Dissertations / Theses on the topic 'Sintering of silver powder'
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Zhang, Zhiye. "Sintering of Micro-scale and Nanscale Silver Paste for Power Semiconductor Devices Attachment." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/28902.
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Die attachment is one of the most important processes in the packaging of power semiconductor devices. The current die-attach materials/techniques, including conductive adhesives and reflowed solders, can not meet the advance of power conversation application. Silver paste sintering has been widely used in microelectronics and been demonstrated the superior properties. The high processing temperature, however, prevents its application of interconnecting power semiconductor devices. This research focuses processing and characterization of micron-scale and nanoscale silver paste for power semiconductor devices attachment.
Lowering the processing temperature is the essential to implement sintering silver paste for power semiconductor devices attachment. Two low-temperature sintering techniques - pressure-assisted sintering micro-scale silver paste and sintering nanoscale silver paste without external pressure - were developed. With the large external pressure, the sintering temperature of micro-scale silver paste can be significantly lowered. The experimental results show that by using external pressure (>40MPa), the commercial micro-scale silver paste can be sintered to have eighty percent relative density at 240oC, which is compatible with the temperature of solder reflowing. The measured properties including electrical conductivity, thermal conductivity, interfacial thermal resistance, and the shear strength of sintered silver joints, are significantly better than those of the reflowed solder layer. Given only twenty percent of small pores in the submicron range, the reliability of the silver joints is also better than that of the solder joints under the thermal cycled environment. The large external pressure, however, makes this technique difficult to automatically implement and also has a potential to damage the brittle power semiconductor devices.
Reducing silver particles in the paste from micro-size to nanoscale can increases the sintering driving force and thus lowers the sintering temperature. Several approaches were developed to address sintering challenges of nanoscale silver particles, such as particles aggregation and/or agglomeration, and non-densification diffusion at low temperature. These approaches are : nanoscale silver slurry, instead of dry silver powder, is used to keep silver particles stable and prevent their aggregation. Ultrasonic vibration, instead of conventional ball milling, is applied to disperse nanoscale silver particles in the paste from to avoid from agglomerating. Selected organics in the paste are applied to delay the onset of mass-diffusion and prevent non-densification diffusion at low temperature. The measured results show that with heat-treatment at 300oC within one hour, the sintered nanoscale silver has significantly improved electrical and thermal properties than reflowed solders. The shear strength of sintered silver interconnection is compatible with that of solder.
The low-temperature sinterable nanoscale silver paste was applied to attach the bare Silicon carbide (SiC) schottky barrier diode (SBD) for high temperature application. Limited burn-out path for organics in the silver layer challenges the sintering die-attach. This difficulty was lessened by reducing organics ratio in the silver paste. The effects of die-size and heating rate on sintering die-attach were also investigated. The single chip packaging of SiC SBD was fabricated by sintering die-attach and wire-bonding. The tested results demonstrate that the sintering nanoscale silver paste can be applied as a viable die-attach solution for high-temperature application.Ph. D.
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Riva, Raphaël. "Solution d'interconnexions pour la haute température." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0064/document.
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Le silicium a atteint sa limite d’utilisation dans de nombreux domaines tels que l’aéronautique. Un verrou concerne la conception de composants de puissance pouvant fonctionner en haute température et/ou en haute tension. Le recours à des matériaux à large bande interdite tels que le carbure de Silicium (SiC) apporte en partie une solution pour répondre à ces besoins. Le packaging doit être adapté à ces nouveaux types de composants et nouveaux environnements de fonctionnement. Or, il s’avère que l’intégration planaire (2D), composé de fils de câblage et de report de composants par brasure, ne peut plus répondre à ces attentes. Cette thèse a pour objectif de développer un module de puissance tridimensionnel pour la haute température de type bras d’onduleur destiné à l’aéronautique. Une nouvelle structure 3D originale constituée de deux puces en carbure de silicium, d’attaches par frittage d’argent et d’une encapsulation par du parylène HT a été mise au point. Ses différents éléments constitutifs, les raisons de leur choix, ainsi que la réalisation pratique de la structure sont présentés dans ce manuscrit. Nous nous intéressons ensuite à un mode de défaillance particulier aux attaches d’argent fritté : La migration d’argent. Une étude expérimentale permet de définir les conditions de déclenchement de cette défaillance. Elle est prolongée et analysée par des simulations numériquesSilicon has reached its usage limit in many areas such as aeronautics. One of the challenges is the design of power components operable in high temperature and/or high voltage. The use of wide bandgap materials such as silicon carbide (SiC) provides in part a solution to meet these requirements. The packaging must be adapted to these new types of components and new operating environnement. However, it appears that the planar integration (2D), consisting of wire-bonding and soldered components-attach, can not meet these expectations. This thesis aims to develop a three dimensional power module for the high temperature aeronautics applications. A new original 3D structure made of two silicon carbide dies, silver-sintered die-attaches and an encapsulation by parylene HT has been developed. Its various constituting elements, the reason for their choice, and the pratical realization of the structure are presented in this manuscript. Then, we focus on a failure mode specific to silver-sintered attaches : The silver migration. An experimental study allows to define the triggering conditions of this failure. It is extended and analyzed by numerical simulations
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Blackmore, Katherine Ann 1969. "Sintering of heterogeneous glass powder compacts." Thesis, The University of Arizona, 1995. http://hdl.handle.net/10150/291349.
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A modification of Scherer's Self-Consistent model and a new model, the Interlocking Cell model, have been developed to characterize the sintering behavior of mixtures of two glass powders. The theoretical sintering curves predicted by both these models are compared to each other and to experimental densification behaviors. Viscosities extrapolated from homogeneous sintering curves of sol-gel derived powders are transient and cannot be predicted based on composition alone. These transient viscosities have a significant effect on the sintering kinetics. The Self-Consistent and Interlocking Cell models assume very different microstructural changes during sintering. However, differences between the two models can just be distinguished using experimental densification curves of sol-gel cordierite based glass mixtures.
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Hascoët, Stanislas. "Mise en oeuvre de nouveaux matériaux d’assemblage dans les modules multipuces de puissance (MCM)." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0123/document.
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L’introduction des composants grand gap dans le domaine de l’électronique de puissance requiert une optimisation de son environnement (packaging). En effet, les températures auxquelles peuvent être utilisés ce type de composants sont bien souvent plus grandes que celles supportables par le reste du module. De nouvelles techniques d’assemblage sont à l’étude et notamment certaines à base de frittage d’argent. Ces procédés présentent l’avantage de réaliser l’assemblage à une température modérée (similaire à celle d’une brasure), mais toutefois inférieure à celle de fusion de l’argent. La température de fusion du joint d’attache reste celle du matériau massif (plus de 900°C pour l’argent). Cette technique permet donc de réaliser des attaches pouvant fonctionner à très haute température. Ce travail de thèse a porté sur la mise en oeuvre d’une attache de puce par frittage d’argent. Après une étude des paramètres du procédé permettant d’obtenir la meilleure tenue mécanique (cisaillement), nous avons mis en évidence l’effet prépondérant de la finition des pièces à joindre. Lorsque la finition du substrat est de l’argent, aucun problème d’interface n’est observé et les assemblages sont fiables à t0 et en vieillissement. Généralement, la finition standard pour l’électronique de puissance est constituée d’une couche de nickel et d’or. Pour cette finition, le mécanisme semble différent selon l’épaisseur d’or présente sur le substrat ainsi que l’atmosphère utilisée pour le traitement thermique ou encore la charge appliquée. Globalement, plus l’épaisseur d’or est importante, moindre est l’accroche. Ce comportement semble fortement lié à la diffusion extrêmement rapide de l’argent en surface de l’or (et dans l’or). Cette diffusion a pour conséquence la formation d’une couche de solution solide or-argent. Cette couche a pour source de matière les grains d’argent qui permettent l’adhérence du joint d’argent fritté sur le substrat. Lorsque le volume d’or disponible pour la formation de cette couche est grand, la croissance de celle-ci est favorisée (en termes de surface et d’épaisseur). Cette croissance engendre une consommation des « piliers » d’argent et donc un affaiblissement de l’attache. L’application de pression semble augmenter fortement la concentration de piliers et améliore les résultats, tandis que sous azote, la diffusion de l’argent en surface de l’or semble inhibée, permettant l’obtention de bons résultats (à t0 et après cyclage). Ces résultats ont été mis en pratique pour la réalisation de plusieurs prototypes, dont l’un a été testé électriquement et ce de façon fonctionnelle à plus de 300°CUse of wide band gap chip in the power electronic industry requires an optimization of the close environment (packaging). Indeed, the can often sustain lower temperature than the die, especially the solder that are used to bond the parts of the module. Consequently, new bonding methods are investigated to enhance the performance of the packages. Silver sintering bonding technique is one the most promising. This method allow to bond parts at moderate temperature and the formed joint to operate at very high temperature (until the melting point of silver). This work is focused on the development of this bonding technique in the case of bonding a dies on a substrate. A study of the influence of the different parameters on the strength of the formed bond has been done. It revealed a major influence of the finishes of the bonded parts. Bonding on silver finished substrate results in good mechanical strength of the bond even after ageing. Furthermore, no interface issues are observed. However, the most used finish for power electronic is not silver but nickel-gold. Regarding this type of finish, the bond quality depends on the gold thickness, sintering profile and also sintering atmosphere. A solid solution of silver and gold seems to develop on the surface of the substrate, decreasing the section of the silver grains in contact with the substrate. Thus the mechanical strength of the assembly is decreased. This effect should be limited by the gold available for the Au-Ag solid solution growth. When sintering under nitrogen, the diffusion of silver on the gold surface is much lower than under air. Good results have been obtained with these configurations and even after ageing. Adding pressure during the thermal treatment seems also to minimize the phenomenon, probably by increasing the number of silver grains in contact with the substrate surface and so reducing the free surface for Au-Ag layer formation. Those results have been used to build prototypes, one of whom has been electrically tested with success at temperatures up to 300°C
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Marsh, P. "Sintering of mixed powders." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282832.
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Dhavale, Tushar. "Low power laser sintering of iron powder." Thesis, University of the West of England, Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522529.
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Booysen, Gerrie Jacobus. "Bridge tooling through layered sintering of powder." Thesis, Bloemfontein : Central University of Technology, Free State, 2007. http://hdl.handle.net/11462/72.
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Thesis (M. Tech.) - Central University of Technology, Free State, 2007Faster mould production methods will undeniably impact positively on the product development community. Rapid Tooling (RT) concepts, in context with the product development process and related product development theories, were analysed. Conventional tooling techniques used such as epoxy plastic tooling and machined injection moulding techniques were used as point of departure for the research work, which focused on Laser Sintering of powder materials. The new generation RT materials that are available at the Central University of Technology, Free State, are a vast improvement on the old materials. RT materials are constantly being developed and the project aims were to stay abreast with the latest developments. The thesis gives a complete overview of all related technologies, and also an in-depth discussion of both the Selective Laser Sintering (SLS) and Laser Sintering (LS) processes. Mould size limitations, as well as general tooling design issues, polishing and finishing techniques were all taken into account. Data has been collected to compare mould inserts grown with RP machines with that of conventionally machined tools. Aspects such as tool life, part quality, lead times and cost were used as parameters to determine the differences and make recommendations. Through analysis of several experiments and industrial case studies, RT through sintered materials was proven as a capable technology, giving the option of an intermediate (bridge tooling) or even a final step of tooling. Recommendations for future use were made in terms of insert size and geometry, accuracy, durability and shrinkages, to ensure the feasibility of the RT process in SA.
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Eane, Radu Bogdan. "Metal powder effects on selective laser sintering." Thesis, University of Leeds, 2002. http://etheses.whiterose.ac.uk/4016/.
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Manufacturing functional prototypes and different tools using conventional methods usually is a time consuming process with multiple steps. The global economic pressure to get products to market faster has resulted in the development of several Rapid Prototyping (RP) techniques. Layer manufacturing technologies are gaining increasing attention in the manufacturing sector. They have the potential to produce tooling either indirectly or directly, and powder metal based layer manufacture systems are considered to be an effective way of producing rapid tooling. Selective Laser Sintering (SLS) is one of several available layer manufacture technologies. SLS is a sintering process in which designed parts are built up layer by layer from the bottom up using different powder materials. A laser beam scans the powder bed, filling in the outline of each layer’s CAD-image by heating the selected powder pattern to fuse it. This work reports on the results of an experimental study examining the potential of the selective laser sintering process to produce metallic parts using stainless steel powder. One material, a stainless steel powder and one sintering station research machine, which was constructed in Leeds, were used during the research. A step-by-step investigation was conducted. The research started with sintered tracks and finished with multiple layer sintering. The purpose was to find successful conditions and to establish the main problems that need to be overcome. The main achievements of this thesis have been to develop laser power and scan speed sintering maps for a stainless steel powder. 1 he maps have established conditions in which multiple layer blocks can be created, have established strategies to enable large areas to be sintered without warping and show that powder particle size has an important influence on sintering and on the position of the boundaries in the sintering maps. Although this investigation answered some questions, it also raised several more which are presented at the end of this thesis for future work.
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Kempen, Daniel. "Thermomechanical modelling of powder compaction and sintering." Doctoral thesis, Università degli studi di Trento, 2019. https://hdl.handle.net/11572/369024.
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An elastic-visco-plastic thermomechanical model for cold forming of ceramic powders and subsequent sintering is introduced and based on micromechanical modelling of the compaction process of granulates. Micromechanics is shown to yield an upper-bound estimate to the compaction curve of a granular material, which compares well with other models and finite element simulations. The parameters of the thermomechanical model are determined on the basis of available data and dilatometer experiments. Finally, after computer implementation, validation of the model is performed with a specially designed ceramic piece showing zones of different density. The mechanical model is found to accurately describe forming and sintering of stoneware ceramics and can therefore be used to analyze and optimize industrial processes involving compaction of powders and subsequent firing of the greens.
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Silver, Kathleen G. "Processing of nano-sized boron carbide powder." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/26476.
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Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Speyer, Robert; Committee Member: Judson, Elizabeth; Committee Member: Sanders, Thomas. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Subrahmanyam, Gowri. "Sintering and its enhancement in ferrous powder compacts." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/32009.
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Sintering maps have been developed for pure iron compacts. The maps have been drawn as a function of various sintering parameters such as particle size, green density, time and temperature. Two sets of diagrams have been drawn to define the sintering kinetics, namely, the field map and the neck growth/shrinkage map. A new and simple method has been developed to construct the field maps, which define the dominant mechanisms of mass transport that contribute to neck growth under a given set of conditions of sintering. Shrinkage maps, which show how far the neck is growing or give % linear shrinkage for a given neck size and temperature, are generated by numerically integrating, the sum of the contributions to neck growth from the different mechanisms of transport. The model developed is based on ideal geometry and does not take into account complex phenomena such as grain growth, pore coalescence or pore growth.
The sintering equations and diagrams that have been developed for pure iron compacts have been used effectively in the present study to predict and analyze the results of experiments involving various attempts to enhance sintering in such compacts.
Small additions of a selected group of elements were made to iron compacts in an attempt to provide activation of solid state sintering similar to that which is obtained when tungsten powder compacts are doped with nickel. A few of the dopants used with iron compacts produced a small increase in shrinkage and densification for a given set of sintering conditions. Based on the present results and on the several studies of tungsten - nickel compacts which are reported in the literature, a new theory of dopant activated sintering has been proposed. Consistent with this model, it is suggested that certain criteria must be met by the dopant-base metal combination if activated sintering is to be
observed.
Sintering enhancement based on ferrite stabilization in two systems, iron - phosphorus and iron - silicon has been studied. This approach to solid state sintering enhancement proved to be highly effective and it is believed to have important practical applications in the P/M parts industry. The results of these experiments were consistent with predictions
based on the sintering theory and maps appropriate to the conditions of sintering employed.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Chen, Xiaolin. "Particle packing, compaction and sintering in powder metallurgy." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0014/NQ34746.pdf.
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Hauser, Carl. "Selective laser sintering of a stainless steel powder." Thesis, University of Leeds, 2003. http://etheses.whiterose.ac.uk/2631/.
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The research presented in this thesis was part of a larger collaborated project (LastForm Programme) to research engineering solutions for the rapid manufacture of large scale (0.5m – 5.0m in length) low, medium and high temperature tooling (from room temperature to 1000C) for use in the automotive and aerospace industry. All research was conducted using small scale investigations but with a final discussion including implications of the work in future large scale planning. The aim of the work presented in this thesis was to develop current understanding about the sintering and melting behaviour of metal powders by Selective Laser Sintering (SLS). The powder used in the research was an argon atomised austenitic stainless steel of type 314s HC. The powder was supplied in four batches, each differentiated by particle size distribution; -300+150m, -150+75m, -75+38m and -38m. The characteristics of each powder, in particular flow properties, differed considerably allowing powder handling and powder flow during melting to also be explored in this work. Three different environmental conditions were also investigated to asses the role of atmospheric and residual (powder) oxygen: (1) air atmosphere (control), (2) argon atmosphere and (3) argon atmosphere with argon percolation through the powder layer. In this, the design of an environmental control chamber and its integration into a research SLS machine was central to the work. Experimental studies of the selective laser sintering/melting process on room temperature stainless steel 314s powder beds has been successfully carried out. The methodology was progressive; from tracks to layers to multiple layers. Single tracks were produced by melting the powder by varying laser power and scan speed. Results from experiments have been used to construct a series of process maps. Each map successfully charts the heating and melting behaviour of the irradiated powder. Behaviours can now be predicted with reasonable accuracy over a dense power and speed range, including laser powers up to 200W and scan speeds up to 50mm/s. The experiments also allowed melt pool geometries to be investigated. Three types of melt cross-section were categorised; flattened, rounded and bell shape. Flat tracks generally occurred at low speed (0.5mm/s) but also occurred up to 4mm/s at lower power (77W). Rounded tracks occurred between 1mm/s and 4mm/s and had a much larger area than expected. In the rounded track regime tracks sink well into the powder bed. Powder to either side of a track collapses into it, leaving a trench surrounding the track. The admission of extra powder is thought to be one cause of increased mass. However, a remaining question that still needs answering is what causes the change from a flattened to a rounded track. Values of laser absorptivity were also estimated from track mass per unit length data and from melting boundaries displayed within the process maps. The results showed that absorptivity changed considerably depending on the powder, process conditions and atmospheric conditions. Within an argon atmosphere an „effective‟ absorptivity from mass data was estimated to range from 0.1 to 0.65, the lower value at low speed scanning (0.5mm/s) and the higher value from high speed scanning (>4mm/s). These values were much higher than expected for a CO2 laser. Melt pool balling was found to be a big problem, limiting the process speed at which continuous tracks could be successfully constructed (<12mm/s). Comparisons between a mathematical model developed in this work and experimental results suggested that balling within an air environment occurred when the ratio of melt pool length to width reached a critical value close to . Balling within an argon atmosphere was more difficult to model due to higher viscous melts caused by the take up of surrounding powder. Melted single layers were produced by varying laser power, scan speed, scan length and scan spacing or melt track overlap. Scan length proved to be a significant factor affecting layer warping and surface cracking. Provided the scan length remained below 15mm, layer warping could be largely avoided. Multiple layer blocks were produced by melting layers, one on top of the other. They were constructed over a range of conditions by varying laser power, scan speed, scan spacing and layer thickness. Layer thickness was a crucial parameter in controlling the interfacial bond between layers, but the spreading mechanism proved to be the overriding factor affecting layer thickness and therefore the quality and density of the blocks.
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Zhang, Li 1973. "Shockwave consolidation of nano silver powder into bulk nano structured silver." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100238.
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Bulk nanostructured silver components were fabricated from nano-sized powder using a shockwave consolidation technique. The grain size evolution during compaction, the mechanical properties of the bulk components, and the effect of surface finish on the mechanical behavior were studied. X-Ray diffraction, transmission electron microscopy (TEM), atomic force microscopy (AFM), microhardness, compression testing and shear punch testing at room temperature were used to characterize the materials. Upon consolidation, the average grain size calculated from image analysis of the TEM micrographs was 49+/-22 nm, showing the feasibility of maintaining a nanostructure upon dynamic consolidation. The hardness of the bulk nanostructured components was constant across the diameter with an average of 83+/-1 HV. Compression results showed strength about 390+/-10 MPa and ductility of 23+/-2%, which is well above strength level obtainable from strain hardened Ag components. The AFM results show that samples possessing a surface roughness of 267 nm exhibited a brittle behavior and a reduction in strength of 35% when compared to the smoother surfaces. Dimples were observed for the samples exhibiting plasticity, while an intergranular pattern was identified for the brittle materials. Fracture toughness of 0.2 MPa m was calculated, which confirms the strong relationship between fracture toughness and defects observed in nanomaterials.
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Tahir, Abdul Malik. "Alloy element redistribution during sintering of powder metallurgy steels." Doctoral thesis, KTH, Fysiokemisk strömningsmekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145251.
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Homogenization of alloying elements is desired during sintering of powder metallurgy components. The redistribution processes such as penetration of liquid phase into the interparticle/grain boundaries of solid particles and subsequent solid-state diffusion of alloy element(s) in the base powder, are important for the effective homogenization of alloy element(s) during liquid phase sintering of the mixed powders. The aim of this study is to increase the understanding of alloy element redistribution processes and their effect on the dimensional properties of the compact by means of numerical and experimental techniques. The phase field model coupled with Navier-Stokes equations is used for the simulations of dynamic wetting of millimeter- and micrometer-sized metal drops and liquid phase penetration into interparticle boundaries. The simulations of solid particle rearrangement under the action of capillary forces exerted by the liquid phase are carried out by using the equilibrium equation for a linear elastic material. Thermodynamic and kinetic calculations are performed to predict the phase diagram and the diffusion distances respectively. The test materials used for the experimental studies are three different powder mixes; Fe-2%Cu, Fe-2%Cu-0.5%C, and Fe-2%(Cu-2%Ni-1.5%Si)-0.5%C. Light optical microscopy, energy dispersive X-ray spectroscopy and dilatometry are used to study the microstructure, kinetics of the liquid phase penetration, solid-state diffusion of the Cu, and the dimensional changes during sintering. The wetting simulations are verified by matching the spreading experiments of millimeter-sized metal drops and it is observed that wetting kinetics is much faster for a micrometer-sized drop compared to the millimeter-sized drop. The simulations predicted the liquid phase penetration kinetics and the motion of solid particles during the primary rearrangement stage of liquid phase sintering in agreement with the analytical model. Microscopy revealed that the C addition delayed the penetration of the Cu rich liquid phase into interparticle/grain boundaries of Fe particles, especially into the grain boundaries of large Fe particles, and consequently the Cu diffusion in Fe is also delayed. We propose that the relatively lower magnitude of the sudden volumetric expansion in the master alloy system could be due to the continuous melting of liquid forming master alloy particles.QC 20140515
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Nabeel, Muhammad. "Diffusion of Elemental Additives during Sintering." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-100702.
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The mechanical properties of components made by PM steels are normally inferior to those made by alternative processes. One of the main reasons is that a large amount of pores are present in sintered components. The other main reason is that the alloying elements, particularly Ni, are not uniformly distributed after conventional sintering procedures. This work is aimed at a better understanding of the influence of alloying additions on mechanical properties and homogeneity of the microstructure. The experimental work has been carried out in two trials. Trial 1 was performed to investigate mechanical properties of Distaloy powders (commercial grades) and second trial to examine influence of alloying additions on homogeneity of microstructure. For trial 1, as-sintered and heat treated specimens were produced by mixing commercial powders with two different carbon levels. Whereas, alloying elements were admixed to base iron powder for producing sintered specimens for trial 2. Mechanical properties including dimensional changes, micro-hardness, tensile strength and impact resistance were measured. Distribution of alloying elements was studied using LOM and SEM-EDS analysis. The results obtained show that additions of alloying elements enhance the mechanical properties. Moreover, interaction of C with Cu and Ni as well as interaction between Cu and Ni have a deceive role in determining final properties of the components. The metallographic investigation indicated that major reasons of heterogeneous microstructure are slow diffusion of Ni in Fe matrix and interaction of other alloying elements with Ni. The results of trial 2 showed that addition of Mo and Cu to Ni-containing PM steels improves the distribution of Ni in Fe matrix. Mo results in improved uniformity of microstructure by lowering the chemical potential of carbon. In Ni and Cu containing alloys, the interaction between Ni and Cu is responsible for enhanced distribution of Ni. However, the improved Ni distribution is achieved at the expense of non-uniform distribution of Cu. In Ni-containing PM steels, improved microstructure homogenization can be attained by increasing Ni-Cu interaction, lowering the surface energy of Ni-Cu liquid and decreasing the chemical potential of carbon.
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Albiston, John Nigel. "The activated sintering of silver-tungsten compacts, produced via the reduction of silver tungstate." Thesis, University of Manchester, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329591.
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McWilliams, Brandon A. Zavaliangos Antonios. "Numerical simulation of electric field assisted sintering /." Philadelphia, Pa. : Drexel University, 2008. http://hdl.handle.net/1860/2763.
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Pines, Michael Louis. "Pressureless sintering of powder processed functionally graded metal-ceramic plates." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1999.
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Thesis (M.S.) -- University of Maryland, College Park, 2004.Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Best, Serena M. "Characterisation, sintering and mechanical behaviour of hydroxyapatite ceramics." Thesis, Queen Mary, University of London, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321276.
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Gateaud, Arnaud. "Physical and chemical mechanisms of lubricant removal during stage I of the sintering process." Link to electronic thesis, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-040606-161143/.
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Hall, Bradley Devin. "Powder processing, powder characterization, and mechanical properties of LAST (lead-antimony-silver-tellurium) and LASTT (lead-antimony-silver-tellurium-tin) thermoelectric materials." Diss., Connect to online resource - MSU authorized users, 2008.
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Thesis (M.S.)--Michigan State University. Materials Science and Engineering, 2008.Title from PDF t.p. (viewed on Aug. 7, 2009) Includes bibliographical references (p. 151-159). Also issued in print.
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Kim, Hyungchan. "Low temperature sintering of nanosized ceramic powder YSZ-bismuth oxide system /." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1092765117.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xxvi, 249 p.; also includes graphics (some col.). Includes bibliographical references (p. 241-249).
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Alhambra, Edgar M. "A preliminary attempt at sintering an ultrafine alumina powder using microwaves." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA284978.
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Ip, Samuel Chun Hung. "Study of radiative heat transfer in porous media for sintering applications /." View Abstract or Full-Text, 2002. http://library.ust.hk/cgi/db/thesis.pl?MECH%202002%20IP.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002.Includes bibliographical references (leaves 82-85). Also available in electronic version. Access restricted to campus users.
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Wildan, Muhammad W. "Zirconia-matrix composites reinforced with metal." Thesis, University of Strathclyde, 2000. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21428.
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The aim of this study was to investigate a zirconia-matrix reinforced with metal powder (chromium, iron and stainless steel (AISI 316)) including processing, characterisation, and measurements of their properties (mechanical, thermal and electrical). Zirconia stabilised with 5.4 wt% Y₂0₃ (3 mol%) as the matrix was first studied and followed by an investigation of the effects of metal reinforcement on zirconia-matrix composites. Monolithic zirconia was pressureless sintered in air and argon to observe the effect of sintering atmosphere, while the composites were pressureless sintered in argon to avoid oxidation. Sintering was carried out at various temperatures for 1 hour and 1450°C was chosen to get almost fully dense samples. The density of the fired samples was measured using a mercury balance method and the densification behaviour was analysed using TMA (Thermo-mechanical Analysis). The TMA was also used to measure the coefficient of thermal expansion. In addition, thermal analysis using DTA and TGA was performed to observe reactions and phase transformations. Moreover, optical microscopy and SEM were used to observe the microstructures, XRD was used for phase identification, and mechanical properties including Vickers hardness, fracture toughness and bending strength were measured. The effect of thermal expansion mismatch on thermal stresses was also analysed and discussed. Finally, thermal diffusivity at room temperature and as a function of temperature was measured using a laser flash method, and to complete the study, electrical conductivity at room temperature was also measured. The investigation of monolithic zirconia showed that there was no significant effect of air and argon atmosphere during sintering on density, densification behaviour, microstructures, and properties (mechanical and thermal). Furthermore, the results were in good agreement with that reported by previous researchers. However, the presence of metal in the composites influenced the sintering behaviour and the densification process depends on the metal stability, reactivity, impurity, particle size, and volume fraction. Iron reacted with yttria (zirconia stabiliser), melted and reduced the densification temperature of monolithic zirconia, while chromium and AISI 316 did not significantly affect the densification temperature and did not react with either zirconia or yttria. AISI 316 melted during fabrication. Moreover, all of the metal reinforcements reduced the final shrinkage of monolithic zirconia. In terms of properties, the composites showed an increase in fracture toughness, and a reduction in Vickers hardness and strength with increasing reinforcement content. In addition, the thermal diffusivity of the composites showed an increase with reinforcement content for the zirconia/chromium and zirconia/iron composites, but not for the zirconia/AISI 316 composites due to intrinsic mircocracking. Furthermore, all the composites became electrically conductive with 20 vol% or more of reinforcement. It has been concluded that of those composites the zirconia/chromium system may be considered as having the best combination of properties and although further development is needed for such composites to be used in real applications in structural engineering, the materials may be developed based on these findings. In addition, these findings may be used in development of ceramic/metal joining as composite interlayers are frequently used.
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Bai, Guofeng. "Low-Temperature Sintering of Nanoscale Silver Paste for Semiconductor Device Interconnection." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29409.
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This research has developed a lead-free semiconductor device interconnect technology by studying the processing-microstructure-property relationships of low-temperature sintering of nanoscale silver pastes.
The nanoscale silver pastes have been formulated by adding organic components (dispersant, binder and thinner) into nano-silver particles. The selected organic components have the nano-particle polymeric stabilization, paste processing quality adjustment, and non-densifying diffusion retarding functions and thus help the pastes sinter to ~80% bulk density at temperatures no more than 300°C. It has been found that the low-temperature sintered silver has better electrical, thermal and overall thermomechanical properties compared with the existing semiconductor device interconnecting materials such as solder alloys and conductive epoxies. After solving the organic burnout problems associated with the covered sintering, a lead-free semiconductor device interconnect technology has been designed to be compatible with the existing surface-mounting techniques with potentially low-cost. It has been found that the low-temperature sintered silver joints have high electrical, thermal, and mechanical performance. The reliability of the silver joints has also been studied by the 50-250°C thermal cycling experiment. Finally, the bonging strength drop of the silver joints has been suggested to be ductile fracture in the silver joints as micro-voids nucleated at microscale grain boundaries during the temperature cycling.
The low-temperature silver sintering technology has enabled some benchmark packaging concepts and substantial advantages in future applications.Ph. D.
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Erdem, Derya. "Microwave Sintering And Characterization Of Soft Magnetic Powder Metallurgical Ni-fe Alloys." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613550/index.pdf.
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In this study, prealloyed austenitic stainless steel and premixed soft magnetic Ni-Fe permalloy compacts were consolidated through microwave and conventional sintering routes at combinations of various sintering temperatures and compaction pressures. Sintered alloys were characterized in terms of their densification, microstructural evolution as well as mechanical and magnetic properties. The effect of sintering method in terms of the applied sintering parameters on the final properties of the compacts were investigated in a comparative manner. It was determined that microwave sintered permalloys are superior compared to their conventionally sintered counterparts in densification response, microstructural characteristics such as pore shape and distribution as well as mechanical properties for both austenitic stainless steel and permalloy compacts. However, permeability of the microwave sintered permalloys was inferior to their conventionally sintered counterparts in some cases due to microstructural refinement associated with microwave sintering route.
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Steward, Nigel Ian. "Influence of particle size distribution on the sintering of ceramic powder compacts." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47674.
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Halilovic, Selma. "Evaluation of new powder grade for furnace control pieces in sintering process." Thesis, Uppsala universitet, Tillämpad materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-448371.
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To be able to supervise the quality of a sintering process, furnace control pieces are therefore used. The current furnace control piece is not sensitive enough small variations during insert production. The goal of the project was to find and evaluate a new suitable cemented carbide grade, which better captures temperature variations during sintering process, likewise, evaluate the alternative placing in the production furnace and methods to supervise and follow the status of the sintering process. The cemented carbide grade 592, which is a DQ-grade, captured larger temperature variations during the sintering compared to the current furnace control piece. The process charge for 592 that captured the largest variations also had the highest charge weight, which indicates that the new grade is also sensitive to the charge weight. The purpose of the project was fulfilled when a more suitable cemented carbide grade, 592, was evaluated for both sintering temperatures 1410 ℃ and 1450 ℃.
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Liu, Xin. "Numerical modeling and simulation of selective laser sintering in polymer powder bed." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI012/document.
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La fabrication additive est l’un des secteurs industriels les plus en développent ces dernières années. L’une de ces technologies de fabrication les plus prometteuses est la fusion laser sélective (SLS), et relève d’un intérêt croissant aussi bien industriel qu’académique. Néanmoins, beaucoup de phénomène mis en jeu par ce procédé demeure non encore bien compris, entravant ainsi son développement pour la production de pièces de bonne qualité pour des applications industrielles. L’objectif de cette thèse est de développer un cadre de simulation numérique permettant la simulation du procédé SLS pour des poudres de polymère afin de comprendre les multiples et complexes phénomènes physiques qui se produise lors du frittage laser et d’étudier l’influence des paramètres du procédé sur la qualité du produit final. Contrairement aux approches classiques de modélisation numérique, basées sur la définition de matériaux homogène équivalents pour la résolution des équations de bilan, nous proposons une simulation globale du procédé du frittage laser de poudres, en utilisant la méthode des Eléments Discrets (DEM). Cela consiste en un couplage entre quatre sous-modèles : transferts radiatif dans le milieu granulaire semi-transparent, conduction thermique dans les milieux discrets, coalescence puis densification. Le modèle de transferts par rayonnement concerne l’interaction du faisceau laser avec le lit de poudre. Plusieurs phénomènes sont ainsi pris en compte, notamment la réflexion, la transmission, l’absorption et la réfraction. De plus, une méthode de Monte-Carlo couplée à la méthode du Lancer de rayons est développée afin d’étudier l’influence de la réfraction sur la distribution de l’énergie du laser dans le lit de poudre. Le modèle de conduction dans des milieux discrets décrit la diffusion thermique inter-particules. Finalement, le modèle de frittage décrit les cinétiques de coalescence et de diffusion de l’air dans le polymère et densification du milieu. Cela permet de décrire les cinétiques de fusion des grains, dont l’énergie de surface et la diffusons de l’air sont les deux moteurs principaux. Le couplage entre les différents modèles nous a permis de proposer un modèle numérique global, validé grâce à des comparaisons à des résultats de simulations théoriques et expérimentales, trouvés dans la littérature. Une analyse paramétrique est alors proposée pour la validation du modèle et l’étude du procédé. L’influence de différents paramètres aussi bien du procédé que du matériau sur le champ de température, la densité relative du matériau sa structure, etc , est ainsi investiguée. Les résultats montrent une bonne précision dans la modélisation des différents phénomènes complexes inhérents à ce procédé, et ce travail constitue un potentiel réel pour la modélisation et l’optimisation des procédés de fabrication additive par matériaux granulairesMany industrial and academic interests concerning the additive manufacturing processes are developed in the last decades. As one of the most promising technique of additive manufacturing, the Selective Laser Sintering (SLS) has been valued by both industry and academic. However, it remains that several phenomena are still not well understood in order to properly model the process and propose quality improvement of parts made. The goal of this Ph.D. project is to develop a framework of numerical simulation in order to model the SLS process in polymer powder bed, meanwhile understanding multiple physical phenomena occurring during the process and studying the influence of process parameters on the quality of final product. In contrast to traditional approach, based on the equivalent homogeneous material in numerical modeling of partial differential equations derived from conservation laws, we propose a global model to simulate powder-based additive manufacturing by using the Discrete Element method (DEM). It consists in a coupling between four different physical models: radiative heat transfer, discrete heat conduction, sintering and granular dynamics models. Firstly, the submodel of radiative heat transfer concerns the interaction between the laser beam and powder bed. Several phenomena are considered, including the reflection, transmission, absorption and scattering. Besides, a modified Monte Carlo ray-tracing method is developed in order to study the influence of scattering on the distribution of the deposited laser energy inside the powder bed Furthermore, the submodel of discrete heat conduction describes the inter-particles heat diffusion. Moreover, the sintering submodel concerns the phenomena of coalescence and air diffusion. It describes the melting kinetics of grains, driven by surface tension and the release of entrapped gases inside powder bed. Finally, the granular dynamics submodel concerns the motions and contacts between particles when depositing a new layer of powders. The coupling between these submodels leads to propose a global numerical framework, validated by comparing the results to both simulated and experimental ones from literatures. A parametric study is then proposed for model validation and process analysis. The Influence of different material and process parameters on the evolution of temperature, relative density and materials structure and characteristics are investigated. The results exhibit accurate modeling of the complex phenomena occurring during the SLS process, and the work constitute a great potential in modeling and optimization of additive processes
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Talamantes-Silva, Jose. "Liquid phase sintering of austenitic stainless steel 316L powder using tin and nickel." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287168.
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Hiser, Matthew A. "Powder Processing and Characterization of W-3Ni-1Fe Tungsten Heavy Alloy." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/42512.
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Mechanical alloying, compaction by cold isostatic pressing, and pressureless sintering were used to study the potential for W â 3 wt% Ni â 1 wt% Fe to be processed into the bulk nanocrystalline form as a replacement material for depleted uranium in kinetic energy penetrators. Milling time and sintering temperature were varied from 15 to 100 hours and 1000 to 1300°C respectively. Particle size analysis and SEM showed a bimodal particle size distribution with most of the particles below 10 µm in size. XRD peak broadening analysis showed crystallite size to be reduced to below 50 nm, while peak shifting indicated a reduction in W lattice parameter due to dissolution of Ni and Fe atoms into the W BCC lattice.
Post-sintering bulk characterization showed density increasing strongly with increasing sintering temperature to above 90% of theoretical density at 1200°C. Apparent activation energy for sintering decreased strongly with increasing milling time. SEM micrographs showed a bimodal grain size distribution with some areas of smaller submicron grains and others with larger grains on the order of 1 â 4 µm, likely connected to the bimodal particle size distribution from milling. XRD and SEM also showed the precipitation of two secondary phases during sintering: (Fe, Ni)6W6C incorporating carbon from the grinding media and an FCC solid solution of Ni, Fe, and W. The intermetallic carbide phase will increase strength but reduce ductility of the bulk material, which is not desirable. Micro and macrohardness testing show similar trends as density with a strong correlation with sintering temperature.Master of Science
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Bergman, Ola. "Studies of oxide reduction and nitrogen uptake in sintering of chromium-alloyed steel powder." Licentiate thesis, KTH, Materials Science and Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9555.
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The powder metallurgy (PM) process route is very competitive for mass production of structural steel components with complex shape, due to efficient material utilisation, low energy consumption, and short overall production time. The most commonly used alloying elements are the processing friendly metals Cu, Ni and Mo. However, the prices for these metals are today high and volatile, which threatens to make the PM process less competitive compared to conventional metal forming processes. Consequently, there is a strong desire in the PM industry to increase the use of less costly alloying elements. Cr is an attractive alternative since it, besides low cost, provides high hardenability and also recyclable components. The drawback is that Cr has high affinity for oxygen, which makes oxidation and oxide reduction in PM processing of Cr-alloyed materials a challenging issue. Furthermore, the interaction between nitrogen and Cr-alloyed powder during processing is important to consider, since Cr also has high nitrogen affinity and is prone to form nitrides.
The aim of the research work presented in this thesis was to study oxide reduction and nitrogen uptake in sintering of Cr-alloyed steel powder. Water-atomized powder grades pre-alloyed with 1.5-3% Cr were used as test materials. Sintering experiments were performed in N2/H2 (90/10) atmospheres with test bars pressed to density 7.0-7.2 g/cm3. The oxygen content of the sintering atmosphere was varied and different sintering temperatures and cooling rates were applied. The experimental study has been complemented with thermodynamic calculations using the software Thermo-Calc.
The oxygen partial pressure should be below 4 x 10-18 atm in order to have reducing conditions during sintering at 1120°C of steel powder pre-alloyed with 3% Cr. With graphite added to the powder, conditions are reducing at higher oxygen partial pressures (up to 10-16 atm) due to favourable conditions locally in the material. Sintering at 1120°C for 30 minutes leads to incomplete reduction of Cr-oxides in the Cr-alloyed PM grades, but remaining oxides are not detrimental for mechanical properties of the PM components. Increased sintering temperature is beneficial for the oxide reduction kinetics and practically all oxides are reduced after sintering for 30 minutes above 1200°C. Nitrogen uptake by Cr-alloyed steel powder from N2-based sintering atmospheres is strongly dependent on the cooling rate applied after sintering. No nitrides appear in the sintered material and mechanical properties are not affected when normal cooling rates (0.5-1°C/s) are applied. Very low cooling rates (such as 0.05°C/s) may lead to grain boundary precipitation of Cr-nitrides in the sintered material.
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Deceuster, Andrew Isaac. "Investigation of Joining Micro-Foil Materials with Selective Laser Sintering and Laser Powder Deposition." DigitalCommons@USU, 2009. https://digitalcommons.usu.edu/etd/434.
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Continuous and pulse selective laser sintering and laser powder deposition were used to find a solution to the manufacturing of micro-foil lattice structured components. A full factorial test matrix was used for each process to determine the processes capability to produce continuous tracks for joining the micro-foil materials. The samples were evaluated for dimensional profiles, distortion, and cycle times, to develop selection criteria for implementation of the processes into industry. The selective laser sintering processes were able to join the micro-foil materials into lattice structures with continuous tracks. The laser powder deposition processes were not able to properly join the micro-foil materials into lattice structures. The end results showed that micro-foil lattice structures can be produced using continuous and pulse selective laser sintering.
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Schultz, Jeffrey Patrick. "Modeling Heat Transfer and Densification during Laser Sintering of Viscoelastic Polymers." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/11091.
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Laser sintering (LS) is an additive manufacturing process which uses laser surface heating to induce consolidation of powdered materials. This work investigates some of the process-structure-property relationships for LS of viscoelastic polymers. A one-dimensional closed-form analytical solution for heating of a semi-infinite body, with a convective boundary condition, by a moving surface heat flux was developed. This solution approximates the shape of the Gaussian energy distribution of the laser beam more accurately than previous solutions in the literature. A sintering model that combines the effects of viscoelastic deformation driven by attractive surface forces and viscous flow driven by curvature-based forces was developed. The powder-bed temperature was approximated using the thermal model developed herein. The effect of the enthalpy of melting for semi-crystalline polymers was accounted for using a temperature recovery approach. Time-temperature superposition was used to account for the temperature dependence of the tensile creep compliance. The results of the combined-mechanism sintering model will be compared to the classic Mackenzie-Shuttleworth sintering model. A lab-scale LS unit was constructed to fabricate test specimens for model validation and to test the applicability of materials to LS. In this work, sintering four materials, polycarbonate (PC) and three molecular weights of polyethylene-oxide (PEO) was predicted using the aforementioned thermal and sintering models. Samples were fabricated using the lab-scale LS unit and the sintered microstructures were investigated using scanning electron microscopy. The rheologic, thermal and physical properties of the materials were characterized using standard methods and the relevant properties were used in the models. The choice of an amorphous polymer, PC, and a semi-crystalline polymer, PEO, affords comparison of the effects of the two material forms on contact growth during LS. The three molecular weights of PEO exhibit significantly different tensile creep compliances, however, the thermal and physical properties are essentially the same, and therefore the effect of molecular weight and subsequently the rheologic characteristics on contact growth during LS will be investigated. The effects of particle size, laser power, and bed temperature were also investigated.Ph. D.
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Saha, Deepak. "De-lubrication during sintering of P/M compacts : operative mechanism and process control strategy." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-10014-233109.
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Li, Tao. "Reaction-bonding of Crâ†2Oâ†3 ceramics." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318804.
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Youseffi, M. "Some aspects of the injection moulding of alumina and other engineering ceramics." Thesis, Loughborough University, 1992. https://dspace.lboro.ac.uk/2134/7227.
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The literature concerning the injection moulding of engineering ceramics has been reviewed. This indicated that a number of claims had been made for the successful use of different organic binders during moulding and their removal prior to sintering. However, many of the claims were not supported by detailed/exact eScperimental evidence as to powder-binder compositions, moulding conditions, moulded properties, debinding times/cycles, or details of the structure and properties of the solid ceramic bodies produced. From the available information it was clear that there were few systematic and scientific investigations concerning the understanding of each stage of the injection moulding process. The present research programme has been carried out in two phases as follows. The first phase was concerned with the reinvestigation and re-evaluation of binder systems claimed to be successful for the injection moulding of alumina ceramics. The binders re-investigated included the thermoplastic-based binders such as polystyrene, polyacetal and atactic polypropylene and the water-based methylcellulose (Rivers) binder system. Alumina was chosen as the main powder to be investigated due to its simple handling and, highest applications amongst ceramic materials and on the basis that there is incomplete published work for almost every step of the injection moulding process. During the first stage of this work the optimum properties such as powder-binder compositions, mixing and moulding conditions, debinding properties, green and sintered densities provided by each binder system were determined. The results of these investigations showed that all the previous (re-evaluated) binder systems had major limitations and disadvantages. These included low volume loading (64 % maximum) of the alumina powder resulting in rather low sintered densities (96 % maximum-of theoretical density) and very long debinding times in the case of the thermoplastic-based binders. it ry low alumina volume loading (55 % maximum resulting in a 94 % . sintered theoretical density) and long moulding cycle time (- 5 min) along with adhesion and distortion problems during demoulding occurred in the case of the water-based methylcellulose binder system. Further work did not appear worthwhile. The newly developed binder systems have been used with a number of other powders such as zirconia, silicon nitride, silicon carbide, tungsten carbide-6 weight % cobalt and iron-2 weight % nickel, to establish- whether injection moulding is feasible. Optimum properties such as powder volume loadings, mixing, moulding, demoulding, moulded densities, debinding and some sintered density results showed that these new binder systems can also be used successfully for the injection moulding of other ceramic and metallic powders, although a fuller evaluation of the properties such as optimum sintered densities and mechanical properties is required.
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Demir, Vedat. "Development and application of vacuum heat-treated silicon nitride ceramics." Thesis, University of Newcastle Upon Tyne, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310039.
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Saha, Deepak. "De-lubrication during sintering of P/M compacts: Operative mechanism and process control strategy." Digital WPI, 2004. https://digitalcommons.wpi.edu/etd-theses/1049.
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"De-lubrication is the first stage in a sintering operation, where the lubricants (higher weight hydrocarbons) are removed from the parts by controlled heating. Improper de-lubrication leads to defects such as blistering, sooting, micro-porosity etc in a sintered part. Most of these problems arise, as there exists a gap in the present understanding of de-lubrication. The primary motive of this work is to direct research towards the development of sensors and controls and thus, mitigate the various problems due to improper de-lubrication. Currently, there exists a myriad of lubricants being used during the process of compaction. They include metallic based lubricants, polymers and non-metallic lubricants. In this work, research was limited in understanding the de-lubrication of EBS (Ethylene Bisstearimide), as, it the most commonly used lubricant in the industry. It has replaced commonly used lubricant due to cleaner burnouts, absence of metallic residue and, cost effectiveness. The entire work is divided into three phases: • Phase 1: Ascertained the most important parameters that affect the kinetics of de-lubrication. • Phase 2: Investigated the type of gases released during the decomposition of EBS. • Phase 3: Recommended a control strategy. TGA (Thermo-gravimetric analysis) was used in the phase I, the results clearly show that the rate of heating is the most important parameter during de-lubrication. Identification of gases was performed using the FTIR (Fourier transform infrared spectroscopy) and DUV (Deep ultraviolet spectroscopy). This constituted the second phase of our experiments. The primary gases identified in Phase II were carbon dioxide and a hydrocarbon (hepta-decane). Finally, an empirical model for de-lubrication has been proposed in Phase III. The model was verified in an industrial furnace. It has been observed that there exists a very good correlation between the proposed empirical model and the experiments performed in Phase II of this study. This study lays down the following guidelines for the development of future sensors and controls: • The development of future sensors should focus in the detection of CO2 and hepta-decane. • Rate of heating determines how fast or slow the lubricant decomposes and finally escapes form the compacted part. • The empirical model may be used, as a means to determine the time a part should reside in a furnace for complete lubricant burnout at a given heating rate."
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Pozzi, Francesco. "Direct metal laser sintering of steel with high vanadium content." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13548/.
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La definizione di "rapid prototyping" è ben nota. Ci si riferisce a quell'insieme di tecnologie utilizzate per la realizzazione di oggetti partendo da modelli geometrici molto complicati, realizzando protitipi direttamente dal disegno CAD 3D. Le tecnologie RP sono state poi sviluppate per l'industria artigianale, nell'obiettivo di accelerare la produzione senza perdita di precisione nella costruzione. Tra queste tecniche sono sorte quelle di selective laser sintering.
La sinterizzazione è il processo termico e meccanico per produrre materiali compattando sostanze in polvere, sotto una certa pressione o temperatura; più precisamente, nella sinterizzazione laser le polveri sono riscaldate per un tempo brevissimo.
La fisica che descrive questo processo è piuttosto articolata, dato che la descrizione parte dall'assorbimento di radiazione laser e che comprenderà conduzione termica nella polvere, trasformazione di fase di un materiale eterogeneo, formazione di fase solida con diversi meccanismi di condensazione e lo sviluppo delle diverse microstrutture dell'acciaio.
Il lavoro sperimentale che è stato svolto è la produzione di una polvere di acciaio e vanadio utilizzabile in solid state sintering, ma dato quanto detto, lo studio ha incluso una descrizione più generale del processo della sinterizzazione metallica da polveri.
Nel corso del lavoro si è contribuito alla messa a punto della stampante 3D per sinterizzazione di polveri metalliche realizzata alla 3d4mec, soffermandosi nella ricerca dei parametri ottimali per la stampa di polvere StainlessSteel CX by EOS.
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Youssef, Toni. "Modélisation multiphysique d'un assemblage de puissance haute température destiné à l'environnement aéronautique." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0167/document.
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Le principal défi auquel sont confrontés aujourd'hui les équipementiers aéronautiques est d'augmenter l'utilisation des systèmes électriques à bord de l'avion. De nos jours, le remplacement des systèmes hydrauliques par des actionneurs électriques conduit à placer les systèmes électriques dans un environnement hostile, par exemple dans la nacelle du moteur. L'équipement est soumis à des contraintes sévères telles que des températures élevées et basses, un cycle thermique étendu, une humidité élevée et une basse pression. En conséquence, des efforts doivent être faits pour réduire le poids et le volume du convertisseur de puissance sans perdre ses performances. Pour atteindre cet objectif, la conception de modules de puissance doit permettre un haut niveau d'intégration, d'efficacité et de fiabilité. On s’intéresse en particulier aux dommages causés par la fatigue qui ont une influence significative sur les performances électriques de ces modules. Les tests de performance liés à la fatigue restent des efforts coûteux pour l'équipement aéronautique. Un nombre fini de tests destructifs, par vieillissement accéléré, peut être effectué pour un nombre assez faible de configurations. Le but de ces tests est d'étudier les modes de défaillance apparaissant lors du vieillissement accéléré. Par conséquent, des simulations numériques ont été envisagées, facilement évolutives et utilisables pour un grand nombre de configurations, mais nécessitant des données d'essais expérimentaux. Dans ce manuscrit, quelques modes de défaillances sont étudiés. On propose une méthode numérique intégrant les contraintes principales dans les équipements, à savoir la simulation électrique, thermique et mécanique. Ces trois problèmes physiques ont des temps caractéristiques différents et sont fortement couplés avec un comportement non trivial. Pour optimiser l'utilisation des ressources et avoir une représentation pertinente du problème, un procédé couplé électrique 1D / thermique 3D / mécanique 3D a été implémenté sur un bus de cosimulation. Différents pas de temps, différents niveaux d'abstraction et différentes compétences sont utilisés pour fournir un modèle multiphysique de modules de puissanceToday’s main challenge for aeronautical equipment manufacturers is to respond to the more electrical aircraft regulations. Moreover, there are many applications in aircraft area where high temperature technologies are needed. Nowadays, the replacement of hydraulic systems for electric ones leads to place the power inverters in a harsh environment, for example in the engine nacelle. The equipment is under high constraints such as high and low temperatures, wide temperature cycling, high humidity and low pressure. Combined to these environmental constraints, the new aircraft system is submitted to weight and operating cost reduction. As a consequence, efforts shall be done to reduce weight and volume of the power converter without losing its performance. To reach such a goal, the design of the converter must enable a high level of integration, efficiency and reliability. In particular, fatigue damage has a significant influence on such modules electrical power performance. And fatigue-related performance testing remains a costly endeavor for aeronautical equipment. A finite number of destructive tests can be carried out in specific facilities for a fairly low number of configurations. The purpose of these destructive tests is to investigate the failure modes appearing regarding this accelerated ageing. Therefore numerical simulations have been envisaged since non-destructive, easily evolving and usable for a high number of configurations, though needing data from experimental assays. In this study, we propose a method dealing with the main constraints for such equipment, i.e. electrical, thermal and mechanical simulation. Those three physical problems have different characteristic time and are strongly coupled with a non-trivial behavior. To optimize the resources usage and have a relevant representation of the problem, a 1D electrical / 3D thermal / 3D mechanical coupled method has been implemented over a co-simulation bus. Different time steps, different abstraction levels and different skills are used to provide predictions of the multiphysical fatigue behavior of power modules
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Caliskan, Necmettin Kaan. "Powder Metallurgy Of W-ni-cu Alloys." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12607576/index.pdf.
Full textAbstract:
In the present studythe effects of the powder metallurgical parameters such as the mixing method, compaction pressure, initial tungsten (W) particle size, composition, sintering temperature and sintering time on the sintering behavior of selected high density W-Ni-Cu alloys were investigated. The alloys were produced through conventional powder metallurgy route of mixing, cold compaction and sintering. The total solute (Ni-Cu) content in the produced alloys was kept constant at 10 wt%, while the copper concentration of the solutes was varied from 2.5 wt% to 10 wt%. Mainly liquid phase sintering method was applied in the production of the alloys. The results of the study were based on the density measurements, microstructural characterizations including optical and scanning electron microscopy and mechanical characterizations including hardness measurements. The results showed that the nature of the mixing method applied in the preparation of the powder mixtures has a considerable effect on the final sintered state of W-Ni-Cu alloys. Within the experimental limits of the study, the compaction v pressure and initial W particle size did not seem to affect the densification behavior. It was found that the sintering behavior of W-Ni-Cu alloys investigated in this study was essentially dominated by the Ni content in the alloy and the sintering temperature. A high degree of densification was observed in these alloys with an increase in the Ni content and sintering temperature which was suggested to be due to an increase in the solubility and diffusivity of W in the binder matrix phase with an increase in these parameters, leading to an increase in the overall sintering kinetics. Based on the results obtained in the present study, a model explaining the kinetics of the diffusional processes governing the densification and coarsening behavior of W-Ni-Cu alloys was proposed.
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陳冠宇. "Sintering of Microcrystalline Silver Powder and Its Application in Hydrogen Separation Membrane." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/63240298168362903253.
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碩士國立清華大學
材料科學工程學系
88
Permeation of hydrogen in transition metals is an important catalytic reaction. The preparation and properties of hydrogen permeable membranes have been studied in energy technologies for many years. The palladium-silver alloy membrane has been extensively studied in recent years due to the absence of α→βphase transition and embrittlement associated with hydrogen permeation. In addition to the application for ultra high purity hydrogen separation, it is also widely utilized in recovery or purification of hydrogen in petroleum industry, hydrogen reactor in fuel cells, and methane stream reforming. In the present work, microcrystalline silver powder was used as the substrate material. Porous silver substrate was obtained after sintering at 350oC in air for 1hr. Prior to deposition, the surface was filled with nanocrystalline Pd70Ag30 particles to reduce the pore size, followed by deposition with a Pd70Ag30 alloy film. The palladium-silver alloy film was sputter deposited on the substrate as a separation membrane. The surface and cross-section morphologies of the sintered silver substrates were examined by scanning electron microscopy. Besides, the permeation rate of hydrogen at 250oC was measured by a gas permeation apparatus. A new rotation design was also built for sputter coating on tube substrates. It was observed that a dense and continuous film of a thickness 10μm could be achieved on the modified substrate. The hydrogen permeation flux through the membrane increases monotonically with the pressure but deviates from the Sievert’s law. A rotation design was made and a copper tube was tested. The uniformity of thickness was fairly good.
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Wu, Wei, and 吳惟. "The Effet of the Silver-Palladium Powder Characteristics on Sintering Property of its Thick Film." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/87315701858371380380.
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Trung, Le Manh, and 黎孟忠. "Optimization Sintering on Fiber Laser Sintering of Metallic Powder." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/15072777316117271182.
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碩士明新科技大學
精密機電工程研究所
99
Nowadays, increasing competition requires companies to substantially reduce product development time and rapidly respond to market demands. Rapid prototyping technologies have attracted significant interests from both industry and academia. However, problems in model accuracy \ product quality and material properties have limited their applications. In order to apply these technologies to a wide range of industrial and medical applications, the manufacturing processes of rapid prototyping must be improved. Selective laser sintering (SLS) is one among many different rapid prototyping processes where the parts are built in a layer by layer fashion. Recently, SLS has gained importance due to its ability to process a wide variety of materials. SLS can produce functional prototypes and rapid tooling components, which necessitates the production of high-quality parts. The majority of its applications are in aerospace and rapid tooling, where high accuracy levels have to be met in order to ensure proper functional requirement. Due to this new constraint imposed on SLS in terms of part quality, there is a need to study the process in detail and to improve part accuracies. The objective of this thesis is to investigate the effect of various parameters on rapid prototyping parts for processes of sintering metallic powder using Ytterbium Fiber Optic Laser via the design of experiments (DOE) method. Experiments based on the DOE method were utilized to determine the optimal parameter setting for achieving a minimum amount of porosities in specimens on the SLS process. Analysis of variance (ANOVA) was further conducted to identify significant factors. A regression model predicting percentages of porosities under various conditions was developed when the traditional Taguchi’s approach failed to identify a feasible model due to strong interactions of controlled factors. The significant factors to the process were identified by ANOVA. Four controlled factors including laser power, speed (scan rate), pulse frequencies and scan line spacing (air gap) had significant influence on the sintering process. Future investigation planned to be carried out for achieving multiple quality targets such as the hardness and the density for 3D parts.
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Liu, Su Hao, and 劉書豪. "Constrained sintering of silver paste." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/98998346123891965994.
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Lin, Jiou-Wei, and 林久瑋. "3D metal powder printing sintering parameter studies." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/vbf7f7.
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碩士國立虎尾科技大學
機械與電腦輔助工程系碩士班
105
In the current industry, integrated manufacturing is highly competitive. As 3D printing continue to develop, the techniques and output value are also expending. In the present domestic market, 3D printing with PLA or ABS filament wires are the most common materials. Due to the low-cost and easy operation, the machine is often purchased by schools as a teaching tool. As for the metal 3D printing, it needs to insert protective gas in a closed off space, through laser sintering and stack-build to create an object with metal powder, although such techniques can produce complex parts, very few technical developments are found in the domestic market due to the high cost. The purpose of this study is to focus on the research of 3D metal powder sintering techniques and process. Through laser sintering experiments with different metal powder mixtures to confirm possible powder sintering, then use different laser power, scanning speeds, frequencies and path spacing parameters to conduct powder sintering experiments under different experimental conditions. By using optical microscope and Vickers Hardness tester to verify sintering products and using Taguchi method to find out best parameter combinations. The conclusions of the study are summarized as follow 1.In this study, the powder mixing mechanism was designed and used, the ratio of copper and tin powder for the mixing mechanism was 18: 1 2.If the scanning rate is higher than 30mm/s, the powder indicates insufficient temperature and shows a splash phenomenon which is not conducive to sintering. This will subsequently impact on the porosity and hardness analysis experiments. 3.Through Taguchi analysis, the best combine parameters for pore-space were found. The best pore-space is 4.712%, the laser power is 80%, and the scanning speed is 7mm/s, the frequency is 30k, and the path-space is 0.05mm. 4.Through Taguchi analysis, the best combine parameters for Vickers Hardness were found. The best pore-space is 134.423HV, the laser power is 100%, the scanning speed is 7mm/s, the frequency is 33K, and the path-space is 0.07mm.
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Huang, Guo-Lun, and 黃國倫. "Study on photonic sintering of silver particles." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/86133709735449343460.
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碩士國立中興大學
材料科學與工程學系所
105
By utilizing the drastically reduced sintering temperature of nano-sized particles (NPs), one of the trends in microelectronic packaging is to manufacture highly conductive interconnections at a low processing temperature using metallic nanoparticles. With respect to ligand-protected NPs, the protect shell must be thermally or chemically eliminated, and the NPs need to join together to form continuous conductive networks in order to generate electrical conductance. Considering the increasing demands for interconnects on flexible and stre substrates, this study aims to develop innovative photonic sintering for nano/submicrom Ag nanoparticles on PI substrates using pulsed flash and NIR. Experimental results show that carboxylate-capped Ag NPs with an average diameter of less than 10 nm can be well sintered together and reached an electrical resistivity of 10.2µΩ•cm. If the same NP deposits were exposed with flash light (energy density: 4.7W/cm2) on the deposit side or substrate side for 9 pulses, the electrical resistivities were 11.2µΩ•cm and 8.3µΩ•cm respectively. It was demonstrated that the desorption of carboxylate by photonic means was through the decomposition by the oxidation of CH2 rather than debonding of CO2-. Photonic sintering of NPs by flash pulses might be through melting and resolidifying due to the heat generated from surface plasmon resonance. On the other hand, NIR exposure on NPs brought about a uniformly coarsened sintered structure. Worthy of notice is that submicron-sized Ag particles (SMPs) with an average size of about 250 nm were the first time to be adopted for photonic sintering. Pulsed-flash-sintered SMPs can reached 9.9 •cm, while the electrical resistivity of the optimized mixture of SMPs and NPs subjected to pulsed-flash-sintering can be lowered to 7.32 •cm. Subjected to bending cycles up to 104 times (bending radius of 10 mm, 0.5 Hz), all those sintered structures on PI substrates remained excellent electrical conductance. The increase in electrical resistivity was less than 50%.