In this study, the tribological characteristics of TiN, AlTiN, and AlTiCrN coatings sliding against a SUS420J1 stainless steel pin were investigated in atmospheric and vacuum environments. The coatings were deposited on SUS440C substrates using the arc-physical vapor deposition technique. The friction and wear behavior of the coatings were evaluated based on the systematic analyses of the friction coefficient data as well as the physical and chemical state of the wear track. The results revealed that the friction coefficients of the SUS440C specimen and AlTiCrN coatings increased, whereas those of the TiN and AlTiN coatings decreased when the environment was changed from atmospheric to vacuum. It was confirmed that the formation of an oxide layer and adsorption of oxides on the surface were dominant factors that influenced the tribological behavior in the atmospheric environment. On the other hand, the compatibility, oxidation inhibition, and droplets of the surface mainly affected the frictional characteristics in the vacuum environment. The results of this work are expected to aid in the selection of proper coating materials for tribological systems operating in a vacuum.

Tribology has played an essential role in the advancement of technology and the development of economies all over the globe.  As such, a significant part of the Korean industry has benefitted from design solutions and remedies that stem from tribological considerations. Republic of Korea has grown tremendously in the traditional application fields of tribology such as automotive, manufacturing, heavy industry, shipbuilding, and electronics over the last few decades. Apart from these traditional fields, tribology has been contributing significantly to emerging industries related to energy, environment, and biotechnology in Republic of Korea. In this paper, the status and prospects of tribology in Republic of Korea are presented. The history and activities of the Korean Tribology Society (KTS) are described along with a review of the research works of selected Korean tribologists. Considering the great relevance of friction, wear, and lubrication issues in future sustainability, efforts in tribology will continue to expand in parallel with technology and economic development in Republic of Korea and around the globe.

The outstanding tribological performance of transition metal dichalcogenides (TMDs) is attributed to their unique sandwich microstructure and low interlayer shear stress. This advantageous structure allows TMDs to demonstrate exceptional friction reduction properties. Furthermore, the incorporation of TMDs and amorphous carbon (a-C) in multi-layer structures shows excellent potential for further enhancing tribological and anti-oxidation properties. Amorphous carbon, known for its high ductility, chemical inertness, and excellent wear resistance, significantly contributes to the overall performance of these multi-layer coatings. To gain an in-depth understanding of the tribological mechanism and evolution of TMDs’ multi-layer coatings, a dual in-situ analysis was carried out using a tribometer equipped with a 3D laser microscope and a Raman spectrometer. This innovative approach allowed for a comprehensive evolution of the tribological, topographical, and tribochemical characteristics of both single-layer WS₂ and multi-layer WS₂/C coatings in real time. The findings from the dual in-situ tribotest revealed distinct failure characteristics between the single-layer WS₂ coating and the multi-layer WS₂/C coating. The single-layer WS₂ coating predominantly experienced failure due to mechanical removal, whereas a combination of mechanical removal and tribochemistry primarily influenced the failure of the multi-layer WS₂/C coating. The tribological evolution process of these two coatings can be classified into four stages on the basis of their tribological behavior: the running-in stage, stable friction stage, re-deposition stage, and lubrication failure stage. Each stage represents a distinct phase in the tribological behavior of the coatings and contributes to our understanding of their behavior during sliding.

This work shows that a soft, thin film comprising randomly aligned carbon nanotubes (CNTs) can reduce surface wear more effectively than a homogeneous thin film because of enhanced elastic recoverability and contact stress relief originating from its mesh structure. To investigate the wear characteristics of the mesh structure compared to those of the homogeneous thin film, multi-walled CNTs (MWCNTs) and diamond-like carbon (DLC) thin films were prepared to conduct nanoscale tribological experiments using the atomic force microscopy (AFM). The MWCNT thin film showed unmeasurably low wear compared with the DLC thin film under a certain range of normal load. To demonstrate the wear reduction mechanism of the MWCNT thin film, its indentation and frictional behaviors were assessed. The indentation behavior of the MWCNT thin film revealed repetitive elastic deformation with a wide strain range and a significantly lower elastic modulus than that of the DLC thin film. The permanent deformation of the MWCNT thin film was observed through frictional experiments under relatively high normal load conditions. These results are expected to provide insights into the design of highly wear-resistant surfaces using nanostructures.

A one-step method was developed to create a highly biocompatible micropatterned surface on a diamond-like carbon (DLC) through irradiation with a nitrogen ion beam and thus enhance the biocompatibility of osseointegrated surfaces and biotribological performance of articular surfaces. The biocompatibility and biotribological mechanisms were analyzed in terms of the structure and morphology of DLC. It was demonstrated that a layer enriched in sp³ C–N bonds was formed on the surface of the DLC after nitrogen ion beam irradiation. Moreover, with an increase in the radiation dose, the content of sp³ C–N on the DLC surface increased significantly, and the biocompatibility was positively correlated with it. The adhesion of the MC3T3 osteoblasts increased significantly from 32% to 86% under an irradiation dose of 8 × 10¹⁵ ions/cm². In contrast, the micropattern had a significant negative effect on the adhesion of the osteoblasts as it physically hindered cell expansion and extension. The micropattern with a depth of 37 nm exhibited good friction properties, and the coefficient of friction was reduced by 21% at relatively high speeds.

Polymer gears are used extensively in various applications. However, durability issues have been emerging because of friction at gear tooth contact areas. To extend the lifetime of polymer gears, a low-frictional coating has been considered as a possible strategy. In this study, a finite element simulation method was performed to investigate the contact stress between a pair of coated polymer gears. The simulation included various friction coefficients (COFs) for studying the effects of friction during the operation. Numerical results revealed that the friction causes the contact stress to shift over the roll angle, which is attributed to the direction of the sliding friction based on a free-body diagram. We also investigated the effects of coating and found that a thin coating has little effect on the bulk deformation behavior of the gear. Moreover, the stress distribution in the coating at the pitch point was investigated as the COF increased. Under zero friction, three notable stress regions were observed: 1) the center of the surface, 2) the end of the contact, and 3) the overall contact area. As COF was increased in the micro-slip region of the contact interface, both tensile and compressive stresses in the coating increased. This study provides significant aid to engineers for understanding the stress response of the coating applied to polymer gears to achieve an optimal design.

The benefits of reinforcing polyimide (PI) films with boron nitride (BN) particles and boron nitride nanosheets (BNNSs) were assessed with the aim of enhancing their thermal, optical, and mechanical properties for flexible device applications. BNNSs were prepared from BN particles using a liquid-phase exfoliation method assisted by an ultrasonic probe-type sonicator and centrifugator. PI-based composite films blended with BNNSs and BN particles were fabricated at various concentrations via mechanical stirring and spin coating. The transparency of the PI/BNNS composite films remained almost the same as that of pure PI films up to 3 wt.% whereas the transparency of the PI/BN composite films decreased with increasing concentration of the BN fillers at 550 nm. The thermal stability improved significantly with increasing concentrations of both BN and BNNS relative to that of pure PI films. The temperature for 5% weight loss of the PI/BNNS composite film was higher than that of the PI/BN composite film at the same filler concentration. The composite films with 2 wt.% BN or BNNS showed the lowest wear rate, and the PI/BNNS composite films showed more stable frictional behavior compared to the PI/BN composite films. In addition, bending tests showed that the PI/BNNS composite films exhibited excellent flexibility compared to the PI/BN composite films. Overall, the results indicate that the BNNS can be effectively used as a filler that can enhance the thermal and mechanical properties of polymer materials for flexible device applications.

Friction and wear phenomena encountered in mechanical systems with moving components are directly related to efficiency, reliability and life of the system. Hence, minimizing and controlling these phenomena to achieve the desired system performance is crucial. Among the numerous strategies developed for reducing friction and wear, coatings have been successfully utilized in various engineering applications to mitigate tribological problems. One of the benefits of coatings is that they may be fabricated using a variety of materials in several different forms and structures to satisfy the requirements of the operating conditions. Among many types, coatings that are comprised of a combination of materials in the form of a multilayer have been gaining much interest due to the added degree of freedom in tailoring the coating property. In this paper, the properties and development status of multilayer coating systems for tribological applications were reviewed with the aim to gain a better understanding regarding their advantages and limitations. Specifically, focus was given to Ti-based and Cr-based coatings since Ti and Cr were identified as important elements in multilayer coating applications. Emphasis was given to materials, design concepts, mechanical properties, deposition method, and friction and wear characteristics of these types of coatings.