This thesis considers two broad categories of shape-preserving transformations: physical transformations, in which the chemistry of the as-grown material remains constant but some structural change is introduced (i.e., conversion of dense silicon nanowires into porous silicon nanowires); and chemical transformations, in which the physical structure of the as-grown material remains constant but the chemical composition is changed (i.e., conversion of SiO2 photonic crystal fibers into MgF¬2 photonic crystal fibers). Part I of this thesis focuses on the development of a process which allows for the introduction of porosity into dense silicon nano- and microstructures (a shape preserving net physical transformation, albeit by chemical means), while Part II focuses on conversion of SiO2-based photonic structures, including three dimensional photonic crystals and hollow-core photonic crystal fibers into Mg2Si or MgF2 replicas with more desirable chemical compositions (a shape preserving net chemical transformation) possessing enhanced optical characteristics.

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In this paper we introduce a novel representation of the significant changes in curvature along the bounding contour of planar shape. We call the representation the curvature primal sketch. We describe an implemented algorithm that computes the curvature primal sketch and illustrate its performance on a set of tool shapes. The curvature primal sketch derives its name from the close analogy to the primal sketch representation advocated by Marr for describing significant intensity changes. We define a set of primitive parameterized curvature discontinuities, and derive expressions for their convolutions with the first and second derivatives of a Gaussian. The convolved primitives, sorted according to the scale at which they are detected, provide us with a multi-scaled interpretation of the contour of a shape.

This thesis is concerned with a novel local threshold segmentation algorithm for digital images incorporating shape information. In image segmentation, most local threshold algorithms are based only on intensity analysis. In many applications where an image contains objects with a similar shape, in addition to the intensity information, some prior known shape attributes could be exploited to improve the segmentation. The goal of this work is to design a local threshold algorithm that includes shape information to enhance the segmentation quality. The algorithm adaptively selects a local threshold. Shape attribute distributions are learned from typical objects in ground truth images. Local threshold for each object in an image to be segmented is chosen to maximize probabilities in these shape attributes distributions. Then for the application of the oil sand image segmentation, a supervised classifier is introduced to further enhance the segmentation accuracy. The algorithm applies a supervised classifier trained by shape features to reject unwanted fragments. To meet different image segmentation intents in practical applications, we investigate a variety of combination of shape attributes and classifiers, and also look for the optimal one. Experiments on oil sand images have shown that the proposed algorithm has superior performance to local threshold approaches based on intensity information in terms of segmentation quality.

The cyclic instability in shape memory characteristics of NiTi-based shape memory alloys (SMAs), such as transformation temperatures, transformation and irrecoverable strains and transformation hysteresis upon thermal and mechanical cycling limits their applications requiring high number of cycles. The main reasons for these instabilities are lattice incompatibility between transforming phases and relatively low lattice resistance against dislocation motion. The objective of this study is to increase the slip resistance and thus, to minimize the plastic accommodation upon phase transformation in NiTi and TiNiPd SMAs. The effects of grain refinement down to submicron to nanorange through Equal Channel Angular Extrusion (ECAE) on the cyclic stability were investigated as potential remedies. The influence of ECAE parameters, such as processing temperature and strain path on the microstructural refinement was explored as well as the corresponding evolution in the stress differential between the yield strength of martensite and the critical stress to induce martensite and SMA characteristics of Ni49.7Ti50.3, Ti50Ni30Pd20, and Ti50.3Ni33.7Pd16 SMAs. Severe plastic deformation via ECAE at temperatures from 300°C up to 450°C refined the grains from 50μm down to a range between 0.03μm and 0.3μm in Ni49.7Ti50.3 and 0.5μm and 1μm in TiNiPd alloys. Regardless of the material, the lower the ECAE temperature and the higher the ECAE strain path, the better the cyclic stability. ECAE led to an increase in the stress differential between the yield strength of martensite and critical stress to induce martensite due to observed microstructural refinement and this increase is responsible for the improvement in the cyclic stability of the aforementioned SMA characteristics in all investigated materials. Addition of Pd to the NiTi alloy reduced the thermal hysteresis from 36°C down to 11°C, and enhanced the cyclic stability of the SMA characteristics. In additions to positive influence of ECAE on cyclic stability, it also led to an increase in the fracture stress levels of the TiNiPd alloys due to the fragmentation or dissolution of the precipitates responsible for the premature failures. ECAE caused a slight reduction in the work output; however it was possible to obtain large stable work outputs under higher stress levels than unprocessed materials.

The cyclic instability in shape memory characteristics of NiTi-based shape memory alloys (SMAs), such as transformation temperatures, transformation and irrecoverable strains and transformation hysteresis upon thermal and mechanical cycling limits their applications requiring high number of cycles. The main reasons for these instabilities are lattice incompatibility between transforming phases and relatively low lattice resistance against dislocation motion. The objective of this study is to increase the slip resistance and thus, to minimize the plastic accommodation upon phase transformation in NiTi and TiNiPd SMAs. The effects of grain refinement down to submicron to nanorange through Equal Channel Angular Extrusion (ECAE) on the cyclic stability were investigated as potential remedies. The influence of ECAE parameters, such as processing temperature and strain path on the microstructural refinement was explored as well as the corresponding evolution in the stress differential between the yield strength of martensite and the critical stress to induce martensite and SMA characteristics of Ni49.7Ti50.3, Ti50Ni30Pd20, and Ti50.3Ni33.7Pd16 SMAs. Severe plastic deformation via ECAE at temperatures from 300°C up to 450°C refined the grains from 50μm down to a range between 0.03μm and 0.3μm in Ni49.7Ti50.3 and 0.5μm and 1μm in TiNiPd alloys. Regardless of the material, the lower the ECAE temperature and the higher the ECAE strain path, the better the cyclic stability. ECAE led to an increase in the stress differential between the yield strength of martensite and critical stress to induce martensite due to observed microstructural refinement and this increase is responsible for the improvement in the cyclic stability of the aforementioned SMA characteristics in all investigated materials. Addition of Pd to the NiTi alloy reduced the thermal hysteresis from 36°C down to 11°C, and enhanced the cyclic stability of the SMA characteristics. In additions to positive influence of ECAE on cyclic stability, it also led to an increase in the fracture stress levels of the TiNiPd alloys due to the fragmentation or dissolution of the precipitates responsible for the premature failures. ECAE caused a slight reduction in the work output; however it was possible to obtain large stable work outputs under higher stress levels than unprocessed materials.

The effects of crystallographic orientation, temperature and heat treatment on superelastic response of Ni45Mn36.5Co5In13.5 single crystals were investigated. Superelastic experiments with and without various magnetic field were conducted under compression on a custom built magneto-thermo-mechanical test setup. Magnetostress, which is the difference in critical stress levels for the martensitic transformation with and without magnetic field, was determined as a function of crystallographic orientation, heat treatment and temperature parameters. Magnetostress of [111] crystals was observed to be much higher than that of [001] crystals with same heat treatment. Water quenched samples have the highest magnetostress among other samples with the same orientation that were oil quenched and furnace cooled. Crystal structure and atomic ordering of the samples were examined using Synchrotron High-Energy X-Ray Diffraction to rationalize observed differences. Magnetostress levels were also traced at various temperatures. A Quantum Design superconducting quantum interference device (SQUID) was utilized to examine the magnetic properties of the material. The difference in saturation magnetization at various temperatures was analyzed to explain the temperature effect on magnetostress. Calculations based on the energy conversion from available magnetic energy to mechanical work output were used to predict the magnetic field dependence of magnetostress, which provides a guideline in material selection for the reversible magnetic field induced martensitic phase transformation. Isothermal superelastic response and load-biased shape memory response of Co48Ni33Al29 single crystals were determined as a function of temperature and stress, respectively. The aim of the work is to provide a new direction to understand the anomaly of transformation strain and hysteresis for ferromagnetic shape memory alloys. Thermo-mechanical behavior of Co48Ni33Al29 single crystal was determined by a custom built thermo-mechanical compression setup based on an electromechanical test frame made by MTS. Transformation strain was observed to decrease with increasing applied stress in isothermal tests or increasing temperature in superelastic experiments. The variation in the lattice constant in martensite and austenite was verified to account for such a trend. It was also discovered that both thermal and stress hysteresis decreased with increasing applied stress and temperature, respectively. Multiple factors may be responsible for the phenomenon, including the increase of dislocation, the compatibility between martensite and austenite phase.

The use of nanostructures has become very common throughout high-tech industries. In order to enhance the applicability of Shape Memory Alloys (SMAs) in systems such as Nano-Electromechanical Systems, the phase transformation behavior of SMA nanostructures should be explored. The primary focus of this work is on the fabrication of metallic nanowires and the characterization of the phase transformation of SMA nanowires. Various metallic nanowires are fabricated through the use of the mechanical pressure injection method. The mechanical pressure injection method is a template assisted nanowire fabrication method in which an anodized aluminum oxide (AAO) template is impregnated with liquid metal. The fabrication procedure of the AAO templates is analyzed in order to determine the effect of the various fabrication steps. Furthermore, metallic nanowires are embedded into polymeric nano bers as a means to incorporate nanowires within other nanostructures. The knowledge obtained through the analysis of the AAO template fabrication guides the fabrication of SMA nanowires of various diameters. The fabrication of SMA nanowires with di fferent diameters is accomplished through the fabrication of AAO templates of varying diameters. The phase transformation behavior of the fabricated SMA nanowires is characterized through transmission electron microscopy. By analyzing the fabricated SMA nanowires, it is found that none of the fabricated SMA nanowires exhibit a size eff ect on the phase transformation. The lack of a size e ffect on the phase transition of SMA nanowires is contrary to the results for SMA nanograins, nanocrystals, and thin films, which all exhibit a size eff ect on the phase transformation. The lack of a size eff ect is further studied through molecular dynamic simulations. These simulations show that free-standing metallic nanowires will exhibit a phase transformation when their diameters are sufficiently small. Furthermore, the application of a constraint on metallic nanowires will inhibit the phase transformation shown for unconstrained metallic nanowires. Therefore, it is concluded that free-standing SMA nanowires will exhibit a phase transformation throughout the nanoscale, but constrained SMA nanowires will reach a critical size below which the phase transformation is inhibited.