Ceramic films hardness

There is considerable experimental work in both metallic and ceramic films, showing that such internal stresses can greatly increase the measured hardness. The simplest explanations are in terms of superimposing an inplane stress on the overall maximum shear stress under the indenter, although Pharr (Bolshakov eta ., 1996 Tsui et al 1996), looking at nanoindentation of A1 films, considers the effect to arise due to pile-up around the indenter, causing the actual depth of penetration, and hence area of the indentation, to be greater than that calculated. 

Bis-trimethylsilylcarbodiimide is used as a monomer in the synthesis of silicon car-bodiimide polymers used as precursors for ceramics. Also, hard silicon carbonitride films are obtained by RF plasma-enhanced chemical vapor deposition of bis(trimethyl-silyl)carbodiimide. ... 

The objective of this research Is the examination of the effects of ion bombardment on the structure of thin ceramic films on ceramic substrates. The material combinations will Include oxide films that have (a) no solid solubility, (b) limited solid solubility, and (c) complete solid solubility with the substrate material (also an oxide). Techniques for determination of elastic and plastic properties of thin films or coatings on ceramic substrates and for the determination of the strength of the bond between the film and substrate, which are currently being developed, will be used to determine the hardness, elastic modulus, and adherence of each material combint tion. The main testing techniques will be the ultra-low load micro-indentation tester (Nanaindenter) and thermal cycling tests. 

In conclusion, one should choose an appropriate multilayer system for different application purposes. For the case of fatigue wear, multilayer films consisting of two hard materials with different shear modulus, such as DLCAVC multilayer film [115], would satisfy the requirement for wear resistance. While for abrasive wear, multilayer films consisting of hard ceramic layers and soft metal layers, such as TiN/Ti and CrN/Cr [116,117] multilayer films are more competent. 

The importance of materials science to U.S. competitiveness can hardly be overstated. Key materials science areas underlie virtually every facet of modem life. Semiconductors underpin our electronics industry. Optical fibers are essential for communications. Superconducting materials will probably affect many areas ceramics, composites, and thin films are having a big impact now in transportation, construction, manufacturing, and even in sports—tennis rackets are an example. 

It can be seen that ceramic multilayer structures have been produced with increments of the hardness of up to 60 GPa, increasing the hardness by up to a factor of almost 3. Initial work in this area has developed a number of ideas, such as the effect of modulus mismatch, which in some cases give good agreement with the models suggested but in many others do not. It is suggested that at least some of this discrepancy can be accounted for by differences in the microstructure and residual stress-state of the film, both of which are often poorly characterized. Furthermore there is very little direct evidence about how these structures deform and in particular about how different layers must be strained in order to accommodate the indenter when it is pressed into the sample. Further advances in this area will require the greater use of numerical techniques to analyse the complex stress and strain behaviour under the indentation, coupled with the use of recently developed techniques that allow the localized deformation behaviour to be observed in detail. 

The process itself is more art than science. There is hardly any information in the open scientific literature. Most publications have to do with spray drying of ceramic powders (ref. 15 and references therein, ref. 16). There are also some standard books about spray drying [17]. Important process parameters are the viscosity of the liquid, the solids content of the suspension, the film-forming characteristics, the type of atomizer, the temperature, the rotation speed of the wheel, gas velocity, etc. 

The initial properties of bonded films as applied vary considerably depending on the type of binder, the ratio of binder to molybdenum disulphide and other components, the nature of the drying or curing process, and the way in which the film was applied, in particular there is a wide variation in hardness from very soft (silicones and alkyds) to very hard (metals and ceramics), and this has important implications for the way in which a film is used and even the purpose for which it is used. 

Numerous ceramics are deposited via chemical vapor deposition. Oxide, carbide, nitride, and boride films can all be produced from gas phase precursors. This section gives details on the production-scale reactions for materials that are widely produced. In addition, a survey of the latest research including novel precursors and chemical reactions is provided. The discussion begins with the mature technologies of silicon dioxide, aluminum oxide, and silicon nitride CVD. Then the focus turns to the deposition of thin films having characteristics that are attractive for future applications in microelectronics, micromachinery, and hard coatings for tools and parts. These materials include aluminum nitride, boron nitride, titanium nitride, titanium dioxide, silicon carbide, and mixed-metal oxides such as those of the perovskite structure and those used as high To superconductors. 

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