Ag-based low-emissivity (low-E) window coatings allow for important energy savings. However, in architectural applications, it is required that the coating be deposited prior to tempering the glass. During this process, several mechanisms can lead to coating degradation: amongst these, Ag interaction with contaminants, which present increased diffusivity at high temperatures, is particularly important. Even when appropriate barrier layers are present, any defects can become highly visible following tempering. This work aims to isolate the effect of different contaminants, to evaluate their impact on Ag degradation alone, in combination with other contaminants, and at defect sites. To do so, partial stacks with various barrier layer configurations are deposited on substrates with different contaminant concentrations and tempered in controlled atmospheres in order to selectively enable contaminant diffusion in otherwise identical coatings. Subsequent scanning electron microscopy measurements allow to identify the distinct effects of Na and O2 on Ag dewetting and correlate these to electrical and optical changes. Defects are then generated in a controlled fashion using a microscratch tester. Quantitative analysis of defect visibility is extracted from dark-field photographs of the scratched samples. Controlling for the presence of different defect types within the scratches and the availability of atmospheric and substrate contaminants, their effects on scratch visibility accentuation are evaluated. Scanning and transmission electron microscopy observations reveal that buckling defects, whose formation during tempering is facilitated by Ag dewetting, lead to the highest visibility due to formation of small, highly scattering Ag nanoparticles within the buckled areas.

Engineering amorphous dielectric films with tunable thermal conductivity is advantageous for the thermal management of semiconductor devices and thermal insulation of aerospace applications. Here, we demonstrate that incorporating dense dispersed amorphous Al(Ti)N (~1 nm or above) nanoparticles having phase volume fractions from 6 to 70 %, has a negligible effect on the intrinsic thermal conductivity of the amorphous Si3N4 matrix (~2 W m-1K-1), in which the wave-like 'propagons' in Allen-Feldmann theory are believed to be unsupressed and non-tuned. By contrast, incorporating (5-15 nm) crystalline TiN phases significantly increases the thermal conductivity (up to 15 W m-1K-1). Critically, the micrometre-thick Si3N4/AlN and Si3N4/TiN amorphous matrix dual-phase nanocomposite coatings exhibit excellent thermal stability upon exposure to ambient air at 1000 °C for 50 h. These findings shed light on the phonon transport mechanism regarding the effects of the second phase and pave a design pathway for engineering amorphous coatings displaying unprecedented high thermal conductivity and excellent thermal stability.

In recent nanomaterials research, combining nanoporous carbons with metallic nanoparticles, like palladium (Pd), has emerged as a focus due to their potential in energy, environmental and biomedical fields. This study presents a novel approach for synthesizing Pd-decorated carbons using magnetron sputter deposition. This method allows for the functionalization of nanoporous carbon surfaces with Pd nano-sized islands, creating metal–carbon nanocomposites through brief deposition times of up to 15 s. The present research utilized direct current magnetron sputtering to deposit Pd islands on a flexible activated carbon cloth substrate. The surface chemistry, microstructure, morphology and pore structure were analyzed using a variety of material characterization techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, gas sorption analysis and scanning electron microscopy. The results showed Pd islands of varying sizes distributed across the cloth’s carbon fibers, achieving high-purity surface modifications without the use of chemicals. The synthesis method preserves the nanoporous structure of the carbon cloth substrate while adding functional Pd islands, which could be potentially useful in emerging fields like hydrogen storage, fuel cells and biosensors. This approach demonstrates the possibility of creating high-quality metal–carbon composites using a simple, clean and economical method, expanding the possibilities for future nanomaterial-based applications.

As the sweet crude oil reserves decline, refiners must treat sulfur-rich heavy oil, requiring harsher operating conditions, which are detrimental to process equipment. Application of coatings on critical components protects surfaces against sulfidation, corrosion, and fouling, extends the equipment's lifetime, and reduces the frequency of costly turnarounds. In the present work, we coated Inconel 625 and Inconel 718 substrates with amorphous alumina thin films at room temperature using reactive RF magnetron sputtering. Annealing of the deposited coatings at 800, 900, and 1000 degrees C increased hardness, improved adhesion, and generated crystalline polymorphs, predominantly gamma-Al2O3 at lower temperatures, while alpha-Al2O3 was present at 1000 degrees C. The annealed substrates formed thermally grown oxides (TGOs), which interacted with the alumina coatings. The TGOs followed grain boundaries in the case of IN718 and a crater-like pattern on IN625. Annealed substrate precipitates generated columnar-like protrusions responsible for inducing crack propagation, which exhibited TGO formation. After 2 h exposure to heavy oil (containing 0.06 g g(-1) sulfur) at 450 degrees C and 11.3 MPa the as-deposited amorphous alumina presented no clear sign of adherent fouling, while the 1000 degrees C annealed crystalline alumina surfaces presented evidence of fouling.

(Al,Si)(3)(Zr,Ti)-D0(22)/D0(23) are phases that may form in aerospace and automotive aluminium alloys. The substitution of Zr/Ti in these solid solutions is widely reported in the literature; however, it remains relatively unexplored for Si. In this work, in situ precipitation of (Al,Si)(3)(Zr,Ti)-D0(22)/D0(23) intermetallics was performed using Al-Si-Zr-Ti alloys. The precipitation, sedimentation and concentration of numerous intermetallic particles were accomplished by filtrating the residual molten aluminium using a temperature/pressure-controlled vessel adapted with a PoDFA filter. A combination of SEM, TEM, XRD and EMP analysis allowed the identification of (Al,Si)(3)(Zr,Ti)-D0(22)/D0(23) intermetallics concentrated within..-FCC matrices of non-Si-doped (sample S2) and Si-doped (samples S4 and S6) alloys. EDS analysis confirmed that Zr and Ti substitute each other in the D0(22) and D0(23) phases, whereas Si substitutes in Al sites. Acceptance of Si inside the D0(23) phase was not expected according to FTlite (FactSage) and TCAL7 (Thermo-Calc) databases. Additionally, Si was found to enhance the formation of (Al,Si)(3)(Zr,Ti)-D0(22) intermetallics with high Zr-content, contrary to FactSage 7.3 predictions. TEM results showed intermetallic/FCC crystal coherency for samples S2 and S6, implying that these intermetallics acted as nucleation sites for the Al-phase due to their small lattice mismatch. Furthermore, Si site occupancy was calculated for both (Al,Si)(3)Ti-D0(22) and (Al,Si)(3)Zr-D0(23) phases via DFT, showing that sites 2b and 4e are the most favorable for Si occupation, respectively. Finally, a thermodynamic model is derived to describe Si substitution upon solidification. Experimental and numerical examinations indicate that Si substitution preferentially occurs in the D0(22) intermetallics compared to the D0(23) phase.

Ti-Al-N coatings were prepared by cathodic arc deposition on Inconel 718 substrates at different values of constant substrate bias voltage, aiming to produce samples with different self-developed residual stress (RS) depth profiles through the thickness of the coatings. RS profile measurements and structural characterization were performed on a laboratory-scale x-ray diffraction system (x-ray energy of 8 keV) and in a synchrotron x-ray radiation facility (x-ray energy of 15 keV). Mechanical testing to obtain hardness and Young’s modulus values was performed by instrumented nanoindentation. The results indicate higher compressive RS at the film/substrate interface that decays to lower compressive stress or mild tensile stress at the film surface. Surface hardness and the compressive RS value of the coating increase with larger values of the substrate bias voltage. By comparing the stress characterization done on a laboratory scale and at the synchrotron facility, one observes a generally good agreement, indicating that these analyses may be conducted at a smaller scale and with less costly equipment, and still maintain a reliable precision. The work presents and reviews in detail the methodology of the RS depth-profile analysis. The highest hardness of 31.1 GPa and near-substrate compressive RS around −10 GPa were obtained for a bias of −100 V. Transmission electron microscopy results indicate that regions with higher compressive stresses are found to have smaller columns and denser structure, while portions of the same sample with mild compressive or tensile stresses present larger column size and are richer in hexagonal phases. The findings demonstrate the complex interplay between stress, microstructure, and ultimately mechanical properties in industrially produced Ti-Al-N coatings and indicate that any successful strategy to mitigate stress development should consider the inhomogeneous self-developed stress gradients present even in coatings deposited under constant and controlled conditions.

Thermal radiation represents a significant portion of the thermal heat transfer from the hot gases of an engine to its metallic components. Thermal barrier coatings (TBCs) are used to protect those components from heat and must, therefore, be effective blockers of radiative heat. The porous microstructure of TBCs causes them to be highly reflective in the visible and near-infrared wavelength ranges through the scattering of light. This microstructure, however, is susceptible to degradation. In this study, we establish a clear link between the porosity of a TBC and its ability to reflect heat through radiation scattering by extracting the scattering coefficient of two coatings with different microstructures and quantifying their pore space. Using deep learning trained image segmentation models on high resolution SEM cross-sections, we identify the proportion of the pore space comprised of pores 2 mu m in diameter or smaller and show that these are responsible for most of the scattering. The pore size distribution is also confirmed with mercury infiltration porosimetry. The coatings are then subjected to cyclic heat treatments at 1450 K for a total of 1111 h to induce sintering of the microstructure. This results in a reduction of the scattering coefficient by around 20 % for both samples, which is attributed to a reduction in the space occupied by pores 2 mu m and less in diameter. Finally, a model is built for finite-difference time-domain (FDTD) simulations using high resolution SEM cross-sections to calculate the reflectivity and transmission of the TBCs. The results exhibit good agreement with our experimental data, showing that such models could be used in the future to predict the effect of degradation on a TBC's optical properties.

Thermal barrier coatings (TBCs), which protect metallic components in aircraft engines thanks their low thermal conductivity, must also be effective blockers of radiative heat. While their porous microstructure makes them highly reflective to visible and infrared light through scattering, it also renders them susceptible to degradation, particularly due to calcium-magnesium-alumino-silicate (CMAS) infiltration. This study explores its effect on the optical scattering coefficient of TBC yttria-stabilized zirconia (YSZ) topcoats deposited by atmospheric plasma spray (APS) with two different microstructures. Different CMAS compositions are investigated by isothermal melting into the coatings, resulting in a significant decrease of their reduced scattering coefficients by around 50%. To further study the evolution of their performance as the pores are filled, atomic layer deposition (ALD) is used to mimic CMAS infiltration in a controllable fashion. The results show that most of the performance loss occurs with very little material inserted into the pores and that a saturation point is quickly reached. This is explained by two mechanisms: pores approximately 2 mu m in diameter and less are responsible for most of the optical performance and are filled up rapidly, while the refractive index contrast at every pore's interface di-minishes when material fills the voids. The obtained minimum scattering coefficient value is approximately half that of a pristine sample and matches with the values obtained by the CMAS melting approach. Finite-difference time-domain (FDTD) modeling is also shown to corroborate the observed saturation behavior and demonstrated to be a suitable tool for the design and optimization of future TBCs.

Formation of the high-temperature α-Al2O3 phase during Plasma Electrolytic Oxidation of aluminium at ambient bulk temperatures has been previously attributed to local microdischarge events providing multiple melting-solidification cycles in micro-volumes of the surface oxide layer. In this work, it is demonstrated that the α phase can be formed even if the microdischarge is fully suppressed under specific processing conditions. Oxide layers produced in the post-sparking anodising mode were studied by FIB, TEM, EBSD, EDS and GDOES techniques to reveal microstructural and chemical evolutions that accompany the γ to α alumina transition. Our results provide strong evidence that the α phase can form spontaneously in regions of oxide with the appropriate temperature, grain size and impurity distributions in the γ-Al2O3 matrix that allow sufficient mobility of α/γ grain boundaries. Ionic migration within the oxide and hydrothermal dissolution/precipitation in the associated microporous network that facilitate species mobility at the grain boundaries allow the critical temperature for activation of γ→α transition to be reduced. Overall, it is suggested that oxide layer growth can be considered in terms of a relatively simple Plug Flow Reactor model. This can help predict the phase transition kinetics depending on key processing parameters such as current density and frequency of pulse polarisation, thus enabling optimum control of coating microstructure for specific application requirements.

ZrO2 coatings deposited by low duty cycle pulsed DC magnetron sputtering exhibit good optical properties, low compressive stress (-110 MPa), and excellent mechanical properties (a hardness of ~14 GPa, a toughness of > 3 MPa∙m-2).

One of the key challenges for the development of high-performance fusion materials is to design materials capable of maintaining mechanical and structural integrity under the extreme levels of displacement damage, high temperature and transmutation rates. High-entropy alloys (HEAs) and other concentrated alloys have attracted attention with regards to their performance under fusion conditions. In recent years, a number of investigations of the irradiation responses of HEAs have peaked the community's interest in them, such as the work of Kumar et al. (2016), who examined Fe27Ni28Mn27Cr18 at doses as high as 10 dpa. In this work, we study Fe28Ni28Mn26Cr18 concentrated multicomponent alloy with irradiation doses as high as 20 dpa. We find the presence of Cr rich bcc precipitates in both the un-irradiated and in the irradiated condition, and the presence of dislocation loops only in the irradiated state. We correlate the features found with irradiation hardening by the continuous stiffness method (CSM) depth-sensing nanoindentation technique and see that the change in the bulk hardness increases significantly at 20 dpa for temperatures 450 °C. These results indicate that the alloy is neither stable as a single phase after annealing at 900 °C, nor particularly resistant to irradiation hardening.

Transition metal dichalcogenides such as MoS2 are widely used as solid lubricants for vacuum applications. On the other hand, diamond-like carbon coatings exhibit excellent sliding properties in the ambient environment. Our Mo-S-C coatings deposited by pulsed d.c. sputtering combine both structures to obtain stable properties regardless of the testing conditions. The coatings were studied using HR-TEM and Raman spectroscopy, revealing amorphous nature of the coating. The tribological properties were evaluated by pin-on-disc method. The results showed high lubrication ability in all the testing conditions. HR-TEM and Raman spectroscopy were employed to show the structural characteristics of the wear traces. Our results indicate that the low-friction effect should be attributed to carbon structure re-arrangement since expected wear-induced MoS2 formation was not observed.

Interface engineering is essential to enhance and to maintain the performance of protective coatings on metallic substrates. Plasma pre-treatments and coating deposition processes have shown to be an ideal solution to improve Ti-6Al-4V alloy mechanical and tribological properties, while enhancing components' durability. In the present work, we study model Titanium Nitride (TiN) coatings with three interface engineering surface treatment approaches using: a) Argon plasma, b) Titanium implantation, and c) plasma surface nitriding. In particular, we investigate the influence of the plasma pre-treatments on the microstructure, mechanical properties, especially residual stress (RS) and adhesion, of TiN coatings on Ti-6Al-4V substrates. X-Ray Diffraction, Transmission Electron Microscopy, and Transmission Kikuchi Diffraction were used as complementary techniques to evaluate the crystallographic and microstructural properties of the interfaces created by the three pre-treatment methods in order to elucidate their effect on the evolution of microstructure, hardness, RS and adhesion. The RS study involved surface and depth profiles through the coating-substrate system. Compressive RS values were found to vary between -1 GPa and -4 GPa throughout the TiN coatings, and from -0.2 to -0.8 GPa across the different interfaces. In addition, a strong RS anisotropy in dependence on the way how the substrate has been fixed to the holder (rigidly clamped or freely attached) shows a significant difference in the RS with a deviation of >100% in dependence on the orientation of coated samples during the XRD measurements. Experimental results show that Ar plasma and Ti implantation form interfaces with (200) and (111) preferential orientations within the TiN layers that exhibited a hardness of up to similar to 29 GPa and a Young's modulus of similar to 350 GPa.

A nanoporous and large surface area (similar to 800 m(2)/g) graphene-based material was produced by plasma treatment of natural flake graphite and was subsequently surface decorated with platinum (Pt) nanosized particles via thermal reduction of a Pt precursor (chloroplatinic acid). The carbon-metal nanocomposite showed a similar to 2 wt% loading of well-dispersed Pt nanoparticles (<2 nm) across its porous graphene surface, while neither a significant surface chemistry alteration nor a pore structure degradation was observed due to the Pt decoration procedure. The presence of Pt seems to slightly promote the hydrogen sorption behavior at room temperature with respect to the pure graphene, thus implying the rise of "weak" chemisorption phenomena, including a potential hydrogen "spillover" effect. The findings of this experimental study provide insights for the development of novel graphene-based nanocomposites for hydrogen storage applications at ambient conditions. (C) 2020 The Authors. Published by Elsevier Ltd.

The performance and integrity of coated engineering components rely on the time required for the appearance of defects and cracks and their propagation, leading to delamination of the coating and degradation of the substrate. Optimizing the coating's mechanical properties such as hardness, residual stress (RS), and adhesion is essential to delay crack onset and propagation. In the present work, we investigate the mechanical properties, and the failure mechanisms of model TiN coatings reactively sputtered onto Ti-6Al-4V substrates while comparing three interface engineering approaches to enhance the system durability: a) Argon plasma treatment, b) plasma surface nitriding, and c) Titanium implantation. The TiN coatings possessed a hardness of similar to 29 GPa and a Young's modulus of similar to 350 GPa. Multi-reflection grazing incidence X-ray diffraction was used to assess the compressive RS depth profile. Each interface engineering process induced RS variation in the coating and the adjacent interfacial area and in the substrate's near-surface layer ranging from -1 GPa to -2.2 GPa with different gradients. Cohesive failure, crack evolution and fracture toughness were studied using micro-scratch and micro-tensile tests, while the surface grain deformation behaviour and surface cracks on fractured Ti-6Al-4V with various interface treatments and TiN coatings were identified by SEM image and elasto-plastic property analyses. We found a close correlation between the RS of the coatings or the interface layers and the fracture mechanism. Specifically, higher compressive RS led to an enhanced interfacial shear strength and a critical energy release rate of around 550 to 790 MPa, and of similar to 18 J/m(2), respectively.

A new technique for determination of residual stress in thin films and coatings has been presented. The method consists of focused ion beam milling to create a lamella of thin film, followed by analysis of stress driven buckling profile of undercut lamella (beam) to extract residual stress. The residual stresses in crystalline TiN and Al2O3 films, produced by reactive magnetron sputtering and thermal oxidation, respectively, have been successfully determined by this new technique and validated by conventional X-ray diffraction and photoluminescence piezospectroscopy techniques, respectively. This new technique successfully measures and tracks the evolution of residual stress in as-deposited and different thermally cycled amorphous SiAlN films induced by thermal mismatch or relieved via mechanical twinning in interlayer, where diffraction methods are not applicable, thereby evaluating the thermal cycling performance of amorphous SiAlN coatings for protection of Ti at high temperature.

In recent years, a major challenge facing the power generation industry is delamination of Stellite-hardfaced coatings from high-temperature valves. In order to meet this challenge, IN82 buffer layer was evaluated to replace the problematic S21 buffer layer. S6 and either S21 or IN82 hardfacing alloys were deposited onto F91 steel substrates using plasma-transferred arc hardfacing. Aging was conducted at temperatures between 550 and 650 degrees C for three exposure durations within a one-year period. A comparative study was carried out on the microstructure and mechanical properties of IN82 and S21 hardfaced specimens. The F91/S21 interface is unstable during aging because a hard and brittle interfacial layer grows, which significantly reduces the impact energy of S21 hardfaced specimens. In contrast, the F91/IN82 interface is microstructurally much more stable than the F91/S21 interface; an interfacial band, part of the F91 steel, and some discrete M23C6 carbides along this band grow during aging at 650 degrees C for 8760 h. The impact energy loss of the IN82 specimens is much less significant than that of the S21 specimens. Moreover, the toughness degradation is not related to the F91/IN82 interface, but rather to coarsening and precipitation of the intergranular/interdendritic carbides in the IN82 bulk material during aging. To conclude, the IN82 buffer layer is a good alternative to replace the problematic S21 buffer layer, enhancing the durability of the S6 coating components. However, the hardness of the S6 top layer is compromised due to dilution of Fe and Ni. To maintain its hardness, more S6 layers can be deposited and process optimization can be undertaken to reduce dilution in the applications where wear resistance is critical.

Indium tin oxide (ITO) thin films, used in many optoelectronic applications, are typically grown to a thickness of a maximum of a few hundred nanometres. In this work, the composition, microstructure and optical/electrical properties of thick ITO coatings deposited by radio frequency magnetron sputtering from a ceramic ITO target in an Ar/O2 gas mixture (total O2 flow of 1%) on unheated glass substrates are reported for the first time. In contrast to the commonly observed (200) or (400) preferential orientations in ITO thin films, the approximately 3.3 μm thick coatings display a (622) preferential orientation. The ITO coatings exhibit a purely nanocrystalline structure and show good electrical and optical properties, such as an electrical resistivity of 1.3 × 10−1 Ω·cm, optical transmittance at 550 nm of ~60% and optical band gap of 2.9 eV. The initial results presented here are expected to provide useful information for future studies on the synthesis of high-quality thick ITO coatings.

Disbonding and delamination of Stellite-hardfaced coatings from high-temperature valves have presented a major challenge to the power generation industry. In order to study how the interfacial microstructure of Stellite-hardfaced coatings might damage valve integrity during service, a series of aging experiments were conducted at temperatures ranging from 550 to 650 degrees C over three durations within a one-year period. After high-temperature exposure, the hardfacing interface was characterized using innovative Charpy U-notch specimens. It was observed that the impact energy decreased significantly (by at least 92%) after aging. The fractographic analysis revealed that the fractures of the aged hardfacing specimens were brittle. It is proposed that the interfacial layer formed during aging provides a brittle crack propagation pathway. The reduction in absorbed impact energy is mainly associated with the formation of hard and brittle M23C6 carbides along the hardfacing interface. The more the M23C6 carbides grow, the smaller the absorbed impact energy becomes. The presence of the sigma phase would also contribute to the decrease of the absorbed impact energy. It is proposed that the microstructural factors contributing to the delamination of Stellite-hardfaced coatings in service are the formation of hard and brittle M23C6 carbides and sigma phase.

In the context of protecting Mg-based nano-objects for potential hydrogen storage applications, the potential of C:H layer as a barrier polymer material deposited by the plasma-enhanced chemical vapor deposition process is examined. Corrosion tests reveal (a) good barrier properties of the C:H layer and (b) suggest an increase in the internal stress with the power dissipated in the plasma. The latter is attributed to an increase in the cross-linking density of the coatings accompanied by an increase in the stiffness as shown by nanoindentation measurements. Finally, for a given set of plasma parameters, Mg-based nanowires were successfully enrobed by the C:H coatings as evidenced by scanning electron microscopy measurements.