There is an upsurge of research interest on Ni-based superalloys additively manufactured (AM) in aerospace sectors. However, achieving the accuracy and quality of the AM part is a challenging task because it is a process of adding material layer by layer with different process parameters. Hence, defects can be observed, and these defects have a detrimental effect on the mechanical properties of the material. Also, AM materials commonly portray a columnar grain structure which also makes it difficult to determine the average grain size because while using the commonly used intercept method, the grain boundaries do not intercept to the test line appropriately. It is important to measure the defects and grain size before performing mechanical testing on the material. Defect measurement and grain size measurements are usually measured manually which results in longer lead time. This work is addressed towards testing recipes in the automated image analysis software to optimize the lead time with good accuracy. Haynes 282, a γ' strengthened superalloy is used in this work. It was assumed that 1,5mm of material from the surface will be machined away so defects had to be measured in this region of interest. The image analysis tools used to test its potentials are MIPAR and ImageJ. Initially, five images in MIPAR and Image J were tested keeping the manual measurements as a benchmark. From this part, it was concluded that metallography and image quality play an important role in the automated measurement. Also, basic Image J software cannot give the measurements of lack of fusion in terms of caliper diameter (longest measurable diameter). Hence, MIPAR was chosen for the application because it was more promising. In the next part, 15 samples were used with manual measurements from a stitched sample and batch processing with MIPAR. The total caliper diameter results were plotted to compare manual measurements and MIPAR. It was observed that scratches were measured as lack of fusion defects at few instances by MIPAR which were further refined using a post-processing function. The defect density results were plotted and compared as well. Due to the difference in calculation of region of interest, the difference in results was observed.To perform the grain size measurement, Haynes 282 was used in HIP and heat treated condition, achieving equiaxed grains. The etchant should be appropriate to reveal the grains. Hence four different etchants were used in this study hydrogen peroxide+HCl, Kallings (electro etch), Kallings (swab) and diluted oxalic acid. This measurement was performed on the material which was cut along the build direction as well as 90º to the growth direction. Since there is no standard for additively manufactured material yet, the results were tested with hall-petch equation to be convinced of the results obtained. It was observed that MIPAR recipe portrayed good results. The results of manual measurements and MIPAR measurements were plotted and compared. It was observed that Hydrogen peroxide and Kallings (swab) showed the grains evidently but twin boundaries were revealed as well. MIPAR calculated the twin boundaries as grains so it over calculated than manual measurements. Kallings (electro etch) and diluted oxalic acid did not reveal the grains so it was difficult for MIPAR to identify the grains.

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This thesis provides a research into properties of nickel-based single crystal superalloys. The underlying quantitative relationship between alloy chemistry and the important properties have been studied. To design new grade of single crystal superalloys, computational modelling methods have been proposed which build on the findings of composition-microstructure-property relationships. A physical model for the creep deformation of single crystal superalloys is presented, in which the dependence of the kinetics of creep deformation on alloy chemistry is rationalised. The rate-controlling step is considered to be climb of dislocations at the matrix/particle interfaces and their rate of escape from trapped configurations. The effects of microstructural scale precipitate size, geometry and spacing are also studied. A first order estimate for the rate of creep deformation emerges from the model, which is useful for the purposes of alloy design. Three new single crystal superalloys have been isolated using theory-based computational modelling approaches, termed Alloys-By-Design methods. They are (i) an oxidation-resistant low Re-containing alloy with balanced properties, intended for general-purpose gas turbine applications; (ii) an alloy containing 5.6 wt.% Re and 2.6 wt.% Ru suitable for high performance jet engine applications, and (iii) a cheap, corrosion-resistant alloy for power generation applications. The new alloys have been manufactured using investment casting techniques, and their creep and oxidation behaviour evaluated. The multicomponent composition space pertinent to the single crystal nickel-based superalloys has been mapped and searched, by using newly developed numerical algorithms. This allowed compositions of alloys conferring the microstructures needed for optimal properties to be identified, at a resolution of 0.1 wt.%. Databases have been constructed which contain all appropriate compositions available in these systems. When coupled with composition- and microstructure-dependent property models, the databases can be searched to identify new alloys predicted to exhibit the very best properties or combinations of them.

Les superalliages monocristallins à base de nickel sont couramment utilisés dans la fabrication des aubes de turbines à gaz aéronautiques. En service, ces pièces mécaniques sont soumises à des sollicitations mécaniques et thermiques sévères. La composition chimique et la microstructure de ces superalliages monocristallins ont été optimisées à travers différentes générations d'alliages dans le but de résister au fluage à des températures supérieures à 1100°C. Pour protéger ces matériaux des agressions environnementales (oxydation isotherme et cyclique à très haute température, corrosion à moyenne et haute température), les aubes de turbine sont généralement revêtues d'une couche de NiAlPt ou de MCrAlY (M=Ni, Co). Le procédé de dépôt et les traitements thermomécaniques entrainent la formation d'une zone d'interdiffusion entre le revêtement et le substrat. De plus, la microstructure des différentes zones (le superalliage, le revêtement et la zone d'interdiffusion) évolue en service du fait de l'effet combiné des sollicitations mécaniques et thermiques. De telles évolutions sont susceptibles d'affecter localement les propriétés mécaniques des aubes de turbine. Les revêtements MCrAlY ont fait l'objet de nombreuses études portant sur l'oxydation et la corrosion à haute température. L'abattement des propriétés mécaniques du superalliage du fait de la présence du revêtement a été largement étudié sur le système complet, c'est à dire le superalliage revêtu. Ces études ont eu pour but d'estimer une épaisseur de superalliage qui soit considérée comme non porteuse de la charge, et ce indépendamment de la taille de la zone d'interdiffusion. L'affinement des modèles prédictifs de comportement mécanique et de durée de vie des matériaux requiert une base de données relative aux propriétés locales et à leur évolution au cours du vieillissement. Ces données n'étaient pas disponibles jusqu'à ce jour. Ce travail a donc porté sur la caractérisation microstructurale et mécanique de la zone d'interdiffusion du système MC2 revêtu de NiCoCrAlYTa par co-déposition électrolytique. Des éprouvettes de traction ont été extraites des différentes zones de ce système à gradient de propriétés à l'état de réception et aussi dans des états vieillis avec ou sans contrainte appliquée. Elles ont été ensuite testées mécaniquement à haute température dans des conditions environnementales optimisées de façon à limiter les effets induits par l'oxydation sur le comportement mécanique d'éprouvettes aussi minces. Ces échantillons de 20 à 400 μm d'épaisseur ont été obtenus en utilisant une machine de rodage afin de limiter l'impact de la méthode d'usinage sur l'état de contrainte résiduel. Deux bancs d'essais mécaniques ont spécialement été développés dans le cadre de cette étude pour réaliser des essais de fluage et de traction sur ces échantillons ultra-minces sous atmosphère contrôlée jusqu'à 1200°C. Les résultats obtenus sur ces échantillons minces ont été comparés aux résultats d'essais conduits sur des éprouvettes massives. L'effet « paroi mince » a été exploré parallèlement afin de statuer sur la possibilité d'utiliser ces données pour décrire le gradient de comportement du système. / Monocrystalline nickel based superalloys are the most suitable materials for the design of high performance turbine blades. In service, these mechanical parts undergo both harsh mechanical and thermal solicitations. The chemical composition and also microstructure of these superalloys have been optimized through different generations to resist creep deformation at temperature higher than 1373K. To protect these materials from environment stresses (isothermal and cyclic oxidation at high temperature, intermediate temperature corrosion) blades are generally coated with a NiAlPt or MCrAlY layer (M=Ni, Co). Both deposition process and thermomechanical treatment generate an interdiffusion zone (IDZ) between the coating and the substrate. Moreover, the microstructure of the different strata (superalloy, coating and interdiffusion zone) evolve in service due to the combine effect of high temperature and stress. Such evolutions may locally affect the mechanical properties of turbine blades. MCrAlY coatings have been studied extensively from an oxidation and hot corrosion point of view. The drop of mechanical properties of superalloys because of the presence of coating has been investigated on full system, so that to say the coated superalloy. These study aims to estimate a none bearing thickness of the superalloy independently from the size of the interdiffusion zone. Refinement of predictive models on mechanical behaviour and lifetime of materials require data relative to local properties and their evolution when ageing. These data were not available until now. Hence, this work deals with microstructural and mechanical characterisation of the interdiffusion zone of the system MC2 coated with NiCoCrAlYTa by electrochemical codeposition. Tensile specimens were extracted from the different zones of this functionally graded material on “as received” state and after ageing with and without applied stress. Then, these specimens were mechanically tested at high temperature in optimised controlled atmosphere in order to prevent ultrathin specimens from oxidation effects on the mechanical behaviour. These specimens in a range of 20 to 400μm thick were obtained by use of a lapping machine in order to limit the impact of gritting on residual stress. Two mechanical test rigs were especially designed for this study to perform creep and tensile testing on these ultrathin specimens under controlled atmosphere at temperature up to 1473K. Results obtained from these ultrathin specimens were compared with testing conducted on bulk materials. The “size effect” was explored in parallel so that to conclude on the feasibility of using these data to quantify the behaviour gradient of this system.

Este projeto faz parte de uma Rede Interdisciplinar de Pesquisa em Superligas no Brasil (Projeto Pró-Engenharias - CAPES), que tem como objetivo o desenvolvimento técnico e científico do Brasil nesta classe de materiais. A rede é composta por especialistas de estabelecida competência em assuntos fundamentais para o desenvolvimento de materiais estruturais, tais como: fusão em vácuo, solidificação direcional, relações orientação-propriedade, tratamentos térmicos, fluência, fadiga em alta temperatura, oxidação e corrosão a quente. Assim, na parte que compete a este pesquisador, foram estudadas as propriedades de fadiga em altas temperaturas da liga MAR-M247 e de uma nova liga, a liga MAR-M247 modificada pela substituição do Ta pelo Nb, e sendo doravante denominada MAR-M247(Nb). Foram desenvolvidos estudos correlacionando parâmetros intrínsecos do material, como composição química e microestrutura adicionalmente a parâmetros extrínsecos, tais como: temperatura, estudo de oxidação, propriedades de fadiga, ensaios de tração em temperatura ambiente, 250, 500, 700, 800, 900 e 1000ºC, conforme as normas AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM) E 8M-00 e ASTM E 21-00. Em relação aos ensaios de fadiga foram realizados ensaios de nucleação de trincas , conforme a norma ASTM E466-07 e os resultados foram apresentados na forma de curvas S-N e analisados estatisticamente segunda a norma ASTM E739-10. Para auxiliar na definição dos micromecanismos de fadiga, as superfícies de fratura foram analisadas utilizando o microscópio eletrônico de varredura (MEV) e microscópio ótico estereoscópico (MO). Foi realizado ensaio de oxidação para verificar a susceptibilidade a oxidação das ligas, sendo este um dos fatores que afetam a vida em fadiga em alta temperatura. / This project is part of an interdisciplinary network of Research in Super League in Brazil (Project Pro-Engineering - CAPES), which aims to technical and scientific development of Brazil in this class of materials. The network is composed of experts of established competence in matters fundamental to the development of structural materials, such as: vacuum melting, directional solidification, relationships property-oriented, heat treatment, creep, fatigue in high temperature oxidation and hot corrosion. Thus, at the racing this researcher, were studied the fatigue properties at high temperatures MAR-M247 alloy and a new league, which in reality is the MAR-M247 alloy modified by replacing the Ta by Nb, and being hereinafter referred to as MAR-M247 (Nb). Were designed studies correlating parameters intrinsic material, such as chemical composition and microstructure, with extrinsic parameters such as: temperature and type of loading, with the properties fatigue. Thus, tensile tests at room temperature environment, 250, 500, 700 and 900ºC, and tests for compression at temperatures of 700 and 900ºC were performed to determine the elastic behavior and elastoplastic material, according to the ASTM E-8M 00, ASTM E 21-00 and ASTM E209-00. Were also conducted testing of fatigue crack nucleation, as ASTM E466-07. The results were presented at form of SN curves and statistically analyzed the second ASTM E739-10. To assist in the definition of micromechanics of fatigue, the fracture surfaces were examined in a scanning electron microscope (SEM) and stereoscopic optical microscope (OM). Was oxidation test performed to check susceptibility to oxidation of the alloy, which is the factor affecting the fatigue life.

Superligas de níquel são materiais mundialmente empregados nas áreas de petróleo e gás natural, aeroespacial e nuclear. A Incoloy® 945 uma liga desenvolvida em meados dos anos 2000, para ser uma liga hibrida entre a Inconel® 718 e Incoloy® 925, concebendo uma liga com propriedades mecânicas e anticorrosivas capaz de suportar as mais adversas operações de serviço. Neste trabalho foram determinadas algumas características mecânicas do material, após laminação a frio, seguindo duas diferentes rotas de tratamento térmico. Foram realizados testes de dureza Vickers e tração, onde mostrou que a rota experimental criada no IPEN (por intermédio da análise por calorimetria exploratória diferencial), tem a mesma resistência mecânica do que a rota comercialmente usada, contudo possui uma maior ductilidade. O material demonstra uma excepcional união resistência mecânica e ductilidade, podendo ser empregada no uso de tubulações e válvulas de alta complexidade de manufatura, para a exploração das camadas do pré-sal. / Nickel super alloy materials are used worldwide in the areas of oil and gas, aerospace and nuclear. The Incoloy® 945 an alloy developed in the mid-2000s, to be a hybrid alloy between the Inconel® 718 and Incoloy® 925 by designing an alloy with mechanical and anti-corrosion properties able to withstand the most adverse service operations. In this work we were determined some mechanical characteristics of the material after cold rolling, following two different routes of heat treatment. Hardness Vickers tests and traction test were conducted, which showed that the experimental route created at IPEN (through analysis by differential scanning calorimetry), has the same mechanical strength than the route used commercially, it nevertheless has a higher ductility. The material shows an exceptional union strength and ductility and can be used in the use of pipes and high complexity manufacturing valves for the operation of the pre-salt layers.