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.

Ni50.6Ti49.4 single and Ni52Ti48 polycrystalline shape memory alloy samples were subjected to aging under a uniaxial stress, to form a single Ni4Ti3 precipitate variant and to investigate the effects of single versus multi-variant coherent precipitates on the shape memory characteristics including two-way shape memory effect (TWSME). Shape memory and superelasticity properties along with the effects of stress and temperature on the transformation temperatures, strain, hysteresis, dimensional stability, and R-phase formation were investigated. This was accomplished through the use of isobaric thermal cycling and superelasticity experiments and various microscopy techniques that included transmission electron microscopy (TEM), scanning electron microscopy, and optical microcopy. The results showed that it is feasible to use constrained aging to bias R-phase martensite variants upon cooling from austenite without any external stress, however, accomplishing this with B19’martensite was much harder as complete TWSME was only found in the Ni50.6Ti49.4 single crystalline sample oriented along the [112] direction. The onset of irrecoverable strain corresponded to the R-phase temperature hysteresis increase in the single crystalline samples regardless of the aging conditions. Through TEM analysis it was discovered that [112] and [114] twins were found in austenite due to plastic deformation of martensite during the superelasticity experiments. Since [112] twins are theoretically impossible to form in austenite, and since martensite was plastically deformed, [112] austenite twins were attributed to the transformation of compound twins in martensite, in particular [113] martensite twins formed during the plastic deformation of martensite, into austenite twins. In the Ni52Ti48 polycrystalline samples, a compressive R-phase variant was biased through constrained aging under 100 and 200 MPa uniaxial tensile stresses at 400°C and 450°C. Aging, in all conditions, produced a high density of Ni4Ti3 precipitates that was most likely responsible for the small transformation strain observed, less that 2%, upon transformation to martensite. In the future, samples with compositions between 50.8 and 51.5 Ni atomic percent, in addition to altered solution and aging heat treatments as compared to those used in this study should be investigated as it is believed that samples with these compositions will yield better and consistent TWSME responses through constrained aging.

Ni-Mn-Ga is a ferromagnetic shape memory alloy that can be used for future sensors and actuators. It has been shown that magnetic field can induce phase transformation and consequently large strain in stoichiometric Ni2MnGa. Since then considerable progress has been made in understanding the underlying science of shape memory and ferromagnetic shape memory in bulk materials. Ni-Mn-Ga thin films, however is a relatively under explored area. Ferromagnetic shape memory alloy thin films are conceived as the future MEMS sensor and actuator materials. With a 9.5 percent strain rate reported from magnetic reorientation, Ni-Mn-Ga thin films hold great promise as actuator materials. Thin films come with a number of advantages and challenges as compared to their bulk counterparts. While properties like mechanical strength, uniformity are much better in thin film form, high stress and constraint from the substrate pose a significant challenge for reorientation and shape memory behavior. In either case, it is very important to understand their behavior and examine their properties. This thesis is an effort to contribute to the literature of Ni-Mn-Ga thin films as ferromagnetic shape memory alloys. The focus of this project is to develop a recipe for fabricating NiMnGa thin films with desired composition and microstructure and hence unique properties for future MEMS actuator materials and characterize their properties to aid better understanding of their behavior. In this project NiMnGa thin films have been fabricated using magnetron sputtering on a variety of substrates. Magnetron sputtering technique allows us to tailor the composition of films which is crucial for controlling the phase transformation properties of NiMnGa films. The composition is tailored by varying several deposition parameters. Microstructure of the films has been investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Mechanical properties of as-deposited films have been probed using nano-indentation technique. The chemistry of sputtered films is determined quantitatively by wavelength dispersive X-ray spectroscopy (WDS). Phase transformation is studied by using a combination of differential scanning calorimetry (DSC), in-situ heating in TEM and in-situ XRD instruments. Magnetic properties of films are examined using superconducting quantum interface device (SQUID).

New materials always have the possibility of revolutionizing manufacturing processes and the way we live. Bronze, steel alloys, vulcanized rubber, ceramics, and fiber optic cables are just of few of the materials man has discovered which improved his quality of life. One of the more recent additions to the field of material science are materials that exhibit what is known as the shape memory effect. Both metals and synthetic polymers can acquire this property through processing and chemistry. However while shape memory polymers hold a lot of promise, it will require more research and development to make them affordable and useful in large scale applications. / text

No description available.

An electro-mechanical device was developed to provide mechanical stimulation to cell populations for the purpose of studying how mechanical signals affect cell activity. The system can dynamically deform cubes of hydrogel seeded with cells by applying combinations of normal and shear forces to the faces of the hydrogel cube using plastic pads attached to the cube. The compact device was fabricated using rapid prototyping methods with ABS plastic and uses shape memory alloy actuator wires to generate the necessary forces. The actuator wires can be independently activated in sequence to create stimulation routines involving compression, tension and shear forces. All of the components can be sterilized and are corrosion resistant so they are not affected by the high humidity environment of a tissue incubator where cell stimulation studies are performed. The system fits inside a standard plastic lab container measuring 7 cm tall by 4 cm in diameter to maintain sterile conditions and hold the liquid culture medium required by the cells. During operation the hydrogel cube and the contact pads are submerged in the culture medium. The shape memory alloy actuators have been modeled in a two step process: 1) the electrothermal model, relating input electrical current to the wire temperature due to resistive heating and 2) the thermomechanical model relating the wire temperature to the wire strain and actuator stroke due to the shape memory effect. Testing was completed to validate the models and calibrate the shape memory alloy actuators. There was good agreement between the model predictions and the experimental results. For experiments with a hydrogel cube with sides measuring 1 cm, the system was capable of compressing the hydrogel cube up to 8 %, and generating shear strains of up to 7%. Tensile strains were much smaller at 0.9%. The dynamic deformations were applied at a frequency of 0.5 Hz. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2008-08-12 10:23:15.672

The development of active 'smart materials', which are materials that can change their physical properties when subject to an external stimulus such as a thermal, mechanical or magnetic energy, are expected to significantly enhance technology developments in future years. These new materials can be integrated into existing technologies to increase efficiency, performance, durability and size reduction.

Thesis (M.S.V.)--University of Toledo, 2004. / Typescript. "A thesis [submitted] as partial fulfillment of the requirements of the Master of Science degree in Civil Engineering." Includes bibliographical references (leaves 63-64).

In the last twenty years Reversible Shape-Memory (RSM) alloys have become the source of considerable technological interest as a result of their ability to generate spontaneous and reversible changes of shape on thermal cycling. This has led to the development of a range of reversible shape-memory devices for thermostatic sensing applications. In these devices the alloy is subjected to several thousand shape-memory cycles and the stability of the reversible shape-memory is therefore an important alloy property. Data on the effect of shape-memory cycling on the long-term stability of the reversible shape-memory, however, is extremely limited. The present work, conducted to fill this gap, has shown that there is an inherent instability in the reversible shape-memory, with changes in the operating temperatures and cumulative reductions in the maximum shape-strain output of actuators on long-term thermal cycling under conditions simulating real devices. Extensive investigation has shown that these instabilities result from a number of sources, ageing of the shape-memory martensites and most importantly from morphological disruptions in the "trained" martensites caused by two-stage stress-induced transformation and due to the build-up of transformation-induced dislocation debris. This shape-strain degradation has also been successfully modelled by means of a simple two-stage stress-induced martensitic transformation model.

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