Reports of the influence of surface roughness on the adhesion and tribological performance of contemporary nitride coatings with different layer designs are still scarce in the literature. Therefore, in this study, we evaluated the behavior of a single-layer TiAlN, a bilayer TiAlN/CN_x, and a nanolayer AlTiN/TiN coating. Coatings were deposited in an industrial magnetron sputtering unit on the substrates of EN 100Cr6 steel, prepared to four degrees of surface roughness (Sa = 10–550 nm). The coatings’ adhesion was determined by scratch tests performed perpendicular and parallel to the machining marks. Dry reciprocating sliding tests in air were employed to evaluate the coatings’ tribological behavior against an Al₂O₃ ball. Before and after the tests, coating properties were characterized by 3D profilometry, confocal microscopy, and energy dispersive spectroscopy. Deposition of all coatings significantly altered the surface topography and increased the roughness of the samples. No general rule could be established for the effect of surface roughness on tribological behavior and adhesion of different hard coatings. For very fine surface finishes the adhesion and tribological performance of TiAlN and TiAlN/CN_x coatings was independent of the surface roughness. For the roughest surfaces, a decrease in adhesion and an increase in the wear rate were observed. The AlTiN/TiN coating exhibited the largest sensitivity of adhesion to roughness and scratching direction. The coefficient of friction and wear rate increased when AlTiN/TiN roughness exceeded Sa ≈ 100 nm.

Nitinol (NiTi) alloy is a widely used material for the production of orthodontic archwires. Its corrosion behavior in conditions that exist in the oral cavity still remains a great characterization challenge. The motivation behind this work is to reveal the influence of commercially available mouthwashes on NiTi orthodontic archwires by performing non-electrochemical corrosion tests and quantifying the changes in the nanotopography of commercially available NiTi orthodontic wires. In this study, we examined the behavior of NiTi alloy archwires exposed for 21.5 days to different corrosive media: artificial saliva, Eludril^®, Aquafresh^®, and Listerine^®. The corrosion was characterized by contact mode atomic force microscopy (AFM) before and after the corrosion tests. A novel analysis methodology was developed to obtain insight into locations of material gain or material loss based on standard surface roughness parameters Sa, Sdr, Ssk, and S10z. The developed methodology revealed that fluoride-containing mouthwashes (Aquafresh^® and Listerine^®) dominantly cause material loss, while chloride-containing mouthwash (Eludril^®) can cause both material loss and material gain. The sample exposed to artificial saliva did not display significant changes in any parameter.

Aluminium alloys are extensively employed across modern industries, appreciated for their advantageous combination of low weight, corrosion resistance, strength, and ductility. Nonetheless, casting defects—including inclusions, porosity, hydrogen absorption, and particularly bifilms—can significantly compromise the mechanical properties of cast components. The present investigation centres on bifilm-related defects, which originate from the oxidation behaviour of aluminium alloys. Upon exposure to air, a thin oxide layer instantly forms on the molten metal surface. When disrupted, this film is immediately replaced by a new one, and such layers can become entrained within the melt during various stages of processing. Once inside the liquid metal, these oxide films retain their structural integrity due to their inert nature, remaining as compacted and folded entities that do not dissolve or disperse. Their presence has a pronounced negative impact on mechanical properties and can result in internal discontinuities that reduce mechanical properties and manifest as leak paths after machining. While bifilms can be introduced during melting, charging, or refining, the pouring phase presents a critical opportunity for their entrapment. Thus, the design of the gating system becomes essential. In this preliminary study, the role of flow dynamics during mould filling was examined by comparing two distinctly configured gating systems in sand casting of aluminium alloy: a top-gated setup promoting turbulent flow, and a bottom-gated arrangement intended to minimize flow disturbance. Advanced simulation using Magmasoft software confirmed the expected flow behaviours, illustrating greater splashing and air entrapment in the top-gated configuration. Following casting, samples were machined and subjected to tensile testing. Results demonstrated a statistically significant increase in ultimate tensile strength for specimens produced via the bottom-gated system. This exploratory experiment lays the groundwork for continued investigations into bifilm mitigation through optimized gating design.

The high-temperature performance of PVD hard coatings used on hot-work tooling is strongly influenced by the thermo-mechanical stability of the underlying substrate. However, the mechanisms by which substrate degradation governs coating failure remain insufficiently discussed in literature. This study systematically investigates how substrate condition (pristine versus plasma nitrided hot-work tool steel EN X37CrMoV5-1) affects the tribological behaviour and coating integrity of an industrially deposited nanolayered TiAlN/TiSiN coating under sliding contact from room temperature to 700 °C. At temperatures up to 600 °C, the coating retained its hardness and exhibited wear rates up to one order of magnitude lower (≈10⁻⁶ mm³/Nm) than at room temperature due to protective tribo-oxide film formation. On the non-nitrided substrate, decrease of substrate hardness above 500 °C induced inter- and trans-columnar cracking within the coating. These cracks spanned across the entire thickness of the coating. As a result of cracking, steps formed on the coating’s surface which created obstacles for counterbody sliding and increased the friction coefficient to ≈ 1.2. The cracks enabled Fe–O intrusion which filled the wear tracks at 600 °C and 700 °C, reduced coefficient of friction and ultimately destroyed the coating. In contrast, plasma nitriding improved load-bearing support which eliminated crack formation, prevented Fe–O penetration, and enabled more stable friction behaviour. Coating failure occurred at 700 °C on nitrided and at 600 °C on untreated steel. The results clarify the mechanisms by which substrate degradation governs coating failure and provide guidance for designing more reliable coating/substrate systems for high-temperature applications.