Search Results (253)

Titanium alloys are frequently subjected to surface treatments to enhance their biocompatibility and corrosion resistance in biological environments. Plasma electrolytic oxidation (PEO) is an environmentally friendly electrochemical technique capable of forming oxide layers characterized by high corrosion resistance, biocompatibility, and strong adhesion to the substrate. In this study, the PEO process was performed using a low-melting-point ternary eutectic electrolyte composed of Ca(NO₃)₂–NaNO₃–KNO₃ (41–17–42 wt.%) with the addition of ammonium dihydrogen phosphate (ADP). The use of this electrolyte system enables a reduction in the operating temperature from 280 to 160 °C. The effects of applied voltage from 200 to 400V, current frequency from 50 to 1000 Hz, and ADP concentrations of 0.1, 0.5, 1, 2, and 5 wt.% on the growth of titanium oxide composite coatings on a Ti-6Al-4V substrate were investigated. The incorporation of Ca and P was confirmed by phase and chemical composition analysis, while scanning electron microscopy (SEM) revealed a porous surface morphology typical of PEO coatings. Corrosion resistance in Hank’s solution, evaluated via Tafel plot fitting of potentiodynamic polarization curves, demonstrated a substantial improvement in electrochemical performance of the PEO-treated samples. The corrosion current decreased from 552 to 219 nA/cm², and the corrosion potential shifted from −102 to 793 mV vs. the Reference Hydrogen Electrode (RHE) compared to the uncoated alloy. These findings indicate optimal PEO processing parameters for producing composite oxide coatings on Ti-6Al-4V alloy surfaces with enhanced corrosion resistance and potential bioactivity, which are attributed to the incorporation of Ca and P into the coating structure. Full article

The degradation process of HVOF-MCrAlY + APS-nanostructured YSZ (APS-nYSZ) thermal barrier coatings, produced using gas turbine OEM-approved MCrAlY powders, is investigated by studying the TGO growth and crack propagation behaviors in a thermal cycling environment. The TGO growth yields a parabolic mechanism on the surfaces of all HVOF-MCrAlYs, and the growth rate increases with the aluminum content in the “classical” MCrAlYs. The APS-nYSZ layer comprises micro-structured YSZ (mYSZ) and nanostructured YSZ (nYSZ) zones. Both mYSZ/mYSZ and mYSZ/nYSZ interfaces appear to be crack nucleation sites, resulting in crack propagation and consequent crack coalescence within the APS-nYSZ layer in the APS-nYSZ/HVOF-MCrAlY vicinity. Crack propagation in the TBCs can be characterized as a steady-state crack propagation stage, where crack length has a nearly linear relationship with TGO thickness, and an accelerating crack propagation stage, which is apparently a result of the coalescence of neighboring cracks. All TBCs fail in the same way as APS-/HVOF-MCrAlY + APS-conventional YSZ analogs, but the difference in thermal cycling lives is not substantial, although the HVOF-low Al-NiCrAlY encounters chemical failure in the early stage of thermal cycling. Full article

This study investigates the fabrication, nanomechanical behavior, and tribological performance of nanostructured superlattice coatings (NSCs) composed of alternating TiAlSiNb-N/TiCr-CN bilayers. Deposited via High-Power Ion-Plasma Magnetron Sputtering (HiPIPMS) onto 100Cr6 steel substrates, the coatings achieved nanohardness values of ~25 GPa and elastic moduli up to ~415 GPa. A novel empirical method was applied to extract stress–strain field (SSF) gradient and divergence profiles from nanoindentation load–displacement data. These profiles revealed complex, depth-dependent oscillations attributed to alternating strain-hardening and strain-softening mechanisms. Fourier analysis identified dominant spatial wavelengths, DWL, ranging from 4.3 to 42.7 nm. Characteristic wavelengths WL1 and WL2, representing fine and coarse oscillatory modes, were 8.2–9.2 nm and 16.8–22.1 nm, respectively, aligning with the superlattice period and grain-scale features. The hyperfine structure exhibited non-stationary behavior, with dominant wavelengths decreasing from ~5 nm to ~1.5 nm as the indentation depth increased. We attribute the SSF gradient and divergence spatial oscillations to alternating strain-hardening and strain-softening deformation mechanisms within the near-surface layer during progressive loading. This cyclic hardening–softening behavior was consistently observed across all NSC samples, suggesting it represents a general phenomenon in thin film/substrate systems under incremental nanoindentation loading. The proposed SSF gradient–divergence framework enhances nanoindentation analytical capabilities, offering a tool for characterizing thin-film coatings and guiding advanced tribological material design. Full article

When nitriding 38CrMoAl steel, there are areas that need to be protected, as the process may interfere with subsequent steps. The large-scale demand for anti-nitriding coatings has driven the investigation and development of more effective anti-nitriding coatings. In this study, various anti-nitriding coating formulations were applied to the surface of 38CrMoAl steel samples via brushing. Following the nitriding treatment, SEM, EDS, and hardness tests were performed to systematically investigate the effects of the considered formulations on the mechanical and microstructural properties of the 38CrMoAl steel. The experimental results indicated that the hardness values for all the samples remained below 600 HV, demonstrating that coatings composed of tin powder, lead powder, and various oxides possess anti-nitriding abilities, to a certain degree. The lead powder formulation exhibited the best anti-nitriding performance, achieving an average surface hardness of 273.48 HV. No nitriding layer was observed in the cross-section, and no nitrogen (N) was detected on either the surface or in the cross-section. In comparison, the samples coated with tin/lead and tin/lead/alumina formulas demonstrated relatively lower anti-nitriding capabilities, with an average surface hardness below 320 HV, satisfying the hardness requirements for anti-nitriding coatings while preventing the formation of a nitriding layer. Full article

This study systematically investigates the influence of nitrogen (N₂) flow rates and nitrocarburized (PNC) interlayers on the mechanical and tribological properties of TiAlN coatings deposited on 300M steel substrates via magnetron sputtering. The coatings were fabricated under three N₂ flow rates (30, 90, and 150 sccm), with microstructure evolution, elemental composition, and phase transitions analyzed using SEM, EDS, AFM, and XRD. The results indicate that the PNC/TiAlN composite coatings exhibited superior interfacial adhesion and load-bearing capacity compared to standalone TiAlN coatings, attributed to the graded hardness transition and stress distribution optimization at the coating–substrate interface. Nanoindentation tests revealed enhanced hardness and elastic modulus in PNC/TiAlN systems under high N₂ flow conditions. Tribological evaluations demonstrated that the composite coatings achieved lower specific wear rates (25.23 × 10⁻⁸ mm³·N⁻¹·m⁻¹) under 7.3 N, outperforming monolithic TiAlN coatings by mitigating abrasive wear and delamination. The synergy between N₂ flow modulation and nitrocarburizing pretreatment effectively optimized coating–substrate compatibility, establishing a robust framework for designing wear-resistant TiAlN coatings in extreme service environments. This work provides critical insights into tailoring PVD coating architectures for aerospace and heavy-load applications. Full article

Biomaterials play a crucial role in the long-term success of bone implant treatment. The accumulation of bacterial biofilm on the implants induces inflammation, leading to implant failure. Modification of the implant surface with bioactive molecules is one of the strategies to improve biomaterial compatibility and limit inflammation. In this study, whey protein isolate (WPI) fibrillar coatings were used as a matrix to incorporate biologically active phenolic compound phloroglucinol (PG) at different concentrations (0.1% and 0.5%) on titanium alloy (Ti6Al4V) scaffolds. Successful Ti6Al4V coatings were validated by X-ray photoelectron spectroscopy (XPS), showing a decrease in %Ti and increases in %C, %N, and %O, which demonstrate the presence of the protein layer. The biological activity of PG-enriched WPI (WPI/PG) coatings was assessed using bone-forming cells, human bone marrow-derived mesenchymal stem cells (BM-MSCs). WPI/PG coatings modulated the behavior of BM-MSCs but did not have a negative impact on cell viability. A WPI with higher concentrations of PG increased gene expression relative to osteogenesis and reduced the pro-inflammatory response of BM-MSCs after biofilm stimulation. Autoclaving reduced WPI/PG bioactivity compared to filtration. By using WPI/PG coatings, this study addresses the challenge of improving osteogenic potential while limiting biofilm-induced inflammation at the Ti6Al4V surface. These coatings represent a promising strategy to enhance implant bioactivity. Full article

Ti6Al4V alloy is one of the most widely used orthopedic implants due to its low density, high strength and good biocompatibility, but surface tribology limits its service life and performance. In this paper, a layer of dynamic double-network hydrogel based on a Schiff base bond and a hydrogen bond was grafted on the surface of Ti6Al4V alloy by the mussel chemical self-assembly method. The -NH₂ of acrylamide (AM) and -CHO of vanillin (VA) formed Schiff base bonds to form the first layer of a cross-linked network, a large number of hydrogen bonds were formed between the -OH of vanillin and the -OH of sodium alginate (SA) to provide the second layer of the cross-linked network and the network was properly regulated by introducing core–shell polymer nanoparticles (PDCS). Dynamic self-healing bonds, Schiff base bonds and hydrogen bonds endow qPDCS/SA/VA/AM hydrogels with self-healing ability, and the network structure destroyed under high strain (250%) can be rebuilt under low strain (1%). In the second cycle, G’ and G can recover almost the same value. PDCS/SA/VA/AM hydrogel coating can achieve dynamic repair through reversible Schiff base bond dissociation–recombination during friction, while 1000ppmPDCS/SA/VA/AM hydrogel coating can achieve stable friction reduction and low wear under multiple loads. Under 0.5 N load, the average friction coefficient of 1000ppmPDCS/SA/VA/AM hydrogel coating is as low as 0.157, which is 67.74% lower than the uncoated Ti6Al4V surface under the same load. Under 2 N load, 1000ppmPDCS/SA/VA/AM hydrogel coating remains stable and low-friction, and the average coefficient of friction (ACOF) can reach 0.130, which is 59.27% lower than the uncoated Ti6Al4V surface under the same load. The design idea of the hydrogel network regulated by core–shell polymer nanoparticles (PDCS) to achieve low friction and low wear provides a new strategy for biolubricating materials. Full article

The preparation of high-performance hard coatings on the surface of cemented carbide PCB (printed circuit board) microdrills can effectively decrease the rapid tool wear that occurs during cutting. In this study, arc ion plating technology was employed to deposit conventional AlTiN columnar crystal single-layer coatings and AlTiN nanocrystalline single-layer coatings on the cemented carbide substrates of PCB microdrills. Additionally, a novel AlTiN composite coating with alternating columnar and nanocrystalline layers was designed and deposited. The mechanical properties and morphological characteristics of the three coating structures were analyzed using an indentation tester and scanning electron microscopy. The above three coated PCB microdrills were tested under the same conditions, and the cutting performance and tool wear mechanisms were compared and analyzed. The results show that the primary wear mechanisms for AlTiN-coated PCB microdrills are abrasive wear and coating flaking, and that the microdrill with the AlTiN columnar/nanocrystalline multilayer composite coating has the longest tool life. The novel AlTiN columnar/nanocrystalline composite coating exhibits superior interfacial adhesion strength, higher toughness, and better surface quality, and, hence, is more suitable for the high-speed drilling of PCB microholes. Full article

To increase the wear and corrosion resistance of (α + β) titanium-aluminium-vanadium (Ti6Al4V) alloy, ceramic tantalum oxide coatings were deposited by direct current (DC) magnetron sputtering at three different substrate temperatures—400, 450, and 500 °C. The crystallographic structure, surface morphology, chemical compositions, film adhesion, and hardness of the coatings were described using XRD, SEM, EDS, scratch tests, and microhardness measurements. The samples’ ability to withstand corrosion was assessed using electrochemical studies. Results revealed that thin films have an amorphous or crystalline structure dependent on temperature. The film’s thicknesses varied between 560 and 600 nm. With the increase in deposition temperature, the hardness of the film rose. All oxide coatings were tightly adherent to the titanium alloy substrate, and critical force increased from about 8.6 up to 20 N when the temperature rose from 400 to 500 °C. During the polarisation investigations, after 1 h of immersion, a drop in current density (j_corr) verified an improvement in the corrosion resistance of the amorphous and well-crystalline coatings. A two-layer model of the surface film accurately describes the coated systems’ electrochemical behaviour. However, according to the EIS analysis, the well-crystalline film deteriorates greatly, whereas the amorphous film prevents penetration during the 7-day immersion test in SBF. The wettability tests demonstrated the hydrophilic nature of the coatings, and after seven days, the mineralisation of calcium phosphate proves the coatings become bioactive in simulated bodily fluid (SBF). Thus, we produced films of tantalum oxide, which, with the proper deposition parameters, may prove to be appropriate surfaces for titanium-based implant bio-applications. Full article

Residual stresses in multilayer thin coatings represent a complex multiscale phenomenon arising from the intricate interplay of multiple factors, including the number and thickness of layers, material properties of the layers and substrate, coefficient of thermal expansion (CTE) mismatch, deposition technique and growth mechanism, as well as process parameters and environmental conditions. A multiscale approach to residual stress measurement is essential for a comprehensive understanding of stress distribution in such systems. To investigate this, two AlGaN/GaN multilayer coatings with distinct layer architectures were deposited on sapphire substrates using metalorganic vapor phase epitaxy (MOVPE). High-resolution X-ray diffraction (HRXRD) was employed to confirm their epitaxial growth and structural characteristics. Focused ion beam (FIB) cross-sectioning and transmission electron microscopy (TEM) lamella preparation were performed to analyze the coating structure and determine layer thickness. Residual stresses within the multilayer coatings were evaluated using two complementary techniques: High-Resolution Scanning Transmission Electron Microscopy—Graphical Phase Analysis (HRSTEM-GPA) and Focused Ion Beam—Digital Image Correlation (FIB-DIC). HRSTEM-GPA enables atomic-resolution strain mapping, making it particularly suited for investigating interface-related stresses, while FIB-DIC facilitates microscale stress evaluation. The residual strain values obtained using the FIB-DIC and HRSTEM-GPA methods were −3.2 × 10⁻³ and −4.55 × 10⁻³, respectively. This study confirms that residual stress measurements at different spatial resolutions are both reliable and comparable at the required coating depths and locations, provided that a critical assessment of the characteristic scale of each method is performed. Full article

Self-cleaning coatings for solar mirrors aim to reduce water usage for cleaning, cut down on maintenance costs for solar fields, and lower the overall electricity production costs in concentrated solar power (CSP) systems. Various approaches have been developed for mirrors with back surface (BSM) and front surface (FSM) architectures, all sharing the characteristic that the self-cleaning coating serves as the outermost layer, acting as a “skin” that protects against fouling. A recent trend in this field is to enhance this “skin” with sensing capabilities, allowing it to self-monitor its performance in terms of soiling or failure, contributing to the digitalization of solar fields and CSP technology. Building on previous work with auxetic aluminum nitrides and ZnO transparent composites, which were developed to replace alumina as the self-cleaning layer in BSMs, this study explores the potential of adding sensing properties to these coatings. The approach leverages the piezoelectric properties of the materials, which can be linked to dust accumulation and surface soiling, as well as their electrical resistive behavior, which can help monitor potential failures. The promising d33 values of sputtered piezoelectric AlN and the tailored electrical properties of ZnO composites, combined with their self-cleaning effects and optical clarity across the full solar spectrum, suggest that these coatings could serve as an intelligent, self-aware skin for solar mirrors. Full article

This study investigates the influence of rare earth elements Ce and Y on the evolution of inclusions in T91 steel by melting experimental steels with varying Ce-Y contents in a vacuum induction melting furnace. The results show that the inclusions in the steel without rare earth are mainly composed of Mg-Al-O oxides, (Nb, V, Ti)(C, N) carbonitrides, and composite inclusions formed by carbonitrides coated oxides, and all of them have obvious edges and corners. Upon the addition of different concentrations of Ce and Y, the oxygen content in the steel significantly decreased, and the inclusions were modified into spherical rare earth oxides, sulfides, and oxy-sulfides. Additionally, no large-sized primary carbonitrides were observed. The average size of the inclusions was reduced from 2.8 μm in the non-rare-earth-added steel to 1.7 μm and 1.9 μm with rare earth addition. Thermodynamic analysis indicates that the possible inclusions precipitated in the steel with varying Ce contents include Ce₂O₃, Ce₂O₂S, Y₂O₃, Y₂S₃, and CeS. With the increase in Ce content, the rare earth inclusions Y₂S₃, Y₂O_3, and CeS can be transformed into Ce₂O₂S and Ce₂O₃. There are two kinds of reactions in the process of high-temperature homogenization: one is the internal transformation reaction of inclusions, which makes Y easier to aggregate in the inner layer, and the other is the reaction of Y₂S₃→CeS and Y₂O₃ + Y₂S₃→Ce₂O₂S due to the diffusion of Ce in the matrix to the inclusions. Combined with the mismatch analysis, it can be seen that Al₂O₃ has the best effect on the heterogeneous nucleation of carbonitrides during the solidification of molten steel. Among the rare earth inclusions, only Ce₂O₃ may become the nucleation core of carbonitrides, and the rest are more difficult to form heterogeneous nucleation. Therefore, by Ce-Y composite addition, increasing the Y/Ce ratio can reduce the formation of Ce₂O₃, which can avoid the precipitation of primary carbonitride and ultimately improve the dispersion strengthening effect. This study is of great significance for understanding the mechanism of rare earth elements in steel and provides theoretical guidance for the composition design and industrial trial production of rare earth steel. Full article

The main focus of this work is the successful deposition of hard and wear-resistant TiAlCN coating on the surface of GCr15 bearing steel by means of magnetron sputtering technology. The phase composition of the chromium nitride transition layer was monitored by precisely controlling the nitrogen (N₂) flow rate to strengthen the bonding between the TiAlCN coating and the GCr15 bearing steel surface. It was found that coating performance reached the optimal state at a N₂ flow rate of 40 sccm, yielding a hardness of 23.3 GPa, a friction coefficient of only 0.27, and a wear rate of 0.19 × 10⁻⁸ mm³/N·m. Full article

The present work introduces a new solar selective absorber coating (SSAC) for the receiver tube of Concentrated Solar Power (CSP) systems, proposing silver as an infrared reflector for application at 550 °C. In the past, the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) has developed SSACs suitable for applications at 550 °C, featuring solar absorbers based on graded multilayer cermet of WN-AlN and W-Al₂O₃ and an infrared reflector of tungsten. Although these coatings ensured properly stable photothermal performance at 550 °C, due to the low tungsten diffusivity, their hemispherical emittance could be reduced by using metals with higher reflectance in the infrared region, like silver. However, the high diffusivity of silver compromises its use at high temperatures. This last drawback has been addressed by foreseeing two stabilizing layers enclosing the Ag infrared reflector. One W stabilizing layer was placed between the substrate and the Ag infrared reflector, whereas a second stabilizing layer, selected among aluminum nitride deposited with a low and high nitrogen flow and aluminum oxide deposited at a low oxygen flow, was placed between the Ag infrared reflector and the solar absorber. Accelerated aging tests revealed a negligible (not detectable) degradation of the solar absorptance for the new SSACs. Furthermore, the hemispherical emittance at 550 °C increased by 0.75% and 0.42% for solar coatings with aluminum nitride stabilizing layers deposited through a high and low nitrogen flow, respectively. Differently, the increase was evaluated as being equal to 0.08% for the solar coating with an aluminum oxide stabilizing layer deposited through a low oxygen flow. The manufactured solar coating with a stabilizing layer of aluminum nitride deposited with a low nitrogen flow exhibited a solar absorptance of 95%, comparable to ENEA coatings incorporating a W infrared reflector for applications at 550 °C, whereas the estimated hemispherical emittance at 550 °C was 2% lower than that of the best ENEA coating with a W infrared reflector for the same temperature. Full article

The article presents the results of a comparison of the wear resistance of coatings with a two-layer architecture (adhesion layer–wear-resistant layer) of Zr-ZrN, Zr-(Zr,Ti)N, Zr,Hf-(Zr,Hf)N, Zr,Nb-(Zr,Nb)N, Zr,Hf-(Ti,Zr,Hf)N, and Zr,Nb-(Ti,Zr,Nb)N coatings, deposited on a titanium alloy substrate. The wear resistance was studied using two different counterbodies: Al₂O₃ and steel. When in contact with the Al₂O₃ counterbodies, the best wear resistance was demonstrated by samples with Zr,Hf-(Zr,Hf)N and Zr,Nb-(Zr,Nb,Ti)N coatings. In tests conducted in contact with the steel counterbody, the best resistance was demonstrated by samples with Zr-ZrN and Zr,Hf-(Ti,Zr,Hf)N coatings. The wear resistance of samples with (Zr,Hf)N and (Zr,Nb,Ti)N coatings was 2.5–3.3 times higher than that of the uncoated sample. The Zr,Nb adhesion layer ensures better adhesion of the coating to the substrate. It was found that not only the adhesion strength of the adhesion layer to the substrate and coating is of significant importance but also the strength of the adhesion layer itself. The surface film of titanium oxide must be completely etched off to ensure maximum strength of the adhesive bond between the coating and the substrate. It has been established that the adhesion of the coating and the titanium substrate is also affected by the characteristics of the outer (wear-resistant) coating layer, which is the composition and structure of the wear-resistant coating layer. Delamination can occur both at the boundary of the adhesive layer with the substrate and at the boundary of the wear-resistant and adhesive layers of the coating depending on the strength of the adhesive bonds in the corresponding pair. It is necessary to ensure a good combination of properties both in the substrate–adhesion layer system and in the adhesion layer–wear-resistant layer system. Full article