Dissertationen zum Thema „Cobalt-based alloy“

The diploma thesis deals with the topic of machinability of materials. The theoretical part describes the aspects according to which machinability can be evaluated. The material side of the thesis is focused on various types of difficult-to-machine materials. The cobalt alloy UmCo50 belongs to the group of difficult-to-machine materials and it is the subject of the experimental part. UmCo50 is an alloy for high temperature use. The primary aim of the thesis was to monitor the wear of the selected cutting tool when turning this alloy. Other aspects of the selected machining process were also monitored, such as force effects or the quality of the machined surface. Despite the fact that machinability of tested materials cannot be expressed in terms of the absolute value of a quantity, it is necessary to compare the various aspects of the machining processes by reference materials. However, certain conditions of this comparison must be met. Based on this, a comparison of tested and reference material was performed.

Les maladies cardio-vasculaires sont la principale cause de mortalité dans le monde. Parmi celles-ci, et une des plus importantes, se trouve l'athérosclérose. Cette maladie se traduit par la formation d'une plaque sur les parois artérielles réduisant alors le diamètre luminal. La plaque d'athérome entrave la circulation du sang et peut se compliquer par la formation d'un thrombus artérielle pouvant provoquer un infarctus du myocarde. Une intervention capable de rétablir le flux (recanalisation) est alors nécessaire. Dans le cas des artères coronaires, l'intervention coronaire est percutanée (ICP) et consiste à amener et déployer jusqu'au site malade, une endoprothèse, appelé aussi stent. Un stent est un petit treillis métallique tubulaire qui permet de rouvrir la lumière de l'artère et de rétablir la circulation sanguine. Il sert aussi de support à l'artère malade pour empêcher son affaissement. Cependant, après implantation, certaines complications sont induites, telle que la resténose intra-stent (ISR) qui se caractérise par la réduction de la lumière de l'artère, reconduisant les problèmes créés par la plaque d'athérome. Ce phénomène est essentiellement dû à une prolifération excessive des cellules musculaires lisses, et qui résulte d'une lésion de l'endothélium lors de l'implantation. Afin de limiter cette complication, la première approche a été de changer les matériaux utilisés pour ces endoprothèses. Les principaux alliages utilisés pour fabriquer des stents sont l'acier inoxydable, les alliages de nitinol et ceux de chrome cobalt, plus particulièrement le L605. Ce dernier, dû à ses propriétés mécaniques, permet la fabrication de dispositifs plus minces, donc moins de métaux présents dans le corps humain, et a démontré induire moins de complications cliniques. Néanmoins, malgré la diminution des complications par rapport aux autres alliages, les endoprothèses nues en L605 ne s'intègrent que peu ou pas du tout dans le tissu artériel de l'hôte. Pour répondre aux exigences biologiques et cliniques, l'idéal serait d'avoir un dispositif qui favoriserait le recouvrement du dispositif par l'endothélium, ou « endothélialisation » et qui aurait un faible potentiel thrombotique et inflammatoire. L'approche couramment utilisée pour répondre à ces critères est de recourir à des dispositifs qui libèrent des médicaments anti-inflammatoires. Pour ce faire, il faut recouvrir les dispositifs métalliques avec des revêtements à base de polymères, en tant que couche intermédiaire, fonctionnalisée ensuite par des molécules bioactives. Toutefois, les dépôts de ces couches polymériques impliquent l'utilisation de chimie en solution incluant des solvants organiques. En outre, ces dernières démontrent avoir une faible adhésion au substrat métallique, dû au procédé utilisé, mais aussi un manque de cohésion. Lors de la procédure d'implantation, les stents subissent une déformation plastique, comme ces revêtements manquent de résistance, ils ont tendance à fissurer ou délaminer. Ce projet de recherche s'insère donc dans cette problématique générale, et propose une nouvelle approche qui permettrait d'éviter ce revêtement polymérique, tout en apportant les propriétés biologiques recherchées. Pour ce faire, la modification de surface proposée implique la fonctionnalisation directe des surfaces métalliques par un procédé plasma. Ce procédé permet de ne pas modifier les propriétés de cœur du matériau, et de créer des groupes fonctionnels en surface, ici des groupes amine réactifs (NH₂), qui servent de points d'ancrage pour le greffage ultérieur des molécules bioactives d'intérêt. En résumé, ce procédé original peut être divisé en 3 parties principales : a) préparation de la surface, b) fonctionnalisation par plasma et c) greffage de molécules bioactives. Tout au long de ce projet de recherche, l'optimisation de chaque partie a été réalisée en vue d'obtenir les propriétés adéquates et nécessaires pour l'application cardiovasculaire visée. Concernant la partie a), c'est-à-dire la préparation de la surface, les traitements suivants ont été testés : électropolissage, traitements thermiques et implantation ionique par immersion dans un plasma. Ces modifications ont été optimisées en vue d'obtenir une couche d'oxyde stable sous déformation présentant la meilleure résistance possible à la corrosion, tout en démontrant la plus haute efficacité d'amination directe par plasma pour la partie b). Enfin, en ce qui concerne le bloc c), le greffage de molécule bioactive, deux bras de liaison différents ont été étudiés pour évaluer leur impact sur la conformation et la performance biologique. Cette étude a été effectuée avec un peptide bioactif dérivé de la molécule d'adhésion des cellules endothéliales et des plaquettes (PECAM-1 ou CD31), en raison de ses propriétés anti-inflammatoire, anti-thrombotique et pro-endothélialisation. Les 2 bras d'ancrage testés sont un à chaine courte, l'anhydride glutarique (GA), contenant seulement 5 atomes de carbone, et un à longue chaine (600 atomes), le polyéthylène glycol (PEG) choisi aussi pour ses propriétés anti-adhérentes. Tout d'abord, cette stratégie a été développée sur des échantillons plats, qui facilitaient grandement les analyses de surface, telles que XPS et ToF-SIMS, et donc les processus d'optimisation de chaque étape, comme la résistance à la déformation, corrosion et l'analyse des propriétés biologiques. Ceci a permis de démontrer que le prétraitement de surface optimal pour les substrats L605 était l'électropolissage, agissant sur sa couche d'oxyde passive pour une efficacité maximale lors de l'étape d'amination. Le bras de liaison qui a démontré le plus grand potentiel pour immobiliser le peptide d'intérêt est le PEG, avec une augmentation significative de la migration et viabilité des cellules endothéliales, par rapport au substrat métallique nu. De plus, le greffage du peptide sur le PEG ajoutait des propriétés anti-thrombotique et anti-inflammatoire par rapport aux échantillons électropolis. Ce procédé a été ensuite adapté à des stents, dont la configuration 3D est très complexe. Après optimisation, les stents pegylées + peptides biomimétiques (Plasma-P8RI) ont été testés in vivo par implantation dans les coronaires de porc porcin pendant 7 jours et 28 jours et leur potentiel de ré-endothélialisation et anti-resténotique ont été évalués. Il a été constaté que la stratégie proposée dans ce projet de recherche favorisait la ré-endothélialisation après 7 jours par rapport au DES (Drug Eluting Stent) commercial, et limitait l'adhérence des leucocytes et des plaquettes lorsque comparé au BMS (Bare Metal Stent). Après 28 jours d'implantation le diamètre luminal des artères n'était pas réduit sur le stent Plasma-P8RI, ce qui signifie que ces stents modifiés ne présentaient pas de risque de resténose, contrairement aux BMS. Ce projet de recherche a permis de développer et de valider une stratégie prometteuse consistant à immobiliser directement des molécules bioactives sur des dispositifs cardiovasculaires en L605, alliage de chrome-cobalt. A notre connaissance, cette approche n'a jamais été rapportée dans la littérature à notre connaissance. Cette stratégie originale, dépourvue des limites associées à l'usage des polymères et basée sur un procédé plasma, présente des avantages évidents et ouvre la voie vers le développement de dispositifs cardiovasculaires innovants.
Cardiovascular diseases represent the leading cause of death in the world. Among them is atherosclerosis that characterizes by the formation of a plaque on the arterial walls that narrows the lumen diameter. This atherosclerotic plaque disrupts the blood flow and can be complicated by thrombosis which can ultimately lead to myocardial infarction. Efficient revascularization is mandatory to treat this disease and a percutaneous coronary intervention (PCI) is performed complemented with the deployment of a stent. Stents are tiny wire mesh that reopens the artery, re-establishing the blood flow whilst supporting the artery avoiding its collapse. Nevertheless, complications after stent implantation exist and in-stent restenosis (ISR) is one of the major concerns. This complication is characterized by the reduction of the lumen diameter, similar to an atherosclerotic plaque, and it is associated to the wound caused on the endothelium by the stent implantation followed by the over-proliferation of smooth muscle cells. One of the first strategies to decrease ISR involved the manufacture of stents using different alloys such as stainless steel, nitinol and cobalt chromium alloys (L605). The latest alloy, L605, has generated significant interest because it allows the fabrication of thinner devices, which have decreased post-implantation clinical complications. Nonetheless, despite the decrease in ISR, when compared to other alloys, the integration of L605 bare metal stents in the host tissue is minimal or inexistent. Thus, enhanced biological properties, such as endothelialisation, low thrombosis activity and anti-inflammatory behaviour represent mandatory requirements for clinical applications. To confer these properties onto metallic devices, polymeric-based coatings, as an intermediate layer to further functionalize with bioactive molecules, are often deposited. Nonetheless, major techniques to deposit these polymeric coatings involve the use of wet-chemistry and do not ensure total resistance during the stent implantation procedure due to lack of cohesion and delamination of the polymeric layer. Thus, a novel approach that foregoes this previously mandatory coating step was developed in this research project. This novel approach involves the use of plasma-based techniques to create functional groups (reactive amine groups, -NH₂), directly onto the metallic surface without modifying the bulk properties, that can be used as anchor points for the further grafting of bioactive molecules of interest. Briefly, this novel approach can be divided in 3 blocks: a) Surface preparation, b) plasma functionalization and c) bioactive molecule grafting. Throughout this research project the optimization of these main blocks was performed aiming for the desired cardiovascular application. Concerning block a), surface preparation, electropolishing, thermal treatments and plasma immersion ion implantations were performed to obtain an oxide layer deformation and corrosion resistant whilst demonstrating the highest direct plasma amination efficiency, for block b). Finally, as regards block c), bioactive molecule grafting, two different linking arms were studied to assess their impact on conformation, and the biological performance of a bioactive peptide derived from the platelet endothelial cell adhesion molecule (PECAM-1 or CD31) due to its pro-endothelialization, anti-inflammatory and anti-thrombotic potential: Glutaric anhydride (GA), as a short chain spacer of 5 carbons, and polyethylene glycol (PEG), as a long chain spacer with antifouling properties. Initially, this strategy was developed on flat samples where using a combination of high-resolution surface characterizations techniques, such as XPS and ToF-SIMS, and corrosion, deformation and biological tests it was confirmed that the optimal surface pre-treatment for L605 was electropolishing, due to its passive oxide layer and that it further allowed to obtain the highest amination efficiency. Furthermore, the best linking arm to immobilize the peptide was PEG, which demonstrated a significantly increase on endothelial cell viability with a faster migration, when compared to the bare metallic substrate. Moreover, peptides immobilized by PEG demonstrated that endothelial cells attached to the surface presented an anti-thrombotic and anti-inflammatory phenotype, when compared to electropolished samples. Thus, this biomimetic surface was selected for an in vivo trial in porcine model to evaluate its potential re-endothelialization and anti-restenotic activity. It was found that by directly attaching a CD31 agonist onto the bare metal stent by this strategy improved re-endothelialization after 7 days when compared to commercial DES, with further, low adhesion of leukocytes and platelets when compared to BMS. Moreover, after 28 days of implantation, Plasma-P8RI did not present a significant decrease on the lumen diameter, which was not the case for BMS that presented in-stent restenosis after this period. Overall, this research project allowed the development and validation of a promising strategy to directly immobilize bioactive molecules onto L605 cobalt chromium cardiovascular devices, providing clear advantages of medical devices currently on the market. Furthermore, to the best of our knowledge, such plasma-based multi-step strategy has never been previously reported in literature.

The aims of this study are: to prove the possibility that cobalt-based alloys can be produced with the addition of several alloying elements, such as chromium, molybdenum, nickel and tungsten; and to gain an understanding of the mechanism of electro-deoxidation. This study reports, for the first time, the successful production of metallic Co, Co-30Cr, Co-30Cr-7Mo, Co-27Cr-10Ni and Co-27Cr-12.5W. Preparatory work was conducted to construct some of the electrochemical equipment used and to determine reduction conditions. Mechanistic studies were performed through the use of constant voltage, and constant potential, chronoamperometry; as well as cyclic voltammetry. Fully and partially reduced samples were analysed using a variety of techniques, which included XRD, SEM, Electra oxygen analysis, and optical microscopy. This work also introduces constant current chronopotentiometry as a new technique to FFC investigations. This technique is used, for the first time, to determine mechanistic information about the electro-deoxidation of single and multiple oxide precursors. Electro-deoxidations are completed at a variety of constant currents and the resulting data is used to construct a novel type of Tafel plot.

Dans le domaine du forgeage à chaud de pièces aéronautiques, les matrices en acier sont couramment rechargées, sur quelques millimètres d’épaisseur, par un alliage base cobalt (Stellite 21) déposé par procédé de soudage à l’arc (MIG). Dans le cadre de ce travail de thèse, ce rechargement « classique» est comparé à des rechargements Stellite 21 et Stellite 6 déposés par deux procédés émergents dans ce domaine, le PTA et le LASER. L’objectif est d’apporter des éléments de compréhension aux mécanismes d’endommagement de surface, notamment par écoulement plastique, de ces différents rechargements afin de dégager des voies d’amélioration pour augmenter la durée de vie des matrices. Pour cela, des essais tribologiques (semi-industriels et laboratoire) ont été mis en œuvre pour créer des endommagements de surface comparables à ceux observés sur matrices industrielles. Associées à ces essais, des investigations microstructurales, structurales et mécaniques multi-échelles ont été réalisées (traction, flexion, microdureté, MO, MEB, MEB-STEM, DRX, EBSD). Selon les couples « nuance/procédé » de rechargement, des mécanismes de déformation plastique par glissement des dislocations parfaites et par transformation de phase CFC en HC ont été identifiés. L’activation de ce dernier a pu être reliée à la température de transformation allotropique CFC/HC du cobalt. Cette température dépend à la fois (i) des éléments d’addition, variant en fonction de la nuance déposée (Cr, C,...), (ii) de la dilution (variation de la teneur en Fe) liée aux paramètres de soudage et (iii) du nombre de couches déposées. De plus, une influence significative de la transformation de phase sur l’évolution du coefficient de frottement a été mise en évidence. En effet, dans le cas où la transformation de phase n’est pas observée, le coefficient de frottement est stable durant l'essai alors qu'une chute de la courbe de coefficient de frottement a été reliée avec la transformation de phase CFC en HC. Parallèlement, l'écoulement plastique des dendrites est observé en extrême surface sur quelques dizaines de micromètre d'épaisseur dans la direction de glissement. Cet écoulement est associé à une forte texturation morphologique et cristallographique de la phase identifiée (CFC ou HC), avec une orientation des plans de plus grande densité atomique parallèlement à la surface de glissement. Les résultats montrent également que sous sollicitations tribologiques, un important durcissement est observé en surface (jusqu'à 90%) et une corrélation a pu être établie entre l'augmentation de la microdureté et le taux de déformation plastique
In the field of hot forging of aeronautical parts, the steel dies are commonly hardfaced, on few millimeters thick, by a cobalt-based alloy (Stellite 21) deposited by arc welding (MIG). As part of this thesis, this "classic" hardfacing is compared to Stellite 21 and Stellite 6 hardfacings deposited by two emerging processes in this area, the PTA and the LASER one. The objective is to assess surface damage mechanisms, especially induced by plastic strain, of these various hardfacings. Tribological tests (laboratory and semi-industrial) were used to create surface damage comparable to those observed in industrial dies. Associated with these tests, multiscale microstructural, structural and mechanical investigations have been performed (tensile, bending, microhardness, OM, SEM, STEM, XRD, EBSD). According to the « material/process » couple, plastic strain mechanisms by perfect dislocation glide and by FCC to HCP phase transformation have been identified. The activation of the latter has been connected to the temperature of the allotropic phase transformation (FCC/HCP) in cobalt. This temperature depends on (i) the alloying elements, varying according to the deposited grade (Cr, C, ...), (ii) the dilution (Fe content evolution) connected to the welding parameters and (iii) the number of deposited layer. Moreover, a significant influence of the phase transformation on the evolution of the friction coefficient has been evidenced. Indeed, if the phase transformation is not observed, the friction coefficient is stable during the test, while a drop of the friction coefficient curve is connected with the FCC to HCP phase transformation. Moreover, the plastic flow of dendrites is observed at the extreme surface, on a few tens of micrometres in thickness, in the direction of sliding. It is associated with a high morphologic and crystallographic texturing of the identified phase (FCC or HCP), with the highest atomic density planes mostly oriented parallel to the sliding surface. The results also show that, under tribological laodings, a significant hardening is observed on the surface (up to 90%) and a correlation has been established between the increase in the microhardness and the plastic deformation ratio

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A indústria busca uma melhor otimização e performance de seus equipamentos, há muito notou-se a importância da contenção do desgaste para o aumento de vida útil dos componentes de máquinas. Em condições operacionais onde há o desgaste por abrasão, comumente faz-se o endurecimento da camada superficial ou a aplicação de uma liga mais nobre e de dureza mais elevada, visando conter este desgaste. A técnica também é chamada de revestimento. Entender melhor os parâmetros que influenciam nos resultados da aplicação destes revestimentos torna-se importante possibilitando menores perdas e uma maior economia, pois busca-se como alvo trabalhar com a melhor performance do revestimento. Objetivou-se neste trabalho o estudo das ligas a base de Cobalto que são aplicadas cada vez mais rotineiramente nas indústrias petroquímicas, onde os componentes e órgãos de máquinas estão expostos a condições severas de desgaste por abrasão e corrosão além da severidade dos trabalhos a altas temperaturas e pressão. Relacionando o desgaste, as ligas a base de Cobalto possuem uma posição destacada e a liga é conhecida comercialmente como “Stellite 6”. Em alguns trabalhos é chamada também de liga coringa por sua versatilidade e destaque em especial. Neste trabalho procurou-se variar as velocidades de resfriamento em cinco patamares, analisou-se a influência da diluição na micro-dureza e os efeitos da variação da velocidade de resfriamento no mecanismo de endurecimento. A aplicação do revestimento ocorreu em três camadas através do processo TIG. Verificamos ainda a interferência da diluição na dureza em cada camada de revestimento. A terceira e última camada foi a que apresentou maior dureza devido à menor diluição com o metal base principalmente no corpo de prova que possuía à menor velocidade de resfriamento devido ao tempo para a formação de precipitados e carbonetos na liga metálica.
The industry searchs a better optimization and performance of their equipment, long noted the importance of containment to increase the wear life of components of machines. In operating conditions where there is wear by abrasion, usually it is the hardening of the surface layer or the application of a more noble alloy and high hardness, wear it to contain. The technique also called hardfacing. Better understand the parameters that influence the results of applying these coatings becomes important because it enables lower losses and greater economy as it seeks to target work with the best performance of the coating. The objective of this research is complements the study of cobalt-based alloys that are applied more routinely in petrochemical industries, where the component units and machines are exposed to severe conditions of wear by abrasion and corrosion than the severity of the work at high temperatures and pressure. Relating the wear, the cobalt-based alloys have a prominent position and the league is known commercially as “Stellite 6”. Some work is also called the league wildcard for its versatility and highlight in particular. In this work we have tried to vary the speed of cooling in five steps, looked up the influence of dilution on micro hardness and the effects of variation in the rate of cooling in the hardening mechanism. The application of the coating occurred in three layers using the TIG process. We note also the interference of dilution in hardness in each layer of coating. The third and final layer was the one with higher hardness due to less dilution with the base metal mainly in the body of evidence that had the lowest rate of cooling due to the time for the formation of precipitates and carbides in the metal.

碩士
國立臺灣科技大學
機械工程系
99
The purpose of this work is to study the hot-corrosion behavior of a Co-based superalloy (Haynes 188; HA-188) over the temperature range of 750 – 850 ℃ in static air with a 2 mg/cm2 NaCl deposit, and in particular, to systematically understand the hot-corrosion mechanism of the alloy. The results showed that the oxide-scales formed on the HA-188 alloy after hot corrosion were nonprotective. In addition, the precipictates of Cr23C6 along grain boundaries of the alloy preferentially reacted with chlorine, which resulted in a severe granular corrosion and a Cr-depleted zone. The volatilization of the chlorides gradually increased with increasing temperature, which in turn reduced the partial pressures of chlorine in the scale/substrate boundary, thereby leading a slower corrosion rate at 850 ℃. Haynes 188 contained with 14% tungsten, the oxide and chloride of tungsten that formated after NaCl hot corrosion have high volatility, caused the largely weight loss on the dynamics curve. In addition it was found that the HA-188 alloy exhibited a better hot-corrosion resistance, as compared to those of the Fe-based steels (430SS, 304SS, 310SS, 253MA, and 353MA) under the previous studies in our laboratory. It may be concluded that the hot-corrosion resistance of the Co-based superalloy is much superior to those of Fe-based steels.

碩士
義守大學
材料科學與工程學系碩士班
97
The cobalt-based alloy of cobalt-based bimetallic cylinder was chosen to investigate its corrosion behavior by immersing in three acid solutions (6% FeCl3, 20% HCl, 60% H2SO4) with different immersion time (5 minutes, 30 minutes, 3 hours, 0.5 days, 1 day, 2 days, 3 days). In addition, the electrochemical experiments, such as open circuit potential and dynamic polarization tests, were also employed to understand the changes of the corrosion current and voltage in the same acid solutions. After the immersion test and electrochemical experiments, optical microscopy (OM) was employed to observe the morphology of corroded surface. The phase was identified by X-ray diffractometer (XRD). scanning electron microscope (SEM) was used to examine the microstructure., and inductively coupled plasma atomic emission spectroscopy (ICP-OES) were conducted to determine the metal ion species. The results show that the cobalt-based alloy consists of Co, W3CoB3, σ-CrCo, Co0.72Fe0.28 and σ-FeCr can be distinguished to Co-rich, Cr-rich and W-rich phases. According to the results of immersion test, the corrosion rate cobalt-based alloy decreases with increasing immersion time. Both the weight loss and the corrosion depth increases while immersion time increases. The relative corrosion resistance of cobalt-based alloy to acid solution is 6% FeCl3>20% HCl>60% H2SO4. The results of dynamic polarization test shows that no significant passivation occurs in the solutions of 6% FeCl3 and 20% HCl when the current increased, but slight passivation occurred in the solution of 60% H2SO4 (-119mV to-55mV). Comparing the results of open circuit potential tests with dynamic polarization tests, the cobalt-based alloy immersed in the solution of 6% FeCl3 has been attacked at 5 minutes, while the Co-based alloy starts to be attacked at 0.5 day at last in the solutions of 20% HCl and 60% H2SO4. All the results of the Co-based alloy in the three solutions exist the silicon oxide, iron chromium oxide and cobalt iron oxide. Morphological examination observation revealed that the Co-rich phase has worse corrosion resistance than the other two phases.

碩士
國立臺灣大學
機械工程學研究所
99
In this research, Co-based alloy Stellite6（Co-28Cr-4W-1.1C）and Ni-based alloy Deloro60（Ni-14.4Cr-3.2B-4.4Si）were clad on carbon steel using high frequency induction heating. With different processing parameters, the properties of the clad layer were studied through observing the microstructure, measuring the chemical composition and hardness distribution, indentifying the phases in the layer, and conducting the corrosion test. The results show that the microstructure of Co-based alloy layer can be divided into dendrite, interdendritic eutectics and needle structure. If the microstructure of the clad layer is dendrite and interdendritic eutectics, the matrix is Co-rich solid solution containing chromium, iron and other elements with network M7C3 carbide distributed along the grain boundary. The hardness of the clad layer will decrease with increasing the heating time. However, when the content of iron is more than 40％, the microstructure will transform into needle structure, and the hardness of the clad layer will increase with increasing the heating time. Ni-based alloy layer consists of γ-Ni matrix, Ni3B, Ni31Si12, CrB, Cr7C3 and Ni-Cr-Fe compounds. The interface compound of Ni-Cr-Fe will increase and both CrB and Cr7C3 will decrease with increasing the heating time, leading to a slightly decrease in the hardness near the interface. In the clad layer, the coarsening of CrB and Cr7C3 becomes more obvious as the heating time increases. In other words, the volume fraction of hardening phases（CrB and Cr7C3）increases and lead to the increasing of hardness. High heating power and short heating time will increase the compounds of CrB and Cr7C3 as well as the volume fraction ofγ-Ni and Ni3B ,and lead to increase in hardness of the clad layer. The specimen clad with Co-based alloy or Ni-based alloy has excellent resistance to the corrosion of hydrochloric acid, nitric acid and sulfuric acid. No matter which alloy is clad, the ability of anti-corrosion will decrease with increasing the heating time, owing to the dilution of iron in the clad layer.

碩士
國立臺灣大學
機械工程學研究所
94
SUS304, S45C, and SK3 are cladded with cobalt-based Stellite 6 alloy by means of high frequency induction heating. The influence of heating power and heating time on the microstructure, hardness and chemical compositions of the caldded layer has been studied. The results show that there are two types of microstructure in the cladded layer depending on the heating power and heating time if SUS304 is used as base metal. They are cellular dendrite and columnar dendrite. When the heating power or the heating time increases, the hardness of the cladded layer will decrease. The content of Co and Fe within the grain is much more than that at the grain boundary, but the content of Cr and W is more at the grain boundary. If S45C or SK3 is used as base metal, there are three types of microstructure in the cladded layer depending on the heating power and heating time. They are cellular dendrite, columnar dendrite and needle structure. If the microstructure of the cladded layer is cellular dendrite or column dendrite, the hardness of the cladded layer will decrease with increasing the heating power or heating time. If the needle structure appears, the hardness of the cladded layer will increase with increasing the heating power or heating time owing to the precipitation of carbide in the matrix. No matter what the microstructure is, the content of Co and Fe within the grain is much more than that at the grain boundary, but the content of Cr and W is more at the grain boundary.

碩士
國立成功大學
材料科學及工程學系碩博士班
96
In this study cobalt-based alloy of as-casted, after 1.2% and 7.7% cold-rolled was used to investigate the effect of cold rolling on the preferred orientation and the magnetic flux. The chemical composition and phase identification of the cobalt-based alloy were analyzed using induced-couple plasma (ICP) method and x-ray diffraction (XRD), respectively. Microstructures of samples were characterized by optical microscopy (OM) and scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) was served to identify the chemical composition of phases. Magnetization and preferred orientation behavior were measured by vibrating sample magnetometer (VSM) and pole figures of {2-1-10} and {2-1-13}, respectively. It was observed that a hcp phase of Co and a fcc phase of Co5Zr exist in all samples from XRD results. The fcc phase of Co was found in the target center of as-casted and after 1.2% cold-rolling, and in the half radius region of the sample after 1.2% cold-rolling. After cold rolling up to 1.2% it was not able to observe a strong rolling texture from the {2-1-10} and {2-1-13} pole figures. The magnetic flux decreases with increasing cold rolling.

碩士
國立中興大學
化學工程學系所
104
In this study, the optimize ratio of the Nickel(II) Chloride and Cobalt(Π) acetate tetrahydrate precursors has been found to synthesize alloy Ni-Co nanoparticles (NPs) loading on graphene oxide(GO). The NiCo NPs were prepared by polyalcohol reduction method to form bulk NiCo, and the TEM and SEM images will be investigated. The XRD and SME sutdies will determine the crystalline phase and morphology of the bimetallic alloy. A supercapacitor has been constructed by using an electrochemical double-layer, Nickel-Cobalt alloy (NiCo) anode and platinum sheet cathode immerse in KOH electrolyte. Besides, using carbon nanomaterials like graphene oxide (GO) incorporating with NiCo NPs further increases the capacitance. It shows that the SEM image of the NiCo NPs incorporates on GO surface. Consequently, it has found that the optimized NiCo ratio as electrode material and it possesses good stability and properties as a supercapacitor. In the study, we can synthesize sizes of particles about 75nm and measure capacitance of these samples. Without graphene oxide, the Ni15Co posssesses the higher capacitance over 100 Fg-1. Using carbon nanomaterials like graphene oxide (GO) incorporating with NiCo NPs further increases the capacitance. Comparing with Ni15Co NPs, it has much better capacitances. Otherwise, we try the cycles of GC and get the capacitance retention. Without grapheme oxide, NiCo NPs has better capacitance retention.

碩士
遠東科技大學
機械工程研究所在職專班
107
In this study, Stellite6 alloys were respectively overlaid on spheroidal graphite(SG) cast irons with 3.0 wt% carbon and 2.8 wt% silicon by plasma transferred arc (PTA) process in the fixed overlaying speed, travel speed and overlaying current by changing the additive content of NbC in the Stellite6 alloys. To explore its influence on the solidification structure of the overlayer and the interface region. In the study, we also used the overlayer with the NbC additve in cobalt-base superalloys for the cutting wear test to explore the effects of different the additive content of NbC in the Stellite6 alloys on the microhardness, the amount of carbides and the cutting wear characteristics of the overlayer. The results reveal that the Stellite6 overlayer melted on SG cast iron with 3.0 wt% carbon and 2.8 wt% silicon under overlaying current (I=100A) is a dendritic structure with M7C3 and M23C6 carbides and matrix structure is -Co. The micro-hardness (Hv) and bulk hardness (HRC) of the overlayer increases with the addition amount of NbC. The results of the cutting wear test show that the flank wear of the Stellite6 cobalt-based alloy overlayer does not increase with the addition of NbC, but it is found that when 30 wt% NbC carbide is added, that have better wear resistance. In the cutting wear test, the wear mechanisms of overlayers are mainly plastic groove, surface polish and adhesive wear as adhered to overlayers. Others minor mechanicsms include brittle crack and fracture. Among these, the case to plastic groove includes microcutting and plough. Keywords: plasma transferred arc, overlaying current, Stellite alloy, spheroidal graphite cast iron, wear .

博士
義守大學
材料科學與工程學系博士班
98
Vacuum induction melting (VIM) and hardfacing alloys are widely used process and materials, but seldom studies were made to fabricate hardfacing alloys using VIM and study their microstructure, wear and corrosion behaviors. Therefore, this study used Ni-based, Ni-WC and Co-based alloy powders repectively to make bimetals upon AISI 4140 steel substrate, and then studied their microstructure, wear and corrosion behaviors. Phase identification of the original alloy powders shows that the Ni-based alloy powder mainly consists of γ-Ni, Ni31Si12, Cr2B and Cr7C3. The tungsten carbide particle consists of WC and W2C. The Co-based alloy powder mainly consists of Co, σ-CrCo and W3CoB3. The phase transformation path during heating of Ni-based alloy is γ-Ni + Ni31Si12 + Cr2B + Cr7C3 → L1 + Cr2B + Cr7C3 → L2 + Cr7C3; and transformation during cooling is L3 + Ni3B + CrB + Cr7C3 → γ-Ni + Ni3Si + Ni3B + CrB + Cr7C3. In addition, it was found that iron diffused from 4140 steel suppresses the formation of Ni3B in Ni-based alloy and forms a (Fe, Ni) solid solution with no other second phase. For the bimetallic alloy coatings, the microstructure of the Ni-based alloy coating mainly consists of γ-Ni, Ni3Si, Ni3B, CrB and Cr7C3. The microstructure of the Ni-WC coating mainly consists of γ-Ni, Ni3Si, Ni3B, Cr7C3, WC, W2C, CrB, CrB2, and Cr1.8W3.2B3. The Co1200, the Co-based alloy coating obtained at 1200℃, mainly consists of Co, W3CoB3, σ-CrCo, Co0.72Fe0.28 and σ-CrFe. The Co1250, the Co-based alloy coating obtained at 1250℃, mainly consists of Co, M7W6 (M=Co or Fe), Co3B, σ-CrCo, Co0.72Fe0.28 and σ-CrFe. The hardness from high to low is Ni-WC coating, Co1200, Ni-based alloy coating and Co1250, the trend is relation between the relative area fraction and hardness of hard phase and the iron diluction. The results of the wear tests show that the relative wear resistance is Ni-WC alloy coating ＞ Co1200 ＞ Ni-based alloy coating. The major wear behaviors of the Ni-WC coating are fatigue, oxidation wear and fracture of tungsten carbide particle at lower load and sliding velocity, while the major wear behaviors of Co1200 are fatigue, oxidation wear and delamination. The major wear behaviors of the Ni-WC coating are abrasion, fracture of tungsten carbide particle and delamination at lower load and sliding velocity, while the major wear behaviors of Co1200 are abrasion and delamination. The results of immersion tests show that in solutions of 20%HCl and 6%FeCl3, the corrosion rate of every alloy coatings decreases with increasing immersion time, while in the solution of 60%H2SO4, the corrosion rate increases firstly and then stabilize after a time period. All of these four alloy coatings have the worst corrosion resistance in the solutions of 6%FeCl3 and the the best corrosion resistance in the solutions of 60%H2SO4. The matrix of each alloy coatings dominates its corrosion rate. The matrix is firstly attacked by the soluctions and then develops into an infiltrating path to cause further corrosion on the fresh surface in both the solutions of 20%HCl and 6%FeCl3. However, an oxide layer forms to protect the fresh surface from further corrosion in the solution of 60%H2SO4.

碩士
國立中正大學
機械系
89
Study was carried out to evaluate the oxidation surface and the high temperature wear characteristics of Cobalt-based and Nickel-based laser clad layers. In order to probe into the characteristics of oxidation layer, location and composition of oxide were analyzed by scanning electron microscopy (SEM) and energy dispersive X-Ray Spectrometry (EDS) and oxidation resistance was obtained by thermogravimetry analysis (TGA). Besides, the influence of the high temperature oxidation and thermal fatigue on high temperature wear test results was another focal point which was analyzed by energy dispersive X-Ray Spectrometry and observing wear trace. Finally, we compared the high temperature wear test results with wear theories to infer our wear mechanism and differentiated which wear theory it belongs to. The result shows that the sequence of oxidation resistance was：Stellite 6, Stellite 6 with 50%Cr3C2, and Colmonoy 88. In addition, major element of their oxide was Cr. High temperature wear test results show that the wear resistance of high temperature oxidation was better than thermal fatigue and explains that all oxidation layers were advantageous for wear resistance. Moreover, major factors which affect high temperature wear test results were oxidation layer characteristics and cracks. Surface analysis results shows that major wear mechanisms were adhesive mechanism and detach mechanism. Compared with wear theories results, high temperature wear test results belonged to Quinn’s oxidation wear theory, i.e. oxidation wear mechanism.