TRIP-assisted multiphase steels exhibit an excellent balance of strength and ductility, which makes them very attractive for the automotive industry. These remarkable mechanical properties can be attributed mainly to the continuous transformation of retained austenite into martensite during straining (TRansformation Induced Plasticity). The aim of this thesis was to clarify the interaction between the hot rolling conditions, the formation of microstructure, and the resulting mechanical properties. Various rolling simulation techniques were employed to determine how the composite microstructure is formed during the various steps of multi-stage thermomechanical processing. The interaction between deformation and phase transformation is highlighted, particularly from the viewpoint of the transformation texture.

Chromium martensitic hot-work tool steel (AISI H13) is commonly used as die material in hot forming techniques such as die casting, hot rolling, extrusion and hot forging. They are developed to endure the severe conditions by high mechanical properties attained by a complex microstructure. Even though the hot-work tool steel has been improved over the years by alloying and heat treatment, damages still occur. Thermal fatigue is believed to be one of the most common failure mechanisms in hot forming tools. In this thesis tools used in hot forging and die casting were examined to determine damage, material response, thermal fatigue crack initiation and propagation. Different chromium martensitic hot-work tool steels, heat treated at four different austenitizing temperatures were experimentally tested in thermal fatigue and isothermal fatigue. The materials were then evaluated using X-ray line broadening analysis and transmission electron microscopy to explore the relation between fatigue softening and the change in microstructure. The high temperature fatigue softening was also simulated using an elasto-plastic, non-linear kinematic and isotropic model. The model was implemented in a numerical simulation to support the integration of die design, tool steel properties and its use. It was found that the dominant damage mechanisms in the investigated tools were thermal fatigue and that tool material experiences a three stage softening at high temperature loading. The primary stage was concluded to be influenced by the dislocation density and the second stage by the temper resistance i.e. carbide morphology. The microstructural changes during the softening stages were also connected to the non-linear kinematic and isotropic model. The general aim of this thesis is to increase the knowledge of the chromium martensitic hot-work tool steel damage, performance and microstructure.

Financial analysts play an intermediary role in financial markets, resulting in two steps for information to be fully absorbed into the stock price: analysts reaction to information, and investors reaction to analysts recommendations. Thus any observed inefficiency in stock pricing could result from two possibilities: analysts failed to fully incorporate the market information into their stock analysis, or the information released in the analysts report is not fully believed by investors. <p>The documented optimism of financial analysts may suggest the possibility of the later case. To test the accuracy of analysts from another perspective, we follow a market microstructure model and use intraday market data to estimate the probability of an information event, the probability of good or bad news, and the rates that different traders arrive at the market. <p>By comparing those estimates based on days with and without recommendation changes, we find inconsistent results with regard to a difference in the probability of an information event. For some stocks, we do observe an increase in the likelihood of news on days when analysts change their recommendations, but this is not the case for most stocks. However, even though they are inaccurate most of the time, uninformed investors usually believe financial analysts. Furthermore, it seems that uninformed investors disbelieve analyst recommendation changes at those instances when analysts are most accurate. <p> Because of this, we hypothesise that market makers might suspect that orders in the opposite direction of an analysts recommendation change are more likely to come from informed traders. This is consistent with the intuition that most traders are uninformed and will simply follow the advice of a perceived expert, and therefore those that dont follow that advice may be more likely to have special information of their own. We check whether there are any differences in the probability of information-based trading (PIN) and for the conditional probability of information-based trading conditioned on sell (PIN|sell) and buy (PIN|buy) between days with and without recommendation changes. We did not find any significant difference, indicating that although we may observe a higher arrival rate of informed traders on recommendation change days, the probabilities of information-based trading do not change substantially. More informed traders seem to come to the market merely because the higher arrival rate of uninformed traders on recommendation days gives them a good opportunity to camouflage their behaviour. And the specialists likely would not have to change their behaviour on those days by increasing or shifting bid-ask spreads since the increased costs from the higher volume of informed trading are balanced by increased profits from the higher volume of uninformed trading. <p>Furthermore, regression of the probabilities of informed trading (conditional or unconditional) on firm size, trading volume, and volatility of daily return shows nothing significant, so we werent able to identify influential factors that affect informed trading or explain differences in informed trading between firms.

Financial analysts play an intermediary role in financial markets, resulting in two steps for information to be fully absorbed into the stock price: analysts reaction to information, and investors reaction to analysts recommendations. Thus any observed inefficiency in stock pricing could result from two possibilities: analysts failed to fully incorporate the market information into their stock analysis, or the information released in the analysts report is not fully believed by investors. <p>The documented optimism of financial analysts may suggest the possibility of the later case. To test the accuracy of analysts from another perspective, we follow a market microstructure model and use intraday market data to estimate the probability of an information event, the probability of good or bad news, and the rates that different traders arrive at the market. <p>By comparing those estimates based on days with and without recommendation changes, we find inconsistent results with regard to a difference in the probability of an information event. For some stocks, we do observe an increase in the likelihood of news on days when analysts change their recommendations, but this is not the case for most stocks. However, even though they are inaccurate most of the time, uninformed investors usually believe financial analysts. Furthermore, it seems that uninformed investors disbelieve analyst recommendation changes at those instances when analysts are most accurate. <p> Because of this, we hypothesise that market makers might suspect that orders in the opposite direction of an analysts recommendation change are more likely to come from informed traders. This is consistent with the intuition that most traders are uninformed and will simply follow the advice of a perceived expert, and therefore those that dont follow that advice may be more likely to have special information of their own. We check whether there are any differences in the probability of information-based trading (PIN) and for the conditional probability of information-based trading conditioned on sell (PIN|sell) and buy (PIN|buy) between days with and without recommendation changes. We did not find any significant difference, indicating that although we may observe a higher arrival rate of informed traders on recommendation change days, the probabilities of information-based trading do not change substantially. More informed traders seem to come to the market merely because the higher arrival rate of uninformed traders on recommendation days gives them a good opportunity to camouflage their behaviour. And the specialists likely would not have to change their behaviour on those days by increasing or shifting bid-ask spreads since the increased costs from the higher volume of informed trading are balanced by increased profits from the higher volume of uninformed trading. <p>Furthermore, regression of the probabilities of informed trading (conditional or unconditional) on firm size, trading volume, and volatility of daily return shows nothing significant, so we werent able to identify influential factors that affect informed trading or explain differences in informed trading between firms.

Recent interests on the plastic deformation of strontium titanate (SrTiO3) are derived from its unusual ductile-to-brittle-to-ductile transition (DBDT). The transition is divided into three regimes (A, B and C) corresponding to the temperature range of 113 K to 1053 K (-160oC to 780oC), 1053 K to ~ 1503 K (780oC to ~ 1230oC) and ~ 1503 K to 1873 K (~ 1230oC to 1600oC), discovered by Sigle and colleagues in the MPI-Stuttgart. We report the dislocation substructures in (001) single crystal SrTiO3 deformed by Vickers indentation at room temperature, studied by scanning and transmission electron microscopy (SEM and TEM). Dislocation dipoles of screw and edge character are observed and confirmed by inside-outside contrast using g-vector by weak-beam dark field imaging. They are formed by edge trapping, jog dragging and cross slip-pinching off. Similar to dipole breaking off in deformed sapphire (£\-Al2O3) at 1200oC and £^-TiAl intermetallic at room temperature, the dipoles pinch off at one end, and emit a string of loops at trail. Two sets of slip systems {110}<-11 0> and {100}<011> are activated under both 100 g and 1 kg load. The suggestion is that plastic deformation has reached the stage II work hardening, which is characterized by multiplication of dislocations through cross slip, interactions between dislocations, and operating of multiple slip systems. In nanoindentation experiments, it is generally believed that the shear stress at the onset of plasticity can approach the theoretical shear strength of an ideal. Here we report direct evidence that plasticity in a single crystal SrTiO3 can begin at very small forces, remarkably. However, the shear stresses associated with these very small forces is excess the theoretical shear strength of SrTiO3 (16.1 GPa). Our observations entail correlating quantitative load¡Vdisplacement measurements with individual stage microstructure during nanoindentation experiments in a transmission electron microscope. We also report direct evidence that with the prevalent notion that the first obvious displacement excursion in a nanoindentation test is indicative of the onset of plastic deformation. The SrTiO3 deforms elastically before the pop-in depth, but exhibits a plastic-elastic behavior after that. TEM observations reveal that the slip band is the predominant deformation mechanism in SrTiO3 during indentation. The cracks usually initiate at the intersection of slip bands to produce the sessile dislocations with Burger vectors [1-10] (or [110]) along the (110) (or (1-10)) crack plane. In addition, theoretical analysis confirms that the pop-in event is associated with the onset plasticity of SrTiO3. The plastic deformation of (001) single crystal SrTiO3 is investigated using compression along [001] at room temperature. A total plastic strain of ~19+2% is consistently obtained. The stress-strain curve exhibiting four work-hardening stages are describable using the stage 0 of axis rotation, the stage I ¡§easy glide¡¨, the stage II multiple slip and the wall-and-cell structure, and the stage III work softening and dynamic recovery before sample fracture takes place. It is revealed by analyzing the microstructure for each work-hardening stage that the plastic deformation of single crystal SrTiO3 closely resembles that of metals. The primary slip systems of [011](0-11) and [01-1](011) predominate in stage I where plastic deformation occurs by the migration of kink pairs in collinear partial dislocations. The activation of multiple slips including [101](-101) and [10-1](101), and [011](0-11) and [0-11](011) in stage II produces the cell-and-wall structure which is also characteristic of plastically deformed metals. In stage III with decreasing work-hardening rate, the bow-out dislocation interaction from opposite walls results in annihilation. The reaction between dislocations from adjacent walls produces the resultant dislocations with b = [-110] parallel to the load axis [001]. These dislocations are sessile, which eventually leads to sample fracture. We have analyzed the microstructure of <001> SrTiO3 single crystal deformed using compression at room temperature using transmission electron microscopy. A representative stress-strain (£m-£`) curve is established, similar to that for metals it consists of three hardening stages before failure occurs at a strain £` = 19+2%. Dislocation analysis suggests that the primary slip systems in [011](0-11) and [0-11](011) are activated in the £m-£` curve stress plateau region usually addressed as easy glide. Three characteristic features are identified from samples deformed to stage I hardening by easy glide: (a) rectangular glide loops, (b) collinear partials, and (c) kink pairs. Dislocations have predominantly pure edge character. Kink pairs are observed only on the edge segments suggesting that screw dislocations have higher mobility. In easy glide, the migration and annihilation of kink pairs occurring on both the trailing and leading partials lends support to a previous report by Castillo-Rodriguez and Sigle (2011) that dislocation glide is controlled by the long-segment limit of a kink-pair model. Pure edge dislocations are dissociated into collinear partials with b = 1/2[011] (or 1/2[0-11]) by glide in (0-11) (or(011)), and kink pairs are formed on both leading and trailing partials. The suggestion is that in the low-stress regime hardening by dislocation pile-up in stage I is compensated for by kink pair nucleation and migration. The overall hardening rate thus remains unchanged at approximately zero, resembling easy glide in the deformation of metals, over an increasing strain of £` ? 4% before reaching stage II hardening. Microcrack nucleation and propagation behavior in the crack tip was investigated by using transmission electron microscopy (TEM) through compressive test and Vickers indenter. Observation results showed that fracture process was completed in this <001> SrTiO3 single crystal material by connecting dislocations. The crack were nucleated and developed in the dislocation free zone (DFZ) or super thinned area ahead of crack tip under local high stress concentration. The cracks were linked with each other by mutual dislocation emission which expedites the propagation of crack tips effectively. We suggested a dislocation based the Hirsch et al. model of plastic-zone evolution in which dislocations emitted from the crack tip glide away to form a crack-tip plastic zone. Each emitted dislocation reduces the crack tip stress intensity via elastic interactions (the ¡¥¡¥shielding¡¨ effect).

The purpose of this work was to study learn about grain refinement mechanisms and texture development in cast n-type Bi90Sb10 alloy caused by severe plastic deformation. The practical objective is to produce a fine grained and textured microstructure in Bi90Sb10 alloy with enhanced thermoelectric performance and mechanical strength. In the study, twelve millimeter diameter cast bars of Bi90Sb10 alloy were encapsulated in square cross section aluminum 6061 alloy containers. The composite bars were equal channel angular (ECAE) extruded through a 90 degree angle die at high homologous temperature. Various extrusion conditions were studied including punch speed (0.1, 0.3 and 0.6 in/min), extrusion temperature (220, 235 and 250oC), number of extrusion passes (1, 2 and 4), route (A, BC and C), and exit channel area reduction ratio (half and quarter area of inlet channel). The affect of an intermediate long term heat treatment (for 100 hours at 250oC under 10-3 torr vacuum) was explored. Processed materials were characterized by optical microscopy, x-ray diffraction, energy dispersive spectroscopy, wavelength dispersive spectroscopy and scanning electron microscopy. Texture was analyzed using the {006} reflection plane to identify the orientation of the basal poles in processed materials. The cast grains were irregularly shaped, had a grain size of hundreds-of-microns to millimeters, and showed inhomogeneous chemical composition. Severe plastic deformation refines the cast grains through dynamic recrystallization and causes the development of a bimodal microstructure consisting of fine grains (5-30 micron) and coarse grains (50-300 micron). ECAE processing of homogenizied Bi-Sb alloy causes grain refinement and produces a more uniform microstructure. Texture results show that ECAE route C processing gives a similar or slightly stronger texture than ECAE route A processing. In both cases, the basal-plane poles become aligned with the shear direction. Reduction area exit channel extrusion is more effective for both grain refinement and texture enhancement than simple ECAE processing.

Copper has become the metal of choice for metallization, owing to its high electrical and thermal conductivity, relatively higher melting temperature and correspondingly lower rate of diffusivity. Most of the current studies can get high strength copper thin films but on an expense of conductivity. This study proposes a technique to deposit high strength and high conductivity copper thin films on different silicon substrates at room temperature. Single crystal Cu (100) and Cu (111) have been grown on Si (100) and Si (110) substrates, respectively. Single crystal Cu (111) films have a high density of growth twins, oriented parallel to the substrate surface due to low twin boundary energy and a high deposition rate. The yield strengths of these twinned Cu films are much higher than that of bulk copper, with an electrical resistivity value close to that of bulk copper. X-ray diffraction, transmission electron microscopy and nanoindentation techniques were used to show that high density twins are sole reason for the increase in hardness of these thin films. The formation of growth twins and their roles in enhancing the mechanical strength of Cu films while maintaining low resistivity are discussed.

High energy particle (neutron, proton and He ions) irradiation to materials typically leads to deteriorating properties, including void swelling, blistering, embrittlement, fracture and exfoliation of surfaces. This dissertation examines size dependent radiation damage in nanostructured metallic multilayers synthesized by the magnetron sputtering technique at room temperature. It reveals the roles of interface in achieving enhanced radiation tolerance in metallic materials. The microstructure and mechanical properties of as-deposited Cu/V multilayer films are systemically investigated, providing the basis for studying radiation damage mechanisms. Sputter-deposited Cu/V multilayers are subjected to helium (He) ion irradiation at room temperature with a peak dose of 6 displacements per atom (dpa). The average helium bubble density and lattice expansion induced by radiation decrease significantly with decreasing h, where h is individual layer thickness. The magnitude of radiation hardening decreases with decreasing h, and becomes negligible when h is 2.5 nm or less. The interactions between interfaces and radiation induced point defects and the evolution of microstructurs and mechanical behavior are discussed. This study indicates that nearly immiscible Cu/V interfaces spaced a few nm apart can effectively reduce the concentration of radiation induced point defects. Dose dependent radiation damage at room temperature in these Cu/V multilayers is systematically investigated with a peak dose in the range of 1-12 dpa. Peak bubble density increases with increasing dose, but it is much lower in Cu/V 2.5 nm multilayers than that in Cu/V 50 nm specimens. A similar radiation hardening trend is observed in multilayers irradiated at different fluences. Radiation hardening increases with dose and seems to reach saturation at a peak dose of 6 dpa. Negligible hardening for fine ( h less than/equal to 2.5 nm) multilayers is observed at all dose levels. Thermal stability of Cu/V multilayers is revealed by in situ annealing inside a transmission electron microscope. During isothermal annealing at 600 degrees C grain boundary grooving occurs across layer interfaces in Cu/V 50 nm specimens, whereas Cu/V 5 nm multilayers appear rather stable. Annealing of Cu/V multilayers at 400 degrees C leads to hardening of multilayers, whereas softening occurs in Cu/V multilayers annealed at 600 degrees C. The evolution of mechanical properties during annealing is correlated to the degradation of the layer interface and the consequent reduction of interface resistance to the transmission of single dislocation.

This research investigates a novel class of active materials for energy and sensing applications. Magnetocaloric alloys, Gd5Si2Ge2, were developed into a composite with poly(vinylidine flouride) (PVDF), piezoelectric polymer. The giant megnetocaloric property combined with the piezoelectricity creates extraordinary properties for composite materials. The research approach was primarily experimental. Activities include synthesis, characterization, and device design and evaluation. Using the arc melting method, the magenetocaloric samples were created. Multi-length scales characterized using atomic force microscopy (AFM), optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-Ray diffraction (XRD), and X-Ray Photoelectron spectroscopy (XPS). The prototype devices were evaluated for their power generation and efficiency. Through those techniques, the fundamental understanding in the new materials was obtained. The relationships between process-microstructures, microstructure-properties, and structure-power generation were established. Results showed that the phase transformation of the magnetocaloric material at its Curie temperature induced a significant increase in power generation in the peizeoelectric polymer. Such transition was also beneficial for a laminated device for energy harvesting. In addition, it was found that the oxidation that occurred during high temperature melting stabilized the orthorhombic phase at room temperature. The multifunctional composites as well as the laminated structure use the thermal expansion of the magnetocaloric material for energy harvesting, cyclic monitoring, and/or thermal switching. This thesis consists of six chapters. Chapter I provides a history and explanation of the materials used. Chapter II provides an explanation of the motivation for this work. Chapter III addresses the experimental procedures. The results of which are presented in Chapter IV and discussed in Chapter V. The research is summarized and future recommendations are given in Chapter VI.

ABSTRACT For the generation of broadband tunability over 1300 nm to 1600 nm range in optical communications, Cr4+ ions have been demonstrated in a number of hosts including Cr4+:forsterite, Cr4+:Y2SiO5, and Cr4+:YAG. Since YAG is a cubic crystal with Ia-3d space group, its excellent thermal and optical properties has drawn extensive studies. In recent years, various modes of operation using Cr4+:YAG as laser gain medium have been achieved since the first tunable CW laser of Cr4+:YAG bulk gain medium was demonstrated by Shestakov, et al in 1988. Experimentally, the Cr4+:YAG crystal fiber was grown by the laser-heated pedestal growth (LHPG) method which provides outstanding crystal quality and can easily change growth conditions, such as growth speed and core diameter. A double cladding technique was developed with pure YAG, silica/YAG mixture, and pure silica as the core, inner cladding, and outer cladding, respectively. The smallest core diameter we achieved is 11 mm. In this thesis, the fabrication process of the Cr4+:YAG crystal fiber laser involving crystal fiber growth, sample preparation, and coating design will be presented in detail. In order to understand the relation between the microstructure of Cr4+:YAG crystal fibers and the growth conditions, high-resolution transmission electron microscopy (HRTEM) was employed, which reveals the nano-scale information in the core region, the inner-outer cladding interface, and the mechanism of inter-diffusion process during growth. In addition, the thesis also describes the specimen preparation procedures of crystal fibers for the HRTEM analysis. Furthermore, quantitative analysis of Cr4+:YAG crystal fiber was employed by electron-probe micro-analyzer (EPMA) and energy dispersive X-ray spectrometer (EDX), showing accurate characterization of the constitute elements and concentrations. The comparison of Cr4+ fluorescence and dopant concentration of CaO and Cr2O3 will also be presented in this thesis.