The objective of this work is to understand the structure-property relationships in a pseudoelastic composition of polycrystalline NiTiPt (Ti-42.7 at% Ni-7.5 at% Pt). Structural characterization of the alloy includes grain size determination and texture analysis while the thermo-mechanical properties are explored using tensile testing. Variation in heat treatment is used as a vehicle to modify microstructure. The results are compared to experiments on Ni-rich NiTi alloy wires (Ti-51.0 at% Ni), which are in commercial use in various biomedical applications. With regards to microstructure, both alloys exhibit a <111> fiber texture along the wire drawing axis, however the NiTiPt alloy's grain size is smaller than that of the Ni-rich NiTi wires, while the latter materials contain second phase precipitates. Given the nanometer scale grain size in NiTiPt and the dispersed, nanometer scale precipitate size in NiTi, the overall strength and ductility of the alloys are essentially identical when given appropriate heat treatments. Property differences include a much smaller stress hysteresis and smaller temperature dependence of the transformation stress for NiTiPt alloys compared to NiTi alloys. Potential benefits and implications for use in vascular stent applications are discussed.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-27T15:46:57Z No. of bitstreams: 1 ESTEPHANIE NOBRE DANTAS GRASSI - DISSERTAÇÃO PPGEM 2014..pdf: 4659811 bytes, checksum: 9dce2fd88b57abcccbb5be6fa913cf1b (MD5) / Made available in DSpace on 2018-04-27T15:46:57Z (GMT). No. of bitstreams: 1 ESTEPHANIE NOBRE DANTAS GRASSI - DISSERTAÇÃO PPGEM 2014..pdf: 4659811 bytes, checksum: 9dce2fd88b57abcccbb5be6fa913cf1b (MD5) Previous issue date: 2014-08-01 / CNPq / Capes / As Ligas com Memória de Forma (LMF) são um importante grupo de materiais metálicos ativos que respondem a estímulos termomecânicos por meio dos fenômenos do Efeito Memória de Forma (EMF) e da Superelasticidade (SE). Ambos os efeitos permitem recuperar grandes níveis deformações por meio de aquecimento, no primeiro caso, ou do descarregamento mecânico, no segundo. As LMF de NiTi são facilmente encontradas no mercado médico e odontológico em forma de ferramentas e acessórios para tratamentos específicos. Um destes elementos são minimolas helicoidais ortodônticas de NiTi, que alcançam deformações algumas centenas de vezes maiores que elementos unidimensionais de LMF, como fios. Por outro lado, é de amplo conhecimento que uma técnica adequada para manipular propriedades mecânicas de produtos metálicos acabados, além de variar-se a configuração geométrica, é a realização de tratamentos térmicos de recozimento. Principalmente após a realização de trabalho a frio, os recozimentos são capazes de recuperar parcial ou totalmente a mobilidade atômica no metal, o que, no caso das LMF, afeta diretamente o seu comportamento termomecânico. Neste contexto, o principal objetivo deste trabalho é estudar a influência de tratamentos térmicos de recozimento sobre a resposta termomecânica de minimolas de LMF NiTi, originalmente superelásticas. Um planejamento fatorial foi usado para avaliar a influência das variáveis temperatura e tempo de recozimento sobre algumas das principais propriedades termomecânicas das minimolas: constante de mola (rigidez), módulo de elasticidade transversal, capacidade de dissipação de energia, temperaturas de transformação, histere térmica e a entalpia de transformação. Foi demonstrado que tratamentos térmicos a temperaturas na faixa de 500 oC a 600 oC são capazes de converter as minimolas de LMF NiTi do estado superelástico para o estado de atuador, pelo aparecimento do efeito memória de forma. / Shape Memory Alloys (SMA) are an important group of metallic active materials that respond to thermomechanical stimuli through the Shape Memory Effect (SME) or the Superelasticity (SE) phenomena. Both these effects are capable of retrieving large amounts of strain by simple heating, in the former case, or simple mechanical unload, in the latest case. The SMA of the NiTi family composition exhibit superior properties when compared to other compositions, including biocompability, what brings this alloy to be widely used in medical and orthodontic fields in the form of tools and accessories to specific treatments. As an example, mini coil springs of NiTi SMA presenting superelasticity reach strain levels hundreds of times higher than one-dimensional elements, such as wires. However, a more suitable technique to manipulate mechanical properties of metallic finished products is the use of heat treatments like annealing. Mainly after experiencing cold working processes, annealing treatments are capable of partially or totally recover the atomic mobility, witch directly affects thermomechanical response of SMA. In this context, this dissertation work aims to study the influence of annealing heat treatments over thermomechanical behavior of SMA NiTi mini coil springs originally presenting the SE. A factorial design was used to evaluate the influence of temperature and time of annealing over some of the main thermomechanical springs’ properties: spring constant (stiffness), shear modulus, energy dissipation capacity, phase transformation temperatures, thermal hysteresis and transformation enthalpy availability. It was demonstrated that heat treatments between 500°C and 600°C are capable of converting the superelastic state of the mini coil springs to an actuator state, as a result of the shape memory effect appearance.

No description available.

This thesis presents methods for fabricating MicroElectroMechanical System (MEMS) actuators and high-flow gas microvalves using wafer-level integration of Shape Memory Alloys (SMAs) in the form of wires and sheets. The work output per volume of SMA actuators exceeds that of other microactuation mechanisms, such as electrostatic, magnetic and piezoelectric actuation, by more than an order of magnitude, making SMA actuators highly promising for applications requiring high forces and large displacements. The use of SMAs in MEMS has so far been limited, partially due to a lack of cost efficient and reliable wafer-level integration approaches. This thesis presents new methods for wafer-level integration of nickel-titanium SMA sheets and wires. For SMA sheets, a technique for the integration of patterned SMA sheets to silicon wafers using gold-silicon eutectic bonding is demonstrated. A method for selective release of gold-silicon eutectically bonded microstructures by localized electrochemical etching, is also presented. For SMA wires, alignment and placement of NiTi wires is demonstrated forboth a manual approach, using specially built wire frame tools, and a semiautomatic approach, using a commercially available wire bonder. Methods for fixing wires to wafers using either polymers, nickel electroplating or mechanical silicon clamps are also shown. Nickel electroplating offers the most promising permanent fixing technique, since both a strong mechanical and good electrical connection to the wire is achieved during the same process step. Resistively heated microactuators are also fabricated by integrating prestrained SMA wires onto silicon cantilevers. These microactuators exhibit displacements that are among the highest yet reported. The actuators also feature a relatively low power consumption and high reliability during longterm cycling. New designs for gas microvalves are presented and valves using both SMA sheets and SMA wires for actuation are fabricated. The SMA-sheet microvalve exhibits a pneumatic performance per footprint area, three times higher than that of previous microvalves. The SMA-wire-actuated microvalve also allows control of high gas flows and in addition, offers benefits of lowvoltage actuation and low overall power consumption. / QC 20120514

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-03-16T19:08:32Z No. of bitstreams: 1 JOSIANE DANTAS COSTA - DISSERTAÇÃO PPGEQ 2015..pdf: 2694660 bytes, checksum: b1f464f2e8b29d82a5339c5bd52471b3 (MD5) / Made available in DSpace on 2018-03-16T19:08:32Z (GMT). No. of bitstreams: 1 JOSIANE DANTAS COSTA - DISSERTAÇÃO PPGEQ 2015..pdf: 2694660 bytes, checksum: b1f464f2e8b29d82a5339c5bd52471b3 (MD5) Previous issue date: 2015-09-29 / A liga de Ni-Ti, conhecida por Nitinol, é constituída dos elementos níquel e titânio e vem sendo bastante aplicada nas mais diversas áreas: aeroespacial, automotiva, construção civil, dispositivos médicos e ortodônticos. Esse potencial de aplicação decorre das propriedades particulares de efeito de memória de forma e superelasticidade, associada a uma boa resistência à corrosão e excelente biocompatibilidade. Com intuito de aumentar as aplicações desse material em dispositivos médicos, o desenvolvimento de tecnologias de união torna-se necessário para possibilitar a fabricação das mais diferentes formas geométricas e combinações entre materiais similares e dissimilares. Nesse contexto, é fundamental que se realize estudos sobre a resistência a corrosão da região em que foi feita a união (junta), principalmente quando utilizados processos de soldagem, já que podem deixar falhas induzindo a uma maior suscetibilidade a corrosão. Diante disto, neste trabalho foi realizada a união de fios ortodônticos de Ni-Ti com fios ortodônticos de Ti-Mo através do processo de soldagem TIG (“Tungsten Inert Gas”) autógeno. Como se trata de biomateriais, este estudo teve como objetivo geral avaliar a resistência à corrosão dos fios comerciais íntegros e da junta soldada Ni-Ti/Ti-Mo em solução salina tamponada SBF (“Saline Buffered Phosphate”) que simula o sangue humano, para verificar se a soldagem afetaria a resistência a corrosão das juntas. Os resultados obtidos revelaram que o processo da soldagem TIG utilizado neste trabalho gerou juntas soldadas de excelente qualidade, apresentando uma resistência à corrosão superior à dos fios íntegros. O planejamento experimental utilizado para verificar a influência da temperatura e do tempo do tratamento térmico nos resultados de corrosão, gerou um experimento ótimo com temperatura de 350°C e um tempo de 40 minutos. Este resultado foi confirmado através dos ensaios de espectroscopia de impedância eletroquímica. / The Ni-Ti alloy, known as Nitinol, is made of nickel and titanium elements and has been widely applied in several areas: aerospace, automotive, construction, medical and orthodontic appliances. Nitinol's application potential is due to its particular superelasticity properties and shape memory effect associated with a good corrosion resistance and excellent biocompatibility. In order to increase the applications of this material in medical devices, the development of joining technologies is necessary to enable manufacture of the most different geometric shapes and combinations of similar and dissimilar materials. In this context, it is essential to conduct studies on the corrosion resistance of the region where the union (joint) was done, especially when welding processes are used, as they can leave gaps leading to greater susceptibility to corrosion. With this in mind, this work carried out the union of Ni-Ti orthodontic wire with Ti-Mo orthodontic wire through the autogenous TIG (Tungsten Inert Gas) welding process. As biomaterials are involved, this study aimed to evaluate the corrosion resistance of the upright commercial wire and welded joint Ni-Ti/Ti-Mo in buffered saline solution SBP (Saline Buffered Phosphate) which simulates human blood, to check if the welding would affect the corrosion resistance of the joint. The results revealed that the TIG welding process used in this work generated welds of excellent quality, having a corrosion resistance higher than that of intact wires. The experimental design used to determine the influence of temperature and time of heat treatment on the results of corrosion generated a great experiment with temperature of 350 ° C and a time of 40 minutes. This result was confirmed by means of electrochemical impedance spectroscopy test.

No description available.

This thesis presents methods for the wafer-level integration of shape memory alloy (SMA) and electrostatic actuators to functionalize MEMS devices. The integration methods are based on heterogeneous integration, which is the integration of different materials and technologies. Background information about the actuators and the integration method is provided. SMA microactuators offer the highest work density of all MEMS actuators, however, they are not yet a standard MEMS material, partially due to the lack of proper wafer-level integration methods. This thesis presents methods for the wafer-level heterogeneous integration of bulk SMA sheets and wires with silicon microstructures. First concepts and experiments are presented for integrating SMA actuators with knife gate microvalves, which are introduced in this thesis. These microvalves feature a gate moving out-of-plane to regulate a gas flow and first measurements indicate outstanding pneumatic performance in relation to the consumed silicon footprint area. This part of the work also includes a novel technique for the footprint and thickness independent selective release of Au-Si eutectically bonded microstructures based on localized electrochemical etching. Electrostatic actuators are presented to functionalize MEMS crossbar switches, which are intended for the automated reconfiguration of copper-wire telecommunication networks and must allow to interconnect a number of input lines to a number of output lines in any combination desired. Following the concepts of heterogeneous integration, the device is divided into two parts which are fabricated separately and then assembled. One part contains an array of double-pole single-throw S-shaped actuator MEMS switches. The other part contains a signal line routing network which is interconnected by the switches after assembly of the two parts. The assembly is based on patterned adhesive wafer bonding and results in wafer-level encapsulation of the switch array. During operation, the switches in these arrays must be individually addressable. Instead of controlling each element with individual control lines, this thesis investigates a row/column addressing scheme to individually pull in or pull out single electrostatic actuators in the array with maximum operational reliability, determined by the statistical parameters of the pull-in and pull-out characteristics of the actuators. / QC20100729