their inner structure by means of SEM. In a second step mechanisms leading to these build-ups were simulated on lab-scale. Thereto, original wall surface specimens were covered in adhesion powder of defined particle size. In experiments at different high temperatures between 800 °C and 1200 °C, gas compositions and with varying content levels of CaCO3 in the powders a layered structure similar to the real system could be obtained. Additionally, crack formation at certain defined conditions and under different atmospheres was observed, which is of major interest regarding the chipping behavior of the adhesion material from wall surfaces in application. Through laboratory experiments certain operating conditions within the calcination cycle could be disclosed for which the autonomous discharge of large particle-wall agglomerations is widely enhanced. Thus, a general process optimization to increase the performance of the extraction system was proposed.

MXenes have gained notable attention in tribology due to their excellent wear resistance based on the formation of beneficial tribofilms. However, studies using MXenes as solid lubricants have mainly focused on multi-layer Ti3C2Tx coatings, while little is known about the tribological performance of MXene composites. Therefore, our study aims at scrutinizing and understanding the tribological behavior of MXenes and MXene composites as solid lubricants under reciprocating sliding conditions. Theoretical predictions regarding the resulting interlayer adhesion and coating-substrate adhesion helped to design the hybrid coatings. Multi-layer Ti3C2Tx, molybdenum disulfide (MoS2) and two hybrid coatings using Ti3C2Tx and MoS2 (random mixture and sandwich-like) were spray-coated onto steel substrates with a coating thickness of about 800 nm. Dry sliding tests using a steel ball as counter-body were carried out at room temperature. The coatings' morphology and formed tribofilms were holistically characterized by scanning and transmission electron microscopy (SEM, TEM) as well as X-ray photoelectron spectroscopy (XPS). Our results demonstrate that both hybrid coatings notably reduce friction and wear, outperforming their respective pure coatings (Ti3C2Tx and MoS2). This is attributed to synergistic effects between Ti3C2Tx and MoS2, with adhesion forces appearing to be the governing mechanism in enhancing the formation of stable tribofilms. Numerical calculations validate our experimental results, verifying that hybrid coatings exhibit low interlayer friction and high adhesion to ferrous substrates. Consequently, our work reveals the potential of Ti3C2Tx/MoS2 hybrid coatings to further optimize friction and wear.