Al-Pt MOCVD coatings for the protection of Ti6242 alloy against oxidation at elevated temperature

Results on isothermal oxidation at 873K for 90 h of Al-Pt coatings on Ti6242 coupons are reported. These coatings were obtained by low temperature, low pressure metalorganic chemical vapor deposition using Me3(MeCp)Pt(VI) and dimethylethylamine alane. Three coating architectures were investigated, namely pure Al, Pt and Al sequential sublayers, and co-deposited Al and Pt. Oxidation kinetics revealed a strong transient oxidation regime followed by a diffusion driven parabolic one. Such coatings allow to decrease oxidation kinetics more than one order of magnitude compared with those of the bare Ti6242. Scanning electron microscopy, second ion mass spectrometry, X-ray diffraction and transmission electron microscopy revealed that these coatings present a rough surface morphology. They are dense, they develop scales composed of γ-Al2O3 and δ-Al2O3 and they prevent titanium diffusion from the alloy to the surface. It is concluded that coatings produced by this process show promise for use as effective protection against oxidation of Ti6242 alloys and consequently they may raise the maximum operating temperature tolerated by corresponding parts in helicopter turboengines

Preliminary study of a solar selective coating system using black cobalt oxide for high temperature solar collectors

Black cobalt oxide coatings (high solar absorptance layer) were deposited on thin layers of silver or gold (low emittance layer) which had been previously deposited on oxidized (diffusion barrier layer) stainless steel substrates. The reflectance properties of these coatings were measured at various thicknesses of cobalt for integrated values of the solar and infrared spectrum. The values of absorptance and emittance were calculated from the measured reflectance values, before and after exposure in air at 650 C for approximately 1000 hours. Absorptance and emittance were interdependent functions of the weight of cobalt oxide. Also, these cobalt oxide/noble metal/oxide diffusion barrier coatings have absorptances greater than 0.90 and emittances of approximately 0.20 even after about 1000 hours at 650 C

Improving turbine engine compressor performance retention through airfoil coatings

In order to evaluate the potential effectiveness of coatings in limiting erosive damage to compressor airfoils, an effort was initiated to evaluate candidate coatings for substrate alloys typically used in commercial engine high compressor blades. Laboratory and rig erosion testing of plasma deposited and diffusion coatings described in this paper have shown the potential of a two to four fold improvement in erosion life. The selective application of these coatings to approximately the outer third of the airfoil avoids coating the fatigue critical region of the blade, thus providing erosion resistance potentially without compromising the fatigue strength of the blade. Both the plasma and the diffusion coatings also offer the advantage of low initial cost and a multi-source production base

Vapor grown silicon dioxide improves transistor base-collector junctions

Vapor grown silicon dioxide layer protects base-collector junction in silicon planar transistors during the emitter diffusion process. This oxide fills in any imperfections that exist in the thermally grown oxide layer and is of greater thickness than that layer. This process is used to deposit protective silicon dioxide coatings on optical surfaces

Mechanisms of High Temperature Degradation of Thermal Barrier Coatings.

Thermal barrier coatings (TBCs) are crucial for increasing the turbine inlet temperature (and hence efficiency) of gas turbine engines. The thesis describes PhD research aimed at improving understanding of the thermal cycling failure mechanisms of electron beam physical vapour deposited (EB-PVD) yttria stabilised zirconia (YSZ) TBCs on single crystal superalloys. The research consisted of three different stages. The first stage involved designing a coupled one-dimensional thermodynamic-kinetic oxidation and diffusion model capable of predicting the concentration profiles of alloying elements in a single-phase γ nickel-rich Ni-Al-Cr ternary alloy by the finite difference method. The aim of this investigation was to improve the understanding of interactions between alloying species and developing oxide. The model demonstrated that in the early stages of oxidation, Al consumption by oxide scale growth is faster than Al replenishment by diffusion towards the scale, resulting in an initial Al depletion in the alloy near the scale. The second stage involved a systematic study of the life-time of TBC systems on different single crystal superalloys. The study aimed at demonstrating that the compatibility of modern nickel-based single crystal superalloys with TBC systems is influenced strongly by the content of alloying element additions in the superalloy substrate. The results can be explained by postulating that the fracture toughness parameters controlling decohesion are influenced strongly by small changes in composition arising from interdiffusion with the bond coat, which itself inherits elemental changes from the substrate. The final stage of study involved a detailed study of different bond coats (two β-structured Pt-Al types and a γ/γ’ Pt-diffusion type) in TBC systems based on an EB-PVD YSZ top coat and a substrate material of CMSX-4 superalloy. Generation of stress in the thermally grown oxide (TGO) on thermal cycling, and its relief by plastic deformation and fracture, were investigated experimentally in detail

Development and fabrication of lithium-doped solar cells

The application of contacts and coatings after lithium diffusion provides good electrical output and satisfactory contact adhesion by sintering for short times at temperatures less than the lithium diffusion temperature. High output and repeatability are obtainable from both oxygen-rich and oxygen-lean silicon. These fabrication sequence alterations have led to higher cell output, better appearance, and increased contact strength

Отримання комплексних дифузійних шарів з використанням композиційних насичуючих середовищ

The process of obtaining aluminum, titanium, siliconized, nickel layers is an effective method to increase the reliability and durability of machine parts, tools by creating protective layers on the surface of workpieces with a unique set of physic-chemical properties. One of the most effective methods for producing diffusion layers, which have high mechanical, physical, and chemical characteristics, is diffuse saturation of the surface of metals using composite saturating environments. The large amount of theoretical and experimental material based on the use of precision methods for studying the phase and chemical composition of a diffusion layer allows us to state that in many cases of the chemical-thermal treatment of the formation of a diffusion layer it does not obey equilibrium conditions, but proceeds intermittently and can begin with the formation of a higher phase or medium composition. The structure of the diffusion layer in this case is not equilibrium. Among the various factors influencing the mechanism of formation of a diffusion layer with an uneven structure, the main ones are the initial conditions preceding the process of diffusion of elements into a metal, directly or indirectly depend on a number of physicochemical and kinetic factors of saturation, especially significant when it comes to compositional saturating environment presented in this study. Copper-based alloys served as initial data for the study. Based on the analysis of the requirements for the layer and the selected method of saturation of the metal to obtain a diffusion layer, the method of diffusion of surface saturation from a solid phase in an active gas medium is selected. This method provides high surface quality, and it is the simplest and most effective in laboratory practice, is well reproduced in a production environment, and it does not require special sophisticated equipment, realizing it.Процес отримання алюмінієвих, титанових, силіційованих, нікельованих шарів є ефективним методом підвищення надійності та довговічності деталей машин, інструментів за рахунок створення захисних шарів на поверхні оброблюваних деталей, які мають унікальний набір фізико-хімічних властивостей. Одним з найбільш ефективних методів отримання дифузійних шарів, які володіють високими механічними, фізичними та хімічними характеристиками, є дифузійне насичення поверхні металів із застосуванням композиційних насичуючих середовищ. Наявний великий теоретичний і експериментальний матеріал, який ґрунтується на застосуванні прецизійних методів дослідження фазового і хімічного складів дифузійного шару, дозволяє стверджувати, що у багатьох випадках практики хіміко-термічної обробки утворення дифузійного шару не підкоряється рівноважним умовам, а протікає переривчасто і може розпочатися з утворення фази вищого або середнього складу. Структура дифузійного шару в цьому випадку не є рівноважною. Серед різних чинників, що впливають на механізм формування дифузійного шару з нерівномірною структурою, головними є початкові умови, передуючі процесу дифузії елементів у метал, які прямо або побічно залежать від ряду фізико-хімічних і кінетичних чинників насичення, особливо значимих, якщо йдеться про композиційне насичуюче середовище, представлене в цьому дослідженні. Сплави на основі міді служили вихідними даними для вивчення. На основі аналізу вимог до шару та обраного способу насичення металу для отримання дифузійного шару обрано метод дифузії насичення поверхні від твердої фази в активному газовому середовищі. Цей метод забезпечує високу якість поверхні, і він є найпростішим і найбільш дієвий у лабораторній практиці, добре відтворюється у виробничих умовах, і він не вимагає спеціального складного обладнання, реалізуючи його

Corrosion Resistance of Steel/Zinc with Silicate Nanoparticles/Polyurethane Paint Systems in NaCl Solution

Surface characteristics and corrosion behaviour of bare electrogalvanized steel coated with polymer/nano-silicate particles added to the electrogalvanizing bath were studied by scanning electron microscopy (SEM), energy dispersive spectrometer (EDXS) and electrochemical impedance spectroscopy (EIS). After applying a barrier polyurethane paint, the paint hardness, porosity, flexibility, colour, gloss, blistering and rusting degrees, and anticorrosive protective properties in 0.05 mol·L-1 NaCl solution were also evaluated. The results correlated well and, being demonstrative of the very slow deterioration rate of the immersed coated electrogalvanized steel, they enabled to assume that if a chemically analogous but thicker coating system was applied; it could be an acceptable alternative in real service conditions.Fil: Célia R. Tomachuk. Energy And Nuclearresearch Institute; BrasilFil: Elsner, Cecilia Ines. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; ArgentinaFil: Di Sarli, Alejandro Ramón. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; Argentin

Oxygen diffusion barrier coating

A method for coating a titanium panel or foil with aluminum and amorphous silicon to provide an oxygen barrier abrogating oxidation of the substrate metal is developed. The process is accomplished with known inexpensive procedures common in materials research laboratories, i.e., electron beam deposition and sputtering. The procedures are conductive to treating foil gage titanium and result in submicron layers which virtually add no weight to the titanium. There are no costly heating steps. The coatings blend with the substrate titanium until separate mechanical properties are subsumed by those of the substrate without cracking or spallation. This method appreciably increases the ability of titanium to mechanically perform in high thermal environments such as those witnessed on structures of space vehicles during re-entr