ICMCTF 2026 Session MA-ThP: Protective and High-temperature Coatings Poster Session

AISI 316L stainless steel is widely employed in mechanical and aerospace components; however, its tribological performance is often limited under dry and high-temperature sliding conditions. In this study, a solid-lubricating TiB₂:h-BN:a-C nanocomposite coating was deposited on 316L substrates using closed-field unbalanced magnetron sputtering (CFUBMS) with a hybrid HiPIMS + pulsed-DC power configuration. The coating architecture integrates hard TiB₂ domains for load support, h-BN for lamellar lubrication and thermal stability, and amorphous carbon for low shear and transfer-film formation. A Cr interlayer was introduced to improve interfacial bonding and accommodate residual stresses at the film–substrate interface. The tribological response of the coatings was evaluated under three different environments: dry sliding at room temperature, elevated temperature (300 °C), and boundary-lubricated contact with SAE 50 oil. Results demonstrated that the TiB₂:h-BN:a-C coating effectively reduced friction and wear compared with the uncoated steel, maintaining stable performance across varying temperature and lubrication regimes. Scratch testing further indicated strong adhesion and cohesive integrity. These findings confirm the effectiveness of TiB₂:h-BN:a-C nanocomposites as multifunctional protective coatings for extending the durability of stainless steel components operating under diverse tribo-mechanical conditions.

Protecting components operating in harsh environments, such as in energy production, aviation, and the tooling industry, is essential for ensuring sustainability and long service life. Solid particle erosion (SPE) occurs when high-velocity solid particles impact a material surface, leading to repeated mechanical damage and material loss. This phenomenon critically affects components such as turbine blades, compressor parts, and piping systems. A thorough understanding of SPE is therefore key to improving material durability and performance under erosive conditions. Ti_1-xAl_xN protective coatings are widely applied due to their excellent oxidation, corrosion, and erosion resistance. However, increasing operational temperatures demand the development of new coating materials. Alloying Ti_1-xAl_xN with Ta and Si has shown promising improvements in oxidation and corrosion resistance [1,2], yet their behavior under SPE conditions remains insufficiently understood.

The objective of the present study is to investigate the solid particle erosion resistance of Ti_1-xAl_xN and Ti_1-x-y-zAl_xTa_ySi_zN thin films. Accordingly, the coatings were deposited via cathodic arc evaporation using an industrial-scale Oerlikon Balzers INNOVA 1.0 system. SPE tests were performed employing a Jet Erosion Tester with corundum (Al₂O₃) particles at 70 m/s and impingement angles of 30° and 90°. Crater analysis by synchrotron nano-diffraction was employed to assess stress evolution induced by SPE, complemented by profilometry, scanning electron microscopy and transmission electron microscopy characterization. Both coatings demonstrate a significant reduction in mass erosion rates, with approximately 90% decrease compared to uncoated substrates. Synchrotron measurements reveal a clear influence of the as-deposited residual stress state on the stresses induced during erosion.
These results provide new insights into the interplay between residual stress and erosion-induced deformation in multicomponent Ti_1-xAl_xN based coatings, contributing to the development of next-generation protective materials for high-temperature and erosive environments.
[1] X. Sun et al., Surf. Coat. Technol. 461 (2023) 129428.
[2] A.R. Shugurov et al., Vacuum. 216 (2023) 112422.

This study investigates the influence of the B₄C–SiC ratio in the boriding media’s electrical behavior and its effect on the growth of FeB–Fe₂B layers in AISI 8620 steel during Pulsed-DC Powder-Pack Boriding (PDCPB) process. Five boriding media with different B₄C–SiC ratios were analyzed to determine their electrical resistance, resistivity, and conductivity, both experimentally and through an equivalent circuit model. The electrical field distribution was simulated using COMSOL Multiphysics. The findings reveal three key effects: i) A transition threshold where SiC begins to dominate the semiconducting behavior of the boriding media, significantly increasing its electrical resistance and electric field intensity (up to ~2.1 × 10³ V m^-1); ii) A strong correlation between the boriding media composition and the availability of B atoms during diffusion, which governs the kinetics of FeB and Fe₂B formation;
iii) A reduction of up to 30 µm in total boride layer thickness when SiC content ≥ 80 wt%, due to limited B dissociation and dopant trapping effects.

This study investigates the impact of Si and Y alloying on the microstructure and mechanical properties of Cr–Mn–Mo-based high- and medium-entropy nitride thin films. These films are fabricated by reactive DC magnetron sputtering, employing a combination of both ab initio calculations and experimental analysis. While the Cr–Mn–Mo–N system, in its pure form, displays a stable face-centred cubic (fcc) structure with a negative formation energy (E_f ), the latter is known to decrease further with alloying with Si, Y, or both, thus enhancing thermodynamic stability. However, the process of alloying is accompanied by an increase in unit cell distortion, which in turn leads to the destabilization of the crystal structure – manifesting itself in amorphization of experimental thin films, with increasing alloying contents.

Chemical analysis of the grown films revealed that silicon and yttrium promoted nitrogen incorporation. However, complete stoichiometric metal-to-nitrogen ratios were not achieved, and systems with a considerable amount of nitrogen vacancies are formed. Similarly, simulations elucidated a prominent trend of nitrogen vacancies to relax alloy related cell distortions. Structural analyses confirmed the formation of a single-phase fcc solid solution presented here, with lattice expansion and crystallite size refinement being induced by increasing alloying concentrations. Furthermore, the simulations determined both nitrogen vacancy concentration and chemical composition to have a significant impact on ductility, with the highest levels of this property being observed at low nitrogen vacancy levels and when alloying with either Si or Y individually. These predictions showed a fair match with ductility estimates from experiment. More prominently, predictions of elastic properties from experiment and simulation agreed within error range, demonstrating that alloying has a beneficial effect on hardness without compromising the material's elasticity, with Si alloying alone achieving the highest hardness values of 20.5 GPa. An analysis of chemical bonding in the compounds found a synergistic sharing of nitrogen atoms between tetrahedral coordinated silicon species and yttrium atoms, mediated through N-vacancy introduction, as possible explanation for the good mechanical performance of the thin films.

Titanium diboride (TiB₂) is currently the most wide spread boride coating used in industry. The TiB₂ coating exhibit outstanding properties such as high hardness 40 – 50 GPa, high elastic modulus ≥ 500 GPa, high chemical inertness, high melting point above 3000 °C, and low propensity for sticking to soft metals. Thanks to these outstanding properties, the TiB₂ coatingis used in many applications for machining non-ferrous metals such as titanium, nickel, and aluminium alloys.

The main drawbacks of metal diborides are their generally low oxidation resistance (typically between 600 – 700°C for TiB₂) and brittleness. As productivity demands from customers increase, the cutting speed and feed rate of tool also rise, leading to elevated temperatures at the contact interface between the workpiece and the tool. Therefore, there is a strong incentive to enhance the oxidation resistance and/or reduce the coefficient of friction between the coating and the workpiece to lower the thermal load on the coating.

This study investigates the effect of alloying diboride materials with transition metals onthe boron-to-metal coating stoichiometry (x = B/Me), as well as on the mechanical properties, tribological properties, oxidation resistance of the coating. The influence of these improved coating properties was subsequently evaluated in a cutting test, specifically during side milling of Inconel 718 and drilling of Ti-6Al-4V (Ti grade 5) alloys.

The coatings were deposited using a PLATIT Pi411 coating machine equipped with LACS^® technology. This technology enables magnetron sputtering to be performed from a central cylindrical cathode (SCiL^®) while simultaneously running a cathodic arc evaporation process from cylindrical cathodes located in the chamber door (LARC^®). For this study, metal boride (MeB_x) coatings were deposited by concurrent magnetron sputtering of a MeB₂ target and cathodic arc evaporation of a Me target (Me = Ti, TiSi, and Cr) to tune the coating stoichiometry and composition. The sputtering targets consisted of diboride rings (TiB₂, VB₂, TaB₂ and W₂B₅) arranged to obtain either pure or mixed alloy coatings.

EDX, XRD and HRTEM analysis revealed that MeB_x + Me alloying strategy decreases the B/Me ratio from 2.0 to 1.5 throughout the coating, resulting in a nanolaminate microstructure in which the growth of MeB_x nanolayer is interrupted by Me nanolayer. Nanoindentation and isothermal annealing tests showed that, while reducing the coating’s B/Me ratio lowers the average hardness from about 45 GPa to 35 – 40 GPa, it simultaneously doubles the oxidation resistance of the coating.

High-entropy carbide (HEC) thin films (Al,Mo,Ta,V,W)C were reactively deposited on sapphire substrates with varying Si content to investigate its influence on microstructure, mechanical performance, thermal stability, and oxidation behavior. All coatings exhibit a single-phase face-centered cubic structure, with lattice parameters decreasing from ~4.34 Å for Si-free HEC to ~4.24 Å for the 7-at%-Si containing HEC-Si7, indicating preferential substitution of Si into the metallic sublattice, because fcc-SiC would have a lattice parameter of 4.35 Å. Si addition transformed the microstructure from coarse, columnar grains to smooth, dense, and near-amorphous surfaces, and shifted the preferred growth orientation from random to (200).

Machining austenitic stainless steel presents significant challenges due to various factors. One key issue is the material's low thermal conductivity, which can lead to thermal overload on the cutting tool. Additionally, these materials tend to adhere to the tool's cutting edge, resulting in adhesive wear and the formation of a built-up edge. To enhance tool performance, ceramic coatings can be applied, as they improve hot hardness and provide thermal and chemical insulation.

This study focused on evaluating the effect of the Ti/Al ratio in titanium, aluminum, and nitrogen-based coatings during the turning process of AISI 304 stainless steel. The coatings investigated were Ti0.56Al0.44N (TiAlN – Futura Nano®) and Ti0.37Al0.63N (AlTiN – Latuma®), both produced by Oerlikon Balzers Revestimentos Metálicos LTDA. Characterization of the coatings through Energy Dispersive X-ray Spectroscopy (EDS) revealed that the atomic ratio of Ti to Al in the Ti0.56Al0.44N coating is 1.27, while for the Ti0.37Al0.63N coating, the ratio is 0.59.

Machining tests were conducted on a CNC lathe equipped for cutting force acquisition, which was monitored over time until the end of the tool's life. To assess tool wear, the surface roughness of the workpiece was measured using a profilometer after each force test, and the tool geometry was analyzed using a scanning electron microscope (SEM). Preliminary results suggest that the tool coated with Ti0.37Al0.63N may exhibit lower cutting forces and a longer tool life compared to the Ti0.56Al0.44N coating. Additionally, nanoindentation tests indicated that the Ti0.37Al0.63N coating has a higher hardness than the Ti0.56Al0.44N coating, resulting in greater wear resistance.

Keywords: PVD Coatings, Tool Wear, Cutting Forces.