Dissertations / Theses on the topic 'HVOF SPRAYED'

Three HVOF and a VPS CoNiCrAlY coating were sprayed using Praxair CO-210-24 and Sulzer Metco Amdry 9951 powders. All coatings were subject to vacuum annealing treatments at different temperatures for different exposure times in order to achieve equilibrium microstructures in all test samples. Both HVOF and VPS, as sprayed and heat treated coatings were oxidised at 850°C and 1100°C for periods of up to 250 hours. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD) and laser diffraction powder size analyses were used in order to analyse the powder particle size distribution and characterise the microstructure of the as-received powders, as-sprayed coatings and annealed and oxidised coatings. Thermogravimetric analysis (TGA) was carried out on as-sprayed and heat treated HVOF and VPS coatings at 1100°C for 96 hours in order to compare the oxidation rate of HVOF and VPS coatings and investigate the effect of microstructure and heat treatment on the oxidation rate of both types of coatings. Furthermore, micro hardness, nano hardness and dynamic mechanical analysis (DMA) with a 3-point bend clamp were used in order to study the hardness and Young’s modulus of as-sprayed and annealed HVOF and VPS coatings. The Eshelby inclusion model and image analyses were used in order to further investigate the effect of microstructure on the mechanical properties of these coatings. It was observed that heat treatment prior to oxidation will change the dual oxide layer observed for the as-sprayed oxidised coatings to a single alumina layer for the heat treated and oxidised coatings. Furthermore, it was observed that microstructural features such as porosity and oxide stringers have an effect on the oxidation rate of coatings. A model was presented indicating the role of oxide stringers and porosity on the resulting heat treated microstructure and oxidation rate. It was also understood that the beginning stage of oxidation can play an important role on the oxidation behaviour (oxidation rate and different oxides present) of both HVOF and VPS coatings. It was observed that annealing will change the microstructure of the coatings and affect their mechanical properties. It was seen that annealing reduced the hardness of the thermally sprayed coatings while it had increased the Young’s modulus of the coatings. It was also observed that features such as porosity levels and β volume fraction have an effect on the mechanical properties of the coatings.

Gas nitriding is known as a convenient process to improve the wear resistance of steel components. A precipitation-free hardening by low-temperature processes is established to retain the good corrosion resistance of stainless steel. In cases of thermal spray coatings, the interstitial solvation is achieved without an additional surface activation step. The open porosity permits the penetration of the donator media and leads to a structural diffusion. An inhomogeneous diffusion enrichment occurs at the single spray particle edges within the coating’s microstructure. A decreasing diffusion depth is found with increasing surface distance. The present study investigates an adjusted process management for low-temperature gas nitriding of high velocity oxy-fuel-sprayed AISI 316L coatings. To maintain a homogeneous diffusion depth within the coating, a pressure modulation during the process is studied. Additionally, the use of cracked gas as donator is examined. The process management is designed without an additional surface activation step. Regardless of surface distance, microstructural investigations reveal a homogeneous diffusion depth by a reduced processing time. The constant hardening depth allows a reliable prediction of the coatings’ properties. An enhanced hardness and improved wear resistance is found in comparison with the as-sprayed coating condition.

The Seamless Stressometer® roll (Seamless STR) is used to measure the flatness of aluminum and steel strip when there is an extreme demand on the surface finish. To protect the roll and strip, the roll is coated with two layers deposited by high velocity oxygen fueled spraying (HVOF), Cr-Ni(Si,B) closest to the roll and WC-Co on top. This solution has several disadvantages; high cost and complicated logistics, corrosion sensitivity and high residual stresses creates the need for two coatings which in turn complicates the process. Cobalt is, in addition, sensitive to low pH coolants and environmentally unfriendly. These problems have given rise to the idea of switching both the method and material of the coating. In the first part of this work, high velocity air fueled spraying (HVAF) was evaluated as an alternative deposition method. Three materials, Cr3C2-NiCr, WC-Co and WC-CrC-Ni were deposited on steel coupons with varying chamber pressure, powder feed rate and distance from the nozzle, in order to evaluate if HVAF can be a valid technique for use in this application and to optimize the spraying recipe. The objectives were to get a sufficiently high thickness per sweep, to be able to make the depositions in a manageable number of sweeps, and to get low porosity, since the coatings need to be dense to be hard and possible to polish smooth. The tests showed that all three materials can be sprayed with the high settings on the parameters to obtain coatings that exceeded the set limits of the objectives. In the second part of this work, the recipe obtained from the first part was used to deposit samples for further analysis. The coatings were compared regarding cost, hardness, friction, wear and pick-up properties to evaluate if a switch in material from WC-Co was possible. The coatings showed both similarities and differences. The friction was very similar for the three materials. Cr3C2-NiCr was substantially cheaper than the other two, had lower hardness and higher porosity, but still probably acceptable values, and was satisfactory regarding wear and pick-up. WC-Co and WC-CrC-Ni were very similar to each other regarding cost, hardness and porosity but WC-Co was the best regarding wear and pick-up, where WC-CrC-Ni was the worst. The only clear advantage of WC-CrC-Ni over WC-Co is the lack of cobalt. Taking everything into consideration, including the fact that the wear and pick-up tests in this work was quite exaggerated, Cr3C2-NiCr is an interesting option for this application due to its low cost and acceptable test results, WC-Co had the best results but is expensive and contains cobalt and WC-CrC-Ni had as good results as WC-Co except for the wear and pick-up tests and does not contain cobalt.

In a variety of engineering applications, components are subjected to corrosive environment. Protective coatings are essential to improve the functional performances and/or extend the lifetime of the components. Thermal sprayingas a cost-effective coating deposition technique offers high flexibility in coatings' chemistry/morphology/microstructure design. However, the inherent pores formed during spraying limit the use of coatings for corrosion protection. The recently developed supersonic spray method, High-Velocity-Air-Fuel (HVAF), brings significant advantages in terms of cost and coating properties. Although severely reduced, the pores are not completely eliminated even with the HVAF process. In view of the above gap to have a high quality coating, bi-layer coatings have been developed to improve the corrosion resistance of the coatings. In a bi-layer coating, an intermediate layer is deposited on the substrate before spraying the coating. The electrochemical behavior of each layer is important to ensure a good corrosion protection. The corrosion behavior of the layers strongly depends on coating composition and microstructure, which are affected by feedstock material and spraying process. Therefore, the objective of the researchis to explore the relationships between feedstock material, spraying process, microstructure and corrosion behavior of bi-layer coatings. A specific motivationis to understand the corrosion mechanisms of the intermediate layer which forms the basis for developing superior protective coatings. Cr3C2-NiCr top layer and intermediate layers (Fe-, Co- and Ni-based) were sprayed by different thermal spraying processes. Microstructure analysis, as well as various corrosion tests, e.g., electrochemical, salt spray and immersion tests were performed. The results showed a direct link between the corrosion potential (Ecorr) of the intermediate layer and the corrosion mechanisms. It was found that the higher corrosion resistance of Ni-based coatings than Fe- and Co-based coatings was due to higher Ecorr of the coating in the galvanic couple with top layers. Inter-lamellar boundaries and interconnected pores reduced the corrosion resistance of intermediate layers, however a sufficient reservoir of protective scale-forming elements (such as Cr or Al) improved the corrosion behavior.

The overall aim of this research project was to expand the understanding of the deposition of titanium and the nickel-based superalloy Inconel 718 by spray deposition methods. The spray processes employed were cold spraying and high velocity oxy-fuel (HVOF) thermal spraying. The first part of the work was undertaken to expand the understanding of the deposition of titanium by cold spraying; the HVOF process is unsuitable for Ti because of the metal's high reactivity. The deposits were produced from commercially pure titanium using cold spray equipment designed in the University. Using helium gas, the effects of different powder particle size ranges, types of substrate, substrate preparation methods, and spray parameter conditions on deposit formation were investigated. Using a simple one-dimensional model of compressible gas flow and particle acceleration, particle velocity distributions were calculated to aid interpretation of experimental data. Results show that titanium can be successfully cold sprayed onto substrates of Ti6AI4V and mild steel, with the critical velocity for deposition of this powder type of approximately 690 m s-1. The level of porosity was generally in the range of 13-23% and the adhesive bond strength was dependent on surface preparation but independent of gas pressure with values ranging from 22 MPa to 10 MPa for ground and grit blasted substrates respectively. This compares with a value of around 80 MPa which is typical for well adhered HVOF sprayed coatings. The second part of the study was concerned with comparing the deposition of Inconel 718 by cold spraying and HVOF thermal spraying; the latter employed a JP5000 liquid fuel gun. A Tecnar DPV-2000 instrument was used to systematically investigate the effect of changes in spray parameters (spraying stand-off distance, oxygen/fuel ratio, total mass flow rate, combustion pressure), on particle velocity and temperature during HVOF spraying. It was found that generally the particle velocity was more strongly affected by the stand-off distance and combustion pressure of the spraying gun whereas the particle temperature was mostly influenced by the particle size and combustion pressure. The microstructures of coatings sprayed under 4 different well controlled conditions were investigated and changes in the morphology of splats and partially melted particles in the coating were related to the particle temperature and velocity at impact. The HVOF had high bond strength and low oxygen level of typically 0.45 wt% (corresponding to an oxide content of less than 1.6 wt.%). By contrast, in the cold sprayed coatings, the bonding was considerably low (-14 MPa), independently from the process conditions. It was found that the process parameter that mainly affected the properties of the cold sprayed deposits was the gas pressure. More specifically, the microhardness of the coatings increased with the pressure whereas the relative porosity decreased.

The aim of this thesis was to modify microstructure and coating-substrate interface of CoNiCrAlY coatings deposited by HVOF and cold spray on Inconel 718 substrates. Electron beam remelting and annealing in a protective atmosphere were used to modify the coatings. Microstructure, chemical and phase composition were analyzed. The effect of beam current, transversal velocity and beam defocus on remelted depth was evaluated. As-sprayed microstructure and chemical composition of coatings were analyzed and compared with remelted samples. The effect of annealing of the as-sprayed and remelted samples was evaluated. Remelted layers exhibited dendritic structure. Chemical composition changed only after remelting of interface and part of a substrate. When only the coating was remelted, chemical composition remained the same. Phases coarsened after the annealing. Chemical composition changed after annealing due to the diffusion.

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<br>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

Tungsten carbide (WC) based metallic matrix coatings sprayed using high velocity air fuel (HVAF) technique have attracted increasing attention as they show excellent tribological performance in various wear conditions. In the HVAF method, particles’ in-flight temperature and velocity can be influenced by the process variables including nozzle configuration as well as feedstock particle size range. On the other hand, the chemistry of metallic binder can also play a key role in determining both properties and performance of these coatings. In this thesis, characteristics and tribological behaviour of HVAF-sprayed WC-based coatings were investigated employing four different nozzle configurations (4L2, 4L4, 5L2and 5L4), and three different feedstock particle sizes of WC-CoCr feedstock powder (5/20, 5/30 and 15/45 μm). Also, characteristics and performance of coatings processed with four different WC-based feedstocks comprising alternative binders to traditionally used CoCr (namely CoCr, NiMoCrFeCo,FeNiCrMoCu and FeCrAl) were investigated. Characteristics of the coatings were explored by conducting scanning electron microscopy observations, microindentation testing and X-ray diffraction analysis. Performance of the coatings was evaluated by conducting sliding wear, dry jet erosion wear and sand rubber wheel abrasion wear testing. Moreover, material removal mechanisms in the coatings subjected to the above tests were investigated through post wear analysis. X-ray diffraction analysis showed that no considerable phase change compared to the starting feedstock was observed in any of the coatings sprayed by HVAF technique. It was revealed that decrease in powder particle size range can result in an improvement in microstructural characteristics, such as homogeneity and density, as well as hardness of the coatings. Besides, it can lead to a substantial improvement in wear performance of the coatings. It was shown that using various nozzle configurations does not result in any considerable change in characteristics or performance of the HVAF-sprayed WC-CoCr coatings. It was further shown that, by decreasing particle sizes from coarse to medium or fine, a significant difference can be observed. While wear mechanisms for medium and fine feedstock coatings were dominated by ploughing and fracture of individual carbide grains, for the coarse feedstock coatings ploughing and grooving along with the local removal of coating material were observed. Hardness values for all the four coatings with different binder chemistries were in a narrow range of 1100 – 1300 HV0.3. WC-NiMoCrFeCo and WC-FeNiCrMoCu coatings showed better or comparable sliding wear performance compared to WC-CoCr coating (as reference). WC-FeNiCrMoCu and WC-FeCrAl coatings showed comparable performance under erosion conditions while all the three binder alternatives yielded slightly inferior coating performance under abrasion wear, compared to the reference coating. While ploughing was the common wear mechanism in all the four coatings, pitting was noted in coatings with CoCr and FeNiCrMoCu binders in case of sliding wear.<br>Populärvetenskaplig Sammanfattning Cermet-beläggningar består av WC-partiklar inbäddade i ett metallbindemedel,sprutat med High Velocity Air Fuel (HVAF) uppvisar utmärkt tribologiskprestanda under olika slitage förhållanden. Med HVAF-tekniken kan partiklarnasflygtemperatur och hastighet påverkas av konfigurationen av den utrustning somanvänds såväl som partikelstorleksintervallet för råmaterialet. Därtill kan kemin hos det metalliska bindemedlet spela en nyckelroll för beläggningarnas egenskaper och prestanda. I denna avhandling undersöktes egenskaper och tribologiskt beteende hos HVAF-besprutade WC-baserade beläggningar. Undersökningen gjordes genom att använda fyra olika uppsättningar av ändra sprutparametrar förHVAF-processen där fyra olika munstyckskonfigurationer (4L2, 4L4, 5L2 och5L4) och tre olika partikelstorleksintervaller av WC-CoCr råvarupulver (5/20,5/30 och 15/45 μm). Studieegenskaper och prestanda för alla deponerade beläggningar, påverkan av processvariabler (olika munstyckskonfigurationer och olika partikelstorlekar) undersöktes. Dessutom undersöktes egenskaper och prestanda för tre olika WC-baserade råvaror med alternativa bindemedel till CoCr (NiMoCrFeCo, FeNiCrMoCu och FeCrAl) och jämfördes med WC-CoCrbeläggningsom referens. Beläggningens egenskaper undersöktes genom att genomföra SEM-analys, mikroindragningstest och röntgenanalys. Beläggningens prestanda utvärderades genom att utföra glidförslitning, erosionsslitage under torra förhållanden och test med torr sand/gummihjulanordning. Vidare undersöktes mekanismer för materialavlägsning i beläggningarna med ovanstående tester genom analys efter slitage. Ingen avsevärd fasförändring observerades för alla beläggningar som besprutades med HVAF-teknik. Det avslöjades att minskning av pulvrets genomsnittliga partikelstorlek resulterade i en förbättring av mikrostrukturella egenskaper, såsom homogenitet och densitet, samt beläggningarnas hårdhetsvärde. Dessutom leder det till en avsevärd förbättring av beläggningens slitageförmåga. Det visades att användning av olika munstycken till HVAF-processen inte resulterar i en avsevärd förändring i egenskaper eller prestanda hos WC-CoCr-beläggningarna. När det gäller förslitningsmekanismer visades det att genom att minska partikelstorleken från grov till medium eller fin sågs en avsevärd skillnad. För beläggningar besprutade med fina och medelstora partiklar dominerades förslitningsmekanismer av plöjningsslitage och sprickor av enskilda hårdmetallkorn. För grova beläggningar observerades plöjningsslitage och spårning tillsammans med avlägsnande av material. Ingen signifikant skillnad i mikrostruktur eller fasförändring observerades i alla beläggningar med alternativa bindemedel såväl som WC-CoCr som referensbeläggning. Hårdhetsvärdet för alla de fyra beläggningarna låg inom x intervallet 1100 - 1300 HV0.3. NiMoCrFeCo och FeNiCrMoCu visade bättre eller jämförbar glidförmåga med referensbeläggningen. FeNiCrMoCu och FeCrAl visade jämförbara prestanda under erosionsförhållanden och alla de tre undersökta beläggningsmaterialen visade något sämre prestanda under nötningsslitage jämfört med referensbeläggningen. Medan plöjningsslitage var den vanliga förslitningsmekanismen i alla de fyra beläggningarna noterades gropning i beläggningarna CoCr och FeNiCrMoCu vid glidförslitning.

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<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>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.<br>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.

L'hydroxyapatite (HAp) et le verre bioactif (BG) 45S5 sont largement utilisés comme précurseurs des revêtements fabriqués par projection thermique pour améliorer la biocompatibilité des implants biomédicaux. Ceci, en raison de la structure similaire de l'HAp avec le tissu osseux et la haute réactivité de ce BG en milieu biologique, ce qui permet la croissance rapide du tissu osseux à sa surface. La projection combinée des deux matériaux permet d’obtenirdes revêtements hautement bioactifs et stables par rapport aux revêtements individuels. De plus, la bioactivité de l'HAp et la radio-opacité de BG45S5 peuvent être améliorées en utilisant comme matières premières des sources naturelles, telles que l'HAp issue d'os de bovins (BHAp) et en ajoutant des radiopacifiants tels que l’oxyde de bismuth (Bi2O3) à la structure du BG. Par conséquent, des revêtements combinés avec une bioactivité et une opacité accrues vis-à-vis des rayons X peuvent être obtenus pour améliorer le diagnostic non invasif par radiographie des implants biomédicaux revêtus.Cette recherche présente le développement de couches épaisses biocompatibles et opacifiées réalisées par projection thermique, flamme haute vitesse (High-Velocity Oxygen Fuel, HVOF) et plasma (Atmospheric Plasma Spray, APS). La composition chimique, la structure, la microstructure et la bioactivité des couches radio-opaques de BHAp/BG45S5+Bi2O3 obtenues sont étudiées ainsi que les propriétés des matériaux de départ. ainsi que la projection gradient du revêtement combiné. En particulier, la bioactivité de différentes architectures de revêtements (monocouches, couches à gradient de matériaux et multicouches) a été évaluée. Les résultats expérimentaux montrent que la poudre de départ de BHAp est principalement constituée d’apatite carbonée de type B avec une pureté élevée de la phase HAp. Les poudres de bioverre BG45S5 fabriquées en laboratoire présentent une composition chimique et des propriétés physiques très similaires à celles du BG45S5 commercial.Un pourcentage en poids de 1 à 20 % d’oxyde de bismuth Bi2O3 a été ajouté au verre bioactif pour modifier sa radio-opacité. Les images radiographiques des composés BG45S5 + x% Bi2O3 montrent que le bioverre avec 10% en poids d’oxyde de bismuth permet d’augmenter de 3,6 fois l’opacité du bioverre de manière homogène sans affecter de manière notable ses propriétés structurales et thermiques. En ce qui concerne les revêtements réalisés par projection thermique, la teneur en CO32- et en Mg dans la poudre de BHAp conduit à la formation de dolomite dans la phase cristalline de la surface du revêtement monocouche de BHAp réalisé par HVOF alors que celui réalisé par APS ne montre aucune phase secondaire cristalline à sa surface. Une couche d'apatite typique est mise en évidence à la surface des deux revêtements après 3 jours d'immersion dans un fluide corporel simulé (SBF), cependantle revêtement monocouche de BHAp réalisé par HVOF montre une délamination après 5 jours d'immersion. Par conséquent, la projection plasma APS a été choisie pour élaborer les revêtements monocouches de BHAp, BG45S5, BG45S5+10wt.% Bi2O3 et le revêtement à gradient de composition de BHAp/BG45S5+10wt. % Bi2O3. Le revêtement monocouche de BG45S5 + 10wt.% Bi2O3 a une microstructure et une structure amorphe similaires à celles du revêtement monocouche de BG45S5 sans Bi2O3 réalisé par projection plasma de la poudre commerciale . Cependant, une délamination et une vitesse réduite de formation de la couche d'apatite ont été observées. Le revêtement à gradient de composition de BHAp/BG45S5+10 wt. % Bi2O3 montre un taux de croissance de la couche d'apatite similaire à celui du revêtement monocouche de BG45S5+10wt. % Bi2O3. La formation d'apatite observée après 10 jours d'immersion dans un fluide corporel simulé ne présente pas de délaminage à la surface du revêtement grâce au gradient de composition du BG45S5 10 wt. % Bi2O3 combiné au BHAp<br>Hydroxyapatite (HAp) and bioactive glass (BG45S5) are widely employed as precursors of thermally sprayed coatings to enhance the biocompatibility of biomedical implants. This, due to the similar structure of HAp with the bone tissue and the high reactivity of BG with biological media allowing the rapid bone tissue ingrowth on its surface. The combined deposition of both materials leads to build-up highly bioactive coatings with proper stability in comparison with single coatings. Furthermore, the HAp bioactivity and the BG45S5 radiopacity can be improved by obtaining the first from natural sources, as bovine-derived HAp (BHAp), and the second through the addition of radio-opacifiers as Bi2O3 to the BG structure. Consequently, coatings with augmented both, biocompatibility and x-rays opacity that allow improving the bioactivity and facilitate the use of non-invasive diagnostic methods, can be achieved. This research presents the development of biocompatible and opacified thick coatings deposited by High-Velocity Oxygen Fuel (HVOF) and Atmospheric Plasma Spray (APS) techniques. The chemical composition, structure, and microstructure of radiopaque BHAp/BG45S5+Bi2O3 coatings were studied, as well as the properties of raw materials were also analyzed. Afterward, the bioactivity of several coatings’ architecture, i.e., monolayers, graded, and multilayers, were assessed. The experimental results show that BHAp feedstock powder is mainly carbonated B-type apatite with a high purity HAp phase. The lab-made BG45S5 powders exhibit the chemical composition and physical properties with a substantial similarity compared to commercial BG45S5. The weight percent of 1 up to 20 of Bi2O3 was added to the bioactive glass to modify its radiopacity. Radiographic images of BG45S5+Bi2O3 show that 10 wt.% of the opacified material allows increasing the opacity of the BG mixture homogeneously by 3.6 times with no considerable effects on its structural and thermal properties. Regarding the thermally sprayed coatings, CO32- and the Mg contents on BHAp lead to the formation of dolomite in the crystalline phase of the surface of single HVOF BHAp coating. Single BHAp APS coating does not exhibit any secondary phases in its surface crystalline content. A typical apatite layer is evidenced after 3 days of immersion in simulated body fluid (SBF) in the surface of both coatings and single BHAp HVOF coating show delamination after 5 days of immersion. Thus, APS was chosen to spray and analyze single BG45S5, BG45S5+10 wt.% Bi2O3 and gradual BHAp/BG45S5+10 wt.% Bi2O3 coatings. Single BG45S5+10 wt.% Bi2O3 coating shows similar microstructure and amorphous structure in comparison with the plasma-sprayed single coating using commercial BG45S5 feedstock powder without Bi2O3. However, delamination and a reduced rate of apatite layer formation are observed. Graded BHAp/BG45S5+10 wt. % Bi2O3 coating shows a similar rate of apatite layer growth compared to single BG45S5+10 wt. % Bi2O3 coating. Nevertheless, the apatite formation after 10 days of immersion in SBF and no delamination are observed on the surface of the coating due to the graded deposition of BG45S5+10 wt. % Bi2O3 combined with BHAp

The investigation of high-entropy alloys (HEAs) has revealed many promising properties. HEAs with a high share of Al and Ti are suitable for the formation of lightweight materials. Investigations of the alloy system AlCoCrFeNiTi showed high strength, hardness, ductility, and wear resistance, which makes this special alloy interesting for surface engineering and particularly for thermal spray technology. In this study, the suitability of inert gas-atomised HEA powder for high-velocity-oxygen-fuel (HVOF) thermal spray is investigated. This process allows for high particle velocities and comparatively low process temperatures, resulting in dense coatings with a low oxidation. The microstructure and phase composition of the atomised powder and the HVOF coating were investigated, as well as the wear behaviour under various conditions. A multiphase microstructure was revealed for the powder and coating, whereas a chemically ordered bcc phase occurred as the main phase. The thermal spray process resulted in a slightly changed lattice parameter of the main phase and an additional phase. In comparison with a hard chrome-plated sample, an increase in wear resistance was achieved. Furthermore, no brittle behaviour occurred under abrasive load in the scratch test. The investigation of wear tracks showed only minor cracking and spallation under maximum load.

Die Habilitation befasst sich mit neuen Verfahren und Anwendungen des Thermischen Spritzens, beleuchtet anhand einer internationalen Umfrage den Forschungsbedarf der Branche und liefert zahlreiche Lösungen, die im Rahmen von grundlagenorientierten und industrienahen Forschungsvorhaben erarbeitet wurden. Der Fokus der Arbeit liegt auf der Verbesserung individueller Arbeitsschritte der Prozesskette des Thermischen Spritzens, wobei Ergebnisse aus den Bereichen Werkstoffentwicklung, Prozessoptimierung, Qualitätssicherung und Nachbearbeitung zusammengeführt und durch konkrete Anwendungsbeispiele hinterlegt werden. Im Detail werden die Aspekte Herstellung leistungsfähiger und preiswerter Spritzzusätze (Wasserverdüsung von Metallpulvern, Hochenergiekugelmahlen, Agglomerieren und Sintern sowie Fülldrahtherstellung), die Verbesserung der Prozessführung (numerisch optimierte Spritzbrenner und automatisierbare Online-Prozessdiagnostikmethoden) und die Steigerung der Leistungsfähigkeit der Beschichtungen durch mechanische Nachbearbeitung sowie Versieglung behandelt. Anwendungsbezogen werden das Beschichten von Hochleistungspolymeren und CFC-Leichtbaustrukturen untersucht. Um Anknüpfungspunkte für weiterführende Forschungsarbeiten zu schaffen, schließt die Arbeit mit der Darstellung von Entwicklungstrends und zeigt Arbeitsgebiete auf, die perspektivisch von thermisch gespritzten Schichten profitieren können.

Cold spray is a novel coating method. Due to its low-temperature character, it has a potential to replace the high-temperature thermal spray processes in some applications. The presented work analyzes the microstructure and the phase composition of pure metal coatings deposited by cold spraying and evaluates selected mechanical properties. Specimens prepared by readily used HVOF industrial technology were used for comparison purposes.

Devido à necessidade de obtenção de uma superfície resistente ao desgaste e a oxidação, os cilindros hidráulicos são tradicionalmente revestidos com cromo duro eletrodepositado. Todavia, este tipo de revestimento apresenta uma redução gradual do coeficiente de atrito, interferindo diretamente na lubrificação da haste, ocasionando danos aos elementos de vedação e promovendo consequentes vazamentos. Outro apelo contrário à utilização do processo de revestimento com cromo é a presença, em elevados níveis, de cromo hexavalente Cr+6, apresentando alto poder cancerígeno e de contaminação ambiental. Atualmente, o processo de aspersão térmica em alta velocidade (HVOF - High Velocity Oxi-Fuel) se caracteriza como uma técnica de revestimento alternativa ao cromo duro, utilizando materiais compósitos (metal-cerâmico), os quais propiciam baixas taxas de desgaste. Este trabalho tem como objetivo avaliar o desempenho de revestimentos aplicados em hastes de cilindros hidráulicos revestidas com WC-CoCr pelo processo HVOF, em comparação ao revestimento de cromo duro eletrodepositado. As técnicas de caracterização empregadas foram divididas em duas etapas, sendo que a primeira foi: análise microestrutural, ensaios de dureza e desgaste, medições de rugosidade e perfilometria, em corpos de prova planos e, na segunda etapa, a análise dos revestimentos adquiridos através de uma bancada de testes de hastes de cilindros hidráulicos, onde a caracterização foi obtida através de, medições específicas dos principais parâmetros de rugosidades aplicadas a superfícies de vedação, como Rz, Rmáx e Rmr, desgaste visuais das hastes e vedações e medições de vazamento de óleo. Ao final, os resultados mostram que o revestimento aspergido, indica características competitivas em relação à eletrodeposição de cromo, podendo ser aplicado em hastes de cilindros hidráulicos com algumas vantagens, como por exemplo, maior resistência ao desgaste, menor coeficiente de atrito, menores taxas de vazamento e melhores condições finais de superfícies.<br>To obtain a surface that is resistant to wear and oxidation, hydraulic cylinders are typically coated with in hard chromium through the process of electroplating process. However, this type of coating displays a gradual reduction of the friction coefficient as the lubrication directly interferes with the shaft mechanism, which in turn causes damage to the sealing elements and promotes subsequent leakage. Another disadvantage in using the electroplated hard chromium process is the presence of high level hexavalent chromium Cr+6 which is not only carcinogenic, but also extremely contaminating to the environment. Currently, the alternative process of high-speed thermal spraying (HVOF - High Velocity Oxy-Fuel), as opposed to hard chrome coating, uses composite materials (metalceramic) possessing low wear rates. This study aims to evaluate and compare the performance of hydraulic cylinder rods coated with WC-CoCr in the HVOF process, and those coated with electroplated hard chromium. The characterization techniques employed were divided into two steps, the first of which was: microstructural analysis, testing the hardness, wear, roughness and profilometry and on specimens plans and, in the second step, analysis of the coating obtained through a bench test rods of hydraulic cylinders, where the characterization was through achieved , specific measurement of the main parameters of roughness applied to sealing surfaces, as Rz, Rmáx and Rmr, wear visual of the rods and seals and measurements of oil leakage. At the end, the results show that the sprayed coating, indicate competitive characteristics in relation to the electrodeposition of chromium, which can be applied in rods of hydraulic cylinders with some advantages, such as improved wear resistance, coefficient friction low, lower rates of leakage and condition final better surface.

Properties of samples and their coatings may be affected by the electron beam. This paper deals with the analysis of the microstructure, phase and chemical composition and the determination of mechanical characteristics of inconel steel substrate and CoNiCrAlY coatings deposited via different types of thermal spraying (HVOF, cold spray), in combination with modifications by the electron beam technology. During the study it was found that the deposition did not change the chemical composition. Further it was found that the interaction of the electron beam with the material did not change the chemical composition, but there is a change in the structure and a reduction of porosity and surface roughness, resulting in a change of mechanical properties such as decreasing hardness or increase of the modulus of elasticity.

La réalisation de revêtements projetés de haute qualité passe par une bonne cohésion du dépôt et une adhérence élevée des revêtements sur leur substrat. Du fait de leur mode d'élaboration, les microstructures des interfaces dépôt/substrat et particule/particule obtenues par projection thermique sont complexes et les propriétés en dépendant hétérogènes. Afin d'optimiser l'adhérence des revêtements, il est nécessaire d'établir des relations entre microstructure et résistance de ces interfaces. C'est l'objet de cette étude. Le système modèle cuivre projeté sur aluminium a été retenu non seulement pour son fort potentiel industriel mais également pour la grande réactivité métallurgique du couple (Al, Cu). Des interfaces présentant des propriétés métallurgiques variées ont ainsi pu être obtenues, en jouant sur les procédés et conditions de projection. Ces interfaces ont été analysées à des échelles fines. Des caractérisations quantitatives des propriétés métallurgiques et morphologiques de ces interfaces ont aussi été réalisées. Un essai d'adhérence original, utilisant le phénomène de choc laser, a été développé pour déterminer l'adhérence de revêtements épais (quelques centaines de microns) correspondant à ces interfaces. L'essai LASAT (pour LASer Adhérence Test) s'est avéré particulièrement sensible aux propriétés des interfaces et approprié à leur étude locale. L'association des analyses fines et quantitatives des interfaces avec l'évaluation de leur résistance par l'essai de choc laser a permis d'identifier les principaux mécanismes d'adhérence responsables de la bonne tenue des revêtements de Cu sur Al et/ou des particules de Cu sur celles déjà déposées, dans le cas de projections plasma, HVOF et cold spray. L'influence de la propreté et de la morphologie des interfaces sur l'adhérence des dépôts projetés a été, en particulier, étudiée. Enfin, des outils de simulation ont permis de reproduire les phénomènes intervenant aux interfaces obtenues par projection thermique et ainsi de préciser les modes de formation des liaisons interfaciales.

The purpose of this research work was to develop a nozzle capable of depositing dense CoNiCrAlY coatings via cold gas dynamic spray (CGDS) as well as compare the oxidation performance of bond coats manufactured by CGDS, high-velocity oxy-fuel (HVOF) and air plasma spray (APS) at temperatures of 1000°C and 1100°C. The work was divided in two sections, the design and manufacturing of a CGDS nozzle with an optimal profile for the deposition of CoNiCrAlY powders and the comparison of the oxidation performance of CoNiCrAlY bond coats. Throughout this work, it was shown that the quality of coatings deposited via CGDS can be increased by the use of a nozzle of optimal profile and that early formation of protective α-Al2O3 due to an oxidation temperature of 1100°C as opposed to 1000°C is beneficial to the overall oxidation performance of CoNiCrAlY coatings.

The master thesis is dealing with characterization of the structure and properties of the YSZ thermal barrier coating deposited by water hybrid plasma spray technology on the CoNiCrAlY bond coats modified by using electron beam and vacuum annealing. Deposition of the bond coats was performed via high velocity oxy-fuel technology and cold spray. In case of experimental evaluation, the microstructure and chemical composition of the ceramic top coat deposited with powder and suspension feedstock was analyzed. The same analysis procedure was used also for bond coats after electron beam remelting by using two sets of parameters. Furthermore, the changes in microstructure and chemical composition of the remelted and annealed bond coats was evaluated. Eventually, the micromechanical properties of the top coats and the bond coats were measured. The ceramic top coats deposited with powder feedstock exhibited the structure composed by splats, while the top coats deposited in form of suspension showed fine structure with columnar grains. The dendritic structure was observed on remelted bond coats. The annealing process had an influence on the structure in form of coarsened phases and the chemical composition was changed due to diffusion of the elements.

碩士<br>國立高雄應用科技大學<br>機械與精密工程研究所<br>96<br>ABSTRACT Capable of the characteristics of high velocity and low temperature combustion gases, the high velocity oxygen fuel (HVOF) thermal spray technique has become very popular for generating the WC-Co coatings. In this study, two WC-12Co coatings were deposited onto JIS SS41 mild steel substrate by the HVOF process using two kinds of commercially available feedstock powders produced by agglomerated method and fused-crushed method separately. The coatings were annealing heat treated at different temperatures (6000C, 8000C and 10000C) in an argon atmosphere chamber. The coatings were then evaluated in the as sprayed and heat treated conditions. The microstructure and phase composition of coatings were analyzed by optical and scanning electron microscopy and x-ray diffraction. Coatings were also characterized by their hardness, abrasive wear resistance and wear mechanisms. The results indicate that the powders exhibit various degrees of phase transformation during the spray process depending on type of powders. The hardness of as sprayed and heat treated conditions agglomerated coatings are higher than that of fused-crushed coatings and the hardness of both coatings increase with increasing heat treatment temperature. For the as sprayed and 6000C heat treated conditions, the wear resistance of agglomerated coatings are worse than the counterpart, but better for the 800 0C and 1000 0C heat treated conditions. Compared with the mild steel in wear resistance , the fused-crushed coatings are 20.7 times the mild steel for the as sprayed conditions and 34 times for the 10000C heat treated conditions; the agglomerated coatings are 19 and 39.7 times respectively.

Corrosion and Wear, or combination of both, are the main causes of degradation of metals used in various industrial sector. Degradation of the metals can be slowed down by adding a layer of resistant coating on metal surface. This coating separates the base metal from a corrosive environment, reduces wear and improves the appearance of the metal. The workpiece after coating becomes a composite that have properties far better than the substrate alone. There are various coating techniques, HVOF is one of the most important and widely used process to protect the metals from wear, corrosion by providing hard and dense coatings. WC coating done by the high velocity oxy fuel (HVOF) spray method is the widely used method for providing a layer of corrosive resistance to a wide range of materials which are used in many different industries. In this study, Tungsten carbide (WC-12CO) Coating, HVOF Spray method was studied in great detail. Tungsten Carbide coating was done on a SUS400 Stainless steel substrate using HVOF Spray Process. And, Experiment was done to analyse the various effect of different parameters namely, oxygen rate, propane (fuel) rate, powder rate, spray distance on hardness and surface roughness of a SUS 400 Stainless Steel substrate. Process optimization was done by using Taguchi and ANOVA methods. It was found that, achieving maximum hardness was greatly depended on propane (fuel) rate followed by powder rate, spray distance and oxygen rate. Hardness decreases with increasing fuel rate. And, achieving minimum surface roughness was greatly depended on spray distance followed by oxygen rate, propane (fuel) rate, powder rate. Surface Roughness increases with increasing spray distance.

碩士<br>國立臺北科技大學<br>機電整合研究所<br>93<br>Thermal spraying technology has been used in industry extensively. High velocity oxy-fuel (HVOF) process WC/Co coating is suitable for aviations, vehicles, printings and petroleum industry especially in erosions, abrasions and high temperatures environment. It is extremely important to characterize the WC/Co powder to understand the performance of the coating. Otherwise, nanostructured WC/Co powders have been succeeded commercialize so HVOF deposits nanostructured WC/Co coating has been highly regarded. Due to the surface/volume ratio of nanostructured WC/Co powder, it’s strength is greater then conventional films. The temperature of nanostructure powder during deposition is higher than conventional powders. Therefore, nanostructure WC/Co can yield a high density and high hardness coating. Nevertheless, if the temperature is higher than conventional, this can lead to nanostructured WC becoming decarbonized and brittle W, W2C and amorphous etc. In this study six HVOF parameters were used to process three types of commercial WC/Co powders. Then the powders were analyzed to compare the characteristics of each. For instance, the powder’s property, coating’s composition, porosity, microstructure, hardness, ware lose machine and four points bending with AE to comprehend toughness were studied. The consequences show the nanostructure coating has higher density, hardness, toughness and lower porosity but wear resistance is worse than conventional coating. Divide coating crash by four points bending test into three steps, the initial step is some micro cracks which direction is parallel with surface be developed at bounding. The second step is others micro cracks which direction is angular with surface been developed. By keeping increase the bending stress, both of two kinds of micro cracks been enhanced to macro cracks and growth the other macro cracks which is vertical with surface. Otherwise, the major of wear lose machine can be divided into two types too. Consequently, nanostructured WC/Co coating has improved in certain of mechanical performance but not all of them. But it appears possible that the desired properties may be obtained by optimizing the spraying parameters. Therefore, nanostructured WC/Co powders may soon be applied commercially.

碩士<br>國立高雄應用科技大學<br>機械與精密工程研究所<br>101<br>Capable of the characteristics of high velocity and low temperature combustion gases, the high velocity oxygen fuel (HVOF) thermal spray technique has become very popular for generating the WC-Co coating. In this study, the WC-12Co coating were deposited onto JIS SS41 mild steel substract by the HVOF process using the commercially available feedstock powders produced by fused-crushed method. The coating were different. One was without annealing treatment, and the other was annealing heat treated at 1000 in an argon atmosphere chamber. The coatings were evaluated in the organizational structure and wear mechanisms. The coating thickness of coatings were analyzed by optical microscope and scanning electron microscope. The microstructure and phase composition of coatings were analyzed by x-ray diffraction and transmission electron microscope. The results indicate that the coatings had various degrees of phase transformation during the spray process depending on annealing treatment or not. There had many reasons cause the of the coating without annealing treatment was worse than the other. One was W2C and W, which was decarbonization and decomposition by WC. And after 1000 annealing treatment, there was produced a phase of η. In spraying process, the hardness and brittle of the binder phase was results from W and C melted into base phase. W2C would affect wear mechanisms on coating that without annealing treatment.

No<br>This study investigates the effect of heat treatment on changes in microstructure and wear behaviour of WC-NiCr coatings. Two feedstock powders with a similar chemical composition and different particle sizes (near nano-structured WC-17NiCr and microstructured WC-15NiCr) were used. High-velocity oxyfuel spraying technique was used to deposit coatings on to a mild steel substrate using identical spraying parameters. Coated samples were then heat treated in a nitrogen atmosphere at 500 and 700°C. The effect of heat treatment on changes in hardness and wear performance of the coatings was studied using microstructural analysis, micro-hardness indentation and abrasive wear tests. The results showed that the heat treatment increased the hardness of both coatings and a corresponding increase in wear resistance was recorded. The formation of a brittle CrWO4 phase in the microstructured coating resulted in brittle fracture of the coating and this gave lower wear resistance compared to the nanostructured coatings.

碩士<br>國立臺北科技大學<br>機電整合研究所<br>96<br>This study focuses on the effects of the reflowing process on the physical properties、hardness analysis and wear test by four Ni-based self-fluxing alloy powders with different particle size mixed WC-Co powder by different weight ratio under reflowing temperature 950°C、1000°C and 1050°C by nitrogen in atmospheric pressure after thermal spray. The results show that the dense coatings can be prepared and also exhibit good hardness and wear performance at reflowing temperature of 950℃. On the phase change, chromium increases the hardness of the coatings by the formation of hard phase with carbon and boron, nickel react with boron into a hard phase and the others change into Ni-solution. According to the elevated temperature, the hardness is decreased but the porosity is increasing because of the grain growth. On the wear resistance, each coating has worse hardness and better wears resistance, especially the coating adding WC-Co. The major wear mechanisms are based on abrasive wear、adhesive wear and surface fatigue. The TSM2002 coating after 950°C reflowing has the hardness which his more than 700Hv and exhibits the porosity under 1% which is the best coating with wearability among these four coatings.

碩士<br>國立高雄應用科技大學<br>機械工程系<br>106<br>For the purpose of improving operational efficiency of combined cycle plants, increasing the inlet fuel gas temperature of gas turbines has become the international trend of power plants development nowadays. However, while under the influence of elevated temperatures and hot corrosion environment, hot section components are rapidly in a performance degradation and even crack. The characteristics of ceramics of Thermal Barrier Coating(TBC) at thermal durability and thermal insulation, not only can increase the inlet fuel gas temperature of gas turbines but also reduce the surface temperature of substrates.On top of that, it may also enhance the thermal efficiency of plant units and prolong the plant service life. This research emphasizes on investigating two substrates,SUS304 and Hastelloy X, applying with High Velocity Oxygen fuel System (HVOF) thermal spraying MCrAIY alloy bond coat and with APS thermal spraying ZrO2-Y2O3 Zirconia ceramic as top coat to form Thermal Barrier Coating(TBC).We used Optical and Scanning Electron Microscope (SEM) to observe coating of microstructures, including the thickness of coating, porosity, oxide, crack and unmelted particle. Furthermore, we used X-ray Energy Dispersive Spectroscopy, X-ray Diffraction and Micro-hardness Test in order to compare the difference of micro-structures and mechanical properties on coating of two specimens. The experiment result has revealed that both of coating specimens have no obvious degradation; coating and bonding strength are in quite good performance and no coating spallation situation. In addition, MCrAIY alloy coating by HVOF has higher micro-hardness value, which average value is about1.25～1.50 times than the one coating by APS. HVOF, since with high speed in-flight powder particles hitting the substrate in high velocity, it may form the coating with characteristics of high bonding strength, high hardness and high density. On the other hand, the coating by APS has much loose structure and relatively more voids. Thus, due to the high porosity, the characteristics of thermal insulation and thermal shock resistance of coating are being promoted.

碩士<br>國立高雄應用科技大學<br>機械工程系<br>105<br>Due to its advantages such as fast flame velocity, bonding strength, high density and low porosity, thermal coatings applied by High Velocity Oxygen Fuel thermal spray technique is widely used in the industry and aero components. The study uses commercial spray powder that is cobalt-based on substrate material Inconel 718 and observes the flame characteristics of the two processes (HVOGF and HVOLF) with monitoring system during thermal spray process. The characteristics to be observed include the velocity of molten particles, plume temperature and total intensity. The metallographic structure of the unmelted particles and porosity are also examined with SEM. Furthermore, the surface hardness, micro-hardness and bonding strength are to be examined with applicable equipment as well. After the experiment and observation, the study reviews the metallographic and mechanic differences between the two coatings that are produced by these two heat sources. The result of the experiment shows that velocity of particles produced by HVOLF is 1.23 times faster than those produced by HVOGF. However, there is no apparent difference between the plume temperature and surface hardness produced by these two heat sources. Moreover, because of greater flying speed of the melted powder produced by HVOLF, it has greater impact to make more compact metallographic structure and the average values of its micro-hardness and bonding strength which are 1.20 and 1.65 times respectively is higher than those of HVOGF. In this conditions of the experimental parameters, cobalt-based commercial spray powder that uses HVOLF thermal spray process performs better than HVOGF in terms of its mechanical properties such as unmelt particles in the metallographic structure, porosity, micro-hardness and bonding strength.

碩士<br>國立臺北科技大學<br>製造科技研究所<br>97<br>The study is using high velocity oxy-fuel spraying to achieve NiCrBSi self fluxing alloy coating. Moreover, WC or Cr3C2 is added into the self fluxing alloy coating. The coatings were re-melted at 950°C, 1000°C and 1050°C respectively. The relation between different conducting parameters and the coating’s surface formation, microstructure, hardness and porosity is systematically analyzed. At last, the mechanical properties and wear characteristics of the coating are in comparison. The results show the NiCrBSi coating which is treated by re-melting at 950°C results in the presence hardening phases of Ni3B and Cr7C3 and approach of 0% porosity. Besides, the NiCrBSi coating which treated by 1050°C causes the coating itself collapsed, that decrease the hardness of the coating. The NiCrBSi coating with the addition of Cr3C2 can effectively enhance the wear resistance. After the coating was re-melted, it will occurs micro cracks resulting from the phenomenon of decarburization, resulting in decreased hardness of the coating. The NiCrBSi coating with the addition of WC is stacked up by the WC and NiCrBSi. After re-melting, the phase of WC does not change and the porosity is less than 1%. The bonding between the alloy coating and substrates shifts from mechanical bonding to metallurgical bonding. Furthermore, the average hardness of the coating is above 700Hv and the excellent wear resistance at either room temperature or high temperature.

碩士<br>遠東科技大學<br>機械工程研究所<br>103<br>WC/Co thermal spray coating features excellent high hardness, high wear resistance, high elastic modulus, chemical intertness and low coefficient of friction. These unique qualities have made WC/Co coating an ideal candidate for enhancing wear resistance of engineering components such as cutting tools, extrusion molds and rolls etc. With features such as high stacking rate, high adhesion and lower porosity, high velocity oxygen fuel (HVOF) can reduce oxidation of thermal spray coatings and increase their compactness and adhesion. The problem faced by the industry now is that the WC/Co powder is expensive and it is even more costly if they choose the WC/Co nanopowder, which features low loss rate, better coating performance and deposition efficiency, making WC/Co a less competitive thermal spray coating option for wearable components. As such, this study examined the microstructures and coating performance of medium carbon steel substrates respectively coated with HVOF WC/Co, WC/Co reinforced phase cast iron and the same plus graphitizing heat treatment. For the three types of coating, two types of commercial WC/Co powder (WC-12wt%Co and WC-17wt%Co) were used, which were not added with commercial cast iron powder for the first type of coating and were added with the cast iron powder in the ratio 1:1 for the latter two types of coating. The substrates were S50C medium carbon steel and respectively received HVOF WC/Co coating, WC/Co reinforced phase cast iron coating and the same plus graphitizing heat treatment for subsequent characteristic analysis and performance testing.The experimental results show that the HVOF WC/Co coating has main constituent phases including WC, Co, Co6W6C and W2C while the other two types of coating have main constituent phases including WC, Co, Co6W6C, W2C and -Fe. Coating hardness testing reveals that the WC/Co coating is harder than the other two types. Polarization testing shows that the WC-12wt%Co reinforced phase cast iron coating has greater corrosion resistance and better corrosion current density (Icorr.) and corrosion potential (Ecorr.) than the other specimens.

碩士<br>國立中央大學<br>機械工程學系<br>104<br>Fe-base metallic glass is famous for its high hardness high stress and good corrosion resistance. Compare to other kind metallic glass, Fe-base has higher stress and low coast. This study use Fe-Cr-Mo-C-B-Y-Co series composition bond coats on the 304 stainless steel by High Velocity Oxygen Fuel (HVOF) thermal spray. Investigate its mechanical properties and electrochemistry properties. Optical Microscope shows a homogeneous, crack-free surface and cross section. Hardness from 262 ± 24HV to 1066±53HV, In the wearing test, load 5N normal force at WC ball and get wearing resistance is about 5.3105(Nm/mm3). The wearing performance is better than SKD11(7.4104(Nm/mm3)). In the scratch test, HVOF coating also shows lower friction coefficient than SKD11 . The anodic polarization measurement of HVOF coating, we get the corrosion voltage is 0.2V, corrosion current is 8.510-6 A. For comparison we use 316SS and get corrosion voltage is -0.43V, corrosion current is 2.510-5 A. This test result shows HVOF coating exhibits a higher corrosion resistance, than the 316SS in 3.5 wt% Sodiμm chloride solution. Also we can observe significant pitting in 316SS by Optical Microscope. According to the result, Fe-base metallic glass coating by HVOF thermal spray, can improve the wearing performance and corrosion resistance.

Die Habilitation befasst sich mit neuen Verfahren und Anwendungen des Thermischen Spritzens, beleuchtet anhand einer internationalen Umfrage den Forschungsbedarf der Branche und liefert zahlreiche Lösungen, die im Rahmen von grundlagenorientierten und industrienahen Forschungsvorhaben erarbeitet wurden. Der Fokus der Arbeit liegt auf der Verbesserung individueller Arbeitsschritte der Prozesskette des Thermischen Spritzens, wobei Ergebnisse aus den Bereichen Werkstoffentwicklung, Prozessoptimierung, Qualitätssicherung und Nachbearbeitung zusammengeführt und durch konkrete Anwendungsbeispiele hinterlegt werden. Im Detail werden die Aspekte Herstellung leistungsfähiger und preiswerter Spritzzusätze (Wasserverdüsung von Metallpulvern, Hochenergiekugelmahlen, Agglomerieren und Sintern sowie Fülldrahtherstellung), die Verbesserung der Prozessführung (numerisch optimierte Spritzbrenner und automatisierbare Online-Prozessdiagnostikmethoden) und die Steigerung der Leistungsfähigkeit der Beschichtungen durch mechanische Nachbearbeitung sowie Versieglung behandelt. Anwendungsbezogen werden das Beschichten von Hochleistungspolymeren und CFC-Leichtbaustrukturen untersucht. Um Anknüpfungspunkte für weiterführende Forschungsarbeiten zu schaffen, schließt die Arbeit mit der Darstellung von Entwicklungstrends und zeigt Arbeitsgebiete auf, die perspektivisch von thermisch gespritzten Schichten profitieren können.

Intake and exhaust valves operating in diesel engines for naval propulsion suffer from several problems due to the combined and synergistic effects of mechanical stresses and a chemically harsh environment. Degradation mechanisms like wear and corrosion act on different sections of the valve, with the result that each part undergoes a different kind of damage. The present work particularly focuses on degradation phenomena such as low temperature corrosion and erosive wear on the stem; hot corrosion on the bottom of the head of the valve; wear on the seat ring. In order to prevent the valves from degrading, a possible solution is the application of protective coatings that may extend the service life of the components by preserving the mechanical properties of substrate materials, while improving the oxidation and corrosion resistance of the surface. The objective of this study is the development, testing and optimization of a system of corrosion and wear resistant coatings for the stem, bottom and seat ring of the valves. The analysis of the degradation mechanisms occurring on each section of the valves led to the selection of materials that could be suitable for the protection of the substrate. Specifically, two different kinds of ceramic-metallic coatings were selected for the protection of the stem and the bottom of the valves, while a modification of the state-of-the art coating applied on the seat ring was performed.