The textures of two IF steels and a high purity $ alpha$-iron were determined after deformation in torsion over the temperature range 20-840$ sp circ$C. The three characteristic bcc torsion fibres are described in detail and the locations of some important ideal orientations are identified on the $ {110 }$ pole figure. At room temperature, these are the F(110)(001), J1 (011) (211), J2 (110) (112), D1 (112) (111), D2 (112) (111), E1 (011) (111) and E2 (011) (111). At elevated temperatures, the conditions were chosen so that dynamic recrystallization (DRX) took place in the ferrite and that static recrystallization was avoided during cooling after deformation. The DRX textures differ from those observed at room temperature and are dominated by the D2 (112) (111), D1 (112) (111) and E2 (011) (111) components. The D2 becomes increasingly important as the strain is increased, which leads to weakening of the D1 and disappearance of the E2 at large strains. / Deformation textures were simulated using the rate sensitive theory of crystal plasticity. These called for lengthening to take place, in agreement with the measured length changes. The simulated and experimentally observed 'tilt' phenomena are similar to those commonly reported in the literature for fcc materials. The explanation of this phenomenon developed for the latter materials is extended to bcc metals. The development of torsion textures is discussed in terms of the rotation rate vector R, the divergence-convergence properties of orientation flow, and the stability parameter S. / DRX textures were simulated using a model based on sequential deformation, nucleation and growth steps. The types of oriented nucleation and selective growth required to reproduce the experimentally observed textures are discussed. The simulations indicate that the low energy nucleation mechanism plays a dominant role in the formation of bcc DRX textures. The results are also interpreted in terms of the continuous (in situ) and discontinuous mechanisms of dynamic recrystallization.

The influence of Al, Mn and Ti on the hot ductility of four low C steels has been examined. / Ductility troughs were exhibited by all the steels. These could be related to the austenite-to-ferrite phase transformation and grain boundary precipitation behavior. When no precipitation took place at the austenite grain boundaries, the trough occurred by intergranular failure. Fracture surfaces revealed microvoid coalescence, with voids associated with MnS inclusions. / Increasing the Mn in the steels lowers the $ gamma to alpha$ transformation temperature, causing the trough to be moved to lower temperatures. It also decreases the volume fraction of MnS inclusions within the ferrite film. Increasing the Al level caused AlN to be precipitated at the austenite grain boundaries, extending the trough to higher temperatures into the single phase austenite region. / The addition of Ti results in a fine austenite grain size after the solution treatment and impedes AlN precipitation. This leads to improved ductility in the austenite region. / When austenite recrystallization occurs during deformation, any voids which have initiated at the boundaries are trapped within the newly recrystallized grains. Intergranular failure cannot progress and the ductility is high.

<p> The primary focus of the first portion of this study is to compare physical and mechanical properties of a model epoxy that has been toughened with one of three different types of rubber-based modifier: a traditional telechelic oligomer (phase separates into micro-size particles), a core-shell latex particle (preformed nano-scale particles) and a triblock copolymer (self-assembles into nano-scale particles). The effect of modifier content on the physical properties of the matrix was determined using several thermal analysis methods, which provided insight into any inherent alterations of the epoxy matrix. Although the primary objective is to study the role of particle size on the fracture toughness, stiffness and strength were also determined since these properties are often reduced in rubber-toughened epoxies. It was found that since the CSR- and SBM-modified epoxies are composed of less rubber, thermal and mechanical properties of the epoxy were better maintained. In order to better understand the fracture behavior and mechanisms of the three types of rubber particles utilized in this study, extensive microscopy analysis was conducted. Scanning transmission electron microscopy (STEM) was used to quantify the volume fraction of particles, transmission optical microscopy (TOM) was used to determine plastic damage zone size, and scanning electron microscopy (SEM) was used to assess void growth in the plastic zone after fracture. By quantifying these characteristics, it was then possible to model the plastic damage zone size as well as the fracture toughness to elucidate the behavior of the rubber-modified epoxies. It was found that localized shear yielding and matrix void growth are the active toughening mechanisms in all rubber-modified epoxies in this study, however, matrix void growth was more prevalent. The second portion of this study investigated the use of three acrylate-based triblocks and four acrylate-based diblocks to modify a model epoxy system. By varying block lengths and the polarity of the epoxy-miscible blocks, a variety of morphologies were generated (such as spherical micelles, layer particles and worm-like micelles). It was found that in some cases, the epoxy-miscible block did not yield domains substantial enough to facilitate increases in toughness. Overall, the thermal and mechanical properties of the acrylate-based triblock- and diblock-modified epoxies were found to be similar to CTBN-modified epoxy, which was used as a control. However, there were properties that were improved with the acrylate-based diblock-modified epoxies when compared to the acrylate-based triblock modified epoxies. Specifically, the viscosity penalty of the diblock-modified epoxies was shown to be a marked improvement over the triblock-modified epoxies, especially given that the fracture toughness values are similar. This reduction in the viscosity penalty becomes an important criterion when considering processing procedures and applications. Additionally, comparing the morphology of the resulting modified-epoxies utilizing atomic force microscopy (AFM) and scanning electron microscopy (SEM) led to a better understanding of the relationship between the particle morphology obtained and the physical properties of the acrylate-based rubber-modified epoxy systems in this research.</p>

No description available.

Cathode erosion continues to be a problem hindering the widespread application of plasma technology. In this work, cathode erosion for various materials was studied for arcs operating in argon, nitrogen and hydrogen, using a magnetically rotated arc. / Titanium and stainless steel were found to give extremely low erosion rates in argon (0.2 and 0.3 $ mu$g/C respectively). Cupro-nickels were shown to be suitable for nitrogen and hydrogen plasmas. The slope of hydrogen solubility vs. temperature in the cathode material was found to be important in determining hydrogen plasma erosion characteristics. When the plasma gas has a high solubility in the cathode material, or can react with the cathode, a negative erosion rate may result. When gas solubility in the cathode is low, oxide stability and mode of electron emission may govern erosion rate. A high gas solubility in the cathode material, as with hydrogen, can result in mechanical erosion due to micro-explosions in the cathode surface.

The texture of electrodeposits has attracted increasing interest, as it is recognized that it is a possible to benefit from the texture and to improve the various properties of electrodeposits or electrolytic coatings. For example, the corrosion resistance of materials is affected by texture. If appropriate textures are introduced in electrodeposited coatings, their corrosion resistance would be enhanced and the coatings will therefore have a longer service time. Texture development during electrodeposition is still poorly understood, and this makes it difficult to control the texture formation during the electrodeposition processes. In order to better understand the texture formation during electrodeposition, extensive theoretical and experimental investigation are undertaken in this thesis. / A computer model was proposed to describe texture development. In this model, the microstructure of deposit was represented using a two dimensional triangle lattice. The deposit growth was modelled as previously empty lattice sites are being occupied based on fundamental physical rules. The author proposed that the main driving force for the development of microstructure and texture is the minimization of the system's free energy. This results in texture development, and the minimization of the free energy includes deposit's surface energy and occasionally the magnetic energy. Based on this hypothesis, the texture formation during iron electrodeposition and its variation with the deposition condition were simulated. It was demonstrated that the crystallographic anisotropy of deposit's surface energy plays an important role in the formation of the deposit's fibre texture. The study also indicated that the surface-energy anisotropy could be modified by hydrogen co-deposition and the deposit's texture can be modified by varying the current density, temperature, or pH value of the bath. In addition, the study illustrated that the magnetization energy also plays an important role in texture development during electrodeposition of magnetic materials. When external magnetic fields of sufficient strength are applied during the deposition of magnetic materials, the magnetic fields align grains in such a way that the deposits' fibre textures may transform to non-fibre textures. / In order to further justify the minimum-energy texturing mechanism proposed in the model, and to obtain a clear physical picture of the texture formation during electrodeposition, the process of texture development was analyzed using classical thermodynamics. Various experiments were conducted to verify the computer simulation. A positive correlation between the results of the simulation and the experiments were found.

The filtration mechanics of the slip casting and filter pressing ceramic forming processes are analyzed so that better control can be achieved over these processes. The rheological behaviour of alumina suspensions with different solids loadings, particle size distributions and amounts of deflocculant as well as the effects that these suspensions have on the filtration process were studied. / During slip casting the formation of the filter cake occurs as a result of the capillary suction pressure of the pores in the plaster of Paris molds. Therefore, the mold microstructure, density, permeability, suction pressure and the effects that these mold properties have on the filtration process are analyzed as a function of the plaster/water ratio used to form the molds. / During filtration, as the cake thickness increases with casting time, fine particles can be carried along with the filtrate and deposited within the filter cake and/or filter medium thereby clogging and reducing the permeabilities of the porous media. This in turn affects the growth rate as well as the permeability, density and porosity of the cake. Evidence of cake and filter medium clogging was obtained by: (1) SEM analysis of cakes and filter media, (2) surface area measurements of cross-sections of cakes, and (3) measurements of cake thickness as a function of casting time. / A computer model consisting of a network of tubes with a random size distribution has been developed to simulate the filtration process. The model accounts for porous media clogging due to: (1) fine particles depositing on the pore walls and gradually reducing the pore radii and (2) pores trapping particles larger than the pore openings. The network model shows that the permeability of the porous medium is dependent upon its pore size distribution rather than its average pore size. The model also illustrates that minor changes in the pore size distribution due to clogging can significantly affect its permeability and casting rate.

Epoxy-based flexible polymer concrete overlays have been used in the past 15 years in North America to protect the bridge deck from deterioration, to extend the service life, and to improve skid resistant of the riding surface. While 15 years of field applications have demonstrated the effectiveness of the protection offered by the technique, cracking and delamination failures have also been observed. / The purpose of the research reported herein is to understand the mechanism of durability failure of the epoxy polymer concrete overlay system. The tests conducted were water permeability, chloride ion penetration, water absorption, strength loss, temperature cycling, and water vapour pressure. Methods of application of polymer concrete overlay play a key role in the success of the overlay. In addition to the two commonly used methods, the multiple layer and the slurry methods, five new application methods were proposed and evaluated. / It was found that the addition of a primer in the overlay system helps reduce water permeability, and that the thin polymer concrete overlay was much less permeable than the thick asphalt overlay. The temperature cycling tests revealed that no significant delamination occurred after 103 cycles from -50°C to 40°C at an accelerated rate. The rapid chloride ion penetration test confirmed that polymer concrete overlays did provide sufficient protection to stop the chloride ion intrusion. Nevertheless, the epoxy polymer concrete overlays were found to absorb 2--3% of water, which caused a significant strength loss. This strength loss could lead to cracking inside the overlay and accelerate delamination thereafter. The water vapour pressure generated from the saturated concrete substrates was not large enough to promote delamination. Overall, the newly proposed overlay applications methods have proven effective in constructing a thin, durable, less expensive and fast overlay for aged bridge deck protection.

A small addition of elements with a high affinity to oxygen can have a profound effect on the high temperature oxidation behaviour of many metals and alloys. In order to explain the improvement in oxidation resistance, the research was conducted using Ni-NiO as a model system of cation-diffusing oxides, and Ce as a typical reactive element. Three essential techniques were employed to modify the surface of Ni with Ce and CeO2: ion implantation, sol-gel technology, and reactive sputtering. The improvement of Ni oxidation resistance was assessed by oxygen uptake measurements mainly during the early stages but also for long-term exposures at temperatures between 873 and 1073 K in pure oxygen, both at low and atmospheric pressures. The variety of oxides produced were examined in detail by several advanced techniques including Rutherford backscattering spectrometry, Auger electron spectroscopy, secondary ion-mass spectrometry, transmission- and scanning-transmission electron microscopy equipped with electron and x-ray analyzers, atomic force microscopy, infrared spectroscopy, and x-ray diffraction techniques. In order to provide direct evidence regarding the mechanism of oxide growth, a sequential oxidation using oxygen isotopes 16O2/18O2 was conducted. / After conversion to the form of ceramic coating, superficially applied CeO2 sol-gel significantly reduced the Ni oxidation rate as well as changing the NiO morphology and internal microstructure. The extent of the effect depended on coating thickness, size of CeO2 particles, substrate surface finishing and preoxidation before coating. Under optimum conditions, the reduction in the Ni oxidation rate achieved by sol-gel, reactive sputtering, and ion implantation, was similar. It was found that Ni oxidation resistance is controlled by a well-defined NiO sublayer that is composed of randomly-oriented NiO grains and CeO2 particles. Moreover, in this sublayer, the Ce4+ ions segregate to the NiO grain boundaries. At high temperatures, the Ce4+ ions block the outward diffusion of Ni2+ cations along the NiO grain boundaries while allowing the inward diffusion of O2 anions to continue. The "dynamic-segregation mechanism" is proposed in which Ce ions do not statically block the NiO grain boundaries, but actively diffuse along them. It is suggested that the NiO texture and microstructure, which are primarily influenced by the crystallographic orientation of the Ni substrate, are of critical importance for the stability of the reactive element concentration at NiO grain boundaries over the oxidation time.

<p>Structural safety and integrity continues to be an issue of utmost concern in our world today. Existing infrastructures in civil, commercial, and military applications are beginning to see issues associated with age and environmental conditions. In addition, new materials are being put to service that are not yet fully characterized and understood when it comes to long term behavior. In order to assess the structural health of both old and new materials, it is necessary to implement a technique for monitoring wear and tear. Current methods that are being used today typically depend on visual inspection techniques or handheld instruments. These methods are not always ideal for large structures as they become very tedious leading to a substantial amount of both time and money spent. More recently, composite materials have been introduced into applications that can benefit from high strength-to-weight ratio materials. However, the use of more complex materials (such as composites) leads to a high demand of structural health monitoring techniques, since the damage is often internal and not visible to the naked eye. The work performed in this thesis examines the methods that can be used for phase change activation and characterization of sprayable poly(vinylidene) fluoride (PVDF) thin films in order to exploit their piezoelectric characteristics for sensing applications. PVDF is widely accepted to exist in four phases: alpha, beta, gamma, and delta. Alpha phase PVDF is produced directly from the melt and exhibits no piezoelectric properties. The activation or transition from &#945; phase to some combination of beta and/or gamma phase PVDF leads to a polarizable piezoelectric thin film to be used in sensing applications. The work herein presents the methods used to activate phase change in PVDF, such as mechanical stretching, annealing, and chemical composition, to be able to implement PVDF as an impact detection sensor. The results and analysis provided in this thesis will present the possibilities of spray-deposited PVDF thin films in both small-scale and large-scale sensing applications that can be applied to both simple and complex geometries.