"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."

"We focus attention on single-punch compaction of metal powders in cylindrical dies. In one case, we consider solid cylindrical compacts, and take the die walls to be frictionless in order to isolate the effects of initial nonuniformities in powder fill on the final green density distribution of the compact. First, a model is introduced in which the die is filled with n distinct powders that occupy concentric annular regions within the die. The model requires that the balance of mass, the balance of momentum, and a realistic equation of state be satisfied in each region, and includes a plausible constitutive relation that relates the induced radial pressure in each powder region to the corresponding axial pressure and the relative movements of the interfaces that confine the region. For specified powder properties, the model predicts the movements of the interface between the powders, the final density in each region, the pressure maintained in each region, and the total compaction load required. In the special case of two powders (n=2), we predict how the radial movement of the single interface depends on the mismatch between the properties of the two powders. For large values of n, and for powder properties that change gradually from one powder to the next, the model approximates a single powder filled nonuniformly in the die. Finally, a model is developed for a single powder with continuously varying powder properties. Formally, the model may be obtained by taking the limit of the n-powder model as n becomes unbounded. Employing the continuous model, we determine how nonuniformities in initial fill density can be offset by nonuniformities in other powder properties to yield perfectly uniform green densities. In a second case, we consider axisymmetric, hollow, cylindrical compacts, and include the effects of friction at the die wall and the core rod. The ratio of the induced radial pressure to the applied axial pressure is assumed to be constant throughout the compaction, and Coulomb friction acts between the powder and the die wall as well as between the powder and the core rod. We derive a closed form solution for the axial and radial variation of the axial pressure, radial pressure, and shear stress throughout the compact. This solution is combined with a plausible equation of state to predict the final green density distribution and the variation of applied load throughout the compact."

Pressing of metallic powders is a manufacturing process widely investigated in the research field and in the industry. This thesis project is focused on optimizing the pressing process of cemented carbide powder utilized for the production of triangular shaped cutting tool inserts. In particular, the filling of powder into the die cavity was investigated with respect to different pressing parameters. The aim of the project was to obtain a uniform density distribution of the powder into the die cavity, and hence to reduce the variation of the height of the insert obtaining more precise dimension of the latter. The tests were carried out at the Sandvik Coromant production department which is the creator of the project. The optimization of the pressing process was performed according to the Design of experiments theory. The dynamic of the sintering process was also investigated. The results showed a significant improvement in the filling of the die cavity and a significant decrease of the variation of the height of the inserts. The new insert obtained has more precise dimensions and is able to meet the more demanding requirements of the customers. The results achieved are directly applicable to a larger number of products, and indicate the direction to follow for further development of the manufacturing process.

Manufacturing in modern society has taken on a different role than in previous generations. Today’s manufacturing processes involve many different physical phenomenon working in concert to produce the best possible material properties. It is the role of the materials engineer to evaluate, develop, and optimize applications for the successful commercialization of any potential materials. Laser-assisted cold spray (LACS) is a solid state manufacturing process relying on the impact of supersonic particles onto a laser heated surface to create coatings and near net structures. A process such as this that involves thermodynamics, fluid dynamics, heat transfer, diffusion, localized melting, deformation, and recrystallization is the perfect target for developing a data science framework for enabling rapid application development with the purpose of commercializing such a complex technology in a much shorter timescale than was previously possible. A general framework for such an approach will be discussed, followed by the execution of the framework for LACS. Results from the development of such a materials engineering model will be discussed as they relate to the methods used, the effectiveness of the final fitted model, and the application of such a model to solving modern materials engineering challenges.

A dissertation submitted to the faculty of Engineering, University of the Witwatersrand, Johanuesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. / Ferritic stainless steels possess a number of properties which render them superior to austenitic stainless steels in certain applications. The ferritic stainless steels are highly resistant to stress-corrosion cracking and are generally of lower cost. Previous work had shown that the corrosion properties of the ferritic steels were optimised at a chromium content of forty percent. Extensive research had already characterised the mechanical and corrosion behaviour of the Fe"40Cr alloy in the cast and wrought form. This investigation involves the development of the material by powder metallurgy processing. Particular emphasis is placed on a proprietary powder production technique as well as on powder consolidation by Hot Isostatic Pressing. The effect of Ni, Mo, Ru, Nb, Al and Fe additions and well as various techniques of introducing these additions are examined. The unique effect of powder metallurgy manufacture on microstructure and the kinetics of sigma phase formation is highlighted. Corrosion tests in various concentrations of sulphuric acid and an industrial field trial were performed. It was found that combined Ni and Mo contents exceeding four percent resulted in severe embrittlement due to widespread formation of sigma phase during the HIP process. The use of powder metallurgy techniques was also found to enhance the kinetics of sigma phase formation in a particular alley when compared to the as-cast state. Direct additions of Fe powder were successful in inhibiting embrittlement, possibly due to a mechanism of Fe diffusion into Cr-rich regions. This lowered of the Cr content in these regions, thereby reducing the tendency for sigma precipitation. Corrosion tests indicate satisfactory resistance for the Fc-40Cr-2Ni-2Mo alloys in 70 weight percent sulphuric acid at 50°C. Alloys with 0.2 percent Ru additions were found to be especially resistant, due to the role of Ru as a cathodic modifier. The method of mixing and diffusion bonding metallic powders of varying composition was found to be feasible and certain novel combinations of Ni and Fe-rich alloys exhibited satisfactory corrosion resistance. A mathematical diffusion model was found to provide an order of magnitude approximation of the time required for hornogentsation in a certain mixture of powders. / Andrew Chakane 2018

O interesse crescente no desenvolvimento de biomateriais com superfície porosa para aplicações dentárias decorre do suporte propicio ao crescimento do tecido ósseo, aumentando a adesão entre o tecido e material, favorecendo a osteointegração. O titânio pode ser considerado um ótimo material para implantes dentários, pela sua excelente biocompatibilidade, elevada resistência à corrosão e combinação de alta resistência com baixa densidade. Contudo, a alta reatividade do metal no estado líquido acaba dificultando a fabricação de implantes por fundição, sendo a metalurgia do pó composta por técnicas que permitem a obtenção de peças em temperaturas menores de processamento (estado sólido) e com módulo elástico próximo ao do tecido ósseo. O objetivo deste trabalho foi avaliar amostras porosas obtidas pela Metalurgia do Pó (MP) convencional. Inicialmente o pó de titânio comercialmente puro (Ti-cp) obtido pelo processo de hidretação-dehidretação (HDH), foi compactado em matriz uniaxial e sinterizado a vácuo em duas temperaturas,1100 e 1150°C/1h. As amostras sinterizadas foram caracterizadas quanto à densidade, porosidade, microestrutura ( microscopia óptica - MO e microscopia eletrônica de varredura - MEV), fases cristalinas (difração de raios - X - DRX), propriedades mecânicas (microdureza e ensaio de flexão em três pontos), comportamento eletroquímico (potencial de circuito aberto, espectroscopia de impedância eletroquímica e polarização anódica) e o ensaio de imersão foram empregados nas amostras obtidas por (MP) e no titânio fundido. Os resultados indicaram morfologia angular, distribuição granulométrica com média de 45 μm, além de densidade aparente e escoabilidade baixas. Foram obtidas amostras com porosidade de aproximadamente 33% e poros interligados dentro de uma faixa de tamanho de 110 140 μm. As análises por MEV e DRX das amostras sinterizadas indicaram a presença de fase α e poros. As amostras sinterizadas a 1150°C revelaram melhor comportamento mecânico em relação as amsotras sinterizadas a 1100°C. As análises eletroquímicas indicaram a elevada resistência a corrosão do titânio fundido, seguida pela amostra sinterizada 1100°C e finalmente das sinterizadas a 1150°C, quando imersas em solução da saliva artificial. O EDS foi executado para verificar a deposição de elementos na superfície. Testes de citotoxicidade demonstraram que o pó e as amostras sinterizadas não apresentaram qualquer efeito tóxico em culturas celulares. As amostras sinterizadas à 1100°C possuiam grau de porosidade e tamanho de poros que favoreceram o crescimento do tecido ósseo, além do módulo de elasticidade próximo ao tecido ósseo e foram mais resistentes a corrosão na solução simuladora. / The development of materials with a porous surface has been widely studied in the field of biomaterials, because the porous structure allows bone tissue growth, increasing the bonding since the tissue and the material, favoring osteointegration. Given the excellent biocompatibility, high corrosion resistance and combination of high strength with low density, titanium is one of the most suitable materials for dental implants. However, the high reactivity in liquid state ends up hindering their fusion. The technique of powder metallurgy (PM) is an alternative for cost reduction, allowing to obtain superior samples at lower temperatures, closer to the bone tissue in terms of elastic modulus. The objective of this study was to evaluate porous samples obtained by conventional PM. Initially the powder of commercially pure titanium (cp-Ti) was obtained by hydridedehydride (HDH) process, followed by uniaxial pressing and vacuum sintering at 1100 and 1150 °C/1h. The sintered samples were characterized - density, porosity, microstructure (SEM), crystalline phases (XRD), mechanical properties (microhardness and three point bending test), electrochemical behavior (open circuit potential, anodic polarization and electrochemical spectroscopy impedance and immersion essay) applied in porous samples and cast titanim The results indicated angular particle morphology, 45 μm average particle size distribution, low apparent density and flowability. The different processing temperatures enabled to obtain samples with approximately 33 % interconnected porosity and average pore size in 110-140μm range. SEM and XRD analysis of the sintered samples revealed the presence of α phase and pores. Samples sintered at 1150°C showed superior mechanical behavior. Electrochemical analysis (in artificial saliva solution) indicated higher corrosion resistance of cast titanium compared to porous samples . Cytotoxicity tests proved that the powder and sintered samples has no toxic effects on cell cultures. Samples sintered at 1100 °C excels in bone growth stimulation, elasticity modulus and corrosion resistance, due to superior porosity and pore size range properties, creating a material analogous to the bone.

"Despite its maturity, the powder metallurgy (PM) fabrication process continues to rely heavily on indirect methods to determine and predict the quality of its compacts early in the manufacturing line. Currently, the most comprehensive testing is performed on sintered parts, resulting in higher cost and increased waste. This dissertation addresses the need of early inspection by developing a novel approach whereby PM compacts are tested in the green-state without intrusion and with minimal cost per compact tested. The method is based on an infrared detection scheme with two fundamental embodiments. For high resolution applications, or offline testing, an active thermography approach is adopted; electric energy is deposited into the compact in a contact-less fashion to evaluate all parts for cracks, inclusions, or delaminations. As an alternative, for lower resolution high-yield applications, a system based on a passive thermography approach is developed. This system relies on residual heating emanating from the process. Thermal data is then collected and analyzed in an effort to yield part integrity and process stability information. In this dissertation we will discuss our design approach, theoretical modeling aspects, and a proof-of-concept instrument with associated data processing software. We will first describe the underlying physical principles, followed by predictions from the modeling formulation, including a solution of the heat equation. As part of our experimental data processing, we will present results that are collected both in a laboratory setting and in an industrial manufacturing line. The integrity of the compacts is carried out with the aid of a specialized software package."

"The phase content and grain size of titanium dioxide often have a strong influence on properties for a variety of applications. In many cases it would be desirable to produce the stable rutile phase with an ultra-fine particle size (<10nm), but most low temperature synthesis methods produce predominantly the metastable anatase phase. The anatase-rutile transformation in TiO2 is known to be affected by dopant type and concentration, as well as the titanium precursor used in solution chemical synthesis. Recently, use of cavitation in the synthesis process has been shown to yield smaller grain size for a variety of oxides. However, the relative importance of these synthesis variables on the grain size and phase content of TiO2 is not well understood. In this study, Taguchi analysis was used to determine the relative effects of dopants (Sn), titanium precursor (butoxide, sulfate, chloride), and cavitation power on grain size and phase content. Precursor residuals were also measured by analytical chemistry. Grain size and phase content results were analyzed statistically to determine whether there is a size dependence of the anatase-rutile transformation. Results show that grain size is strongly dependent on the concentration of chlorine. Absent chlorine, a definite grain size-phase content correlation exists; rutile content increases as grain size decreases. An L-4 orthogonal Taguchi analysis shows chlorine content and tin content as the major influences on the final product. With minimum grain size and maximum rutile content being considered optimal, our best result was 100% rutile and an average grain size of 5nm, which was achieved by acoustic synthesis with 3% tin dopant and low residual chlorine. "

Este trabalho teve por objetivo desenvolver um processo de sinterização a plasma utilizando gaiola catódica para a sinterização de amostras de alumínio, para atmosferas de argônio, hidrogênio e nitrogênio. Avanços recentes na sinterização a plasma motivaram a investigação sobre seus benefícios para o alumínio e se a técnica de tela ativa, em particular com o uso de gaiola catódica, é capaz de contornar alguns problemas encontrados na sinterização deste material, como a presença de uma camada passiva de óxido e a expansão volumétrica após a sinterização para certos parâmetros de processo. A sinterização foi realizada em três processos: convencional, plasma direto e plasma com gaiola catódica. Para o processo convencional utilizou-se atmosferas de argônio e nitrogênio e, para os processos a plasma, utilizou-se atmosferas de argônio, hidrogênio e nitrogênio. Houve queda na densificação média após a sinterização em todos os processos. Tanto o processo a plasma direto e com gaiola catódica resultaram na menor queda de densificação. A atmosfera de nitrogênio mostrou-se a mais efetiva nos processos avaliados, indo ao encontro com o reportado na literatura consultada. Houve aparente endurecimento superficial das amostras sinterizadas a plasma direto. As amostras sinterizadas a plasma com gaiola catódica obtiveram homogeneidade nos valores de microdureza superficial e transversal entre as atmosferas, concordando com o esperado do uso desta técnica. O processo a plasma direto produziu amostras com maior rugosidade em comparação com os outros processos, não havendo influência significativa da atmosfera de sinterização neste aspecto. Foi detectada a presença de zinco na superfície de amostras provenientes do processo convencional com nitrogênio e do processo a plasma com gaiola catódica utilizando argônio e nitrogênio, sendo confirmado pela análise química. Houve formação de nitreto de alumínio apenas no processo convencional com nitrogênio. O processo a plasma com gaiola catódica mostrou-se o mais promissor por apresentar bons resultados em relação aos obtidos nos outros processos avaliados e por ser capaz de preservar a integridade superficial das amostras. É possível promover a melhora das propriedades superficiais do alumínio com o uso de gaiola catódica através de tratamentos termoquímicos concomitantes com a sinterização, tendo em vista os benefícios relatados na literatura. / This study aimed to develop a plasma sintering process using cathodic cage for sintering aluminum samples for argon, hydrogen and nitrogen atmospheres. Recent advances in plasma sintering motivated the research into its benefits for the aluminum and if the active screen technique, in particular the use of cathodic cage, can overcome some problems encountered in the sintering of this material, as the presence of a passive oxide layer and volumetric expansion after sintering for certain process parameters. Sintering was carried out in three processes: conventional, direct plasma and plasma with cathodic cage. For the conventional process was used argon and nitrogen atmospheres and for the plasma processing was used argon, hydrogen and nitrogen atmospheres. There was a decrease in average densification after sintering in all processes Both the direct plasma and cathodic cage plasma processes resulted in the smallest drop of densification. The nitrogen atmosphere proved to be the most effective in al processes evaluated, meeting with the reported in the literature. There was apparent superficial hardening of the samples sintered in direct plasma. Samples sintered in cathodic cage plasma obtained homogeneity in values of surface and cross section hardness between the atmospheres, according to the expected use of this technique. The direct plasma process produced samples with higher surface roughness compared with other processes, with no apparent influence of the atmosphere in this respect. It was detected the presence of zinc in the sample surface from the conventional process with nitrogen and cathodic cage plasma process with argon and nitrogen being confirmed by chemical analysis. The phase analysis on the sintered samples with nitrogen accused the formation of aluminum nitride for the conventional process. The cathodic cage plasma process proved to be the most promising for showing good results compared to those obtained in the other processes evaluated and to be able to preserve the surface integrity of the samples. It is possible to promote the improvement of the surface properties of aluminum with the use of active screen via thermochemical treatments concomitant with the sintering, in view of the benefits reported in the literature.

TerraPower LLC is designing a fast breed and burn reactor intended to operate for up to 40 years without refueling, designated as the Travelling Wave Reactor (TWR). Various U-Zr alloy fuel designs have been proposed for the TWR that may require a powder feed for fabrication. A simple and economic option for laboratory scale powder production is the Rotating Electrode Process (REP), which produces microsphere shaped powder by melting the tip of a rotating bar with an electric arc. In order to fully characterize this process for various U-Zr alloys and provide the feed material for testing fabrication techniques, a Rotating Electrode System (RES) was designed and built. The RES is largely based on a combination of two designs; an early REP system developed by Starmet Corporation in the 19xxa and a later design optimized for U-Mo powder production by Idaho National Laboratory (INL). The RES designed for this work was improved based on input from vendors specializing in their respective areas of expertise and is capable of atomizing up to a 1.26 cm diameter metal alloy rod at 40,000 RPM. Every component of the machine can be disassembled and transferred through a 35.56 cm (14 in) diameter air lock of a glovebox so that it can operate in a controlled environment. The RES was tested by atomizing various diameter copper rods to prove system functionality. The tests were carried out in air using an argon cover gas in the powder collection chamber, known as the catch pan to limit oxidation rates of the newly generated microspheres. The powder produced showed strong sphericity ranging from 50 µm to 500 µm in diameter. Problems and areas of concern that were encountered during operation have been addressed so that the RES can be further optimized to better atomize U-Zr alloys once transferred into the glovebox.