In this work, multi-layer PECVD SiNx/SiNx and SiNx/SiOy passivations are developed featuring very high soft breakdown strength and tunable stress properties, which would allow for stress engineering and wafer bow minimization. AlGaN/GaN-on-Si wafers (150 mm) with very low initial bow (<5 μm) are processed in a CMOS compatible manner. The effect of the major processing steps, namely passivation and metal deposition, on the wafer bow is continuously monitored. In this process aimed at power devices, relatively thick passivation is needed (1.5 μm), which would induce very high stresses on the wafer if a single-layer deposition is applied. Hence, deposition of multiple layers is explored through mechanical modelling and simulation, leading to a stress-free passivation. The optimized multi-layer dielectric consists of two different SiNx single layers (referred to as T40 and R100), which have opposite stress properties, with T40 being tensile and R100 being compressive. By adjusting the thickness ratio of both layers and the number of total layers, mechanical stress within the multi-layer can be neutralized to achieve stress-free deposition. In addition, the optimization of the film properties includes the electrical properties of the passivation, and is designed primarily for high voltage applications. The developed SiNx/SiNx passivation has a soft breakdown strength with more than 8 MV/cm, and leakage currents below 1 nA/mm2 up to soft breakdown. After dielectric development, Schottky and MIS device characteristics with SiNx/SiNx multi-layers are characterized in DC and pulse mode measurements. As measurements suggest, the developed passivation is suitable for GaN-on-Si HEMT applications.

The performance of optical coating systems are frequently limited by the formation of defects and cracks, hence deteriorating the optical properties, film integrity and durability. Typical anti-reflective coating systems consist of inorganic low index and high index thin oxide films (e.g., SiO2 and ZrO2) on polymeric substrates that can be subjected to complex strain states induced by environmental effects such as thermal excursions or even by the manufacturing process. Any crack in the multi-layer stack is likely to be problematic in terms of optical performance and visual comfort for the wearer and also in terms of the mechanical durability of the stack. To overcome this limitation, the development of predictive tools is essential to improve the design of coatings systems while complementing experimental analyses. Thus, in this work, we performed numerical simulations by means of phase field fracture models relying on the finite element method and the energy minimization principle. Specifically, we developed and implemented a modelling strategy that can be applied as a readily usable dimensioning tool with a potential to optimize and predict the mechanical behaviour of optical coating systems upon crack initiation and propagation.

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.

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.

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.

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 wood flooring sector, good surface mechanical properties, such as abrasion and scratch resistance, are prerequisite. Surface wood protection is provided by finishing systems. Despite coating improvement, scratches formation on wood flooring is unavoidable. A new approach to increase service life is to confer the self-healing property to the finishing system. The most common coatings used for prefinished wood flooring are acrylate UV curable 100% solids coatings. They usually have good mechanical properties and high cross-linking density. The objective of this study was to develop and evaluate an intrinsic self-healing formulation, which is applicable to wood flooring. For this purpose, acrylate formulations were developed with monomers and oligomers carrying hydroxyl groups. To meet the requirements of wood application, hardness, and polymerization conversion of coatings were evaluated. König pendulum damping tests provide information on coating hardness and flexibility. Results around 80 oscillations is acceptable for UV curable wood sealer. The chemical composition was studied by FT-IR spectroscopy while dynamical mechanical analysis (DMA) was performed to determine glass transition temperature and cross-linking density. The self-healing behavior was evaluated by gloss and scratch depth measurements. The formulation’s composition impacted the hydrogen binding quantity, the conversion, the Tg and the cross-linking density. The (hydroxyethyl)methacrylate (HEMA) monomer provided self-healing and acrylated allophanate oligomer allowed self-healing and cross-linking. This study demonstrated that it is possible to combine high cross-linking density and self-healing property, using components with low steric hindrance.

Coating architectures with a microstructure controlled on nanoscale enables the attainment of enhanced mechanical, tribological and other properties. In the present study, we fabricated nanolaminate ZrN/TiN systems with various modulation periods, L, ranging from 1 to 100 nm using pulsed DC magnetron sputtering. It was observed that a modulation period of L = 10 nm is a threshold value for the transition from a periodic to a solid solution structure. We demonstrate that the coatings with L < 10 nm displayed a single-phase solid solution with a Zr-rich composition of Ti0.35Zr0.65N. This indicates the effect of mixing and/or diffusion between the two phases that occurred during the film growth. The crystallite size was found to vary with the modulation periodicity: we obtained 11-12.5 nm for the Ti0.35Zr0.65N solid solution, and 14.5-25 nm for the laminate structure. The solid solution and interface strengthening were found to be the main cause of the hardening of the nanolaminate structure presenting a hardness of 32-35 GPa, significantly higher than for the individual TiN (21 GPa) and ZrN (16 GPa) single-layer coatings. The hard, solid solution system was found to exhibit the highest wear resistance corresponding to the highest values of the H/E and H-3/E-2 ratios related to a high resistance to plastic deformation and a high toughness. Finally, a model for the Ti0.35Zr0.65N solid solution phase formation related to internal residual stress is proposed.

Touchscreens are now commonplace around the world, and easy-to-clean (ETC) coatings are integral in ensuring an enhanced usability and interactivity with these devices. In the present work, we evaluate the durability and study the wear mechanisms of a fluorine-containing easy-to-clean coating on glass using an in situ tribometer (TribTik). The TribTik is equipped with a microscope lens and camera system that allows one to image, in real time, the contact area between the glass substrate and the abrading counterpart. Through this unique combination, the instantaneous coefficient of friction and the contact area's status can be monitored and correlated in situ. The in situ monitoring enables one to stop the abrasion cycles at critical stages of the wear process so that the morphology and composition of the wear tracks can be examined in an effort to understand the wear mechanisms of the ETC. We demonstrate that changes in the instantaneous coefficient of friction (COF) are correlated with changes in the in situ images. Critical stages of wear evolution are also identified via optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Raman analyses. The evolution of the ETC wear mechanism, from start to finish, was found to be described by the following sequence: (1) generation of unconsolidated debris, (2) formation of a layered tribofilm, (3) cracking of the tribofilm, and (4) general failure of the ETC and subsequent damage to the underlying glass substrate. Our study shows that, TribTik, a tribometry system with real-time imaging capability, is a powerful tool to characterize the tribological properties of coatings on touchscreens and/or display substrates.

Disbonding and delamination of Stellite hardfacing used in high-temperature valves have caused serious challenges in the power generation industry in recent years. To determine the microstructural factors that may contribute to the failures, Stellite 21 and Stellite 6 hardfacing alloys were deposited onto an F91 steel substrate using plasma-transferred arc welding. A series of aging experiments simulating service temperatures were conducted at temperatures between 550 and 650 degrees C for exposure times ranging from 1008 to 8760 h. The F91/S21 interface was found to be unstable during aging; a hard layer was formed, consisting mainly of three phases. This layer follows a parabolic rate of growth; its thickness increases as the square root of aging time. The activation energy was determined, which might be associated with carbon diffusion. Complementary characterization methods showed that the three phases in the hard layer are: a BCC-like intermetallic compound, FexCoy; a Cr-rich M23C6-type carbide; and an (Fe,Co)(Cr,Mo)-type sigma phase. The area fraction and the equivalent diameter of the M23C6 carbides increase with aging temperature and time, while the area fraction of the a phase decreases with temperature. Nanoindentation maps showed that both the M23C6 carbides and the sigma phase in the interfacial layer are significantly harder than the other phases. The sigma phase contributes more in the increase of the interfacial layer's hardness at lower temperatures than that at higher temperatures. These hard phases may affect high-temperature valve integrity.

Single splats of commercially pure Ti are deposited onto sapphire by cold spray under two spray conditions to achieve different in-flight powder velocities. The powders used have two morphologies: spherical powder (SP), manufactured by plasma gas atomization, and irregular powder (IP), manufactured by the Armstrong process, with a coral-like morphology. The adhesion strength of the single splats is measured by splat adhesion testing. By use of a specialized in situ scratch tester, interface failure during splat adhesion testing is observed through the sapphire substrate. Particle velocity does not significantly influence the adhesion strength and failure mechanism of SP splats. After deposition, the SP splat has an interface pore in its center which acts as an initiation site for crack propagation during splat adhesion testing. After failure, a well bonded portion of Ti remains on the substrate in the shape of a ring. IP splats deposited at low velocity show similar, well adhering, rings on the surface in localized locations scattered throughout the interface. An increase in velocity for IP splats led to an increase in adhesion strength and a nearly continuous well adhering interface. The behaviour of IP splats is understood by electron channelling contrast images of cross-sections where low velocities resulted in little change in microstructure while high velocities led to a highly deformed microstructure at the interface.

In the present work, we reviewed and studied the fabrication process of hard erosion resistant TiN protective coatings on the inner surfaces of narrow tubes using a Non-Line-Of-Sight (NLOS) approach. Initially, while evaluating the growth of DLC and TiN by the CW RF PECVD process, we found that the use of a hydrocarbon precursor to obtain DLC provides uniform film thickness along the tube axis, while the use of the TiCl4 precursor for TiN leads to a significant thickness nonuniformity of 80% and large differences between the film properties in the middle of the tube compared to the edges. Following detailed plasma analysis, we demonstrate that the uniformity can be substantially enhanced by applying pulsed-DC PECVD, while uniform (better than 20%) hard TiN films were prepared by low-frequency (5 kHz) pulsed-DC PECVD. The TiN films (about 12 μm thick), systematically studied by SEM, XRD, and nanoindentation, when prepared under optimized conditions, exhibit high hardness and reduced Young's modulus (25 and 225 GPa, respectively) corresponding to the (111) preferred crystallographic orientation, and a very low Cl contamination (<3%). The film uniformity has been correlated to that of the discharge light emission intensity along the tube axis, and the microstructural evolution is interpreted in terms of surface densification due to substrate temperature and ion bombardment of the inner surface. The pulsed DC PECVD NLOS process providing TiN coatings with a hardness markedly higher than the hardness of the erodent particles and with a solid particle erosion resistance increased by a factor of >15 compared to the bare substrate is well suited for the protection of aerospace, manufacturing, and other critical components with a complex shape of inner surfaces.

Materials are the key to develop advanced ultra-supercritical (A-USC) steam generators. Operating at temperature up to 760 degrees C and sustained pressure up to 4500 psi. Pressure vessel and piping materials may fail due to creep, oxidation, and erosion. Valves are particularly subjected to loss of function and leakage due to impermeant of the sealing surfaces. New materials, less susceptible to the above damage modes are needed for A-USC technology. Two Ni-based superalloys have been identified as prime candidates for valves based materials. Hardfacing is applied to sealing surfaces to protect them from wear and to reduce friction. Stellite 6 (Cobalt-based alloy) is the benchmark hardfacing owing to its anti -galling properties. However, the latest results tend to indicate that it is not suitable for high pressure application above 700 degrees C. An alternative hardfacing will be required for A-USC. New Ni- and Co- based alloys are being developed for applications where extreme wear is combined with high temperatures and corrosive media. Their chemistry accounts for the excellent dry-running properties of these alloys and makes them very suitable for use in adhesive (metal -to metal) wear. These new alloys have better wear, erosion, and corrosion resistance than Stellite 6 in the temperature range 800 degrees C similar to 1000 degrees C. As such, they have the potential to operate in A-USC. Velan recently developed an instrumented high temperature tribometer in collaboration with Polytechnique Montreal to characterize new alloys including static and dynamic coefficients of friction up to 800 degrees C. We present herein the methodology that has been devolved to explore the effects of elevated temperature on the tribological behavior of those advanced material systems, with the goal of capturing the basis for the specification, design, fabrication, operation, and maintenance of valves for A-USC steam power plants.

The load-carrying capacity and wear resistance of a duplex-coated 316 stainless steel were determined, and a finite element numerical approach was developed to predict and corroborate experimental observations. Low-strength alloys are generally used for highly demanding valve applications due to their superior chemical stability, galvanic corrosion resistance, and lower susceptibility to stress corrosion cracking failure. Hardfacing (using thermal spraying, laser cladding, or plasma transferred arc welding) is currently the most common solution to protect valve components. Hardfacing provides a thick, hardened case that significantly improves tribological performance. However, hardfaced layers provide lower wear resistance compared to vacuum-deposited hard coatings. One solution to further improve hardfacing performance is a duplex approach, which combines the two processes. This study investigates the following materials: a 316 stainless steel base hardfaced with laser-cladded Co-Cr superalloy and topped with a CVD nanostructured W-WC coating. Tribological properties of three configurations were assessed for their ability to delay initiation of plastic deformation and surface cracking under quasistatic loading and for their resistance to dry reciprocal sliding wear. The results demonstrate that finite element modeling allows numerical prediction and comparison of the load-carrying capacity and wear resistance of duplex-coated AISI 316 stainless steel.

Crystalline AlN films are very attractive due to their properties such as high thermal stability and relatively high hardness and piezoelectric response. However, the deposition of dense textured AlN films with superior quality at a high deposition rate remains a challenge. In the present work, a reactive low duty cycle pulsed direct current magnetron sputtering (LDMS) process was employed to deposit AlN films on glass and silicon substrates. An arc-free discharge on the Al target was achieved by using short voltage pulses of 10 μs at a low duty cycle of 10%. The authors optimized the deposition conditions in terms of reactive gas flow, working pressure, average target power, substrate temperature, substrate bias, and the level of target erosion. With the optimized deposition conditions, the authors were able to obtain transparent crystalline AlN films with strong (002) preferential orientation and very good optical and mechanical properties: The AlN films with the highest refractive index of 2.1 present a hardness of up to 22 GPa and a low residual stress of ≈+300 MPa. Meanwhile, a relatively high deposition rate of ≈45 nm/min was achieved. A systematic comparison of the LDMS process with five other magnetron sputtering approaches working at optimized conditions indicated superior performance of the LDMS technique. This approach leads to the most promising results in terms of discharge stability, deposition rate, and film properties, and thus, it shows much promise for reactive deposition of dielectric materials and hard optical coatings.

In the present study, the tribological properties of High Velocity Oxy-Fuel (HVOF) coatings prepared from Fe3Al-based composite powders were investigated. The iron aluminide matrix of the composite powders was reinforced with TiN and TiB2 particles made using two different processing routes: a) an in situ method where fine ceramic particles were formed in the matrix by the reaction between Ti and BN, and b) an ex situ method where preformed coarse TiN and TiB2 particles were added to the matrix. The tribomechanical performance of the coatings was assessed using indentations and pin-on-disc wear tests. Compared to ex situ samples, the Fe3Al-based coatings strengthened with in situ ceramic particles exhibit higher microhardness and wear resistance regardless of the sliding velocity. The presence of voids, cracks and scratches/grooves in the wear track of the in situ coatings and the coating material transferred to the corresponding counterpart suggest that coatings with fine reinforcing particles fail predominantly via delamination and adhesive wear mechanisms. In the case of the ex situ coatings, the presence of a significant amount of hard ceramic particles within the wear track indicates that abrasive wear plays a dominant role in the degradation mechanism. Oxidation wear also contributed to material removal at high sliding velocity since transfer materials inside the wear track contain a high oxygen content compared to the unworn region regardless of the coating type.

In this study we present a new in situ real-time approach to perform and analyze scratch tests of transparent coating/substrates systems. This method allows for the observation of the contact region during the scratching process. As an example, thin TiO2 layers exhibiting stress levels ranging from tensile to compressive were deposited by ion beam assisted evaporation onto plastic substrates. Failure processes obtained using an increasing and a novel decreasing load scratch sequences were then linked to the internal stress in the coatings allowing one to draw a stress management diagram and to evaluate the yield stress of the TiO2 layers. This work enhances the understanding of the optical films' failure mechanisms, and outlines a new pathway to increase measurement reproducibility.

Composite SiO2/SiOCH nanolaminates were deposited on plastic substrates using electron beam evaporation and ion beam assisted chemical vapor deposition processes, respectively. The hybrid mineral/organic SiOCH films were synthesized from an OMCTS precursor, leading to refractive index values similar to that of the pure SiO2. Optical and tribo-mechanical properties of the composite nanolaminates with constant total thickness were studied as a function of the number of SiO2/SiOCH bilayers within the stack. We found that by adjusting the periodicity, one can tailor the mechanical properties of the material, leading to improved scratch resistance witnessed by an increase of the critical load at delamination from 8N to 11N. Based on these findings, such nanolaminate material can easily replace monolithic SiO2 layer in interference stacks to enhance the tribological behavior of optical filters.