Le présent travail a été mené dans le but d’étudier l’influence de la préparation de surface de l’acier SAE 1045 revêtu de l’alliage WC-10%Co- 4%Cr par projection thermique HVOF sur le comportement en fatigue. Avant la projection thermique HVOF, le substrat a été préparé avec trios conditions différentes de rugosité dans le but de fournir différentes propriétés d’adhérence du revêtement sur son substrat. L’analyse microstructurale des systèmes revêtus a été faite par microscopie électronique à balayage. La rugosité du substrat a été évaluée par profilométrie optique et l’adhérence du revêtement sur le substrat par l’essai d’indentation interfaciale. Les modules d’élasticité du substrat et du revêtement ont été déterminés par ultrasons. Le comportement en fatigue du système revêtu a été étudié en flexion rotation (R = -1) en utilisant une contrainte maximum alternée dans le domaine 358-420 MPa. Une simulation numérique utilisant un code de simulation commerciale a été appliquée pour décrire la comportement en fatigue des systèmes revêtus. Cette étude a permis une meilleure compréhension du comportement en fatigue du système revêtu par projection thermique HVOF et la corrélation d’un tel comportement avec les paramètres importants comme la rugosité du substrat, les caractéristiques microstructurales du revêtement et son adhérence au substrat. / The present research work has been carried out in order to study the influence of the surface preparation of a SAE 1045 steel substrate on its fatigue behavior after coating with WC-10%Co-4%Cr deposited by HVOF thermal spraying. Prior to HVOF deposition, the substrate was prepared in three different surface roughness conditions, in order to provide mechanical bonding to the coating. The microstructural analysis of the coated systems was carried out employing SEM techniques. The substrate surface roughness was evaluated by means of optical perfilometry and the adherence of the coating to the substrate was studied employing interface indentation techniques. The elastic modulus of both substrate and coating was determined by means of ultrasound techniques. The fatigue behavior of the substrate-coating system was investigated under rotating bending conditions (R = - 1), employing maximum alternating stresses in the range of 358-420 MPa. A numerical simulation, employing a FEM commercial code, was carried out in order to describe the fatigue behavior of the coated systems. This investigation has allowed a better understanding of the fatigue behavior of the coated systems obtained by HVOF thermal spraying and the correlation of such a behavior with important parameters such substrate roughness, coating microstructural characteristics and its adherence to the substrate

Metal Matrix Composite (MMC) coatings, comprised of a hard ceramic phase embedded in a metallic matrix, are increasingly being applied for many industrial applications to provide cost effective protection against wear and corrosion. Such coatings are commonly produced by thermal spray. Although the most advanced thermal spray techniques, such as high-velocity oxy-fuel (HVOF), produce MMC coatings with total porosity levels lower than 1%, due to the nature of thermal spray MMC coatings, corrosion still takes place. The corrosion processes are dominated by the complex microgalvanic and interfacial mechanisms, as well as by porosity, due to the existence of various defects in HVOF MMC coatings. As a result, HVOF coatings do not ultimately meet the requirements in certain service conditions in operating environments. Therefore, there is a need to find a method of modification of coatings, with significantly reduced microstructural defects and improved cohesive and adhesive strength so that the service life of the coated components can be increased. This work aims to investigate the effects of laser surface treatment on the corrosion and wear performance for Tribaloy 800 (T800), and T800-based WC HVOF-sprayed MMC coatings onto 316L stainless steel substrate. Laser surface treatments have been carried out using a 1.5 kW high power diode laser. Laser operating windows for various coatings have been established for the relationships between the laser operating conditions and melt pool dimensions, in the consideration of formation of cracks and porosity within laser-treated surface layers. Microstructural analysis of the powders, and various coatings before and after laser treatments has been conducted by means of optical and SEM (with EDX) microscopy, electron probe micro-analysis (EPMA), white-light interferometery, and X-ray diffraction, to characterise morphology, chemical composition and phase. Corrosion performance of various coating was evaluated using immersion testing in 3 M H2SO4 at pH ~ 1.27 at room temperature for different periods of time (including 24, 48, 72, 96 and 168 hours), followed by Inductivity Coupled Plasma-optical emission spectrometer (ICP-OES) technique, potentiodynamic polarisation in 0.5 M H2SO4, and electrochemical impedance spectroscopy studies in 0.5 M H2SO4 solution after 1, 3, 6, 12, 24, and 48 hours. Inaddition, dry sliding wear behaviour measured by pin-on-disk and microhardness test of various coatings before and after laser treatment were evaluated.The results indicated that it was possible to achieve full control of melt depth and the degree of melting, particularly full or partial melting of WC particles by proper selection of the laser processing parameters while preventing dilution. Significant improvement of corrosion and wear resistance has been achieved after laser treatment as a result of the elimination of discrete splat-structure, removal of microcrevices and porosity, as well as the reduction of microgalvanic driving force between the WC and the metal matrix by formation of new phases at the interfaces. The degree of melting of WC particles controls the corrosion properties of the laser-treated HVOF coatings. Moreover, the results also suggested that partial melting of WC had positive effect on wear resistance of the coatings.

The depletion of natural resources has long been a concern since the rapid increase in energy consumption in recent years. The gradual increase of pollution worldwide accompanied by energy generation process also started to post threats to the environment. With the evolution of technology and materials, power generation and energy storage with significant improved efficiency can be made possible, and further benefits the reduction of degree of pollution generated. In this research, synthesis, processing, characterization and application of nano materials towards energy generation and energy storage devices are studied. In chapter 2, superior corrosion resistance properties of HVOF thermal spray of TiC and TiB2 coatings on 304H stainless steel, 430, and P91 steels were reported. The coatings successfully served at a protection layer by limiting oxygen penetration, sulfur attack, and decreased the formation of pits and cracks on the substrates at 750°C for up to 800 hours. In chapter 3, continuous smooth TiC nanofibers were successfully synthesized by carbothermal reduction of electrospun titanium based nanofibers. XRD and HR-TEM analysis results indicated the synthesized nanofibers were composed of high purity TiC. Electric conductivity of a single fiber was in the 2.00×10^5 range. Symmetrical cyclic voltammetry curve further indicated good electrochemical properties of the fibers. In addition, the TiC nanofibers also exhibited excellent sintering properties over TiC or TiB2 nanoparticles. Studies on morphology and electrochemical properties of MnOx nanofiber and nanoparticles is reported in chapter 4. MnOx, MnOx/SnO2, and MnOx/CNT nanofibers synthesized using electrospinning method showed specific capacitance of 166.12 F/g, 182 F/g for, and 472 F/g at scan rate of 10mV/s. Analysis results also showed positive impact of conductivity and fiber morphology on the electrochemical properties of the fibers. morphology and electrochemical properties of the MnOx nanoparticles synthesized using solvents with different polarity with gelation pH of 8.5, 9.0 and 10.0 were also studied. Analysis results show the impact of particle sized and morphology on the electrochemical properties. Highest specific capacitance measured for the synthesized nanoparticles was 231.38F/g@10mV/s and 165.13F/g@10mV/s for methanol and mixture of methanol and propanol based MnOx respectively. Effect of solvent polarity of the manganese sol on MnOx formation and phase transformation temperature is also shown in the chapter.

A operação de uma turbina hidráulica para hidrogeração alocada em um rio com sedimentos pode levar ao desgaste erosivo e, consequentemente, manutenção prematura do componente. Visando mitigar esse problema, em geral, aplicam-se revestimentos que aumentam a vida útil das turbinas, mas não eliminam o desgaste erosivo ocorrido, o que leva à necessidade de reparo do componente. O reparo se inicia com a remoção do revestimento remanescente e reconstituição da geometria por solda, para então, reaplicação de um novo revestimento. Nem sempre as regiões afetadas são grandes, o que possibilitaria a aplicação de um reparo por soldagem e também reparo de revestimento localizado na turbina. O reparo sobre o revestimento pode ser aplicado tanto na recuperação de componentes que sofrem desgaste erosivo, bem como, para consertar problemas ocorridos durante o processo de revestimento anterior. O presente trabalho visa compreender e verificar a possibilidade de reparo em um revestimento de WC-10Co-4Cr executado pelo processo de aspersão térmica HVOF (high velocity oxy fuel), bem como, suas limitações em desgaste erosivo. O estudo foca na preparação sobre um revestimento existente (remoção eletroquímica) e aplicação de uma nova camada. Como avaliação inicial o trabalho considerou o ensaio de desgaste erosivo, onde foi encontrado aumento de 22% na quantidade de material erodido nos corpos de prova com reparo. A observação e comparação dos corpos de prova com e sem reparo, utilizando microscopia eletrônica de varredura (MEV), mostra que a diferença em desgaste está na delaminação entre camadas devido à falha coesiva, a qual pôde ser observada através do ensaio de adesão. A falha coesiva pode ser explicada com base em análise por EDS dos corpos de prova, por intermédio da qual foi verificado um aumento na quantidade de oxigênio e, consequentemente, presença de óxido na preparação superficial por remoção eletroquímica. / The operation of a hydraulic turbine for hydropower generation located in a river with sediments can lead to erosive wear, and, as a consequence, premature maintenance of the component. In order to minimize such problem, coatings are applied to increase turbine lifetime, but they do not eliminate erosive wear, which leads to the necessity of component repair. The repair starts with the removal of the remaining coating and reconstitution of the geometry by welding, and then reapplication of a new coating. The affected regions are not necessarily large, which would allow the application of a localized repair by welding and localized repair by coating. The coating repair can be applied in two situations: recovery of components with erosive wear and to fix problems during coating manufacturing. The present work aims to understand and verify the possibility of repair in a WC-10Co-4Cr coating performed by the thermal spraying HVOF process (high velocity oxy fuel), as well as, its limitations in erosive wear. This study focuses in the preparation of an existing coating (electrochemical removal) and application of new coating layers. The start point was an evaluation using an erosion test rig, which indicated an increase of 22% in material removal for the test samples with repair. Using scanning electron microscope (SEM), the test samples with and without repair were compared and showed a wear difference related to delamination between layers due to cohesive failure, which was also observed in the adhesion test. The cohesive failure can be explained by EDS, where it was found a high content of oxygen in the repaired zones, and, as a consequence, presence of oxide in the surface preparation by electrochemical removal.

Desgaste é um dos três principais problemas industriais comumente encontrados, que levam à substituição de componentes e equipamentos em engenharia. A possibilidade de se recuperar esses componentes, ou prepará-Ios para suportar melhor as condições de trabalho, é constantemente estudada e novas técnicas são propostas, sempre no sentido de aumentar a vida útil e reduzir custos operacionais. Esta é a razão para o aumento da importância dos sistemas de revestimentos. O cromo duro eletrolftico tem sido muito utilizado para conferir resistência ao desgaste elou à corrosão, porém as características do processo de deposição eletrolítica do mesmo, com a presença do cromo hexavalente, altamente cancerígeno, têm resultado numa limitação crescente ao seu uso. Devido a isso se tomou necessário o desenvolvimento de novos revestimentos alternativos menos agressivos. Os substitutos mais promissores são os \"cermets\" depositados pelo processo HVOF, que foram produzidos no presente trabalho e comparados com o cromo duro eletrolítico quanto à resistência ao desgaste. Os revestimentos obtidos foram caracterizados por meio de ensaios micrográficos óticos, eletrônicos, raios-x, densidade e ensaios de desgaste dos seguintes tipos: roda de borracha e areia a seco, ensaio abrasivo para carbonetos e micro-abrasivo. O revestimento Cr3 Cr2-NiCr apresentou desempenho geral inferior ao do cromo duro. Entretanto no caso do desgaste micro-abrasivo, onde o mecanismo de desgaste apresentado no mesmo foi misto adesivo-abrasivo, ao contrário dos demais que tiveram características abrasivas, sua resistência ao desgaste foi superior a dos demais. O revestimento constituído de WC-CoCr apresentou o melhor desempenho entre todos os avaliados, o que o indica como um candidato altamente promissor à substituição do cromo / Wear is one of the three main industrial problems, that causes the substitution of components and equipments in engineering. The possibility to recover those components or to prepare them to better support the work conditions is constantly studied and new techniques are proposed, a/ways seeking to increase the life span and to reduce operational eosts. This is the reason why the coating systems are important. The hard ehrome coatings has been traditionally used to improve wear resistance and/or eorrosion resistance. However the eharacteristics of the electroplated deposition proeess, with the presence of the hexavalente ehrome, highly cancerous, result in a growing limitation to its use. Due to that it beeome necessary the development of new less aggressive alternative eoatings. The most promising substitutes are the \"cermets\" deposited by the HVOF process that were produced in the present work and compared with electroplated hard ehrome coatings for wear resistance. The obtained coatings were characterized through optical and electronic mierographics analysis , x-ray, density and submitted to the following types of wear tests: Dry Sand I rubber wheel, Wear test for cemented carbides and mieroabrasive wear test. The coating Cr3Cr2-NiCr presented smaller general performance in comparison with the hard ehrome. However, in the case of the miero-abrasive wear, where the wear mechanism presented was mixed adhesive-abrasive, unlike the others that had only abrasive eharacteristics, the resistance to the wear was superior. The WC-CoCr coating presented the best performance overall, what indicates it as a candidate to the hard ehrome substitution

Made available in DSpace on 2016-12-08T17:19:23Z (GMT). No. of bitstreams: 1 Matheus Machado de Souza.pdf: 5533626 bytes, checksum: a5f582284c7919cc899d81e7de2c62c8 (MD5) Previous issue date: 2014-08-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The use of coatings based in electrolytic chromium deposition causes damages to the environment, since during the process, hexavalent chromium ions are released and these are extremely toxic to nature and man. However, other technologies have been studied as alternatives to the traditional chromium electroplating process. The thermal spray high velocity oxy-fuel (HVOF) is a technique that has shown the best results considering coating quality, porosity, wear resistance, mechanical and adhesive properties. In this work, a comparative study between the hard chromium electroplated and HVOF sprayed coatings was performed, in a condition which the substrate surface has been rectified. Surface properties were checked in terms of adhesion, hardness and microstructure, while the tribological behavior was obtained by pin on disk wear tests, considering the evaluation of wear resistance, friction coefficient and wear mechanisms. The material used as substrate was the SAE 4140 steel; the coatings sprayed by HVOF were WC-Co-Cr and 316L Stainless Steel. As the conditions studied, no adhesion on substrate of 316L coating was observed. For coatings which obtained satisfactory adherence, the tungsten carbide was harder (1750 HV0,1) than chromium (1050 HV0,1). This result was attributed to the low porosity and high hardness of WC and W2C phases contained into sprayed coating. The coat WC-Co-Cr had a better performance and wear resistance, possibly, due to the formation of a great wear resistant tribofilm and the high hardness of the layer. For chromium, the delamination of a fragile tribofilm aggregated with a big quantity of cracks inside the microstructure might explain the pronounced wear. / A utilização de revestimentos a base de cromo eletrolítico traz prejuízos ao meio ambiente, uma vez que durante o processo são liberados íons de cromo extremamente tóxicos à natureza e ao homem. Outras tecnologias vêm sendo estudadas como alternativas ao processo tradicional de cromagem. A aspersão térmica por oxi- ombustível de alta velocidade (HVOF) é a técnica que tem apresentado os melhores resultados sob as óticas de qualidade de revestimento, porosidade, resistência ao desgaste, propriedades mecânicas e adesivas. Neste trabalho foi realizado um estudo comparativo entre o cromo duro eletrodepositado e revestimentos aspergidos (WC-Co-Cr e o Inox 316L) pela técnica de HVOF em uma condição em que a superfície do substrato (aço SAE 4140) foi retificada. As propriedades de superfície foram verificadas em função da adesão, dureza e microestrutura, enquanto que o comportamento tribológico foi obtido por meio de ensaios de desgaste por deslizamento pino sobre disco, com avaliação da resistência ao desgaste, coeficiente de atrito e mecanismos de desgaste. Verificou-se a não adesão ao substrato do revestimento de Inox 316L para as condições estudadas. Quanto a dureza o carbeto de tungstênio apresentou maior valor (1750 HV0,1), bastante superior ao cromo (1050 HV0,1). Resultado atribuído a baixa porosidade e a elevada dureza das fases WC e W2C contidas no revestimento aspergido. O revestimento de WC-Co-Cr teve um melhor desempenho quanto a resistência ao desgaste, possivelmente, em função da formação de um tribofilme resistente ao desgaste e a elevada dureza da camada. Para o cromo, a delaminação de um tribofilme de natureza frágil somada a uma microestrutura com elevada densidade de trincas foram fatores que puderam explicar seu desgaste mais acentuado.

Das thermische Spritzen ist ein industrieller Beschichtungsprozess, der hauptsächlich zum Schutz oder zur Funktionalisierung von Bauteiloberflächen eingesetzt wird. In der Regel werden mit diesem Verfahren Schichten mit einer Dicke von 50 bis zu einigen 100 Mikrometern aufgetragen, die überwiegend durch mechanische Verklammerung haften, wodurch die Materialeigenschaften des Bauteils weitgehend erhalten bleiben. Mit der Einführung von Suspensionen als neue Kategorie der Spritzzusätze etabliert sich gerade eine der weitreichendsten Innovationen der letzten Jahre auf dem Gebiet des thermischen Spritzens. Suspensionen sind Stoffgemische, die aus einer feindispersen, festen Phase, dem Schichtwerkstoff, und einer flüssigen Phase als Trägermedium bestehen. Damit können Partikel mit geringerer Größe in den Beschichtungsprozess eingebracht werden, so dass sich dünnere Schichten und feinere Mikrostrukturen realisieren lassen. Das thermische Spritzen mit Suspensionen erweitert damit den Anwendungsbereich und bildet eine Brückentechnologie zu den Vakuum- Dünnschichtverfahren. Im Fokus dieser Arbeit stehen die drei wichtigen keramischen Werkstoffe Aluminiumoxid, Chromoxid und yttriumstabilisiertes Zirkonoxid, die in der Form von wasserbasierten Suspensionen als Spritzzusätze für das Atmosphärische Plasmaspritzen (APS) und das Hochgeschwindigkeitsflammspritzen (HVOF) verwendet werden. Für die Injektion der Suspension in das Plasma oder die Flamme wird ein automatisiertes Suspensionsfördersystem verwendet. Darüber hinaus werden spezielle mehrteilige Injektoren entwickelt und getestet. Es werden neue Erkenntnisse zur statistischen Auswertung der Zusammenhänge zwischen den Injektionsparametern, den messbaren Eigenschaften der Tropfenwolke während der Zerstäubung, den Partikeleigenschaften im Spritzstrahl und den daraus resultierenden Schichteigenschaften vorgestellt. Dafür wurde eine neue Kenngröße für den Beschichtungserfolg, ein sogenannter Beschichtungsfaktor, hergeleitet, der sich mit vergleichsweise geringem Aufwand bestimmen lässt und außerdem die zusätzlichen Prozessvariablen beim Suspensionsspritzen mit berücksichtigt. Im Anschluss werden Beispiele für wasserbasierte, suspensionsgespritzte Schichten aus den drei keramischen Werkstoffen vorgestellt, bei denen durch entsprechende Charakterisierungsmethoden das Anwendungspotential im Vergleich zu Spritzschichten nach dem Stand der Technik verdeutlicht wird. Die Anwendungsgebiete umfassen dabei die elektrische Isolation, den Verschleißschutz sowie die thermische Isolation. Den Abschluss der Arbeit bildet eine kritische Diskussion der Eignung von wasserbasierten Suspensionen für das thermische Spritzen mit Plasma- und Flammspritzprozessen. Es werden die Vor- und Nachteile dieser Beschichtungstechnik analysiert und Verbesserungsvorschläge sowohl für die weitere Suspensions- als auch für die Anlagenentwicklung unterbreitet.

A operação de uma turbina hidráulica para hidrogeração alocada em um rio com sedimentos pode levar ao desgaste erosivo e, consequentemente, manutenção prematura do componente. Visando mitigar esse problema, em geral, aplicam-se revestimentos que aumentam a vida útil das turbinas, mas não eliminam o desgaste erosivo ocorrido, o que leva à necessidade de reparo do componente. O reparo se inicia com a remoção do revestimento remanescente e reconstituição da geometria por solda, para então, reaplicação de um novo revestimento. Nem sempre as regiões afetadas são grandes, o que possibilitaria a aplicação de um reparo por soldagem e também reparo de revestimento localizado na turbina. O reparo sobre o revestimento pode ser aplicado tanto na recuperação de componentes que sofrem desgaste erosivo, bem como, para consertar problemas ocorridos durante o processo de revestimento anterior. O presente trabalho visa compreender e verificar a possibilidade de reparo em um revestimento de WC-10Co-4Cr executado pelo processo de aspersão térmica HVOF (high velocity oxy fuel), bem como, suas limitações em desgaste erosivo. O estudo foca na preparação sobre um revestimento existente (remoção eletroquímica) e aplicação de uma nova camada. Como avaliação inicial o trabalho considerou o ensaio de desgaste erosivo, onde foi encontrado aumento de 22% na quantidade de material erodido nos corpos de prova com reparo. A observação e comparação dos corpos de prova com e sem reparo, utilizando microscopia eletrônica de varredura (MEV), mostra que a diferença em desgaste está na delaminação entre camadas devido à falha coesiva, a qual pôde ser observada através do ensaio de adesão. A falha coesiva pode ser explicada com base em análise por EDS dos corpos de prova, por intermédio da qual foi verificado um aumento na quantidade de oxigênio e, consequentemente, presença de óxido na preparação superficial por remoção eletroquímica. / The operation of a hydraulic turbine for hydropower generation located in a river with sediments can lead to erosive wear, and, as a consequence, premature maintenance of the component. In order to minimize such problem, coatings are applied to increase turbine lifetime, but they do not eliminate erosive wear, which leads to the necessity of component repair. The repair starts with the removal of the remaining coating and reconstitution of the geometry by welding, and then reapplication of a new coating. The affected regions are not necessarily large, which would allow the application of a localized repair by welding and localized repair by coating. The coating repair can be applied in two situations: recovery of components with erosive wear and to fix problems during coating manufacturing. The present work aims to understand and verify the possibility of repair in a WC-10Co-4Cr coating performed by the thermal spraying HVOF process (high velocity oxy fuel), as well as, its limitations in erosive wear. This study focuses in the preparation of an existing coating (electrochemical removal) and application of new coating layers. The start point was an evaluation using an erosion test rig, which indicated an increase of 22% in material removal for the test samples with repair. Using scanning electron microscope (SEM), the test samples with and without repair were compared and showed a wear difference related to delamination between layers due to cohesive failure, which was also observed in the adhesion test. The cohesive failure can be explained by EDS, where it was found a high content of oxygen in the repaired zones, and, as a consequence, presence of oxide in the surface preparation by electrochemical removal.

Desgaste é um dos três principais problemas industriais comumente encontrados, que levam à substituição de componentes e equipamentos em engenharia. A possibilidade de se recuperar esses componentes, ou prepará-Ios para suportar melhor as condições de trabalho, é constantemente estudada e novas técnicas são propostas, sempre no sentido de aumentar a vida útil e reduzir custos operacionais. Esta é a razão para o aumento da importância dos sistemas de revestimentos. O cromo duro eletrolftico tem sido muito utilizado para conferir resistência ao desgaste elou à corrosão, porém as características do processo de deposição eletrolítica do mesmo, com a presença do cromo hexavalente, altamente cancerígeno, têm resultado numa limitação crescente ao seu uso. Devido a isso se tomou necessário o desenvolvimento de novos revestimentos alternativos menos agressivos. Os substitutos mais promissores são os \"cermets\" depositados pelo processo HVOF, que foram produzidos no presente trabalho e comparados com o cromo duro eletrolítico quanto à resistência ao desgaste. Os revestimentos obtidos foram caracterizados por meio de ensaios micrográficos óticos, eletrônicos, raios-x, densidade e ensaios de desgaste dos seguintes tipos: roda de borracha e areia a seco, ensaio abrasivo para carbonetos e micro-abrasivo. O revestimento Cr3 Cr2-NiCr apresentou desempenho geral inferior ao do cromo duro. Entretanto no caso do desgaste micro-abrasivo, onde o mecanismo de desgaste apresentado no mesmo foi misto adesivo-abrasivo, ao contrário dos demais que tiveram características abrasivas, sua resistência ao desgaste foi superior a dos demais. O revestimento constituído de WC-CoCr apresentou o melhor desempenho entre todos os avaliados, o que o indica como um candidato altamente promissor à substituição do cromo / Wear is one of the three main industrial problems, that causes the substitution of components and equipments in engineering. The possibility to recover those components or to prepare them to better support the work conditions is constantly studied and new techniques are proposed, a/ways seeking to increase the life span and to reduce operational eosts. This is the reason why the coating systems are important. The hard ehrome coatings has been traditionally used to improve wear resistance and/or eorrosion resistance. However the eharacteristics of the electroplated deposition proeess, with the presence of the hexavalente ehrome, highly cancerous, result in a growing limitation to its use. Due to that it beeome necessary the development of new less aggressive alternative eoatings. The most promising substitutes are the \"cermets\" deposited by the HVOF process that were produced in the present work and compared with electroplated hard ehrome coatings for wear resistance. The obtained coatings were characterized through optical and electronic mierographics analysis , x-ray, density and submitted to the following types of wear tests: Dry Sand I rubber wheel, Wear test for cemented carbides and mieroabrasive wear test. The coating Cr3Cr2-NiCr presented smaller general performance in comparison with the hard ehrome. However, in the case of the miero-abrasive wear, where the wear mechanism presented was mixed adhesive-abrasive, unlike the others that had only abrasive eharacteristics, the resistance to the wear was superior. The WC-CoCr coating presented the best performance overall, what indicates it as a candidate to the hard ehrome substitution

Für die Entwicklung neuer Technologien wird mehr und mehr der Einsatz von Spritzschichten benötigt. Hiermit lassen sich die komplexen Anforderungen an die Oberflächeneigenschaften erfüllen. Die thermischen Spritzverfahren werden immer mehr auch zum Mittelpunkt von Industrieanwendungen und bieten ein großes Anwendungsgebiet. Die Steigerung der Produktivität und der Leistung von technischen Anlagen und Maschinen erhöht gleichzeitig auch die Beanspruchung der Bauteile. Daher ist es notwendig, dass hochbeanspruchte oder gefährdete Oberflächen durch thermisches Spritzen geschützt werden, so dass sie den Belastungen besser standhalten. Ebenso führt die allgemeine Rohstoffknappheit dazu, dass Maschinenteile nicht vollständig aus bestimmten Materialien gefertigt werden können. Diese Teile können durch eine geeignete Oberflächenbeschichtung rohstoffsparend und damit kostengünstig hergestellt werden. Ein weiteres Anwendungsgebiet für das thermische Spritzen ist die Reparatur verschlissener Teile. Die hohe Flexibilität des thermischen Spritzens, die geringen Reparaturkosten und die damit verbundenen kurzen Ausfallzeiten kommen der Industrie zu Gute. Nach wie vor existiert keine Online-Prozesskontrolle, welche die relevanten Größen der Wechselwirkung Flamme – Spritzzusatzwerkstoff erfassen kann. Die Schichtoptimierung erfolgt weitestgehend durch eine empirische Veränderung der Spritzparameter und die anschließende Analyse und Zuordnung der Parameter zu den Ergebnissen. Hierbei beschränkt sich die Prozesskontrolle auf das Einstellen konstanter Werte für die regelbaren Eingangsgrößen. Bei diesen Möglichkeiten wird vorausgesetzt, dass bei konstanten Maschineneinstellungen auch ein konstanter Prozess mit reproduzierbaren Ergebnissen vorliegt. Im täglichen Umgang ist jedoch festzustellen, dass die Ergebnisse über einen längeren Zeitraum meist nicht reproduzierbar sind. Eine online arbeitende Meßmethode, die Aussagen über die Geschwindigkeit und Erwärmung der Spritzpartikel macht, liefert die Grundlage für reproduzierbare Ergebnisse. An Stelle der Anlagensteuergrößen werden Partikelparameterkorrelierte Messgrößen überwacht bzw. für eine Steuerung verwendet. Der Zugang zu Flammen- bzw. Partikeltemperatur erfolgt mit Hilfe der optischen Emissionsspektroskopie. In der vorliegenden Arbeit wird das Emissionsspektrum an zwei Orten entlang der Plasmaachse ausgewertet. Aus dem Intensitätsverhältnis von mehreren Spektrallinien eines Elements wird die Temperaturentwicklung der Partikel ermittelt (Temperaturbestimmung an mehreren Orten) und damit auch deren Geschwindigkeit beurteilt. Kenntnisse über die Temperatur- und Geschwindigkeitsverteilung geben die Möglichkeit reproduzierbare Schichten herzustellen, da die Bedingungen zu einem späteren Zeitpunkt exakt reproduziert werden können. Durch fluiddynamische Rechnungen wird der Nachweis erbracht, dass die Temperatur- und Geschwindigkeitsfelder des Plasmas und der injizierten Partikel miteinander korreliert sind. Im Verlauf dieser Arbeit wird weiterhin gezeigt, dass die genannten Messgrößen eine Signifikanz zum Spritzprozess aufweisen. Mögliche Störeinflüsse sowie eine Fehlerbetrachtung ergänzen die gewonnen Aussagen.