Over the past few years a wide range of coatings and surface treatments have been developed to enhance component performance. Increasingly coating architectures are becoming more complex and multilayer, superlattice and graded coating systems are becoming widely available. This offers so many potential coating variants that it is almost impossible to envisage trying all the possibilities to optimise performance. The need for predictive performance models has never been more acute but model development has generally lagged behind the introduction of new coatings. For tribological coatings the mechanics of contact is particularly important if performance is to be understood. This paper briefly reviews developments in numerical simulation and extends recent modelling developments in an energy-based predictive model for the hardness and Young's Modulus of a coated system. The model predictions can be improved by considering the fracture behaviour of the coating.

The shape memory and superelastic effects of martensitic and austenitic NiTi alloys were studied by instrumented indentation experiments. The shape memory effect was quantitatively characterized by the thermo-activated depth recovery ratio of the residual indentation depth. The superelasticity of austenitic NiTi was quantitatively characterized by the depth and work recovery ratios obtained from the load-displacement curves. The shape memory and superelastic effects under different indenters (Berkovich, Vickers, and spherical) and loads were rationalized using the concept of the representative strain and maximum strain. This study demonstrates that instrumented indentation techniques are useful in the quantitative characterization of the shape memory and superelastic effects in micro- and nano-meter length scale.

We have obtained nanostructured hydroxyapatite thin films on titanium alloy substrates by pulsed laser deposition. Deposition was carried out using a KrF excimer laser (248 nm) with the energy density of 4 – 7 J/cm2 at substrate temperatures in the 550°C - 650°C range. The crystallinity of the coatings was probed by X-ray diffraction. Phase transitions from hydroxyapatite to other calcium phosphate compounds were observed with varying the substrate temperature during the growth process. Scanning electron microscopy revealed thin films made up of partially sintered nanoscale grains. The average size of nanoscale grains increased significantly with film thickness, suggesting a growth mechanism involving the coalescence of nanoscale grains. As the laser energy density increases, the hydroxyapatite crystallites in the coatings are oriented preferentially along the c-axis perpendicular to the substrate. Mechanical properties of the highly c-axis oriented coatings such as hardness and Young's modulus were studied by using nanoindentation technique.

The performance of rolling element bearings is enhanced by the application of nanocomposite coatings that are composed of metal carbides incorporated into an amorphous hydrogenated carbon matrix (MC/a-C:H). When applied to the rolling elements in tapered roller bearings, MC/a-C:H coatings were found to help increase fatigue life, rib-roller end scuffing resistance, and false brinelling resistance in poorly lubricated environments. This series of performance tests were conducted with both coated and uncoated rollers. The results are attributed to the minimization of adhesive interactions and desirable counterface micro-polishing due to the presence of the thin hard coatings on rollers in the bearings.

Intrinsic stress in a film-substrate system can have deleterious effects. To facilitate an understanding of stress generation and control film quality, measuring film stress is essential. In recent years research laboratories and industry have increasingly adopted indirect methods, which are usually based on the measurement of substrate deformation. The film stress is calculated by equations relating the stress to the deformation, such as the well-known Stoney's equation. However, when the two principal stresses at each point in the film plane are not equal and their distribution is nonuniform, the local application of Stoney's equation does not provide correct stress results. A numerical technique is presented, which overcomes these limitations and makes accurate stress determination possible.

Double-wall carbon nanotubes (DWCNTs) and single-wall carbon nanotubes (SWCNTs) have been synthesized by the DC abnormal glow discharge plasma CVD method using methane and hydrogen gas on a Si substrate coated with catalyst. Fe(NO3)2 and Mo(CH3COCHCOCH3)2O2 with Al2O3 support were used as catalysts. The growth temperatures were 1000 − 1400°C and the gas pressures were 9kPa - 13kPa. DC plasma was generated between an array of four W cathodes and a Cu disk anode, and the applied power was 4000–10000W (2.5–4.0A per cathode, 400–800V). Samples were characterized by high-resolution transmission electron microscopy (HRTEM) and micro-Raman spectroscopy using 514.5 nm Ar ion laser excitation. The HRTEM images showed that many carbon nanotubes had a concentric cylindrical graphene layer structure (DWCNTs). We measured the diameters of the carbon nanotubes (CNTs) from HRTEM images. The outer diameter of the DWNT was 1.52–1.64nm and the inner diameter of the DWNT was 0.73–0.81nm.

Two new testing techniques, one is for evaluating the ceramics-ceramics and metal-ceramics bond strength, and one is for determining the elastic modulus and fracture strength of brittle coating, were developed respectively. Tensile and shear bond strength were obtained by using compression load on a cross-bonded samples. Rectangular section specimens with surrounding coating or single face coating were used for evaluating the mechanical properties of brittle coating. Analytical formula for the modulus calculation of coatings was derived based on the mechanics of materials. Stress analysis of coated beam provides the expression of the critical stress to fracture in the coating layer. Experimental results confirmed the reliability and convenience of this simple technique.

A synergetic way of combining superior properties of ceramics with that of metals is to apply ceramic coatings over metallic substrates. Also, ceramic coatings provide better protection of the covered metal under concomitant corrosion and wear conditions. Of all the advanced ceramic materials, Al2O3 is widely used due to its low cost and availability in high purity forms. But the alumina coatings made through Air Plasma Spray suffers from major disadvantages such as presence of metastable γ-Al2O3 phase, high surface roughness and porosities. In this paper, we have shown the feasibility of transforming the γ-Al2O3 phase present in the as-sprayed coatings to a thermodynamically stable α-Al2O3 phase. A continuous wave CO2 laser having maximum power of 500W was used to provide a surface specific heating without affecting the metallic substrate. In addition to XRD, Raman scattering and photoluminescence investigations were carried out using a Ar+ laser to confirm the restoration of alpha phase and the reduction in porosity respectively. Also, 1 mW He-Ne laser operating in TEM00 mode was used to examine the reduction of surface roughness using laser scattering technique. The intensity of the specular reflection was used to quantify the surface roughness. Both reduction in surface roughness and porosity were evaluated using SEM micrographs taken on the surface and cross section of the coatings.

The amorphous/polycrystalline Si3N4/CrN and Si3N4/TiN nano-structured multilayer films have been fabricated by RF reactive magnetron sputtering. The microstructure and properties of these films were measured by XRD, HRTEM and nano-indenter There is no superhardness effect in the Si3N4/CrN multilayers. The hardness values of Si3N4/CrN multilayers are between those of the constituent CrN and Si3N4 films at a substrate temperature of 20∼C, and are a little higher than those of Si3N4 films at a deposition temperature of 500°C. However, the superhardness effect was found in Si3N4/ TiN multilayers. The hardness of Si3N4/ TiN multilayers is affected not only by modulation periods, but also by layer thickness ratio and deposition temperature. The maximum hardness value is about 40% higher than the value calculated from the rule of mixtures at a deposition temperature of 500°C and a layer thickness ratio (lSi3N4/ lTiN) of 3 / 1. Based on experimental results, the hardening mechanisms in these multilayers have been discussed.

We have designed a unique synthesis procedure to create nonomaterials of uniform grain size and control the chemistry of interfaces between the grains. The metastability of nanocrystalline materials is a major challenge which can be addressed by controlling the chemistry of interfaces. The hardness of these films having a uniform size was measured as a function of grain size using a nanoindentation technique. It was found that hardness increased with decreasing grain size in accordance with Hall-Petch model. However, below a critical grain size we observed a decrease or softening with a further decrease in grain size. These observations in metals and ceramics are modeled in view of intragrain deformation (Hall-Petch regime) and intergrain deformation (grain boundary shear/sliding )in the softening regime. Since we can change the alloying of interfacial region, we can address the metastability as a function of temperature, which is crucial from applications viewpoint of these materials.

Effects of the indent depth, the distance between the indent and the grain boundary, grain sizes, and crystallographic orientations on the microhardness of annealed coarse-grained polycrystalline α-brass were investigated using a Vickers indenter with indents much smaller than the α-brass grains (ranging from 80 μm to 550 μm). It is found that the microhardness of α-brass crystals shows a strong dependence on the indentation depth when it is smaller than 5 μm and a very weak dependence on both the distance between the indent and the grain boundary and the grain size when the indentation depth is about 5 μm and more. No significant dependence of the microhardness on the crystallographic orientations was observed in the fourteen grains of different orientations studied in this investigation.

Shear measurements were performed on mica surfaces with molecularly thin films of squalane confined between them. Squalane is a branched hydrocarbon liquid that can be in the liquid, glassy or liquid-crystalline state under confinement. The friction forces, especially the transitions between smooth and intermittent (e.g., stick-slip) sliding, were measured over a wide range of applied loads and sliding velocities. The results reveal that, depending on the conditions, qualitatively different behavior can arise in the same system. These include both abrupt and continuous transitions, short and very long transient effects, and chaotic or saw-tooth stick-slip. The differences between these branched and simpler molecules are compared, and the results are analyzed in terms of rate-and-state models traditionally used in the analysis of seismic phenomena.

Two series of CrNx coatings have been deposited in an industrial PVD set-up. It is shown that for an increased ion bombardment on the growing film the hardness (H) and Young's modulus (E) are independent on composition. For these hard coatings the elastic strain to failure or plasticity limit (H/E) is 0.11. The coating fails long before it is stretched to its plasticity limit. Deformation of the coating by 1% already leads to crack formation. It is argued that the cause of this failure is the low work of fracture of the coating combined with flaws in the coating.

This research focuses on identifying the fracture mechanism in thin film silicon membranes and PZT on silicon composite structures under static and dynamic loading conditions. Square silicon membranes with a 3mm side-length and thickness between 1.5 and 3.0μm, with and without 1.5μm of PZT, were pressurized to failure while laser interferometry was used to determine the maximum strain at failure. The strain at fracture of silicon membranes, initiating from the sharp corner radius inside the micromachined cavity, was improved from 0.37% to 0.8% by an isotropic etch of the sharp corner. Fracture of PZT on silicon membranes, tested at the mechanical resonant frequency suggested that fracture initiates in the blanket PZT layers under reversed bending. Etching the PZT from high strain regions along the membrane surface improved the strain at failure of the composite device by 40%.

In the present research, the adhesion properties and failure mechanisms for a ductile thin film on a silicon substrate (Ni/Si) are studied experimentally, and are simulated theoretically. In the experimental research, the relations of the horizontal driving force, vertical displacement and the frictional coefficients with horizontal displacement are measured. Furthermore, the variation of the total energy release rate and the frictional coefficient between contact surfaces are measured through obtaining a frictional effect law. The law displays that the frictional influences on the energy release rate of the total system weakly depend on the thin film thickness. This conclusion leads to that the frictional effect can be eliminated in the toughness ratio relation approximately. So that one can directly obtain the interfacial adhesion toughness from measurements in the micro-scratching test. In addition, the micro-scratching process for the ductile thin film/brittle substrate systems is simulated using the double cohesive zone model. Prediction results of the energy release rate are obtained, and are compared with the experimental results obtained in the present research.

TiN-AlN binary-components have attracted a lot of interests in coatings of high speed cutting tools, due to their higher oxidation resistance, higher hardness, lower internal stresses and better adhesion. Especially, nanometer-scale multilayer structures of AlN/TiN show superior structural and mechanical properties due to their tremendous interface area and become one of the promising candidates for superhard coatings. Here we present a novel method to grow highly aligned TiN/AlN superlattice by pulsed laser deposition. In this method TiN and AlN targets are arranged in a special configuration that they can be ablated in sequence, giving alternate layer by layer growth of TiN(1nm)/AlN(4nm). X-ray diffraction and transmission electron microscopy (TEM) analysis showed the structure to be cubic for both TiN and AlN in the nanoscale multilayers. Microstructure and uniformity for the superlattice structure were studied by TEM and Scanning transmission electron microscopy with Z-contrast (STEM). Nanoindentation results indicated a higher hardness for this new structure than pure AlN and rule-of-mixtures value. Four point probe electrical resistivity measurements showed overall insulating behavior.

The alternation of chitin layers with various compounds allows nature to create novel materials with selective refractive properties. Various organisms employ layered materials for survival; for example, in butterflies such materials cause the apparent disappearance and reappearance during flight to evade predators. The selective light refraction is achieved through control of the thickness and index of refraction of the multiple layers. With the ultimate goal of reproducing these layers, thin single films of chitosan, the soluble form of chitin, and poly(allyl amine) have been prepared and their optical properties analyzed. Ellipsometry, reflectance IR, reflectance spectroscopy, SEM and software modeling were used to characterize these films. Possible applications for optical layered materials range from medical diagnostics to environmental monitoring.

Nanocrystalline diamond films deposited by microwave plasma chemical vapor deposition (MWPCVD) method were observed on Si substrates implanted with phosphor (P) and boron (B) ions at room temperature via scanning electron microscopy (SEM). The relations between the species, energies and doses of implanted impurities and the nucleation, grain size and morphology of diamond were studied. The results present that different nucleation density from 106 cm-2 to 109 cm-2 can be obtained on implanted and unscratched Si, which is larger of 3–6 magnitude orders than that on mirror-polished Si. The nano-structured diamond films can be deposited on scratched Si substrates implanted by higher concentration of phosphor and boron ions. The grain sizes of nano-structured films can be adjusted by controlling the implanted energies and doses, and nano-structured films can be synthesized with low impressive stress. The Raman spectroscopy was employed to analysis the phase purity of nano-structured film, which shows a broad peak at around 1150 cm-1 relative to the nano-structured and tetrahedrally bonded carbon network.

New Low-K dielectric constant materials development is underway. Introducing porosity is one of the ways to lower the dielectric constant. Those are typically spin coated organic filled glasses. The pore size is on the order of a several nanometers and pore introduction compromises mechanical properties of low-K thin films, especially fracture toughness, as these materials are typically brittle.

In our previous studies we have evaluated different low-K dielectric constant materials in terms of their mechanical properties using nanoindentation. It was interesting to see that for a large range of various porous low-K materials the modulus-to-hardness ratio was constant. It was also found that the indenter contact is mostly elastic, as the loading and unloading portions of the load-displacement curve did not show any hysteresis, following indentation depth to the 3/2 power load dependence. Based on these results current analysis explains the observed constant modulus-to-hardness ratio.

The paper also describes the “incompressible” pore effect. As a particle gets smaller, the yield stress increases due to the Hall-Petch effect, but for the nanometer-size particles there are also high surface energy contributions that prevent is from deforming plastically. The same approach can be applied for a nanometer size pore elastic deformation, thus we call it an “incompressible” pore concept.

Many materials properties are tailored by controlling the chemical reactivity of surfaces. Consequently, through chemically active nanopatterning, surfaces can be engineered with nanoscale spatial resolution. This paper describes three techniques that enable the chemical reactivity of silicon surfaces to be customized down to the single molecule limit using scanned probe microscopy (SPM). All three techniques use chemically inert hydrogen passivated silicon as a starting substrate. Injected electrons and/or electric field from a conductive SPM tip locally disrupt the passivation, thus allowing the surface chemistry to be modified. Using ultra-high vacuum scanning tunneling microscopy, feedback controlled lithography leads to electron stimulated desorption of hydrogen from Si(100)-2×1:H with atomic resolution. The resulting dangling bonds preferentially react with gas phase molecules, enabling pre-determined self-directed growth of styrene molecular wires. In ambient conditions, conductive atomic force microscopy (cAFM) is used to grow nanoscale hydrophilic domains on Si(111):H via anodic field induced oxidation (FIO). Due to the chemical contrast between the hydroxyl terminated oxide and the hydrophobic Si(111):H surface, octadecyltrichlorosilane selectively binds to FIO nanopatterns. The final nanolithographic scheme, called liquid phase nanolithography (LPN), employs cAFM on surfaces submerged in organic solvents. By encapsulating the tip-sample junction in a solvent with low water and oxygen solubility, anodic oxidation is suppressed, thus enabling direct molecular attachment to the silicon surface from the liquid phase. In this work, LPN has been used to nanopattern undecylenic acid methyl ester. Nanoscale variations in the frictional properties induced by LPN and FIO are directly measured with lateral force microscopy. Through readily available and well-established chemical protocols, this nanolithography toolkit enables arbitrary materials, including polymers and biological molecules, to be covalently bound to silicon with nanometer spatial resolution.