<p>In powder metallurgy research field, Direct Metal Laser Sintering (DMLS) and Metal Powder Starch Consolidation (MPSC) are relatively new rapid forming techniques to fabricate complex and near net-shaped components. The working principles of DMLS are to melt and fuse metal powder layer by layer in computer controlled systems to pile up components like three dimensional printing. It has been for instance extensively used for mould inserts, die parts, and functional metal prototypes. Another, less explored method, starch consolidation is a pressureless direct casting method which consists principally of mixing powder slurry, casting into moulds, consolidation, drying, and sintering. With a strong focus on both methods, the study here combines several strong material technology sectors; powder, rapid forming, mechanical property testing and surface technology. It covers the processing chain from green body preparation, optimization of</p><p>sintering, nitriding, post sinter heat treatment, to modeling and assessment of material behaviour for end-user applications. An iron based powder and a high vanadium high speed steel powder with low and high carbon contents were used in the DMLS and MPSC processes, respectively. The overall aim of the study is to synthesize near net-shaped powder-based components, to characterize pores and microstructure, and to establish a fundamental understanding of failure mechanisms of powder based materials in bending fatigue, thermal fatigue and wear.</p><p>The study showed the DMLS and MPSC technologies could produce shaped components with a multi-phased structure, controllable nitriding depth and high relative densities in a range of 97 - 99.7 %. Materials' heterogeneity and porosity have detrimental influence on mechanical properties, especially on crack initiation and subsequent propagation.</p>

Rost- und säurebeständige Stähle, wie z.B. der Austenit 1.4404, zeichnen sich durch eine hervorragende Korrosionsbeständigkeit aus. Der Einsatz dieser Stähle war aber aufgrund ihrer schlechten Verschleißeigenschaften bisher eher eingeschränkt. Um diesen Anforderungen gerecht zu werden, ist es notwendig, eine Oberflächenmodifizierung vorzunehmen. Dies kann besonders mit Nitrier- und Carburierverfahren bzw. einer Kombination aus beiden erreicht werden, wobei das im Mischkristall gelöste Chrom nicht zur Ausscheidung als Chromnitrid bzw. Chromcarbid gebracht werden darf. Dazu wurde bereits Mitte der 80-er Jahre das Verfahren der so genannten Tieftemperaturnitrierung entwickelt. Mit Hilfe dieses Verfahrens ist es möglich, auf rost- und säurebeständigen Stählen eine Schicht mit hohem Verschleißwiderstand zu erzeugen, ohne dass es zum Verlust der Korrosionsbeständigkeit kommt. Die werkstoffwissenschaftliche Forschung hat mit dieser überwiegend technologischen Entwicklung nicht Schritt gehalten. Verallgemeinerungsfähige Aussagen über das Korrosionsverhalten dieser verschleißbeständigen Randschichten in Abhängigkeit von ihrer Zusammensetzung und Struktur sind gegenwärtig noch nicht möglich. Die Zielstellung der im Rahmen dieser Arbeit durchzuführenden Untersuchungen besteht deshalb in der Ermittlung vertiefter Kenntnisse über den Zusammenhang zwischen den Behandlungsbedingungen, der Struktur und der chemischen Zusammensetzung der dabei entstehenden Randschichten und ihrem Korrosionsverhalten.

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In powder metallurgy research field, Direct Metal Laser Sintering (DMLS) and Metal Powder Starch Consolidation (MPSC) are relatively new rapid forming techniques to fabricate complex and near net-shaped components. The working principles of DMLS are to melt and fuse metal powder layer by layer in computer controlled systems to pile up components like three dimensional printing. It has been for instance extensively used for mould inserts, die parts, and functional metal prototypes. Another, less explored method, starch consolidation is a pressureless direct casting method which consists principally of mixing powder slurry, casting into moulds, consolidation, drying, and sintering. With a strong focus on both methods, the study here combines several strong material technology sectors; powder, rapid forming, mechanical property testing and surface technology. It covers the processing chain from green body preparation, optimization of sintering, nitriding, post sinter heat treatment, to modeling and assessment of material behaviour for end-user applications. An iron based powder and a high vanadium high speed steel powder with low and high carbon contents were used in the DMLS and MPSC processes, respectively. The overall aim of the study is to synthesize near net-shaped powder-based components, to characterize pores and microstructure, and to establish a fundamental understanding of failure mechanisms of powder based materials in bending fatigue, thermal fatigue and wear. The study showed the DMLS and MPSC technologies could produce shaped components with a multi-phased structure, controllable nitriding depth and high relative densities in a range of 97 - 99.7 %. Materials' heterogeneity and porosity have detrimental influence on mechanical properties, especially on crack initiation and subsequent propagation.

CNPq / Os aços inoxidáveis são amplamente utilizados nas indústrias químicas, petroquímicas, nucleares, de geração de energia, biomédica e de processamento de alimentos. Em geral os aços inoxidáveis apresentam boa resistência à corrosão, entretanto a aplicabilidade destes aços pode ser restringida pela dureza ou pela resistência a corrosão. Usualmente os aços de alta resistência e dureza apresentam elevados teores de carbono, apresentando uma estrutura martensítica, com consequente redução da resistência à corrosão. Por outro lado os aços com maior resistência a corrosão apresentam menor dureza e consequente menor resistência ao desgaste. Diversas soluções têm sido implementadas no sentido de melhorar a resistência a corrosão e ao desgaste simultaneamente desses materiais. Dentre estas a adição de nitrogênio na superfície através da nitretação a plasma, implantação iônica, tratamento térmico de solubilização após nitretação a plasma (SHTPN – Solution Heat Treatment after Plasma Nitriding). Este trabalho tem como objetivo determinar os parâmetros de SHTPN que possibilite obter martensita de nitrogênio na superfície do aço AISI 409, bem como, a avaliação de sua resistência à corrosão. Foi possível verificar uma melhora na resistência à corrosão das condições tratadas por SHTPN, assim como um aumento na resistência mecânica, avaliado pelo perfil de dureza da camada superficial tratada. / Stainless steels are widely used on chemical, petrochemical, nuclear, energy generation, biomedical and food processing industries. In general, stainless steels present good corrosion resistance. However, the application of these materials can be restrained by the hardness and the corrosion resistance. Usually, high strength steels present high carbon content and martensitic structure, what can consequently cause a reduction on corrosion resistance. On the other hand, high corrosion resistance steels present low hardness and weak wear properties. Thereby, many solutions have been made to improve simultaneously wear properties and corrosion resistance of these materials, specially related to the introduction of nitrogen on the surface, through plasma nitriding, ion implantation and SHTPN (Solution Heat Treatment after Plasma Nitriding) processes. The aim of this paper is to determine SHTPN parameters that can form nitrogen martensite on the surface of AISI 409 stailess steel, as well as the evaluation of its corrosion resistance. It was verified an improve on corrosion resistance conditions of SHTPN treated samples. Aditionally, there was an improve on mechanical resistance showed by hardness profiles.

Os aços inoxidáveis martensíticos são amplamente utilizados em aplicações biomédicas devido a sua excelente resistência a corrosão e boas propriedades mecânicas. Entretanto, em aplicações como brocas para a implantodontia, seu desempenho é insatisfatório. Nesta aplicação usualmente utiliza-se de revestimentos como DLC para melhorar a resistência a corrosão, a resistência ao desgaste, bem como, diminuir o coeficiente de atrito broca-osso. Diversos trabalhos na literatura mostram que a nitretação a baixas temperaturas produz camadas superficiais de alta dureza e alta resistência à corrosão. Sabe-se também que o aumento da dureza do substrato melhora o suporte para a adesão do revestimento como o DLC. Estes tratamentos são conhecidos como duplex. Neste trabalho estudou-se o efeito da nitretação a baixa temperatura na resistência à corrosão e dureza de aços inoxidáveis martensiticos do tipo ASTM 420F, bem como, a influência na dureza e resistência à corrosão do tratamento duplex nitretação e DLC. Foram escolhidos cinco parâmetros de nitretação a baixa temperatura, em tempos diferentes para avaliar o comportamento na dureza e resistência à corrosão. O parâmetro que teve o melhor desempenho, atingindo maior dureza e proporcionando uma melhor resistência à corrosão entre os demais, foi a 380°C por 6 horas. Nessa condição, a dureza média de topo foi de 894 HV (1Kgf) e não apresentou corrosão na camada nitretada com revestimento DLC. Pode-se esperar que aplicado essas condições em uma broca cirúrgica, dentro de sua condição de procedimentos cirúrgicos, o desgaste da ferramenta seja menor, uma vez que a sua superfície tem maior dureza do que usualmente comercializada, e mantendo sua resistência à corrosão em ambientes agressivos em que são expostas. / Martensitics stainless steels are used in biomedical applications because of that yours excellent corrosion resistance and good mechanical properties. However, in applications such as drills for implant their performance has been unsatisfactory. This application is usually used how DLC coatings to improve corrosion resistance, wear resistance and to decrease the coefficient of drill bone friction. Several studies in the literature show that nitriding at low temperatures produce surface layers of high hardness and high resistance to corrosion. It is also known that increasing the hardness of the substrate it improves the adhesion of the coating as DLC. These treatments are known as duplex. In this work were studied the effect of low temperature nitriding on the corrosion resistance and hardness of martensitic stainless steel type ASTM 420F, as well as the influence on the hardness and corrosion resistance of nitriding and DLC duplex treatment. Five parameters of nitriding at low temperature, at different times to evaluate the behavior in the hardness and corrosion resistance were chosen. The parameter that had the best performance providing a higher hardness and better corrosion resistance was at 380°C for 6 hours. The average hardness of the drill top was 894 HV (1 Kgf) and not showed corrosion in duplex layer. It can be expected to apply these conditions in a surgical drill, in the tool wear will be less, since the surface has a higher hardness than usually marketed and the drill maintained the resistance to corrosion in aggressive environment that they are exposited.

Made available in DSpace on 2014-12-17T14:06:48Z (GMT). No. of bitstreams: 1 JulioCPB.pdf: 2433728 bytes, checksum: 9509a2a35ebc0e4009df0a9bced418db (MD5) Previous issue date: 2007-11-14 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Plasma process like ionic nitriding and cathodic cage plasma nitriding are utilized in order to become hard surface of steels. The ionic nitriding is already accepted in the industry while cathodic cage plasma nitriding process is in industrial implementation stage. Those process depend of plasma parameters like electronic and ionic temperature (Te, Ti), species density (ne, ni) and of distribution function of these species. In the present work, the plasma used to those two processes has been observed through Optical Emission Spectroscopy OES technique in order to identify presents species in the treatment ambient and relatively quantify them. So plasma of typical mixtures like N2 H2 has been monitored through in order to study evolution of those species during the process. Moreover, it has been realized a systematic study about leaks, also thought OES, that accomplish the evolution of contaminant species arising because there is flux of atmosphere to inside nitriding chamber and in what conditions the species are sufficiently reduced. Finally, to describe the physic mechanism that acts on both coating techniques ionic nitriding and cathodic cage plasma nitriding / Processos a plasma como nitreta??o i?nica e nitrteta??o por gaiola cat?dica s?o utilizados para endurecimento de superf?cies de a?os. A nitreta??o i?nica sendo j? consolidada em aplica??es industriais enquanto que o processo por gaiola cat?dica ainda se encontra em est?gio de pesquisa. Esses processos dependem dos par?metros de plasma como temperatura eletr?nica e de ?ons (Te, Ti), densidade de esp?cies (ne, ni,) e da fun??o de distribui??o das mesmas. No presente trabalho, o plasma utilizado para esses dois processos foi diagnosticado utilizando a t?cnica de Espectroscopia de Emiss?o ?ptica EEO para identificar as esp?cies presentes no ambiente de tratamento e quantifica-las relativamente. Assim, plasma de mistura gasosa t?pica como N2 H2 foi monitorado, com o intuito de estudar a evolu??o dessas esp?cies durante o processo. Al?m disso, foi realizado um estudo sistem?tico, tamb?m atrav?s de EEO, que acompanha a evolu??o das esp?cies contaminantes surgidas em vazamentos de modo a buscar condi??es onde as mesmas s?o suficientemente reduzidas. Finalmente busca-se, atrav?s do diagn?stico de plasma por EEO, descrever o mecanismo f?sico de atua??o das duas t?cnicas de tratamento: nitreta??o i?nica e gaiola cat?dica

Made available in DSpace on 2014-12-17T14:06:50Z (GMT). No. of bitstreams: 1 MariaLMM.pdf: 1059040 bytes, checksum: e385dd512eb484e085eb027acc2a89fe (MD5) Previous issue date: 2008-08-22 / In this research there was an evaluation of the best conditions of nitriding in plasma within a cathodic cage at an atmosphere of 80% N2-20%H2 in samples of tool manganese steel AISI D6, cold working, treated thermally in the following conditions: tension relief, treated thermally to temperature of maximum heat, temperate heat and temperate and temperate heat. A pressure of 2.5mbar and temperatures of 400 and 300?C com treatment time of two and three hours were used to evaluate its performance as cutting tool (punch) of bicycle backs. Hardness, micro-structural aspects (layer thickness, interface, grain size etc), and crystal phases on the surface were appraised. When treated to tension relief, thermally treated to maximum heat temperature, temperature and temperate heat, the samples presented hardness levels of 243HV, 231HV, 832HV, and 653HV, respectively. The best nitrification conditions were: four hours and 300?C for heat samples. A superficial hardness of 1000HV and a 108?m thickness for the nitrided layer were found in these samples / Neste trabalho, foi realizada a avalia??o das melhores condi??es de nitreta??o em plasma com gaiola cat?dica, em atmosfera de 80%N2 - 20%H2 em amostras de a?o ferramenta para trabalho a frio AISI D6, tratado termicamente nas condi??es: al?vio de tens?o, tratado termicamente na temperatura de revenimento m?ximo, temperada e temperada e revenida. Usou-se press?o de 2,5 mbar, temperaturas de 400 e 300?C com tempo de tratamento de 3 e 4 horas, visando avaliar o seu desempenho em ferramenta de corte (pun??o) de rabeiras de bicicletas. Estimou-se a dureza, aspectos microestruturais (espessura da camada, interface, tamanho de gr?o, etc.) e fases cristalinas presentes na superf?cie. As amostras apresentaram n?veis de durezas 243HV, 231HV, 832HV e 653HV para as amostras com al?vio de tens?o, tratada termicamente na temperatura de revenimento m?ximo, temperada e temperada e revenida, respectivamente. As melhores condi??es de nitreta??o foram 4 horas a 300?C para as amostras temperadas e revenidas. As mesmas apresentaram uma dureza superficial em torno de 1000HV e 100?m de espessura para a camada nitretada

Made available in DSpace on 2014-12-17T14:07:08Z (GMT). No. of bitstreams: 1 RomuloRG.pdf: 2022744 bytes, checksum: b56ca8e09a24314d1127c49f3cf2e053 (MD5) Previous issue date: 2006-03-14 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The ionic nitriding process presents some limitations related with the control of the thickness of the layer and its uniformity. Those limitations that happen during the process, are produced due to edge effects, damage caused by arcing arc and hollow cathode, mainly in pieces with complex geometry and under pressures in excess of 1 mbar. A new technique, denominated ASPN (active screen shapes nitriding) it has been used as alternative, for offering many advantages with respect to dc plasma conventional. The developed system presents a configuration in that the samples treated are surrounded by a large metal screen at high voltage cathodic potencials, (varying between 0 and 1200V) and currents up to 1 A. The sample is placed in floting potential or polarized at relatively lower bias voltages by an auxiliary source. As the plasma is not formed directly in the sample surface but in the metal screen, the mentioned effects are eliminated. This mechanism allows investigate ion of the transfer of nitrogen to the substrate. Optical and electronic microscopy are used to exam morphology and structure at the layer. X-ray difration for phase identification and microhardness to evaluate the efficiency of this process with respect to dc conventional nitriding / O processo de nitreta??o i?nica apresenta uma s?rie de limita??es relacionadas com o controle da espessura da camada e de sua uniformidade. Essas limita??es s?o produzidas devido a efeitos de bordas e de c?todo oco que ocorrem durante o processo, principalmente em pe?as com geometria complexa e em press?es do processo superiores a 2 mbar. Assim uma nova t?cnica, denominada ASPN (Active screen plasma nitriding) est? sendo usada como alternativa, por oferecer muitas vantagens em rela??o ao plasma dc convencional. O sistema desenvolvido apresenta uma configura??o em que as amostras a serem tratadas permanecem envolvidas por uma tela que atua como c?todo com tens?o dc variando entre 0 e 1200V e correntes de at? 1 A. A amostra pode permanecer em potencial flutuante ou ser polarizada por uma fonte auxiliar. Como o plasma n?o ? formado diretamente na superf?cie das amostras e sim na tela, os efeitos citados s?o eliminados. Este mecanismo permite investigar a transfer?ncia de nitrog?nio para o substrato por microscopia ?ptica e microscopia eletr?nica de varredura para exames da morfologia e da estrutura, difra??o de raios-X para identifica??o de fases e os ensaios de microdureza permitem avaliar a efici?ncia deste processo em rela??o ? nitreta??o dc convencional

Made available in DSpace on 2014-12-17T14:07:19Z (GMT). No. of bitstreams: 1 KleberJBR.pdf: 2080899 bytes, checksum: a6de36601fae047815a4f83a4734f672 (MD5) Previous issue date: 2007-03-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Nowadays, in the plastic industry are used mills that accomplish the recycling of residues generated in the production of its components. These mills contain cut sheets that suffer accelerated wear, once they are submitted constantly to the tribologic efforts, decreasing its useful life. To reduce this problem, it s used noble steels or takes place superficial treatments. The ionic nitriding process presents some limitations related to the uniformity of the layer in pieces with complex geometry, committing its application in pieces as knives, head offices, engagements, etc. However, the new technique of nitriding in cathodic cage eliminates some problems, as the restrictions rings, inherent to the conventional ionic nitriding. In present work, was studied the use viabilization of steels less noble, as SAE 1020, SAE 4320 and SAE 4340, nitreded by two different techniques, to substitute the AISI 01 steels, usually used in the cut knifes fabrication, seeking to reduce the costs and at the sane time to increase the useful life of these knifes. The steel most viable was the SAE 4340, nitrided in cathodic cage, because it presented uniformity in thickness and in the hardness of the layer, besides of increased 58% in the average its useful life / Atualmente, na ind?stria de pl?sticos s?o utilizados moinhos que realizam a reciclagem dos res?duos gerados na produ??o de seus componentes. Esses moinhos cont?m l?minas de corte que sofrem desgaste acelerado, uma vez que s?o constantemente submetidas a esfor?os tribol?gicos, diminuindo sua vida ?til. Para amenizar este problema, s?o utilizados a?os nobres ou realizam-se tratamentos superficiais nos a?os convencionais. O processo de nitreta??o i?nica apresenta uma s?rie de limita??es relacionadas com a uniformidade da camada em pe?as de geometria complexa, comprometendo sua aplica??o em pe?as como facas, matrizes, engrenagens, etc. Uma nova t?cnica de nitreta??o a plasma, denominada nitreta??o i?nica em gaiola cat?dica elimina alguns problemas, como os an?is de restri??es, inerentes a nitreta??o i?nica convencional. No presente trabalho foi estudado a viabiliza??o do uso de a?os menos nobres como SAE 1020, SAE 4320 e SAE 4340, nitretados por ambas t?cnicas de nitreta??o, em substitui??o aos a?os AISI 01, normalmente usados na fabrica??o de facas de corte, com o objetivo de reduzir os custos e ao mesmo tempo proporcionar o aumento da vida ?til dessas facas de corte. O a?o que apresentou os melhores resultados foi o SAE 4340 nitretado em gaiola cat?dica, pois apresentou uniformidade na espessura e na dureza da camada nitretada, promovendo um aumento m?dio de 58% de sua vida ?til