New insight into the temperature dependent evolution of internal strain in the austenite phase during the martensitic phase transformation in NiTi shape memory alloys is provided via classical molecular dynamics simulations that employ well-established interatomic potentials for NiTi. It is shown, for the first time, that the developed strain tensor in the austenite phase is tetragonal in nature, with exponential temperature-dependence. Equally importantly, it is found that the developed internal strain (parallel to the habit plane) in the austenite varies linearly with the evolving martensite phase fraction. Interestingly, the Richard’s equation is found to describe the temperature dependence of the martensite phase fraction as well as the internal strain components parallel to the habit plane in the austenite phase. An analysis of the temperature dependent phonon dispersion of strained austenite revealed the competition between phonon softening of the TA2 branch and internal strain that leads to stabilization of the austenite phase in the two phase regime.

The purpose of this research was to investigate the surface modifications that take place during the machining of NiTi SMA and Ti-6Al-4V with micro-EDM. This was done by creating an array of blind holes and micro-patterns on both work-pieces. To analyze the machined surface and investigate the results, scanning electron microscope (SEM), energy dispersive X- ray spectroscopy (EDS) and X-ray diffraction (XRD) techniques were employed. In addition, the effects of various operating parameters on the machining performance was studied to identify the optimum parameters for micro-EDM of NiTi SMA and Ti-6Al-4V. Recently, aerospace and biomedical industries have placed a high demand on nonconventional machining processes, which can be used to machine high strength and hardto- cut materials such as Titanium alloys, Shape Memory Alloys (SMA) and Super Alloys. Electrical Discharge Machining (EDM) is one of the non-traditional technologies that remove materials from the workpiece through a series of electrical sparks that occur between the workpiece and cutting tool with the presence of dielectric liquid. Obtaining smooth and defect-free surfaces on both workpieces was one of the challenges due to the re-solidified debris on the machined surface. The experimental results showed that there was significant amount of re-casting and formation of resolidification of debris on the Ti surface after machining. On the other hand, the surface generated in NiTi SMA were comparatively smoother with lesser amount of resolidified debris on the surface. By analyzing the results from XRD and EDS, some elements of electrode and dielectric materials such as Tungsten, Carbon and Oxygen were observed on NiTi and Ti surface after machining. In the study of effect of operating parameters, it was found that the voltage, capacitance and tool rotational speed had significant effect on machining time. The machining time was reduced by increasing the voltage, capacitance and tool rotational speed. The machining time was found to be comparatively higher for machining NiTi SMA than Ti alloy. Comparing all the parameters, the voltage of 60 V, capacitance of 1000 PF, and tool rotational speed of 3500 RPM were selected as optimum parameters for this study. Although signs of tool electrode wear and debris particles on the machined surface were observed for both workpieces during the micro-EDM process, Ti alloy and NiTi SMA could be machined successfully using the micro-EDM process.

Shape memory alloys (SMAs) are materials that show reversible, thermo-elastic, diffusionless, displacive (solid to solid) phase transformation, due to the application of temperature and/ or stress (/strain). Among different SMAs, NiTi is a popular one. NiTi shows reversible phase transformation, the shape memory effect (SME), where irreversible deformations are recovered upon heating, and superelasticity (SE), where large strains imposed at high enough temperatures are fully recovered. Phase transformation process in NiTi SMA is a very complex process that involves the competition between developed internal strain and phonon dispersion instability. In NiTi SMA, phase transformation occurs over a wide range of temperature and/ or stress (strain) which involves, evolution of different crystalline phases (cubic austenite i.e. B2, different monoclinic variant of martensite i.e. B19', and orthorhombic B19 or BCO structures). Further, it is observed from experimental and computational studies that the evolution kinetics and growth rate of different phases in NiTi SMA vary significantly over a wide spectrum of spatio-temporal scales, especially with length scales. At nano-meter length scale, phase transformation temperatures, critical transformation stress (or strain) and phase fraction evolution change significantly with sample or simulation cell size and grain size. Even, below a critical length scale, the phase transformation process stops. All these aspects make NiTi SMA very interesting to the science and engineering research community and in this context, the present focuses on the following aspects. At first this study address the stability, evolution and growth kinetics of different phases (B2 and variants of B19'), at different length scales, starting from the atomic level and ending at the continuum macroscopic level. The effects of simulation cell size, grain size, and presence of free surface and grain boundary on the phase transformation process (transformation temperature, phase fraction evolution kinetics due to temperature) are also demonstrated herein. Next, to couple and transfer the statistical information of length scale dependent phase transformation process, multiscale/ multiphysics methods are used. Here, the computational difficulty from the fact that the representative governing equations (i.e. different sub-methods such as molecular dynamics simulations, phase field simulations and continuum level constitutive/ material models) are only valid or can be implemented over a range of spatiotemporal scales. Therefore, in the present study, a wavelet based multiscale coupling method is used, where simulation results (phase fraction evolution kinetics) from different sub-methods are linked via concurrent multiscale coupling fashion. Finally, these multiscale/ multiphysics simulation results are used to develop/ modify the macro/ continuum scale thermo-mechanical constitutive relations for NiTi SMA. Finally, the improved material model is used to model new devices, such as thermal diodes and smart dampers.

Since NiTi shape memory alloy (SMA) was discovered in the early 1960s, great progress has been made in understanding the properties and mechanisms of NiTi SMA and in developing associated products. For several decades, most of the scientific research and industrial interests on NiTi SMA has focused on its superelastic applications in the biomedical field and shape memory based “smart” devices, which involves the low strain rate (around 0.001 s^-1) response of NiTi SMA. Due to either stress-induced martensite phase transformation or stress induced martensite variant reorientation under the applied load, NiTi SMA has exhibited a high damping capacity in both austenitic and martensitic phase. Recently, there has been an increasing interest in exploitation of the high damping capacity of NiTi SMA to develop high strain rate related applications such as seismic damping elements and energy absorbing devices. However, a systematic study on the influence of strain, strain rate and temperature on the mechanical properties, phase transformation, microstructure and crystal structure is still limited, which leads to the difficulties in the design of products being subjected to high strain rate loading conditions. The four main objectives of the current research are: (1) achieve the single loading and the control of strain, constant strain rate and temperature in high strain rate compression tests of NiTi SMA specimens using Kolsky (split Hopkinson) compression bar; (2) explore the high strain rate compressive responses of NiTi SMA specimens as a function of strain (1.4%, 1.8%, 3.0%, 4.8%, and 9.6%), strain rate (400, 800 and 1200 s^-1), and temperature (room temperature (294 K) and 373 K); (3) characterize and compare the microstructure, phase transformation and crystal structure of NiTi SMAs before and after high strain rate compression; and (4) correlate high strain rate deformation with the changes of microstructure, phase transformation characteristics and crystal structure. Based on the results from this study, it was found that: (1) the compressive stress strain curves of martensitic NiTi SMAs under quasi-static loading conditions are different from those under high strain rate loading conditions, where higher strain hardening was observed; (2) the critical stress and stress plateau of martensitic NiTi SMAs are sensitive to the strain rate and temperature, especially at 373K, which results from the interplay between strain hardening and thermal softening; (3) the microstructure of martensitic NiTi SMA has changed with increasing strain rate at room temperature (294 K), resulting in the reduction in the area of ordered martensite region, while that area increases after deformation at elevated temperature (373K); (4) the phase transformation characteristic temperatures are more sensitive to deformation strain than strain rate; (5) the preferred crystal plane of martensitic NiTi SMA has changed from (11 ̅1)M before compression to (111)M after compression at room temperature (294 K), while the preferred plane remains exactly the same for martensitic NiTi SMA before and after compression at 373 K. Lastly, dynamic recovery and recrystallization are also observed after deformation of martensitic NiTi SMA at 373K.

This thesis focuses on the role of interfacial strain in heterostructures to modify the magnetism of thin ferromagnetic films due to the inverse magnetostrictive effect, defined as the change of magnetization produced in ferromagnetic materials by an external stress. Thus, the magnetic control can be obtained without applying an external field by using heterostructures composed of a non-magnetic layer characterized by a temperature-driven structural phase transition coupled to a ferromagnetic layer. In such heterostructures, the magnetization of the ferromagnetic layer is modified through changes in the stress field at the interface when the structural phase transition in the non-magnetic layer (actuator) is carried out. In this work, we used NiTi shape memory alloy as the actuator to modify the magnetic behavior of ferromagnetic films through the magneto-elastic coupling in novel NiTi/Ni and NiTi/Co heterostructures. NiTi, when near its equiatomic composition, is a shape memory alloy that undergoes a reversible structural phase transition with temperature, providing stress on the ferromagnetic film. We chose this alloy because NiTi exhibits a large recovery stress with transition temperatures above room temperature for Ti-rich NiTi films, which is of interest for technological applications of the heterostructures. Since the right microstructure of NiTi is important to observe structural phase transition and it defines the characteristic of the transition, an extensive review on previous research on NiTi is detailed in this thesis. Thus, to ensure large stress during the NiTi structural transition with temperature, the NiTi alloy must be near its equiatomic composition with a thickness above 800 nm. Both characteristics were confirmed by Rutherford Backscattering analyses. The crystal structure and its transition with temperature were studied by X-ray diffraction measurements. In-plane magnetization and hysteresis measurements with temperature, performed on a superconducting quantum interference device (SQUID) magnetometer, prove the magneto-elastic coupling that was observed as an enhancement in the magnetic moment of the ferromagnetic layer. Such enhancement becomes the feature of magneto-elastic coupling in these novel NiTi/ferromagnetic heterostructures. / Esta tese estuda o papel da tensão interfacial em filmes heterogêneos na modificação do magnetismo de camadas ferromagnéticas finas por meio do efeito magnetoestritivo inverso, definido como a mudança de magnetização produzida em materiais ferromagnéticos por um estresse externo. Tecnologicamente, isto visa ter um grau de controle magnético do material sem a aplicação de um campo externo, usando heteroestruturas compostas por uma camada não magnética caracterizada por uma transição de fase estrutural acionada pela temperatura, acoplada a uma camada ferromagnética. Em tais heteroestruturas, a magnetização da camada ferromagnética é modificada através de alterações no campo de tensão na interface quando a transição de fase estrutural na camada não magnética (atuador) é realizada. Assim, utilizamos a liga com memória de forma NiTi como atuador, para modificar o comportamento magnético de filmes ferromagnéticos através do acoplamento magnetoelástico em novas heteroestruturas de NiTi/Ni e NiTi/Co. O NiTi, quando próximo à sua composição equiatômica, é uma liga com memória de forma que sofre uma transição de fase estrutural reversível com a temperatura, proporcionando tensão no filme ferromagnético. Escolhemos esta liga porque o NiTi apresenta uma grande tensão de recuperação com temperaturas de transição acima da temperatura ambiente, para filmes de NiTi ricos em Ti, o que é de interesse para aplicações tecnológicas das heteroestruturas. A microestrutura do NiTi é fundamental para favorecer a transição de fase estrutural e definir as suas características. Assim, uma extensa revisão de pesquisas anteriores sobre NiTi é detalhada nesta tese. Para garantir um grande estresse durante a transição estrutural do NiTi com a temperatura, o filme de NiTi deve estar próximo de sua composição equiatômica e ter espessura acima de 800 nm. Ambas as características foram confirmadas pelas análises de espectroscopia de retroespalhamento Rutherford. A estrutura cristalina e sua transição com a temperatura foram estudadas por medidas de difração de raios X. Medidas de magnetização e histerese em função da temperatura, com campo aplicado no plano dos filmes, realizadas em um magnetômetro SQUID, comprovaram a existência do acoplamento magnetoelástico, o qual se manifestou através de variações no momento magnético da camada ferromagnética. Essas mudanças de magnetização, observadas principalmente na heteroestrutura com Ni, torna-se a característica principal do acoplamento magnetoelástico nesses novos materiais.

L’objectif de ce travail est d’élaborer et de caractériser pour des applications biomédicalesun matériau auto-enchevêtré à base d’une seule fibre d’alliage à mémoire deforme de type Nickel-Titane. Nous avons optimisé un procédé de fabrication consistantà enchevêtrer et figer un ressort par des traitements thermiques. Les échantillonsont été caractérisés en compression et traction, avec suivi par caméra optique ettomographie in-situ. Les structures obtenues sont homogènes, isotropes, superélastiquesà température ambiante jusqu’à des déformations d’au moins 30%, et peuventdevenir ferroélastiques avec un effet mémoire d’au moins 16% par un traitement thermiqueadditionnel. Leur comportement en compression est consolidant puis dilatantet en traction, légèrement auxétique. Une comparaison avec des milieux similairesconstitués de fils ductiles et viscoélastiques, ainsi qu’avec des simulations par élémentsdiscrets sur des milieux élastiques sans frottement, montre que les propriétésmécaniques des structures auto-enchevêtrées sont contrôlées par leur architecturesingulière, à mi-chemin entre milieux continus et discrets. / The aim of this work is to process and characterize for biomedical applications,self-entangled structures made of a single NiTi shape memory fiber. We have optimizeda processing route consisting in entangling and shape-setting a spring bythermomechanical treatments. The samples were characterized in compression andtension, using optical and x-ray tomographic observations. The structures thus obtainedare homogeneous, isotropic, superelastic at room temperature up to strains ofat least 30%, and can become ferroelastic with a shape memory effect up to at least16% strain by an additional heat treatment. The mechanical behavior in compressionis first consolidating and then dilating, while in tension, the samples are slightlyauxetic. A comparison with similar media made of ductile and viscoelastic fibers,as well as with discrete element simulations on friction-free elastic fibers, show thatthe mechanical properties of these self-entangled structures are controlled by theirunique architecture, in-between continuous and discrete media.

L’objectif de ce travail est d’élaborer et de caractériser pour des applications biomédicalesun matériau auto-enchevêtré à base d’une seule fibre d’alliage à mémoire deforme de type Nickel-Titane. Nous avons optimisé un procédé de fabrication consistantà enchevêtrer et figer un ressort par des traitements thermiques. Les échantillonsont été caractérisés en compression et traction, avec suivi par caméra optique ettomographie in-situ. Les structures obtenues sont homogènes, isotropes, superélastiquesà température ambiante jusqu’à des déformations d’au moins 30%, et peuventdevenir ferroélastiques avec un effet mémoire d’au moins 16% par un traitement thermiqueadditionnel. Leur comportement en compression est consolidant puis dilatantet en traction, légèrement auxétique. Une comparaison avec des milieux similairesconstitués de fils ductiles et viscoélastiques, ainsi qu’avec des simulations par élémentsdiscrets sur des milieux élastiques sans frottement, montre que les propriétésmécaniques des structures auto-enchevêtrées sont contrôlées par leur architecturesingulière, à mi-chemin entre milieux continus et discrets. / The aim of this work is to process and characterize for biomedical applications,self-entangled structures made of a single NiTi shape memory fiber. We have optimizeda processing route consisting in entangling and shape-setting a spring bythermomechanical treatments. The samples were characterized in compression andtension, using optical and x-ray tomographic observations. The structures thus obtainedare homogeneous, isotropic, superelastic at room temperature up to strains ofat least 30%, and can become ferroelastic with a shape memory effect up to at least16% strain by an additional heat treatment. The mechanical behavior in compressionis first consolidating and then dilating, while in tension, the samples are slightlyauxetic. A comparison with similar media made of ductile and viscoelastic fibers,as well as with discrete element simulations on friction-free elastic fibers, show thatthe mechanical properties of these self-entangled structures are controlled by theirunique architecture, in-between continuous and discrete media.

This thesis focuses on the role of interfacial strain in heterostructures to modify the magnetism of thin ferromagnetic films due to the inverse magnetostrictive effect, defined as the change of magnetization produced in ferromagnetic materials by an external stress. Thus, the magnetic control can be obtained without applying an external field by using heterostructures composed of a non-magnetic layer characterized by a temperature-driven structural phase transition coupled to a ferromagnetic layer. In such heterostructures, the magnetization of the ferromagnetic layer is modified through changes in the stress field at the interface when the structural phase transition in the non-magnetic layer (actuator) is carried out. In this work, we used NiTi shape memory alloy as the actuator to modify the magnetic behavior of ferromagnetic films through the magneto-elastic coupling in novel NiTi/Ni and NiTi/Co heterostructures. NiTi, when near its equiatomic composition, is a shape memory alloy that undergoes a reversible structural phase transition with temperature, providing stress on the ferromagnetic film. We chose this alloy because NiTi exhibits a large recovery stress with transition temperatures above room temperature for Ti-rich NiTi films, which is of interest for technological applications of the heterostructures. Since the right microstructure of NiTi is important to observe structural phase transition and it defines the characteristic of the transition, an extensive review on previous research on NiTi is detailed in this thesis. Thus, to ensure large stress during the NiTi structural transition with temperature, the NiTi alloy must be near its equiatomic composition with a thickness above 800 nm. Both characteristics were confirmed by Rutherford Backscattering analyses. The crystal structure and its transition with temperature were studied by X-ray diffraction measurements. In-plane magnetization and hysteresis measurements with temperature, performed on a superconducting quantum interference device (SQUID) magnetometer, prove the magneto-elastic coupling that was observed as an enhancement in the magnetic moment of the ferromagnetic layer. Such enhancement becomes the feature of magneto-elastic coupling in these novel NiTi/ferromagnetic heterostructures. / Esta tese estuda o papel da tensão interfacial em filmes heterogêneos na modificação do magnetismo de camadas ferromagnéticas finas por meio do efeito magnetoestritivo inverso, definido como a mudança de magnetização produzida em materiais ferromagnéticos por um estresse externo. Tecnologicamente, isto visa ter um grau de controle magnético do material sem a aplicação de um campo externo, usando heteroestruturas compostas por uma camada não magnética caracterizada por uma transição de fase estrutural acionada pela temperatura, acoplada a uma camada ferromagnética. Em tais heteroestruturas, a magnetização da camada ferromagnética é modificada através de alterações no campo de tensão na interface quando a transição de fase estrutural na camada não magnética (atuador) é realizada. Assim, utilizamos a liga com memória de forma NiTi como atuador, para modificar o comportamento magnético de filmes ferromagnéticos através do acoplamento magnetoelástico em novas heteroestruturas de NiTi/Ni e NiTi/Co. O NiTi, quando próximo à sua composição equiatômica, é uma liga com memória de forma que sofre uma transição de fase estrutural reversível com a temperatura, proporcionando tensão no filme ferromagnético. Escolhemos esta liga porque o NiTi apresenta uma grande tensão de recuperação com temperaturas de transição acima da temperatura ambiente, para filmes de NiTi ricos em Ti, o que é de interesse para aplicações tecnológicas das heteroestruturas. A microestrutura do NiTi é fundamental para favorecer a transição de fase estrutural e definir as suas características. Assim, uma extensa revisão de pesquisas anteriores sobre NiTi é detalhada nesta tese. Para garantir um grande estresse durante a transição estrutural do NiTi com a temperatura, o filme de NiTi deve estar próximo de sua composição equiatômica e ter espessura acima de 800 nm. Ambas as características foram confirmadas pelas análises de espectroscopia de retroespalhamento Rutherford. A estrutura cristalina e sua transição com a temperatura foram estudadas por medidas de difração de raios X. Medidas de magnetização e histerese em função da temperatura, com campo aplicado no plano dos filmes, realizadas em um magnetômetro SQUID, comprovaram a existência do acoplamento magnetoelástico, o qual se manifestou através de variações no momento magnético da camada ferromagnética. Essas mudanças de magnetização, observadas principalmente na heteroestrutura com Ni, torna-se a característica principal do acoplamento magnetoelástico nesses novos materiais.

Shape memory alloys (SMAs) have been recognized as one of the most promising materials for MEMS micro-actuator applications. Among the available materials, Nickel/Titanium (NiTi) SMAs are more popular because, they exhibit unique properties in shape memory effect (SME) and pseudo-elasticity (PE). In addition NiTi SMA possesses high corrosion resistance, excellent mechanical properties and is also bio¬compatible. NiTi thin-film SMAs have been considered as the most significant material in the field of MEMS applications, which can be patterned with standard lithographic techniques to scale-up for batch production. However, the lack of proper understanding of basic materials’ properties and inability to reproduce, has limited the usage of this material in MEMS devices. The properties of NiTi SMA thin-films are very much sensitive to the elemental composition and structure, which are in turn decided by the deposition process and process parameters. A brief history of NiTi shape memory alloys (SMAs), basic information, transformation characteristics, crystal structure, phase diagram and literature reviewed for the current motivation have been presented in the second chapter In the third chapter, a brief summary about the deposition techniques relevant to NiTi film deposition has been presented. The deposition of NiTi films by a number of deposition techniques such as thermal evaporation, co-evaporation, molecular beam Epitaxy, pulsed laser deposition, flash evaporation, electron beam deposition, filtered arc deposition, ion beam assisted sputter deposition, vacuum plasma spraying, ion beam sputtering, ECR sputtering and magnetron sputtering techniques have been discussed. In order to achieve a precise control over film thickness and composition of the films on to the substrates, the selection of magnetron sputtering has been highlighted. In the present thesis, two prolonged approaches such as DC magnetron sputtering of an alloy target and co-sputtering of elemental targets have been presented. Various characterization techniques used for film thickness, composition, structure, micro¬structure, electrical, phase transformation and mechanical properties have also been briefly presented in the same chapter. In the fourth chapter, description of Conventional Alloy Target Sputtering System has been presented. DC magnetron sputtering of an alloy target with two different atomic ratios (Ni:Ti = 45:55 & 50:50) has been used for depositing the coatings. Several limitations in the reproducibility and repeatability have been observed with single alloy target sputtering, irrespective of the target composition ratio. In addition to this, incorporation of oxygen in the films during and after deposition has been observed, which has limited the extensive usage of this single alloy target system. The limitations regarding control over composition, thickness uniformity over large area have been improved by designing and fabricating a dedicated Three Target Magnetron Co-sputtering System. The vacuum diagnosis of the system under different conditions has been carried out by using PPR-200 Residual Gas Analyzer (RGA), which have included in Appendix I. Similar to alloy target sputtering system, the thickness uniformity and required composition with deposition parameters over a size of 75 mm diameter has been achieved and the process repeatability has been established. Oxygen incorporation in the films during deposition has been minimized by pre-sputtering of Ti target for known duration of time, which has resulted in significant reduction in partial pressure of oxygen in the chamber. The oxide layer formation on film surface has been eliminated by in-situ capping layer (TiN) deposition. In the fifth chapter, the influence of process parameters such as sample locations, substrate to target distance (STD), working pressure (WP), gas flow rates, deposition rates, deposition and annealing temperature, Target power, on the film thickness and composition uniformity have been presented for alloy target sputtering system as well as for the co-sputtering system. The film thicknesses have been measured with stylus method. Film compositions have been determined by energy dispersive X-ray spectroscopy (EDS), Secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS). The working pressure of 1.5 X 10-3 mbar, STD of 90 mm and target power of 100 W have been found to produce coatings having uniform thickness and composition over the given area for alloy target sputtering system. Similar investigations have been carried out for co-sputtered NiTiCu films. The working pressure of 1.5x 10-3 mbar, at a STD of 90 mm, at a rotational speed of 15 rpm and at target powers of 600, 50 and 12 W for Ti, Ni and Cu respectively, have resulted in the thickness and required composition uniformity over a size of 75 mm diameter substrate and the process repeatability has been established. In the Sixth chapter, the influence of process parameters on film structure and micro-structure on the NiTi/NiTiCu films deposited by a single alloy target and co¬sputtering have been studied by different analytical techniques like XRD, TEM, AFM, SEM etc. Phase transformation temperatures and kind of transformations have been investigated by DSC, Resistivity / Temperature and Stress/ Temperature studies and correlations have been established. The process parameters have been optimized for TiN deposition, which act as the capping layer to protect NiTi films from surface oxidation. The variation in mechanical behavior for the NiTi/ NiTiCu films before and after TiN capping by nano-indentation test have also presented. XRD and TEM studies have shown that the NiTi / NiTiCu films deposited at room temperature to 400o C are amorphous. Post-annealing, at a temperature of 450O C or above resulted in the film crystallization with oxide layer formation at the film surface, which has been confirmed by XRD and XTEM studies. In the case of Ni-rich NiTi films, R-phase diffraction peaks have also been identified in addition to the Austenite / Martensite phase. XRD investigations have shown that Ti-rich NiTi and Ni-rich NiTi films have resulted in precipitate free films. In the case of Ti-rich NiTiCu and Ni-rich NiTiCu films, the variations in Ti/Ni target power has resulted in the formation of NiTi 2 and Ni3Ti precipitates along with their parent Martensite and Austenite phases. When the Cu content is increased in NiTiCu films, an increase in number of Martensite phase diffraction peaks in XRD spectrum has been observed. XTEM studies have confirmed formation of oxide layer, inter-metallic layer and interface layer at higher post annealing temperatures. SEM studies have shown that the films deposited at higher gas flow rate results in the columnar micro-structure. In the context of NiTiCu films, the films deposited at higher Ti target power have shown more compact and tightly packed film micro-structure. AFM studies have shown increase in the average crystallite size and film roughness with post annealing temperature and duration. TiN coating has been used as the capping layer onto NiTi / NiTiCu films. Structural and micro-structural comparison of these films before and after TiN coating has resulted the appearance of (111) TiN peak in all TiN capped films. SEM and AFM studies have shown that the film roughness have decreased after capping layer deposition. DSC thermal cycling used to verify the film crystallization temperature has shown the appearance of exothermic peak in NiTi / NiTiCu films. DSC, Resistivity-temperature, stress-temperature response has been confirmed the transformation temperature and kind of transformations in all the films. Residual stress measurements have shown that the crystalline films exhibited lower bi-axial stress in comparison to the amorphous films. Ti-rich NiTi films have shown single phase transformations (M-A and A-M) whereas two phase transformations (M-R-A and A-R-M) have been observed in Ni-rich NiTi films. Higher deposition / annealing temperature have shown the appearance of distinct phase transformation peaks in resistivity vs. temperature studies. In the case of NiTiCu films, the decrease in film crystallization temperature with increase in the Cu content has been observed. The phase transformation temperature evaluated from second thermal cycle has shown decrease in the width of hysteresis loop with increase in the Cu content in NTC films. Nano-indentation studies have been carried out to evaluate the micro-hardness and modulus values of TiN capped and uncapped NiTi / NiTiCu films. The modulus and hardness uniformity have been confirmed for the different location over a diameter of 75 mm. The modulus and hardness values have increased with increase in the substrate and annealing temperature. Increase in the Cu target power has resulted in the increase in the hardness and modulus values under same deposition conditions. TiN coated NiTi / NiTiCu films have shown larger modulus and hardness values than the uncapped films. In the Seventh chapter, the fabrication process and actuation response for silicon dioxide, Aluminum and NiTi SMA coated micro-cantilevers has been discussed. Various nano-structures such as pyramids, beams and pillars by focused ion beam (FIB) micro-machining have been fabricated. High aspect ratio nano-pillars have been selected for micro-compression testing. In summary, this thesis emphasizes on the fabrication of specific sputtering systems relevant to NiTi film deposition and process parameter optimization for desired film thickness and composition uniformity. DC magnetron sputtering of a NiTi alloy target (50:50 and 45:55 at. %) and co-sputtering of elemental targets (Ni, Ti and Cu) have been presented. These films have been investigated for structural, micro-structural, phase transformation and mechanical properties. In-situ deposition of TiN capping layer, on to NiTi / NiTiCu films has been carried out to reduce the oxygen trapping. The fabrication process and actuation response of micro-cantilevers have been described. The etching characteristics to generate various nano-structures viz. pyramids, beams and pillars by focused ion beam (FIB) micro-machining have been investigated and mechanical testing of selected nano-structures have also been reported.

No description available.