No description available.

No description available.

No description available.

No description available.

No description available.

Active research of SMAs has shown that its Seebeck coefficient is sensitive to its martensitic phase transformation and has the potential to determine the SMAs state of transformation. The combination of Shape Memory Alloys, which have a positive Seebeck coefficient, and Constantan which has a negative Seebeck coefficient (-35 mV/K) results in a thermocouple capable of measuring temperature. The work presented in this thesis is based on the development and design of this sensor. This sensor is used to study the hysteretic behaviour of SMAs. Although Shape Memory Alloys (SMAs) exhibit a myriad of nonlinearities, SMAs show two major types of nonlinear hysteresis. During cyclic loading of the SMAs, it is observed that one type of hysteretic behavior depends on the rate of heating the SMAs, whilst the variation of maximum temperature of an SMA in each cycle results in the other hysteretic behavior. This later hysteretic behavior gives rise to major and minor nonlinear loops of SMAs. The present work analyzes the nonlinearities of hysteretic envelopes which gives the different maximum temperatures reached for each hysteretic cycle with respect to stress and strain of the SMA. This work then models this behavior using Adaptive Neuro Fuzzy Inference System (ANFIS) and compares it to experimental results. The nonlinear learning and adaptation of ANFIS architecture makes it suitable to model the temperature path hysteresis of SMAs. / Master of Science

This thesis aims to provide a comprehensive reference on the effective integration of shape memory alloys into architectural design and design. Despite growing interest in SMAs for kinetic structures and adaptive facades, there is currently a fragmented understanding of how to leverage their unique properties in the built environment. Designers lack consolidated resources that map the capacities and limitations of different SMA materials and configurations with respect to functional objectives, manufacturing constraints, and performance goals. My research will gather dispersed knowledge across materials science, mechanics, and fabrication processes relevant to architectural SMAs. After conducting extensive research and different stages of prototyping, a final responsive wall piece will be designed and built that interacts with users responding to different stimuli including touch, sound, or distance. The outcome of this research on the integration of shape memory alloys (SMAs) into architectural design and construction can contribute significantly to designers and the field of architecture in several ways • Unlocking new design possibilities: • Facilitating interdisciplinary collaboration• Developing design guidelines and tools • Advancing responsive architecture• Inspiring future research and innovation / Master of Architecture / This thesis explores how new materials called Shape Memory Alloys (SMAs) can be used to make buildings more dynamic and responsive to their environment. SMAs are special because they can change shape when heated and return to their original form when cooled, much like magic metal. The research shows how SMAs can be used in architecture to create structures that move and adapt in response to changes in their surroundings. For example, building facades made with SMAs can automatically adjust to control sunlight and temperature, making buildings more energy-efficient and comfortable for people inside. A significant part of this study is a project where SMAs are used to create a wall that reacts to touch and other stimuli, bringing the wall to life in a way that interacts with people nearby. This work aims to inspire architects and designers to think beyond static structures and consider how buildings can become more interactive and environmentally friendly. Overall, this research opens up exciting possibilities for the future of building design, making our living and working spaces smarter and more in tune with our needs and the natural world.

In this study, four different NiTi-based shape memory alloys (SMAs) compositions were processed, shape-set, and characterized to evaluate their effectiveness as SMA actuation component for satellite antennas. Three of the compositions were commercially available NiTi wires (90°C Flexinol® actuator NiTi wire and Confluent ADB SE508 NiTi wire), NiTi SM495 plates (ATI Specialty Alloys and Components) and the other composition was in house lab-produced NiTiCu plate. Different shape-setting techniques were performed such as pin and plate, fixtures and dies, and finally a sandwich fixture. The two most promising outcomes were the SE NiTi 508 wire and the NiTiCu plate. A SE NiTi 508 wire was first heat-treated at 550 °C for 3 hours and then it was shape-set at 450 °C for 30 min using a Cu tube which was previously deformed to the desired deployment curvature and fixed on a steel rig. The wire was kept inside the Cu tube during the shape-setting process to obtain the desired curvature. After shape-setting, the wire was thermally cycled multiple times. The results showed that the SE NiTi 508 wire was able to retain its deployment shape successfully after each thermal cycle. Furthermore, a NiTiCu plate was sandwiched between two steel sheets which were shaped into the desired full-deployment shape beforehand. The NiTiCu plate was shape-set at 450 °C for 30 min and then thermally cycled multiple times to test its effectiveness. The NiTiCu plate retained its full-deployment shape successfully after every thermal cycle.

GeTe and Ge2Sb2Te5 alloys are potential candidates for non-volatile phase change random access memories (PCRAM). For electrical data storage applications the materials should have stable amorphous and crystalline phases, fast crystallization time, low power to switch, and high crystallization activation energy (to be stable at normal operating temperatures). Phase change memories can be tuned through compositional variations to achieve sufficient phase change contrast and thermal stability for data retention. Selenium is one of the attractive choices to use as an additive material owing to its flexible amorphous structure and a variety of possible applications in optoelectronics and solar cells. GeSb2Te3Se alloy, in which 25 at.% of Se substituted for Te, show a higher room temperature resistance with respect to parent GeSb2Te4 alloy, but the transition temperature is lowered which will affect the thermal stability. The RESET current observed for Sb65Se35 alloys were reduced and the crystallization speed increased 25 % faster with respect to Ge2Sb2Te5. Alloys of Ga-Sb-Se possess advantages such as higher crystallization temperatures, better data retention, higher switching speed, lower thermal conductivity and lower melting point than the GST, but the resistance ratio is limited to about two orders of magnitude. This affects the resistance contrast and data readability. It is with this background a study has been carried out in GeTe and GeSbTe system with Se doping. Studies on structural, thermal and optical properties of these materials all through the phase transition temperatures would be helpful to explore the feasibility of phase change memory uses. Thin films along with their bulk counterparts such as (GeTe)1-x Sex ( 0 < x ≤ 0.50) and (GST)1-xSex (0 < x ≤ 0.50), including GeTe and GST alloys, have been prepared. The results are presented in four chapters apart from the Introduction and Experimental techniques chapters. The final chapter summarizes the results. Chapter 1 provides an introduction to chalcogenide glasses, phase change memory materials and their applications. The fundamental properties of amorphous solids, basic phase change properties of Ge2Sb2Te5 and GeTe alloys and their applications are presented in detail. Various doping studies on GeTe and Ge2Sb2Te5 reported in literatures are reviewed. The limitations, challenges, future and scope of the present work are presented. In chapter 2, the experimental techniques used for thin film preparation, electrical characterizations, optical characterization and surface characterizations etc. are explained. Chapter 3 deals entirely on Ge2Sb2Te5 films studied throughout the phase transition, by annealing at different temperatures. Changes in sheet resistance, optical transmission, morphology and surface bonding characteristics are analyzed. The crystallization leads to an increase of roughness and the resistance changes to three orders of magnitude at 125 oC. Optical studies show distinct changes in transmittance during phase transitions and the optical parameters are calculated. Band gap contrast and disorder variation with annealing temperatures are explained. The surface bonding characteristics studied by XPS show Ge-Te, Sb-Te bonds are present in both amorphous and crystalline phases. The temperature dependent modifications of the band structure of amorphous GST films at low temperatures have been little explored. The band gap increment of around 0.2 eV is observed at low temperature (4.2 K) compared to room temperature 300 K. Other optical parameters like Urbach energy and B1/2 are studied at different temperatures and are evaluated. The observed changes in optical band gap (Eopt) are fitted to Fan’s one phonon approximation, from which a phonon energy (ћω) corresponding to a frequency of 3.59 THz resulted. The frequency of 3.66 THz optical phonons has already been reported by coherent phonon spectroscopy experiment in amorphous GST. This opens up an indirect method of calculating the phonon frequency of the amorphous phase change materials. Chapter 4 constitutes comparison of optical, electrical and structural investigation of GST and (GST)1-xSex films. It is well known that GST alloys have vacancy in their structure, which leads to the possibility of switching between the amorphous and crystalline states with minimum damage. Added Se may occupy the vacancy or change the bonding characteristics which intern may manifest in the possibility of change in optical and electrical parameters. The structural studies show a direct amorphous to hexagonal transition in (GST)1-xSex, where x ≥ 0.10 at.%. Raman spectra of the as deposited and annealed (GST)1-xSex films show structural modifications. The infrared transmission spectra indicate a shift in absorption edges from low to high photon energy when Se concentration increases in GST. Band gap values calculated from Tauc plot show the band gap increment with Se doping. It is noted that a small amount of Se doping increases the resistance of the amorphous and crystalline phases and maintains the same orders of resistance contrast. This will be beneficial as it improves the thermal stability and reduces the write current in a device. Switching studies show an increasing threshold voltage as the Se doping concentration increases. Chapter 5 comprises compositional dependent investigations of the bulk GeTe chalcogenides alloys added with different selenium concentrations. The XRD investigations on bulk (GeTe)1-xSex (x = 0.0, 0.02, 0.10, 0.20 and 0.50 at.%) alloys show that the crystalline structure of GeTe alloys does not affect ≤ 0.20 at.% of Se concentration. With increasing amount of Se concentration the alloys gets modified in to a homogeneous amorphous structure. This result has been verified from the XRD, Raman, XPS, SEM and DSC measurements. The possibility that Se occupying the Ge vacancy sites in GeTe structure is explained. Since Se is an easy glass former, the amorphousness increases in the alloys due to new amorphous phases formed by the Se with other elements. It is shown from Raman and XPS analysis that the Ge-Te bonds exists up to Se 0.20 at.% alloys. Ge-Se and GeTe2 bonds are increasing with increasing Se at.%. Melting temperature has found decreases and the reduction in melting point may reduces the RESET current. Further studies on switching behavior may bring out its usefulness. Chapter 6 deals with studies on (GeTe)1-xSex films for phase change memory applications based on the insight received from their bulk study. Even at low at.% addition of Se makes the as prepared (GeTe)1-xSex film amorphous. At 200 oC, GeTe crystalline structure is evolved and the intensity of the peaks reduces in the alloys with increase of Se content. At 300 oC, more evolved GeTe crystalline structure is seen compared to 200 oC annealed films whereas 0.20 at.% Se alloy remain amorphous. Resistance and thermal studies shows increase in crystallization temperature. It is expected that Se sits in the vacancies of the GeTe crystalline structural formation. This may also account for the increased threshold voltages with increasing Se doping. The band gap increase with increase of Se at.% signifying the possibility of band gap tuning in the material. Possible explanation for the increased order in GeTe due to Se doping is presented. The modifications in the alloy with Se addition can be explained with the help of chemical bond energy approach. Those bonds having higher energy leads to increased average bond energy of the system and hence the band gap. The XPS core level spectra and Raman spectra investigation clearly shows the GeTe bonds are replaced by Ge-Se bonds and GeTe2 bonds. The 0.10 at.% Se alloy is found to have a higher thermal stability in the amorphous state and maintains a gigantic resistance contrast compared to other Se concentration alloys. This alloy can be considered as an ideal candidate for multilevel PCM applications. Chapter 7 summarizes the major findings from this work and the scope for future work.

NiTi based shape memory alloys (SMA) cover most of the commercially produced shape memory devices and components. The reversible martensitic transformation between the phases B2 (austenite) and B19′ (martensite) is responsible for the shape memory effect in these alloys. The amount of strain which can be regained after a permanent deformation through thermal activation, known as the recoverable strain, is a strong function of crystallographic texture and microstructure. Texture influences the activation of a specific martensite variant during stress induced martensitic (SIM) transformation and also the re-orientation of twinned variants during further deformation. The variant selection decides the amount of recoverable strain. Since the NiTi based shape memory alloys inevitably undergo thermo-mechanical processing in the course of component design, the consequent evolution of texture and microstructure regulate the shape memory behavior. The present thesis is aimed to address this issue in some NiTi alloys that are technologically important for different applications, namely a binary Ni-rich NiTi alloy, a copper containing NiTi alloy and a hafnium containing NiTi alloy. The Ni rich NiTi alloy displays pseudoelastic behavior that can be used for couplings, the NiTiCu alloy provides a controlled thermal hysteresis suitable for actuator applications and the NiTiHf alloy can be used for high temperature applications. The first Chapter of the thesis provides a detailed overview of the existing knowledge related to evolution of microstructure and texture during processing, the transformation texture and its role on the shape memory behavior in NiTi alloys. The second chapter includes the experimental procedure followed to generate different textures, namely unidirectional and cross rolling with and without a subsequent annealing and also the details of the techniques used to characterize the structure, microstructure, texture and mechanical properties. The evolution of texture during thermo-mechanical processing of a Ni rich NiTi alloy and its impact on shape memory behavior is addressed in Chapter 3. The two modes of rolling employed at higher temperature led to the formation of different textures. The texture of unidirectionally rolled samples was characterized by a strong <111>||ND fiber, while a strong Goss {100}<110> component along with <111>||ND fiber was observed in the texture of the cross rolled samples. Annealing of the unidirectionally rolled samples generated a strong <100>||ND fiber, and a weak <111>||ND fiber was observed for the cross rolled samples. Microtexture analyses indicated that dynamically recrystallized grains had significantly different texture compared to the statically annealed material. One of the salient features of this study is the analysis of different twin boundaries with coincident site lattice (CSL) relations that has been observed in the hot rolled material. The origin of these twins has been attributed to deformation. The evolution of twin boundaries with CSL relation has strong influence on texture formation. A few of the important texture components have been found to have CSL relation amongst them. The origin of different texture components were found using intra-grain misorientation parameters. In-situ transformation studies in a scanning electron microscope have confirmed the formation of different types of twins at very low amount of strain in the Ni rich NiTi alloy. A Schmid factor based criterion was used to identify the activation of a particular variant. Trace analysis of the surface relief due to SIM transformation was utilized to confirm the theoretically predicted variant. Schmid criterion has been found to be valid in all the cases. Modulus variation with temperature and strain was studied using dynamical mechanical analysis. Microstructural changes during thermal and thermo-mechanical cycling revealed higher orientation gradient along grain boundaries compared to grain interior. The compatibility condition at the grain boundaries were attributed to higher misorientation development. Misorientation development during cycling loading process is also found to be a strong function of texture. Processing condition and texture has a strong influence on the recoverable strain. Particularly, the strength of <111>||ND fiber is influential in deciding the recoverable strain. Study of microstructure and texture evolution in the TiNiCu SMA and subsequent study on its impact on recoverable strain is presented in Chapter 4. Convincing evidences for the mechanisms operating during different dynamic restoration processes have been presented through microstructural investigation. Texture analysis of the austenite phase showed the formation of <111>||ND fiber. Despite the weakening of texture at larger strain, strength of certain deformation texture components like S {123}<634> and Cu {112}<111> increased, which suggested that texture evolution in TiNiCu alloy deviates from the texture of binary NiTi at large strains. Transformation texture analysis was carried out through electron back scattered diffraction technique, using an in-situ heating stage. The analysis of the results showed predominant activation of <011> type II as well as {11 1 } type I twins. A comparison of martensite and austenite pole figures indicated strong variant selection during phase transformation. Like the binary NiTi alloy, cross rolling of TiNiCu alloy also showed ample changes in the texture of martensite phase through the formation of different texture components. Annealing of both unidirectionally and cross rolled samples led to the weakening of texture. The change in volume fraction of Ti2NiCu precipitates, resulting from different processing conditions, influenced the transformation temperature. In this case also, texture and large intra-grain misorientation governed the recoverable strain. Chapter 5 is dedicated to the study of high temperature NiTiHf alloy. X-ray diffraction and differential scanning calorimetric studies confirmed a two step martensitic transformation, a B19` monoclinic and rhombohedral R-phase martensite in the studied alloy (Ni49.4Ti38.6Hf12). Microstructural investigations showed the formation of dendritic (Ti,Hf)2Ni precipitates along the grain boundary. Evolution of R-phase martensite was always observed along with (Ti,Hf)2Ni precipitates, irrespective of the processing condition. Dissolution of (Ti,Hf)2Ni precipitates by solution treatment suppressed the R phase formation. Strong texture of R-phase martensite confirmed variant selection during martensitic transformation. On the contrary, texture of B19` martensite was always weak, suggesting no preference for variant selection. Rolled material with a relatively strong texture exhibited higher recoverable strain compared to annealed material. Finally, all the significant outcomes of the present investigation are summarized in Chapter 6. Based on the conclusions, suggestions for future work have been mentioned.