Shape memory alloys (SMAs) exhibit unique combination of structural and functional properties and hence have a variety of current and potential applications. The mechanical behaviour of SMAs, in particular the influence of processing on the microstructure, which in turn influences the performance of the alloy, mechanical properties at the nano-scale, and under cyclic loading conditions, are of great current interest. In this thesis, specific issues within each of these broad areas are examined with a view to suggest further optimize/characterize SMAs. They are the following: (a) For thermo-mechanical secondary processing of SMAs, can we identify the optimum combination of temperature- strain rate window that yields a desirable microstructure? (b) How can indentation be used to obtain information about functional properties of shape memory alloys so as to complement traditional methods? (c) How can the information obtained from indentation be utilized for the identification of the alloy composition that yields a high temperature SMA through the combinatorial diffusion couple approach? Towards achieving the first objective, we study the hot deformation behavior of a cast NiTi alloy with a view of controlling the final microstructure. The “processing maps” approach is used to identify the optimum combination of temperature and strain rate for the thermomechanical processing of a SMA system commonly used in actuators applications (NiTiCu). Uniaxial compressions experiments are conducted in the temperature range of 800- 1050 °C and at strain rate range of 10-3 and 102 s-1. 2-D power dissipation efficiency and instability maps are generated and various deformation mechanisms, which operate in different temperature–strain rate regimes, are identified with the aid of these maps. Complementary microstructural analysis of specimens (post deformation) is performed with the help of electron backscattered diffraction (EBSD) analysis to arrive at a processing route which produces stress free grains. A safe window suitable for industrial processing of this alloy which leads to grain refinement and strain-free grains (as calculated by various methods of misorientation analysis representation) is suggested. Regions of the instability (characterized by the same analysis) result in strained microstructure, which in turn can affect the performance of the SMA in a detrimental manner. Next, to extract useful information from indentation responses, microindentation experiments at a range of temperatures (as the shape memory transformation is in progress) are conducted underneath the Vickers indenter. SME was observed to cause a change in the calculated recovery ratios at temperatures above As. Spherical indentation of austenite and martensite show different characteristics in elastic and elasto- plastic regimes but are similar in the plastic regime. NanoECR experiments are also conducted under a spheroconical indenter at room temperature, where the resistance measured is observed to increase during the unloading of room temperature austenite SMA. This is a signature of the reverse transformation back to austenite during the withdrawal of the indenter. Lastly, recovery ratios are monitored in the case of a NiTiPd diffusion couple before and after heat treatment at different temperature intervals using non- contact optical profilometry. The recovery ratio approach is successfully used to determine the useful temperature and %Pd range for a potential NiTiPd high temperature SMA. The method makes high throughput identification of high temperature shape memory alloys possible due to promising alloy compositions being identified at an early stage.

No description available.

The area of research dealing with joining of dissimilar metals has been active in recent time. Although fusion and non-fusion techniques of joining have been effectively used for manufacturing components, a comprehensive scientific understanding of the process is lacking. This void exists both in fusion and non-fusion welding methods. The present investigation addresses some of these aspects. The investigation consists of two sections - Part A and Part B. Part A is on Friction welding and Part B deals with Fusion welding using laser. Each section has two chapters each. Following an introductory chapter, basic aspects of friction welding is presented in chapter 2. Chapter 3 deals with the work on friction welding of Fe-Cu couple. Fe-Cu couple is a system with positive heat of mixing. After a brief introduction on various non-equilibrium processes that can occur in this system, experimental details and results are presented. Using the results an attempt is made to understand the flash formation, formation of pores at the interface and the formation of chemically altered zone. It is observed that a chemically altered layer forms predominantly on the Cu side of the interface. It consists of Fe entrapped as fragments/fine crystals and as solid solution in Cu matrix. This zone has higher thickness at the edges than at the center. The mechanism of formation of this interfacial layer which is central to the joining process is related to the fracture and transport of fragments during plastic deformation. Fe forms solid solution in copper under non-equilibrium conditions promoted by shear energy. Using the concept of ballistic mixing, the formation of solid solution is explored. Using nano-indentation experiments mechanical properties of the weldment is estimated and an attempt is made to correlate mechanical properties with the amount of second element present in that location. The chapter 4 in part A deals with the friction welding of Ni-Ti couple. Ni-Ti system has negative heat of mixing and it forms a number of intermetallics. After a brief introduction to the chapter, various experimental techniques and strategies followed to carry out the experiments are explained. Following these, the results are presented. It is observed that TiNi3 formed at initial stage. Theories based on effective heat of formation and surface energy also predict the nucleation of TiNi3. With the continuation of frictional processes, the formation of TiNi and Ti2Ni phases were also observed. Formation of Ti2Ni was shown to greatly accelerate due to shear process. In this system two complementary processes like ballistic mixing and thermal assisted diffusion accelerate Ti2Ni formation. From mechanical tests it is found that Ti2Ni layer in the weldment is weak and hence formation of Ti2Ni in the weldment is detrimental. In chapter 5 an introduction to fusion welding of dissimilar metals is presented as background materials for the subsequent chapters. Chapter 6 deals with nature of segregation of Ag during laser welding of Fe-Ni couple. Ag is used as a tracer to probe fluid flow in the Fe-Ni couple during laser welding. Ag is immiscible both in Fe and Ni whereas Fe and Ni form a complete solution at an elevated temperature and in liquid state. Besides the experimental work, numerical simulation of the weld pool were carried out using homogeneous mixture model using SIMPLER algorithm. Experiments and simulations indicate that fluid flow is asymmetrical and in the deep penetration welding strong convection in the pool drives the tracer to the top of the pool. Overall distribution of the tracer is due to the combined effect of convection and diffusion. In shallow welding there exists a boundary region where tracer does not penetrate. In chapter 7 the results of instrumented indentation experiments on laser welded Fe-Cu weldment has been presented. It was earlier reported that during laser welding of Fe-Cu couple, a variety of microstructures evolves at various locations in the weldment and hardness of the weldment were found to be very high. Here an attempt has been made to explore in details the origin of such a high hardness. The chapter starts with a description of various microstructures that are observed in this weldment followed by the various procedures used for extracting data from instrumented indentation tests. It is followed by the presentation of the experimental results. It is found that rule of mixture along with Hall-Petch strengthening explains the observed increase in hardness of the weldment. The fine scale microstructure consisting of alternate Fe rich and Cu rich layers increases the hardness of the weldment. On copper side of the weldment, composition and scale of microstructure fluctuates and so also the hardness. Finally in chapter 8 overall conclusions of the various chapters in the thesis have been summarised.

L'optimisation des états de surface constitue un enjeu majeur pour les biomatériaux utilisés dans le domaine biomédical. Le titane (Ti) et ses alliages à base de nickel (NiTi) restent à ce jour les biomatériaux métalliques de prédilection dans nos applications cliniques en Odontologie (implants dentaires, instruments endodontiques, et arcs orthodontiques). Le but de nos recherche est d'optimiser les surfaces du Ti et NiTi en les fonctionnalisant par des films multicouches de polyélectrolytes (FMP). Notre travail propose d'étudier différents paramètres devant être impérativement validés avant d'envisager une quelconque application biomédicale in vivo avec ce type de revêtement. Une recherche bibliographique exhastive appuie notre recherche expérimentale. Le premier axe du travail propose de déterminer si des FMP peuvent effectivement s'adsorber chimiquement sur le Ti et le NiTi. qui plus est, une étude biologique est réalisée avec des cellules humaines pour tester la biocompatibilité des ces surfaces fonctionnalisées. La deuxième partie se concentre sur la biocompatibilité de la couche précurseur des FMP à base de polyéthyléneimine (PEI). Les résultats mettent en lumière une certaine cytotoxicité de la PEI envers des ostéoblastes et des fibroblastes gingivaux humain. Pour clore ce travail, nous réalisons des essais de stérilisation afin d'évaluer l'influence d'un tel procédé sur les FMP en terme de caractérisations physico-chimique et biologique des surfaces. La perspective d'une application biomédicale avec les FMP semble prometteuse, notamment en y introduisant des molécules bioactives. Cependant, bien d'autres paramètres sont encore à étudier avant d'envisager une application expérimentale et/ou clinique in vivo. Nous pouvons citer par exemple, le vieillissement des FMP, leur comportement en milieu salivaire ou fluoré, ou encore leur résistance à l'usure. Ces différents éléments rentrent dans les perspectives d'un projet post-doctoral. / Optimization of surface properties is a fundamental priority for biomaterials uses in biomedical applications. Titanium (Ti) and nickel-titanium alloys (NiTi) are the references in terms of metallic biomaterials for clinical applications in Odontology (Dental implants, endodontic instrumentations, and orthodontic arches). The aim of our work is to study the Ti and NiTi surfaces coated with polyelectrolytes multilayers films (PEM). Our work study various parameters needed to be validated before using this functionalized surface treatment for biomedical and clinical applictions in vivo. The first part of this work aims at defining the possibility to chemically adsorb PEM coating on Ti and on NiTi surfaces. Moreover, we have realized a biological study with human cells to test the biocompatibility of functionalized surfaces. In the second part of this thesis, we tested the biocompatibility of the multilayered structure in regards to the precursor base layer of PEM, the polyethyleneimine (PEI). Our reuslts show that the PEI is not cytotoxic towards osteoblasts and human gingival fibroblasts. Finally, we relaized tests of sterilization to evaluate PEM stability in terms of physico-chemical and biological surface characterizations. The development of specific biomedical applications for PEM is an exciting perspective, especially when these firms are functionalized with bioactive molecules. However, many other parameters murst be studied before imagining an experimental or clinical application in vivo. As an example, PEM degradation as well as behaviour in salivary or fluoride solution, still needs to be tested.

Made available in DSpace on 2014-07-29T15:22:00Z (GMT). No. of bitstreams: 1 dissertacao henrique c m oliveira.pdf: 1002486 bytes, checksum: eddcaf3f31b0f29703a16146f9f05b7d (MD5) Previous issue date: 2010-02-26 / The aim of this study was to determine the errors of procedures that occurred during the preparation of curved root canals after the use of instruments níqueltitânio powered motor managed by specialists in endodontics and dental students. Forty upper and lower molars of humans were randomly divided into two groups of 20, according to traders: G1A-(Molars, specialists in endodontics), G1B-(lower molars, specialists in endodontics), G2A-(molars, dental students), G2B-(lower molars, dental students). The ProTaper Universal System was used to prepare all root canals. The AH PlusTM associated with gutta-percha was used with lateral condensation technique for obturation of all canals. Periapical radiography and cone beam computed tomography (TCFC) were obtained to verify procedural errors occurred during the preparation of root canals. Two examiners evaluated all images for determining the presence or absence of instrument fracture, root perforation (cervical, middle or apical) and deviation original path of the root canal (apical transport). The data were statistically analyzed employing the Chi-square test. The significance level was 5%. The rate of fractured instruments showed no significant differences in the level of experience of operators (p = 1.000). Root perforations and transport apical occurred more frequently in the group of students, without significant differences. While there have been some procedural errors during root canal preparation with experienced and inexperienced operators, the results suggest that the introduction of tools of nickel-titanium engine-driven education / O objetivo deste estudo foi determinar os erros de procedimentos ocorridos durante o preparo de canais radiculares curvos após o uso de instrumentos de níqueltitânio acionados a motor manejados por especialistas em endodontia e estudantes de odontologia. Quarenta molares superiores e inferiores de humanos foram aleatoriamente divididos em dois grupos de 20, de acordo com os operadores: G1A- (molares superiores, especialistas em endodontia), G1B- (molares inferiores, especialistas em endodontia); G2A- (molares superiores, estudantes de odontologia), G2B- (molares inferiores, estudantes de odontologia). O sistema ProTaper Universal foi usado para o preparo de todos os canais radiculares. O cimento AH PlusTM associado com a guta-percha foi usado com a técnica da condensação lateral para a obturação de todos os canais radiculares. Radiografias periapicais e tomografia computadorizada de feixe cônico (TCFC) foram obtidas para verificar erros de procedimentos ocorridos durante o preparo dos canais radiculares. Dois examinadores avaliaram todas as imagens determinando a presença ou ausência de fratura de instrumentos, perfurações radiculares (terço cervical, médio ou apical) e desvio do trajeto original do canal radicular (transporte apical). Os dados foram estatisticamente avaliados empregando-se o teste Qui-quadrado. O nível de significância foi de 5%. A taxa de instrumentos fraturados não mostrou diferenças significantes em relação ao nível de experiência dos operadores (p=1,000). Perfurações radiculares e transportes apicais ocorreram mais frequentemente no grupo dos estudantes, sem diferenças significantes. Embora tenham sido observados alguns erros de procedimentos durante o preparo do canal radicular com operadores experientes e inexperientes, os resultados sugerem que a introdução de instrumentos de níquel-titânio movidos a motor no ensino da graduação parece promissora. Ambos os métodos de imagens permitiram identificar erros operatórios, porém a tomografia computadorizada de feixe cônico apresenta elevado potencial de auxiliar a terapia endodôntica.

Shape memory alloys (SMAs) operating as solid-state actuators pose economic and environmental benefits to the aerospace industry due to their lightweight, compact design, which provides potential for reducing fuel emissions and overall operating cost in aeronautical equipment. Despite wide applicability, the implementation of SMA technology into aerospace-related actuator applications is hindered by harsh environmental conditions, which necessitate extremely high or low transformation temperatures. The versatility of the NiTi-based SMA system shows potential for meeting these demanding material constraints, since transformation temperatures in NiTi can be significantly raised or lowered with ternary alloying elements and/or Ni:Ti ratio adjustments. In this thesis, the expansive transformation capabilities of the NiTi-based SMA system are demonstrated with a low and high-temperature NiTi-based SMA; each encompassing different stages of the SMA development process. First, exploratory work on the NiTiSn SMA system is presented. The viability of NiTiSn alloys as low-temperature SMAs (LTSMAs) was investigated over the course of five alloy heats. The site preference of Sn in near-equiatomic NiTi was examined along with the effects of solution annealing, Ni:Ti ratio adjustments, and precipitation strengthening on the thermomechanical properties of NiTiSn LTSMAs. Second, the thermomechanical processability of NiTiHf high-temperature SMA (HTSMA) wires is presented. The evolution of various microstructural features (grain size reduction, oxide growth, and nano-precipitation) were observed at incremental stages of the hot rolling process and linked to the thermal and mechanical responses of respective HTSMA rods/wires. This work was carried out in an effort to optimize the rolling/drawing process for NiTiHf HTSMAs.

No description available.

O controle da extrusão apical durante a reintervenção endodôntica é essencial para o sucesso do novo tratamento. Nesse contexto, o presente estudo teve como objetivo comparar a quantidade de material sólido extruído na desobturação de canais radiculares variando-se a técnica de esvaziamento e o limite de obturação. Foram utilizados 40 incisivos inferiores previamente tratados divididos em dois grupos de acordo com o limite de obturação estabelecido. Cada grupo foi subdividido em dois subgrupos levando-se em conta a técnica de desobturação empregada; manual (subgrupos A1 e B1) e mecânico-rotatória com limas de Ni-Ti (Quantec LX) (subgrupos A2 e B2). O material sólido extruído foi coletado por meio do sistema de filtração Millipore, levado à secagem em dessecador de sílica e pesado em balança analítica de precisão. Os resultados obtidos foram submetidos a ANOVA para dois fatores de variação sendo em seguida empregado o Teste de Tukey (&#945; = 5%). A técnica de desobturação mecânico-rotatória produziu menor extrusão (0,66mg) que a manual (1,11mg), havendo diferença estatística significante entre elas (p < 0,05). Os canais preenchidos até o vértice radiográfico apresentaram maior quantidade de extrusão (1,38mg) do que os obturados 1 mm aquém do forame (0,39mg), observando-se diferença estatística significante entre eles (p < 0,05). A menor quantidade extrusão foi observada no subgrupo A2 (0,20mg), em que foi empregada a técnica rotatória de desobturação em canais obturados 1mm aquém do forame apical, sendo constatada diferença estatisticamente significante deste subgrupo com os demais (p < 0,05). A extrusão de material sólido durante a desobturação de canais radiculares é influenciado pela técnica empregada e pelo limite apical de obturação. / The apical extrusion control during the endodontic retreatment is essential for the success of the new treatment. The purpose of this study was to compare the quantity of solid apically extruded material during filling removal according the gutta-percha removal technique and root filling limit. Forty mandibular incisors with a single straight canal were selected. The canals were previously endodontically treated and then divided into two groups according the filling level. Each group was subdivided in two groups considering the retreatment technique: stainless steel hand files (subgroups A1 and B1) versus niquel-titanium rotatory instruments (subgroups A2 and B2). The extruded solid material was collected by Millipore filtration system, dried in silica desiccators and weighed in an eletrobalance. The results were analyzed using ANOVA with two variation factors and Tukey Test (&#945; = 5%). The niquel-titanium rotatory instruments produced less extrusion (0,66mg) than the stainless steel hand files (1,11mg), with significant statistical difference between them (p < 0,05). The canals filled until the radiographic apex showed larger amount of extruded material (1,38mg) than those filled 1 mm beyond the foramen (0,39mg). It was observed significant statistical difference between them (p < 0,05). The smaller extruded debris amount was observed in subgroup A2 (0,20mg), in which one the rotary technique was used to remove the gutta-percha of canals filled 1mm beyond the apical foramen. It was verified significant statistical difference of this subgroup with the other ones (p < 0,05). The extrusion of solid material during the gutta-percha removal is influenced by the technique as well as the apical filling limit.

O controle da extrusão apical durante a reintervenção endodôntica é essencial para o sucesso do novo tratamento. Nesse contexto, o presente estudo teve como objetivo comparar a quantidade de material sólido extruído na desobturação de canais radiculares variando-se a técnica de esvaziamento e o limite de obturação. Foram utilizados 40 incisivos inferiores previamente tratados divididos em dois grupos de acordo com o limite de obturação estabelecido. Cada grupo foi subdividido em dois subgrupos levando-se em conta a técnica de desobturação empregada; manual (subgrupos A1 e B1) e mecânico-rotatória com limas de Ni-Ti (Quantec LX) (subgrupos A2 e B2). O material sólido extruído foi coletado por meio do sistema de filtração Millipore, levado à secagem em dessecador de sílica e pesado em balança analítica de precisão. Os resultados obtidos foram submetidos a ANOVA para dois fatores de variação sendo em seguida empregado o Teste de Tukey (&#945; = 5%). A técnica de desobturação mecânico-rotatória produziu menor extrusão (0,66mg) que a manual (1,11mg), havendo diferença estatística significante entre elas (p < 0,05). Os canais preenchidos até o vértice radiográfico apresentaram maior quantidade de extrusão (1,38mg) do que os obturados 1 mm aquém do forame (0,39mg), observando-se diferença estatística significante entre eles (p < 0,05). A menor quantidade extrusão foi observada no subgrupo A2 (0,20mg), em que foi empregada a técnica rotatória de desobturação em canais obturados 1mm aquém do forame apical, sendo constatada diferença estatisticamente significante deste subgrupo com os demais (p < 0,05). A extrusão de material sólido durante a desobturação de canais radiculares é influenciado pela técnica empregada e pelo limite apical de obturação. / The apical extrusion control during the endodontic retreatment is essential for the success of the new treatment. The purpose of this study was to compare the quantity of solid apically extruded material during filling removal according the gutta-percha removal technique and root filling limit. Forty mandibular incisors with a single straight canal were selected. The canals were previously endodontically treated and then divided into two groups according the filling level. Each group was subdivided in two groups considering the retreatment technique: stainless steel hand files (subgroups A1 and B1) versus niquel-titanium rotatory instruments (subgroups A2 and B2). The extruded solid material was collected by Millipore filtration system, dried in silica desiccators and weighed in an eletrobalance. The results were analyzed using ANOVA with two variation factors and Tukey Test (&#945; = 5%). The niquel-titanium rotatory instruments produced less extrusion (0,66mg) than the stainless steel hand files (1,11mg), with significant statistical difference between them (p < 0,05). The canals filled until the radiographic apex showed larger amount of extruded material (1,38mg) than those filled 1 mm beyond the foramen (0,39mg). It was observed significant statistical difference between them (p < 0,05). The smaller extruded debris amount was observed in subgroup A2 (0,20mg), in which one the rotary technique was used to remove the gutta-percha of canals filled 1mm beyond the apical foramen. It was verified significant statistical difference of this subgroup with the other ones (p < 0,05). The extrusion of solid material during the gutta-percha removal is influenced by the technique as well as the apical filling limit.