The aim of this Thesis was on one side to contribute to a better understanding of the phases formed in the TiAlSiN(O) system and the influence of impurities on their properties. On the other side it was also aimed in the Thesis to individually study the phases forming the nanocomposite. In each chapter the individual conclusions from that particular chapter are presented, a summary of the most relevant conclusions and achievements is listed below. ¡à Ti1-xAlxN(O) coatings The optical properties of Ti1-xAlxN(O) coatings were investigated. By changing the Al content in the coatings the properties change from the metallic character of TiN to dielectric character of AlN allowing to obtain spectrally selective coatings. For high Al content the films show low infrared reflectance and high emittance resulting in low equilibrium temperature, characteristics suitable for example for satellite temperature control. While the low emittance and high absorptance of low Al content are adequate for solar absorbers. The thermal stability of the low Al content coatings was investigated and the coatings are stable up to 400 ¨¬C without much change in the optical properties. ¡à SiyNz(O) coatings The silicon oxynitride coatings proved to be themselves interesting for their optical properties, specially the refractive index. The control of the microstructure was the key factor to control the optical properties of the coatings. Low energetic conditions in pure nitrogen atmosphere lead to the formation of closed porosity (nanovoids). The Raman results proved the encapsulation of nitrogen in the pores. Changing the N2 fraction in the gas mixture during deposition allows (at low power) to produce coatings with similar composition and mechanical properties presenting different refractive index by the introduction of the closed porosity. The closed porosity in the coatings is stable in N2 and vacuum up to 900 ¨¬C. Changing the target-substrate distance allows to produce coatings with different size of nanovoids. The possibility to extend the deposition of porous (close porosity) coatings to other systems is demonstrated. Porous silicon coatings were deposited by this method. ¡à nc-Ti1-xAlxN/a-SiyNz(O) coatings It was found from the XRD, SAED, EELS and XPS results, of coatings deposited under low energetic conditions, that the coatings are composed of a nanocrystalline cubic (Ti,Al)N phase embedded in an amorphous silicon oxynitride phase. The presence of oxygen impurities was identified particularly in non biased samples and estimated to be around 10 at% as the upper limit in these particular samples. Oxygen seems to be outside the nitride nanocrystallites, and mainly bond to silicon, forming amorphous silicon oxynitride phases and confirmed to occupy preferentially nitrogen positions (confirmed by HAADF and EFTEM) at the column boundaries. The application of substrate bias and substrate heating during deposition proved to be very efficient in reducing the oxygen incorporation in the coatings originating also denser coatings with improved mechanical properties. The different energetic conditions (either kinetic or thermal) at which the coatings were exposed during growth and the consequently obtained structures express the need for growth models were the transitions between zones can be achieved by a combination of substrate bias and substrate temperature.

This project has as main goal to study the influence of the coating thickness, deposited by arc-PVD- technology, on the wear resistance of coated cemented carbide inserts in three different turning operations. An additional effort has also been made to develop a new test method for evaluating flank wear resistance. Three different coating types (Coating A, Coating B and Coating C) have been studied in three distinctive thicknesses (2, 4 and 6 μ m) for each type. For two of the coating types (Coating A and B) special studies has been done with the thickest coating, creating two additional coating versions of the thickest coating, by changing various deposition parameters, with the aim to enhance the cohesive properties of the coating and lower the residual stresses at the cutting edge. The results show increased crater wear resistance with increased coating thickness for all coating types, but the amount of increase changes with coating type (Coating A>B>C). Flaking wear resistance decreased with increased coating thickness for all coating types. Further the high temperature version of Coating A, showed a significant increase in the flaking wear resistance compared to the standard version of Coating A. The flank wear test showed an increased resistance with thicker coatings in all cases except for the 6 μ m version of Coating C. The flank wear resistance of the most flank wear resistant coatings (Coating B, C) was also successfully examined in a new developed test method. The method suppressed excessive crater wear on the rake face and presented a high abrasive wear rate on the flank and some flaking on the rake face. The amount of flaking is judged not to influence the testing of the flank wear resistance. For all the tested coatings in the new test an increase in the coating thickness resulted in better flank wear resistance.

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Santos.pdf: 17433556 bytes, checksum: 7bab497e48419bd426521c0d16808650 (MD5) Previous issue date: 2017-03-31 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The purpose of this dissertation was to present the evaluation of the aluminum concentration in the cutting tools to analyze the wear after turning. This research consists not only in experimental analyzes, but also in analyzes using computer programs to capture, treat and quantify images. The three cutting tools used in the experimental analysis were made of carbide, as follows: one uncoated tool and two TiAlN coated tools with high and low aluminum contents, respectively. The research methodology used to determine the machining parameters and the characterization of the materials was adapted to the execution conditions available in the two public universities, partners in the scientific development, existing in Amazonas, UFAM and UEA. Some materials characterization techniques were used for both workpiece and the cutting tools. The characterization technique for the workpiece made of cast iron was done through metallography and Rockwell hardness. While, the characterization for the cutting tools and the coverings was performed by determining the parameters of the geometry of the cutting toos and by a Vickers micro-hardness test. In order to study the wear evolution of the cutting tools, turning was performed on the universal lathe changing the cutting tools and their edges according to the machined distances of 60, 120, 180 and 240 mm increasing gradually the number of steps on the workpiece. After the turning, images of the cutting tools were obtained by an optical machine to analyze the wear. In regards to the treatment of images, specialized software was used in the present study. Furthermore, a programming language routine was developed in order to quantify the wearied area. In addition, crater wear depths and material displacement values of the insert during turning were compared to each other. Finally, the results indicate the evolution of the differentiated wear for non-recoating cutting tools. Also, due to the variation of the aluminum percentage in the coating, different performance was observed directly related to the mechanical properties of the samples of the cases studied. / O objetivo nesta dissertação foi apresentar a avaliação da concentração de alumínio nas ferramentas de corte para analisar o desgaste apos a usinagem. Essa pesquisa consiste não somente nas análises experimentais como também nas análises utilizando-se de recursos computacionais para capturar, tratar e quantificar imagens. As três ferramentas utilizadas na analise experimental foram as seguinte: uma pastilha sem revestimento e duas pastilhas possuem revestimento de TiAlN com alto e baixo teor de alumínio, respectivamente. A metodologia da pesquisa utilizada para determinar os parametros de usinagem e a caracterização dos materiais foi adaptada para as condições de execução disponíveis nas duas universidades públicas, parceiras no desenvolvimento científico, existentes no Amazonas, UFAM e UEA. Algumas técnicas de caracterização dos materiais foram adotadas tanto para a peça quanto para as ferramentas de corte. A caracterização da peça de ferro fundido nodular FUCO® FE 55006 foi feita através de metalografia e da determinação da dureza Rockwell, enquanto que a caracterização das ferramentas de corte e dos recobrimentos, foi realizada através da determinação dos parâmetros da geometria das pastilhas e da microdureza Vickers. O processo de usinagem foi realizado no torno mecânico universal alternado-se as ferramentas de corte e suas pontas de acordo com as distancias usinadas de 60, 120, 180 e 240 mm com aumento gradativamente do numero de passos na peça. Após a usinagem, imagens das ferramentas de corte foram obtidas por uma maquina ótica para analisar o desgaste. Com relação ao tratamento de imagens, softwares especializados foram utilizados no presente estudo. Foi desenvolvida uma rotina de linguagem de programação para quantificar a área desgastada. Além disso, profundidades do desgaste de cratera e valores de deslocamento do material das pastilhas, durante a usinagem, foram comparadas entre si. Por fim, os resultados indicam a evolução do desgaste diferenciada para ferramentas de corte sem recobrimento. No que diz respeito a variação da porcentagem de alumínio no recobrimento, os desempenhos foram distintos sendo diretamente relacionados as propriedades mecanicas das amostras para os casos estudados.

The aim of this Thesis was on one side to contribute to a better understanding of the phases formed in the TiAlSiN(O) system and the influence of impurities on their properties. On the other side it was also aimed in the Thesis to individually study the phases forming the nanocomposite. <p><p>In each chapter the individual conclusions from that particular chapter are presented, a summary of the most relevant conclusions and achievements is listed below. <p><p><p>¡à\ / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

O presente trabalho teve como objetivo principal avaliar o efeito dos recobrimentos TiN e TiAlN depositados por PVD a plasma na liga Ti-6Al-4V sob condições de fluência a 600 °C e corrosão em meios contendo cloreto a 25, 60 e 80 °C. O trabalho foi complementado com análises microestruturais e dos revestimentos superficiais utilizando-se as técnicas de difração de raios X, microscopias óptica, eletrônica de varredura e de transmissão, medidas de microdureza e oxidação isotérmica. Os resultados permitiram concluir que a liga Ti-6Al-4V constituída pela configuração de Widmanstätten apresentou dureza média de 343 HV para a condição como recebida. Após os tratamentos por PVD a plasma observou-se um recobrimento à base de TiN de espessura de 2,2 ?m e composição igual a Ti0,7N. O recobrimento a base de TiAlN/TiAlCrN apresentou espessura em torno de 6 ?m e composição igual a (Ti0,38Al0,62)N/(Ti0,31Al0,50Cr0,19)N. As medidas do potencial em circuito aberto e polarização mostraram que a liga Ti-6Al-4V apresentou comportamento ativo com transição ativo-passiva em solução HCl e comportamento passivo em solução NaCl a 25, 60 e 80 °C. As amostras recobertas por TiN e TiAlN/TiAlCrN apresentaram comportamento passivo nas duas soluções corrosivas e em todas as temperaturas estudadas. A amostra revestida por TiN depositado por PVD apresentou os menores valores de taxa secundária em fluência para tensões maiores que 222 MPa, contudo a amostra nitretada a plasma apresentou maiores valores de vida útil e níveis de ductilidade. A análise conjunta dos expoentes de tensão, energia de ativação e estrutura de discordâncias indicaram que o principal mecanismo de deformação por fluência foi controlado por escalagem de discordâncias. O cálculo do parâmetro de tolerância ao dano (W) contribuiu para indicar que os revestimentos TiN e TiAlN/TiAlCrN, apesar de protegerem a superfície da oxidação, diminuíram a capacidade de deformação plástica ao longo do estágio terciário e vida útil da liga Ti-6Al-4V, reduzindo a ductilidade. Finalmente, os tratamentos superficiais utilizados neste trabalho foram eficientes por seu efeito de proteção através da deposição de um elemento cerâmico mais estável na superfície e não por transformações causadas na microestrutura. / This study aimed to evaluate the effect of the plasma-assisted PVD TiN and TiAlN/TiAlCrN coatings in the Ti-6Al-4V alloy under creep conditions at 600 °C and under corrosion conditions in environments containing chloride at 25, 60 and 80 °C. The study was complemented by microstructural and surface coatings analysis using XRD, optical, scanning and transmission electron microscopy, microhardness and isothermal oxidation. The results showed that the Ti-6Al- 4V alloy with Widmanstätten morphology presented an average hardness of 343 HV for as received condition. After treatment by plasma PVD, it was observed a TiN based coating, with 2,2 ?m and composition of Ti0,7N. The TiAlN/TiAlCrN based coating presented 6 ?m of thickness and composition of (Ti0,38Al0,62)N/(Ti0,31Al0,50Cr0,19)N. Anodic polarization and open circuit potential showed that Ti-6Al-4V alloy had active behavior with active - passive transition in HCl solution and passive behavior in NaCl solution at 25, 60 and 80 °C. The TiN and TiAlN/TiAlCrN coated samples showed passive behavior in both corrosive solutions and at all studied temperatures. The TiN coated sample showed the lowest values of secondary creep rate for stresses greater than 222 MPa, however, the plasma nitrided sample showed higher levels of service life and ductility. The analysis of stress exponents, activation energy and dislocations structures indicated that the main mechanism of creep was controlled by climbing dislocations. The damage tolerance parameter (W) calculation contributed to indicate that TiN and TiAlN/TiAlCrN coatings, although protect the surface from oxidation, decreased plastic deformation ability throughout tertiary stage and service life of the Ti-6Al-4V alloy, decreasing ductility. Finally, the surface treatments, used in this study, were efficient for their protective effect by depositing a more stable ceramic compound on surface and not by transformations caused on microstructure.

O presente trabalho teve como objetivo principal avaliar o efeito dos recobrimentos TiN e TiAlN depositados por PVD a plasma na liga Ti-6Al-4V sob condições de fluência a 600 °C e corrosão em meios contendo cloreto a 25, 60 e 80 °C. O trabalho foi complementado com análises microestruturais e dos revestimentos superficiais utilizando-se as técnicas de difração de raios X, microscopias óptica, eletrônica de varredura e de transmissão, medidas de microdureza e oxidação isotérmica. Os resultados permitiram concluir que a liga Ti-6Al-4V constituída pela configuração de Widmanstätten apresentou dureza média de 343 HV para a condição como recebida. Após os tratamentos por PVD a plasma observou-se um recobrimento à base de TiN de espessura de 2,2 ?m e composição igual a Ti0,7N. O recobrimento a base de TiAlN/TiAlCrN apresentou espessura em torno de 6 ?m e composição igual a (Ti0,38Al0,62)N/(Ti0,31Al0,50Cr0,19)N. As medidas do potencial em circuito aberto e polarização mostraram que a liga Ti-6Al-4V apresentou comportamento ativo com transição ativo-passiva em solução HCl e comportamento passivo em solução NaCl a 25, 60 e 80 °C. As amostras recobertas por TiN e TiAlN/TiAlCrN apresentaram comportamento passivo nas duas soluções corrosivas e em todas as temperaturas estudadas. A amostra revestida por TiN depositado por PVD apresentou os menores valores de taxa secundária em fluência para tensões maiores que 222 MPa, contudo a amostra nitretada a plasma apresentou maiores valores de vida útil e níveis de ductilidade. A análise conjunta dos expoentes de tensão, energia de ativação e estrutura de discordâncias indicaram que o principal mecanismo de deformação por fluência foi controlado por escalagem de discordâncias. O cálculo do parâmetro de tolerância ao dano (W) contribuiu para indicar que os revestimentos TiN e TiAlN/TiAlCrN, apesar de protegerem a superfície da oxidação, diminuíram a capacidade de deformação plástica ao longo do estágio terciário e vida útil da liga Ti-6Al-4V, reduzindo a ductilidade. Finalmente, os tratamentos superficiais utilizados neste trabalho foram eficientes por seu efeito de proteção através da deposição de um elemento cerâmico mais estável na superfície e não por transformações causadas na microestrutura. / This study aimed to evaluate the effect of the plasma-assisted PVD TiN and TiAlN/TiAlCrN coatings in the Ti-6Al-4V alloy under creep conditions at 600 °C and under corrosion conditions in environments containing chloride at 25, 60 and 80 °C. The study was complemented by microstructural and surface coatings analysis using XRD, optical, scanning and transmission electron microscopy, microhardness and isothermal oxidation. The results showed that the Ti-6Al- 4V alloy with Widmanstätten morphology presented an average hardness of 343 HV for as received condition. After treatment by plasma PVD, it was observed a TiN based coating, with 2,2 ?m and composition of Ti0,7N. The TiAlN/TiAlCrN based coating presented 6 ?m of thickness and composition of (Ti0,38Al0,62)N/(Ti0,31Al0,50Cr0,19)N. Anodic polarization and open circuit potential showed that Ti-6Al-4V alloy had active behavior with active - passive transition in HCl solution and passive behavior in NaCl solution at 25, 60 and 80 °C. The TiN and TiAlN/TiAlCrN coated samples showed passive behavior in both corrosive solutions and at all studied temperatures. The TiN coated sample showed the lowest values of secondary creep rate for stresses greater than 222 MPa, however, the plasma nitrided sample showed higher levels of service life and ductility. The analysis of stress exponents, activation energy and dislocations structures indicated that the main mechanism of creep was controlled by climbing dislocations. The damage tolerance parameter (W) calculation contributed to indicate that TiN and TiAlN/TiAlCrN coatings, although protect the surface from oxidation, decreased plastic deformation ability throughout tertiary stage and service life of the Ti-6Al-4V alloy, decreasing ductility. Finally, the surface treatments, used in this study, were efficient for their protective effect by depositing a more stable ceramic compound on surface and not by transformations caused on microstructure.

Quaternary cubic (TixCr1 − xAl~ 0.60)1 N1 coatings with 0 &lt; x &lt; 0.33 have been grown using reactive cathodic arc evaporation. When adding Ti the hardness was retained after annealing up to 1100 °C which is a dramatic improvement compared to CrAlN coatings. The coatings showed an age hardening process caused by spinodal decomposition into coherent TiCr- and Al-rich cubic TiCrAlN domains and the formation of hexagonal AlN precipitates and cubic TiCrN domains in the vicinity of the grain boundaries. The improved hardness was attributed to the stabilization of the cubic structure suppressing the formation and growth of hexagonal AlN. Furthermore, the presence of Ti atoms generated incoherent nanometer-sized crystallites within the hexagonal AlN precipitates disrupting the hexagonal lattice during the coarsening process. The addition of Ti promoted the formation of a TiO2 layer over Al2O3 resulting in a lower oxidation resistance. However, by tuning the composition it is possible to design coatings to have both good oxidation resistance and good high temperature mechanical stability. / <p>Funding Agencies|SSF project Designed multicomponent coatings, MultiFilms||</p>

Hard nanostructured TiAlN coatings have gained high importance in the field of protective tribological coatings. Nevertheless, their use regarding high temperature (>800°C) applications such as dry high speed machining still remains a challenge. Addition of elements such as Ta or Y has shown a beneficial impact on these properties. But for a better performance of these coatings, an in-depth understanding of their oxidation and wear mechanisms over a wider range of temperatures is needed which is currently unavailable in the literature. This work investigated the wear and oxidation properties of AlTiTaN hard coatings deposited by reactive magnetron sputtering at a substrate temperature of 250°C. Depending on process conditions, coatings with a preferential crystallographic orientation of cubic {111} or {200} with a columnar microstructure were observed. The oxidation and wear mechanisms for these coatings were investigated between 700°C and 950°C in air for various test durations. Further, the influence of Y doping in AlTiTaN coating was also studied.By combining Dynamic-Secondary Ion Mass Spectrometry ,X-ray diffraction (XRD) and Transmission Electron Microscopy measurements, it was demonstrated that a single amorphous oxide layer comprising of Ti, Al and Ta oxides formed at 700°C became a bilayer composed of a crystalline Al rich layer (protective Al2O3) and a Ti/Ta rich oxide layer at 900°C. The oxidation mechanism was governed primarily by inward diffusion of O at 700°C while from 800°C onwards outward diffusion of Al and inward diffusion of O controlled the reaction rate. A correlation between the oxidation kinetics and wear mechanism of AlTiTaN coatings, investigated at 700°, 800° and 900°C, was established. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

With the immense increase in the computational power available for the material science community in recent years, a range of new discoveries were made possible. Accurate investigations of large scale atomic systems, however, still come with an extremely high computational demand. While the recent development of Graphics Processing Unit (GPU) accelerated supercomputing might offer a solution to some extent, most well known electronic structure codes have yet to be fully ported to utilize this new power. With a soaring demand for new and better materials from both science and industry, a more efficient approach for the investigation of material properties needs to be implemented. The use of Machine Learning (ML) to obtain Interatomic Potentials (IP) which far outperform the classical potentials has increased greatly in recent years. With successful implementation of ML methods utilizing neural networks or Gaussian basis functions, the accuracy of ab-initio methods can be achieved at the demand of simulations with empirical potentials. Most ML approaches, however, require high accuracy data sets to be trained sufficiently. If no such data is available for the system of interest, the immense cost of creating a viable data set from scratch can quickly negate the benefit of using ML. In this diploma project, the elastic and thermodynamic properties of the Ti0.5Al0.5N random alloy at elevated temperature are therefore investigated using an Active Learning (AL) approach with the Machine Learning Interatomic Potentials (MLIP) package. The obtained material properties are found to be in good agreement with results from computationally demanding ab-initio studies of Ti0.5Al0.5N, at a mere fraction of the demand. The AL approach requires no high accuracy data sets or previous knowledge about the system, as the model is initially trained on low accuracy data which is removed from the training set (TS) at a later stage. This allows for an iterative process of improving and expanding the data set used to train the IP, without the need for large amounts of data.

<p>The objective of this research was the further development and characterization of a heavy load, high temperature pin on disc tribometer. The goal of performing this testing on the tribometer is to simulate realistic machining conditions experienced between a tool and workpiece ‘offline’ in order to reduce the number of real machining trials used to select a tool coating and subsequently optimize cutting parameters. This approach is based on the understanding that a change in the cutting speed can alter the tool-chip interface temperature profile, which can change the coefficient of friction (COF) between the tool and workpiece and impact the tool wear mechanisms and rate. Significant modifications were introduced to the tribometer to increase its functionality; a resistance welder was integrated into the setup, and a completely new, fully automated Graphical User Interface was designed using National Instruments Labview software to allow for more careful control of all interacting components and variables. Careful investigations were carried out to understand the sensitivity of COF measurements to various input parameters in order to gain increased confidence in the meaning of COF measurements. Finally, various tool and workpiece material pairs were tested from room temperature to upwards of 900°C near the pin-disc interface and efforts were made to correlate the resulting COF measurements with machining data in the form of tool life and cutting force measurement. This research contributes towards the goals of improving machinability in two ways: first, by screening potential surface engineering treatments on the basis of reduced friction under machining relevant conditions of elevated contact stress and temperature; and secondly, by generating temperature-dependent friction data for different tool and workpiece material pairs that can be used to improve FE simulations of metal cutting.</p> / Master of Applied Science (MASc)