Ce travail a été réalisé dans le cadre d’une collaboration entre le laboratoire de Chimie-Métallurgie de l’INSA de Rennes et le laboratoire de biomatériaux en site osseux (LBSO) de la Faculté de Chirurgie Dentaire de l’Université de Rennes1. L’alliage de titane de type β Ti-27Nb (% at.) a été nitruré pour des applications en implantologie orale parce qu'il possède un bas module d'élasticité, proche de celui de l’os et qu’il est composé uniquement d'éléments biocompatibles. Dans un premier temps l’alliage Ti-27Nb a été synthétisé grâce à un four à induction magnétique selon la technique de fusion en lévitation en creuset froid sectorisé. Un traitement de surface par nitruration en phase gazeuse a ensuite été effectué pour augmenter sa résistance à la corrosion et à l’usure. L’analyse structurale a été réalisée par DRX et par des observations en microscopies optique et électronique à balayage. L’analyse chimique a été effectuée par spectrométrie à dispersion d’énergie. La topographie et la dureté superficielle ont été caractérisées par AFM et par nano-indentation. Des essais tribologiques ont permis d’évaluer le coefficient de frottement et la résistance à l’usure. Pour la caractérisation mécanique des essais de traction conventionnels et cycliques ont été effectués. La biocompatibilité a été évaluée in vitro par des cultures bidimensionnelles de plusieurs populations cellulaires en contact des implants métalliques : ostéoblastes, fibroblastes et cellules épithéliales. Elle a été déclinée en termes de cytotoxicité, de prolifération cellulaire, d’expression génique et de morphologie cellulaire. Les propriétés de l’alliage Ti-27Nb nitruré sont particulièrement intéressantes pour une implantation durable en site osseux. / This work was performed in collaboration with the Metallurgical Chemistry team of the Institute of Chemical Sciences of Rennes and the Biomaterials Laboratory of the Faculty of Dentistry of Université de Rennes1. The low modulus Ti-27Nb (at. %) alloy with non-toxic elements was nitrided for the first time in this study for dental implant applications. The alloy was firstly synthetized by cold crucible levitation melting technique. A high temperature gas nitriding treatment was then carried out in order to improve the wear and corrosion resistance. The structural analysis was performed by X-ray diffraction and the microstructure was observed by optical microscopy and by scanning electron microscopy. The chemical analysis was performed by Energy Dispersion Spectrometry. Superficial mechanical properties were then studied by nano-indentation and ball-on-disc tribological tests. Conventional and tensile tests were realized. The biocompatibility was evaluated by in vitro tests performed on human osteoblasts, fibroblastic cells and epithelial cells. Cell proliferation and differentiation were studied as well as cell morphology. All of the observed properties make the nitrided Ti-27Nb alloy particularly suitable for enhanced longevity of dental implants.

Neste trabalho, foram determinadas as propriedades de tração, fadiga convencional e fadiga por fretting, do aço DIN 1.4112 (DIN X 90 Cr Mo V 18) nitretado por plasma, usado na fabricação de anéis de pistão de motores de combustão interna. Os corpos de prova tratados a 500ºC durante 5 horas. O material nitretado não apresentou valores de alongamento e redução de área possíveis de serem medidos e, tanto o limite de escoamento como o limite de resistência à tração, tiveram valores próximos aos do material temperado e revenido. Os ensaios de fadiga convencional e fadiga por fretting foram realizados em temperatura ambiente, sob carregamento cíclico tração-tração com R=0,1 e freqüência de 30 Hz. O fretting foi conseguido pressionando blocos de contato, feitos a partir de um ferro fundido cinzento, contra o corpo de prova de fadiga, com uma força normal de 100 N. Com o levantamento das curvas S-N para os dois ensaios, foi obtido o fator de redução de resistência FRR=1,62, que o fenômeno de fretting causa na fadiga convencional. Nos ensaios de fadiga por fretting, o pico da força de atrito aumentou com a tensão axial cíclica aplicada, atingindo um valor mínimo de 28 N e no máximo de 76 N. A camada nitretada apresentou microdureza máxima 1288 HV100 e espessura da camada de 91 &#956m. A metalografia revelou na camada nitretada, uma camada de compostos, a zona de difusão e uma zona de transição para o subtrato bem definidas. Foram encontrados nitretos dos tipos &#949 (Fe2-3N) e &#947\'(Fe4N) na superfície da camada nitretada. A análise fratográfica, revelou, em tração, o trincamento da superfície devido à baixa tenacidade da camada nitretada, além da programação de trincas por fadiga abaixo da camada nitretada, nos ensaios de fadiga convencional. Os ensaios de fadiga por fretting produziram acumulação de detritos e a formação de trincas secundárias na área ) na área de contato de fretting. / In the present work, the fretting and plain fatigue properties of plasma nitrided martensitic stainless steel, DIN 1.4112 (DIN X 90 Cr Mo V 18), used in piston rings, were investigated. Both fretting and plain fatigue specimens were treated at 500°C for 5 h. The fretting pads were made of gray cast iron. Both fretting and plain fatigue tests were carried out under a load-controlled condition under stress rate, R=0.1 and frequency of 30 Hz. The S-N curves generated with and without fretting showed the strength reduction factor SRF=1.62 when fretting was applied. In the fretting fatigue, frictional force increased with axial cyclic stress and reached a minimum value of 28 N and maximum value of 60 N. Microhardness measurements have shown that the nitrided case presented a maximum hardness of 1288 HV100 and thickness of 91 &#956m. X-ray diffraction techniques indicated that the compound layer consists of &#949 (Fe2-3N) and &#947\' (Fe4N) phases. Fractographic observations showed superficial cracking in tensile specimens due to the low toughness of the nitrided case and fatigue crack growth below this layer in plain fatigue specimens. Fretting fatigue tests produced accumulation of debris and the formation of secondary cracks at the contact area.

No description available.

Este trabalho apresenta um estudo sobre a formação e evolução da camada de nitretos sobre substrato de ferro com pureza de 99,83% e do aço AISI H12, nitretados por plasma. As camadas foram obtidas com a variação sistemática das condições de nitretação, como temperatura, tempo e frequência do plasma. A atmosfera de trabalho empregada foi a de uma mistura gasosa de 20% N2 + 80% H2, mantida à pressão constante de 6 mbar, sob fluxo. Uma investigação detalhada da camada nitretada das amostras de ferro foi feita através de desgaste mecânico em passos sucessivos e após cada desgaste, as novas camadas foram analisadas por espectroscopia Môssbauer de elétrons de conversão (CEMS) auxiliadas por outras técnicas, como difração de raios X, microdureza e microscopia ótica e eletrônica. As análises superficiais demonstraram que a camada nitretada é formada por uma mistura de nitretos γ-Fe4N, ε-Fe3N e-ε-Fe3,2N, que variam suas proporções com as condições de nitretação. Abaixo desta camada outros nitretos são formados como e ε-FeXN (2≤X≤3,2) e α-Fe16N2. No aço H12, foi estudada a influência da nitretação por plasma em correntes contínua e pulsada. As amostras foram caracterizadas quanto ao perfil de microdureza, perfil de concentração de nitrogênio, difração de raios X e espectroscopia Môssbauer de elétrons de conversão (CEMS) e de raios X de conversão (CXMS). A camada composta próxima à superfície, como vista por CEMS, consiste de uma mistura de γ-Fe4N e ε-FeX(N, C) enquanto a camada próxima à zona de difusão, investigada por CXMS, consiste de uma mistura de fases γ-Fe4N, ε-FeX(N, C) Fex(N, C), α-Fe16N2 e γ-austenita. O crescimento da camada nitretada quando difundida utilizando corrente contínua segue uma lei parabólica, o que não ocorre com o processo com corrente alternada. Este efeito deve ser devido à taxa de \"sputerring\" do catodo e da difusão auxiliada por radiação, que são mais acentuadas no caso de corrente alternada, para tempos de nitretação t ‹ 2h. A situação é revertida para t › 3h. / This work investigates the formation and evolution of nitride layers on a 99.83% pure iron and a AISI H-12 steel substrates by using plasma nitriding processoThe layers were obtained by systematic variation of the nitriding conditions, such as temperature, time and plasma frequency. The employed atmosphere consisted of a gaseous mixture of H2-20% N2, at a constant pressure of 6.0 mbar in f1ux.A detailed investigation of the nitrided layer on iron samples was performed through surface mechanical wear in successive steps. After each step the layer was analysed by Conversion Electron Mõssbauer spectroscopy (CEMS), as well as by other techniques, as X-ray diffraction, microhardness and optical and electronic metallography. The surface analysis of iron samples showed that the nitrided layers are formed bya mixture of γ-Fe4N, ε-Fe3N e-ε-Fe3,2N nitrides, whose proportions have varied with the nitriding conditions. Below this layer, different nitrides are formed, ε-FeXN (2≤X≤3,2) e α-Fe16N2. For H-12 steel substrates it was also studied the influence of direct and pulsed current on the layer. The samples were characterized related to the microhardness profile, nitrogen concentration profile, Xray diffraction and Conversion Electron and X-ray Mõssbauer spectroscopy (CEMS) and (CXMS). The near-surface compound layer, as probed by CEMS, consisted of a mixture of γ-Fe4N e ε-FeX(N, C) phases. The near-diffusion zone compound layer, as probed by CXMS presented a mixture of γ-Fe4N , e ε-FeX(N, C) Fex(N, C), α-Fe16N2e &#947 and- e &#947-austenite phases. For the plasma process, the growth of the nitride layers in direct current follows the parabolic law, what does not occur when process with pulsed current is used. This effect is probably due to cathode rate sputtering and radiation-enhanced diffusion, the latter being more accentuated in the case of pulsed current, for nitriding times t &#8249 2h. The situation is reversed for t &#8250 3h.

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No. of bitstreams: 1 barros_ra_dr_guara.pdf: 24319782 bytes, checksum: f4d58ce4ebe77961a2e94b04cf3515cc (MD5) Previous issue date: 2017-02-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os aços de ultra alta resistência como o aço 4340 tem sido amplamente utilizados pela indústria aeronáutica e aeroespacial em aplicações como trens de pouso de aeronaves e o veículo lançador de satélite brasileiro (VLS), além de um uso extensivo para diversos setores da indústria em geral. Isso se deve, em grande medida, às suas propriedades mecânicas. Este trabalho se propõe a avaliar as propriedades tribológicas do par aço 4340, inicialmente submetido ao tratamento térmico de têmpera e revenimento, e a liga bronze alumínio 630, utilizados em trens de pouso. Será estudado o comportamento destas estruturas após o aço ser submetido a tratamentos de superfície por nitretação a plasma e carbonetação a laser, como forma de melhorar seu desempenho com relação ao atrito e ao desgaste. Neste estudo foi escolhido o ensaio tipo pino-disco para simular a situação real de desgaste. Os discos foram confeccionados a partir do aço AISI/SAE 4340 e os pinos foram feitos da liga bronze-alumínio 630. Foram realizadas análises microestruturais das estruturas e das camadas de compostos formadas devido ao tratamento de superfície, Após os ensaios de desgaste foram feitas observações das superfícies através de microscopia e perfilometria óptica, microscopia eletrônica de varredura, difratometria de raios-X, testes de riscamento (scratching tests), dureza, observação de rugosidade e pesagem dos corpos de prova. Foram levantados os parâmetros do desgaste e alterações microestuturais devido à interação entre as superfícies de contato durante os ensaios de deslizamento. Foi analisada a perda de massa e levantadas as curvas de desgaste e dos parâmetros relacionados ao atrito em função da distância percorrida e/ou do tempo de ensaio. Nos ensaios foram utilizadas três velocidades de ensaio: 0,5; 1,0 e 1,5 m/s. Foi possível o cálculo da taxa de desgaste para cada par e velocidades estudadas. De uma maneira geral constatou-se que os mecanismos de desgaste detectados são semelhantes para todas as condições de superfície dos discos. As imagens mostram que partículas do pino são deformadas sobre o disco, em forma de camadas, evidenciando o mecanismo de adesão. A carbonetação a laser criou uma camada rica em carbono com a presença de grafite que contribuiu para reduzir o coeficiente de atrito e o desgaste do pino, principalmente, para as velocidades de 0,5 e 1,0 m/s. A nitretação a plasma reduziu a perda de massa do disco e do pino, com indicativos de pequena perda de massa para todas as velocidades estudadas; a rugosidade e o aumento do coeficiente de atrito no par pino-disco para as velocidades de 1,0 e 1,5 m/s podem ter sido induzidas por alteração no tipo de desgaste, de adesivo para uma abrasão a três corpos. / Ultra high strength steels as 4340 steel has been widely used by the aerospace industry in applications such as aircraft landing gears and the Brazilian satellite launch vehicle (VLS), plus an extensive use for various sectors of the industry in general. This is due largely to their mechanical properties. This work aims to evaluate the tribological properties of 4340 steel pair, initially submitted to heat treatment of quenching and tempering, and aluminum bronze 630 alloy, used in landing gear. The behavior of these structures after the steel be subjected to surface treatment by plasma nitriding and laser carbonetation will be studied, as a way to improve its performance with respect to friction and wear. For this study, pin-on-disc test was chosen in order to simulate the real situation of wear. The discs were made from 4340 steel and pins were made of aluminium bronze 630 alloy. Micro-structural analyses were undertaken of the structures and compound layers formed due to surface treatment. After the wear tests surface observations were made through microscopy and perfilometry optical, scanning electron microscopy, x-ray diffractometry, x-ray tests, scratching tests, hardness, roughness and weighing of the specimens. Parameters of wear and microestuturals changes were raised due to interaction between the contact surfaces during rehearsals. Loss of mass was analyzed and curves of wear and friction related parameters were plotted in function of the slided distance and/or time of test. In the tests three test velocities were used: 0.5; 1.0 and 1.5 m/s. It was possible to calculate the wear rate for each pair and studied velocities. In general it was noted that the mechanisms of wear detected are similar for all conditions of the surface of the discs. The images show that the particles are bent on the disc, in the form of layers, showing the mechanism of adhesion. The laser carbonetation created a carbon-rich layer with the presence of graphite, which contributed to reduce the friction coefficient and pin wear, mainly for the 0.5 and 1.0 m/s velocities. The plasma nitriding reduced the loss in mass of the disk and pin, with indicative of small mass loss for all velocities studied; the roughness and the increase of the coefficient of friction in the couple pin-disc for the velocities of 1.0 and 1.5 m/s may have been induced by changes in the type of wear, from adhesive wear to a three-body abrasion. / CAPES: 99999.002441/2014-04

No description available.

No description available.

The Pebble Bed Modular Reactor (PBMR) is one of the most technologically advanced developments in South Africa. In order to build a commercially viable demonstration power plant, all the specifically and uniquely designed equipment must first be qualified. All the prototype equipment is tested at the Helium Test Facility (HTF) at Pelindaba. One of the largest components that are tested is the Core Unloading Device (CUD). The main function of the CUD is to unload fuel from the bottom of the reactor core to enable circulation of the fuel core. The CUD housing vessel forms part of the reactor pressure boundary. Pebble-directing valves and other moving machinery are installed inside its machined inner surface. It is essential that the interior surfaces of the CUD are case hardened to provide a corrosion- and wear-resistant layer. Cold welding between the moving metal parts and the machined surface must also be prevented. Nitriding is a case hardening process that adds a hardened wear- and corrosion-resistant layer that will also prevent cold welding of the moving parts in the helium atmosphere. Only a few nitriding furnaces exist that can house a forging as large as the CUD of the PBMR. Commercial nitriding furnaces in South Africa are all too small and have limited flexibility in terms of the nitriding process. The nitriding of a vessel as large as the CUD has not yet been carried out commercially. The aim of this work was to design and develop a custom-made nitriding plant to perform the nitriding of the first PBMR/HTF CUD. Proper process control is essential to ensure that the required nitrided case has been obtained. A new concept for a gas nitriding plant was developed using the nitrided vessel interior as the nitriding process chamber. Before the commencement of detail design, a laboratory test was performed on a scale model vessel to confirm concept feasibility. The design of the plant included the mechanical design of various components essential to the nitriding process. A special stirring fan with an extended length shaft was designed, taking whirling speed into account. Considerable research was performed on the high temperature use of the various components to ensure the safe operation of the plant at temperatures of up to 600°C. Nitriding requires the use of hazardous gases such as ammonia, oxygen and nitrogen. Hydrogen is produced as a by-product and therefore safety was the most important design parameter. Thermohydraulic analyses, i.e. heat transfer and pressure drop calculations in pipes, were also performed to ensure the successful process design of the nitriding plant. The nitriding plant was subsequently constructed and operated to verify the correct design. A large amount of experimental and operating data was captured during the actual operation of the plant. This data was analysed and the thermohydraulic analyses were verified. Nitrided specimens were subjected to hardness and layer thickness tests. The measured temperature of the protruding fan shaft was within the limits predicted by Finite Element Analysis (FEA) models. Graphs of gas flow rates and other operation data confirmed the inverse proportionality between ammonia supply flow rate and measured dissociation rate. The design and operation of the nitriding plant were successful as a nitride layer thickness of 400 μm and hardness of 1 200 Vickers hardness (VHN) was achieved. This research proves that a large pressure vessel can successfully be nitrided using the vessel interior as a process chamber. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2010.

The Pebble Bed Modular Reactor (PBMR) is one of the most technologically advanced developments in South Africa. In order to build a commercially viable demonstration power plant, all the specifically and uniquely designed equipment must first be qualified. All the prototype equipment is tested at the Helium Test Facility (HTF) at Pelindaba. One of the largest components that are tested is the Core Unloading Device (CUD). The main function of the CUD is to unload fuel from the bottom of the reactor core to enable circulation of the fuel core. The CUD housing vessel forms part of the reactor pressure boundary. Pebble-directing valves and other moving machinery are installed inside its machined inner surface. It is essential that the interior surfaces of the CUD are case hardened to provide a corrosion- and wear-resistant layer. Cold welding between the moving metal parts and the machined surface must also be prevented. Nitriding is a case hardening process that adds a hardened wear- and corrosion-resistant layer that will also prevent cold welding of the moving parts in the helium atmosphere. Only a few nitriding furnaces exist that can house a forging as large as the CUD of the PBMR. Commercial nitriding furnaces in South Africa are all too small and have limited flexibility in terms of the nitriding process. The nitriding of a vessel as large as the CUD has not yet been carried out commercially. The aim of this work was to design and develop a custom-made nitriding plant to perform the nitriding of the first PBMR/HTF CUD. Proper process control is essential to ensure that the required nitrided case has been obtained. A new concept for a gas nitriding plant was developed using the nitrided vessel interior as the nitriding process chamber. Before the commencement of detail design, a laboratory test was performed on a scale model vessel to confirm concept feasibility. The design of the plant included the mechanical design of various components essential to the nitriding process. A special stirring fan with an extended length shaft was designed, taking whirling speed into account. Considerable research was performed on the high temperature use of the various components to ensure the safe operation of the plant at temperatures of up to 600°C. Nitriding requires the use of hazardous gases such as ammonia, oxygen and nitrogen. Hydrogen is produced as a by-product and therefore safety was the most important design parameter. Thermohydraulic analyses, i.e. heat transfer and pressure drop calculations in pipes, were also performed to ensure the successful process design of the nitriding plant. The nitriding plant was subsequently constructed and operated to verify the correct design. A large amount of experimental and operating data was captured during the actual operation of the plant. This data was analysed and the thermohydraulic analyses were verified. Nitrided specimens were subjected to hardness and layer thickness tests. The measured temperature of the protruding fan shaft was within the limits predicted by Finite Element Analysis (FEA) models. Graphs of gas flow rates and other operation data confirmed the inverse proportionality between ammonia supply flow rate and measured dissociation rate. The design and operation of the nitriding plant were successful as a nitride layer thickness of 400 μm and hardness of 1 200 Vickers hardness (VHN) was achieved. This research proves that a large pressure vessel can successfully be nitrided using the vessel interior as a process chamber. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2010.

CNPq, CAPES, FINEP / Devido à alta resistência a corrosão, os aços inoxidáveis possuem uma larga aplicabilidade em diversos setores industriais, seja indústria química, petroquímica ou alimentícia. Buscando atender solicitações ainda mais severas, métodos que melhorem a relação resistência à corrosão e propriedades mecânicas destes aços tem sido objeto de estudo de diversos pesquisadores. Com o objetivo de aumentar a resistência mecânica, dureza superficial e resistência à corrosão dos aços inoxidáveis propôs-se a introdução de nitrogênio em solução sólida pelo processo de SHTPN (Solution Heat Treatment after Plasma Nitriding), em desenvolvimento no GrMaTS/UTFPR. O nitrogênio apresenta algumas vantagens como a redução da tendência à precipitação, e a estabilização da camada passiva. Além disso, o nitrogênio reage na área anódica, o que neutraliza o efeito da acidez melhorando assim a resistência a corrosão. Neste trabalho avaliou-se a resistência à corrosão do aço inoxidável ferrítico AISI 409, após a obtenção de uma camada martensítica enriquecida com nitrogênio em solução solida por meio do processo SHTPN. Em seguida foram avaliados os efeitos da temperatura de revenimento (200, 400 e 600 °C) e da temperatura de austenitização (950 e 1050 °C) na microestrutura, dureza e resistência à corrosão da camada martensítica obtida. A resistência à corrosão foi avaliada pela técnica de polarização cíclica em solução de NaCl 0,5 mol/L e os perfis de dureza obtidos por medição de dureza Vickers com carga de 0,05 Kgf (0,49 N). A microestrutura foi avaliada por Microscopia Óptica, Eletrônica de Varredura e por Difração de Raios-X. Os resultados indicam que o tratamento de SHTPN promoveu a formação de uma camada martensítica de nitrogênio, com consequente acréscimo de dureza de 160 HV para 580 HV. O tratamento têmpera após SHTPN não afetou significativamente a dureza do aço, contudo, refinou e melhorou a distribuição da martensita de nitrogênio. Os resultados de corrosão para as condições tratadas e revenidas a 200 °C indicam resistência à corrosão superior ou equivalente à da ferrita do material não tratado (AISI 409). Já as amostras revenidas nas temperaturas de 400 e 600 °C apresentaram um decréscimo na resistência à corrosão, bem como foi observada uma diminuição da dureza da amostra revenida a 600 °C. / Due to high corrosion resistance, stainless steels have a wide applicability in many industrial sectors, such as, chemical, petrochemical and food industries. With the demand for corrosion resistance materials becoming more stringent, methods that improve the relation corrosion resistance and mechanical properties of these steels has been studied by many researchers. In order to increase the mechanical strength, surface hardness and corrosion resistance of stainless steels we proposed the introduction of nitrogen in solid solution by the process of SHTPN (Solution Heat Treatment after Plasma Nitriding), under development in GrMaTS/UTFPR . Nitrogen in solid solution has some advantages over materials that have only carbon in the structure such lower tendency for precipitation and stabilization of the passive layer. In addition, the nitrogen reacts in the anodic area, which neutralizes the effect in the acidity thus improving the corrosion resistance. This research evaluate the corrosion resistance of ferritic stainless steel AISI 409, after obtaining a martensitic layer enriched with nitrogen, in solid solution, by SHTPN process. Effects of tempering temperature (200, 400 and 600 °C) and austenitization temperature (950 to 1050 °C) in the microstructure, hardness and corrosion resistance of martensitic layer obtained. Corrosion resistance was evaluated by cyclic polarization technique, with a NaCl solution 0.5 mol/L, and hardness profiles obtained by measuring the Vickers hardness with a load of 0.05 kgf (0.49 N). Samples microstructure was investigated by optical microscopy, scanning electron microscopy and X- ray diffraction. Results indicate that the treatment of SHTPN promoted the formation of a martensitic nitrogen layer, with consequent increase of hardness of 160 HV to 580 HV on sample surface. Tempering treatments, realized after SHTPN did not significantly affect the hardness of steel, however, has refined and improved the distribution of nitrogen martensite. Corrosion results of sample treated and annealed at 200 °C indicate higher or equal resistance to that of the untreated ferrite materials (AISI 409) corrosion. Samples that were annealed at temperatures of 400 and 600 °C showed a decrease in the corrosion resistance as well as a decrease in hardness was observed in the sample tempered at 600 °C.