ICMCTF 2026 Session MC-ThP: Tribology and Mechanics of Coatings and Surfaces Poster Session

In this work, the wear resistance of Inconel 718 superalloy hardened by the boriding process was evaluated by means of dry sliding. A powder-pack boriding process was used to modify the alloy surface in which nickel borides were obtained in the sample due to the boron diffusion into the substrate material. The thermochemical treatment was carried out at a temperature of 950 °C for 2 and 6 h of exposure time. The Ni2B, Ni4B3 and Ni3B intermetallic compounds formed on the surface of the Inconel 718 superalloy were confirmed by XRD analysis. Berkovich nanoindentation tests were conducted to determine both hardness and Young’s modulus of the borided samples. The dry sliding wear tests were performed on the surface of the borided sample using an alumina ball with diameter of 6 mm, a constant load of 20 N and distances of 50, 100, 150 and 200 m. Wear coefficient was obtained by the Archard’s model. The finite element method using mesh nonlinear adaptivity was used to obtain the stress field during the wear test. Results of the failure mechanisms over the worn tracks showed that the sample with thicker thickness had better wear resistance.

Nickel-based superalloys, such as Inconel 718 and Inconel 625, are widely used in oil and gas industry due to their mechanical and Chemical properties. The extraction and processing environments involve high temperatures, high pressures, and corrosive environments. Nickel alloys offer high mechanical strength at elevated temperatures, and excellent resistance to corrosion and oxidation, ensuring safety and a longer service life for components that use them. Inconel 718 has high corrosion resistance, but its application is limited due to low hardness and wear resistance. One method of solving this problem is to combine heat treatment with application of coatings. The present work carried out a comparative study of the tribological and tribocorrosive properties of nitride Inconel 718 and Inconel 718 with a WC/Co coating, applied by the HVOF method, which was chosen due to the obtention of a dense layer with low porosity, improving the wear resistance of the material. The surfaces were characterized using X-ray diffractometry (XRD), microhardness, and scanning electron microscopy (SEM) techniques. The tribological, tribocorrosive, and corrosive properties were evaluated in five environments: (a) Distilled water saturated with CO2; (b) distilled water with sodium chloride; (c) distilled water saturated with H2S; (d) distilled water with sodium chloride and saturated with CO2; (e) distilled water with sodium chloride, CO2and H2S. Where in the end the surfaces will be compared across three requirements: i) corrosion current and potential, ii) wear rate, iii) wear rate considering the synergistic effect of tribocorrosion.

Oil and gas environments are highly corrosive due to the presence of H₂S, CO₂, and chloride ions, which accelerate material degradation through both chemical and mechanical mechanisms. This study investigates the impact of plasma nitriding on the tribological performance, adhesion, and corrosion resistance of CrAlN/DLC coatings deposited on Inconel 718 substrates. The goal is to develop an alternative surface treatment suitable for extreme oilfield conditions.

The Inconel 718 specimens were aged at 760 °C for 6 hours. Three groups were analyzed: (i) nitrided Inconel 718, (ii) nitrided Inconel 718 with CrAlN/DLC coating, and (iii) Inconel 718 with CrAlN/DLC coating without nitriding. Characterization was conducted using nanoindentation to assess mechanical properties, pin-on-disk testing for wear evaluation, and scratch testing for adhesion. The tribocorrosion performance was evaluated in a simulated oilfield environment. Structural and phase integrity of the coatings were analyzed using Raman spectroscopy and X-ray diffraction (XRD), while surface morphology and failure mechanisms were examined via scanning electron microscopy (SEM).

Plasma nitriding enhances surface hardness and promotes the formation of a diffusion layer, which improves coating adhesion and compatibility with the substrate. This combination reduces friction and wear under tribocorrosive conditions. Additionally, DLC deposition lowers friction coefficients and wear rates, further enhancing resistance to tribocorrosion. Preliminary results indicate that nitriding significantly increases surface hardness and coating adhesion. XRD analysis confirms the structural integrity of CrAlN/DLC coatings after exposure, supporting the proposed surface treatment as a multifunctional solution for harsh oilfield environments.

The transition to a more energy-efficient world requires innovative solutions, with materials science and tribology playing critical roles. Improving lubrication and reducing wear are essential for lowering the carbon footprint, conserving energy, and meeting climate targets. While conventional liquid lubricants perform well under many conditions, extreme environments, such as high or cryogenic temperatures, high contact pressures, vacuum, or radiation, demand the use of solid lubricants combined with advanced materials. However, many solid lubricants, including MoS₂, MXenes, and graphite, oxidize rapidly above approximately 400 °C, limiting their applicability. Developing self-lubricating materials that also provide excellent corrosion and wear resistance is, therefore, crucial. Among solid lubricating coatings, diamond-like carbon (DLC) is one of the most established. Yet, its performance at high temperatures above 400 °C remains questioned, as DLC coatings are suspected to degrade under such conditions. A systematic comparison and extreme condition testing that links tribological performance to coating properties is still missing.

This study investigates different DLC-based thin film materials, classifying them by dominant mechanisms, application ranges, and performance. Several DLC coatings are compared, including non-hydrogenated DLC (a-C), hydrogenated DLC (a-C:H), hydrogenated DLC with an oxide former (a-C:H:Si:O), and tetrahedral amorphous carbon (ta-C). These coatings, which vary in mechanical properties and sp₂/sp₃ ratios, were tribologically tested at different temperatures and loads. Subsequent surface characterization included nanoindentation, Raman spectroscopy to analyze the effects of graphitization after thermal exposure, and X-ray photoelectron spectroscopy. Further insights into the limits of carbon as a solid lubricant are provided through high-resolution characterization techniques such as high-resolution transmission electron microscopy.

In summary, this work highlights the potential of advanced DLC coatings for solid lubrication. It highlights the need for a deeper understanding of their mechanisms and the design of innovative coatings to enable future high-performance applications.

This study investigates the effects of plasma nitriding (400 °C, 3 h, 50% N₂–50% H₂) on MIG-welded H13 tool steel, comparing the microstructural and phase evolution between the weld zone and the base metal. Specimens with dimensions of 10 mm × 10 mm × 20 mm were prepared through precision grinding, polishing and ultrasonic cleaning prior to nitriding.

After nitriding, optical microscopy investigations revealed a clear microstructural distinction between the base and welded regions, with structures typically associated with the high cooling rates in weld beads. The nitrided layers were characterized by X-ray diffraction (XRD) to identify the phases formed during treatment. The analysis confirmed the presence of characteristic nitrided phases (γ′-Fe₄N, ε-Fe₃N, CrN, and Cr₂N) in both regions, though significant differences in nitrogen retention were observed. The Fe₄N and CrN peaks were markedly more intense in the weld region, suggesting enhanced nitrogen incorporation.

Elemental mapping (EDS) of both the weld and base regions after nitriding revealed the presence of silicon- and chromium-rich intermetallic precipitates, as well as a distinct nitrogen diffusion profile characterized by a steep concentration gradient. Nitrogen-rich zones, when compared with the iron maps, indicated that the coexistence of nitrogen, chromium, and molybdenum promotes the formation of compounds with reduced iron content.

This altered diffusion behavior is consistent with the presence of retained austenite in the weld region compared with the base material — a consequence of the rapid cooling during welding — which enhances nitrogen penetration depth while reducing near-surface concentration. These findings are corroborated by comparative EBSD phase analyses.

Nanoindentation measurements confirmed differences in the mechanical behavior of the nitrided layers between the base and welded samples. In both cases, the surface hardness was significantly higher than the untreated substrate, reaching values of approximately 1,313 HV for the welded region and 1,400 HV for the base material.

Magnesium alloys offer advantages such as low density and high specific strength, but their practical application is often limited by insufficient wear and corrosion resistance. Micro-arc oxidation (MAO) is a promising surface treatment for modifying surface characteristics of magnesium alloys. In this study, MAO coatings were formed on AZ31B magnesium alloy using a silicate-based electrolyte, with and without the addition of boric acid.

Coatings were prepared in a boric-acid-free electrolyte and in electrolytes containing 2 g/L and 5 g/L boric acid, respectively. The influence of boric acid addition on coating morphology, discharge behavior, and wear- and corrosion-related characteristics was examined. The results indicate that the presence of boric acid alters the MAO discharge behavior and coating formation, leading to observable differences in coating compactness and surface features. Variations in wear response and electrochemical impedance behavior were observed among the coatings prepared under different electrolyte conditions.

At higher boric acid concentrations, changes in discharge intensity were associated with increased coating porosity, which influenced wear and corrosion behavior. Additional electrolyte modification was explored to assess the effect of conductivity on coating characteristics. These results provide preliminary insight into the role of boric acid in controlling MAO coating formation and wear–corrosion behavior on AZ31B magnesium alloy.

Tribological behavior —friction, wear, and adhesion— depends strongly on the local environment. In air, adsorbed water, oxygen, and organics form boundary films that dominate contact mechanics; reducing pressure thins these films and shifts interactions toward intrinsic solid–solid processes. Ultra–high vacuum (UHV, below 10⁻⁹ mbar) effectively removes physisorbed monolayers on laboratory timescales, exposing atomic–scale adsorption, chemisorption, cold–welding, and intrinsic wear mechanisms otherwise masked at higher pressures. UHV tribology is therefore critical for vacuum–service industries (space mechanisms, semiconductor tools, accelerators, vacuum MEMS), yet remains rare because of specialized chambers, rigorous bakeout, vacuum–compatible instrumentation, and long pumpdown cycles. Commercial UHV tribometry options are limited; PREVAC currently offers a commercial UHV tribometer reaching ~10⁻⁹ mbar. This review synthesizes UHV studies, compares UHV, HV, and atmospheric results for common materials and coatings, and issues practical recommendations to improve industrial uptake and reproducibility.

This work evaluates the tribological performance of Ti6Al4V alloy modified via powder pack boriding for potential use in high-load biomedical implants. The study investigates the mechanical response and structural stability of biphasic TiB₂/TiB layers exposed to two distinct simulated physiological environments: Hanks’ solution and Simulated Body Fluid (SBF), providing a comprehensive insight into the performance of these surfaces in ionic media. Mechanical characterization revealed that the boriding process at 1100 °C for 5 and 20h significantly increases surface hardness, reaching a range of 1900 to 3600 HV for the titanium boride phases. Interfacial integrity was assessed via Rockwell C adhesion tests (VDI 3198), showing a transition from HF3 to HF4 as treatment time increased to 20 h. This shift reflects a highly compressed and hardened surface state that maintains structural integrity without coarse delamination during mechanical contact. The reciprocating sliding results highlighted a reduction in the steady-state Coefficient of Friction (CoF), dropping from 0.40 for the untreated alloy to 0.22 (5 h) and 0.12 (20 h). A significant contrast was observed between the biological fluids: SBF proved to be more aggressive than Hanks’ solution, inducing a 15% increase in the specific wear rate (k) and higher signal tortuosity due to increased ionic activity and chloride-mediated interaction. Despite this, the 20 h condition (28.2 µm thickness) achieved a 97.6% reduction in k (1.60 x10^-6 mm³/Nm) compared to the untreated reference (61.87 mm³/Nm ). Morphological analysis via optical profilometry confirmed that the boride layers do not fail by traditional material removal. Instead, they exhibit a sinking-in effect, where the hard ceramic layer is pressed into the thermally softened substrate. This mechanism was quantified through the Plastic Deformation Ratio (PDR), which decreased from 0.33 in the untreated alloy to 0.05 in the 20 h condition. These findings demonstrate that a 20 h boriding treatment is critical to providing the necessary load-bearing capacity and dimensional stability required for orthopedic applications in iogenic environments.

As much as 23 % of the world’s energy is consumed in tribological contacts and reducing friction and wear can have a substantial environmental impact. However, the large majority of lubricants and additives, still based on crude oil, are becoming less and less sustainable: environmentally friendly alternatives are in dire need. Hypericin, a natural constituent of St. John’s wort commonly known as antidepressant/antiviral/antibiotic medicinal, is here revealed to have an outstanding potential as friction modifier. Indeed, sustainable superlubricity performance, with friction coefficient below 0.01 under boundary lubrication, is observed when adding hypericin to glycerol to lubricate steel/SiC tribopairs. XPS and Raman spectroscopies revealed the formation of graphitic structures on surfaces rubbed in the presence of hypericin and High-Resolution-Transmission-Electron microscopy on focused ion-beam cross-sections evidenced the first stage of tribofilm polymerization and subsequent formation of graphene. First-principles calculations elucidate the thermodynamic forces driving graphene-formation induced by mechanochemical reactions. The process, tribologically promoted, was monitored in real-time by (ab-initio) molecular dynamics. Formation of graphene patches was found to strongly correlate with friction coefficient reductions up to the superlubricity limit. This work suggests an unconventional way towards formation of graphene-like materials through mechanochemistry and reveals the great potential of pharmacopeia-derived molecules as newly-emerging environment-friendly lubricant additives for industrial applications, opening new ways to formulate water-based lubricants, nowadays considered a strategic oils-alternative to reduce carbon footprint.