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Metallurgical Applications of Isostatic Hot-Pressing
Published in Ian L. Spain, Jac Paauwe, High Pressure Technology, 2017
Hot-pressing on the other hand is essentially a sintering operation, the product of which is a fully densified and sintered compact. It has always been considered to be the ultimate process for producing a fully-dense component from a substance otherwise only available as a powder. Although it has sometimes been said that hot-pressing is no more than combining cold-pressing and sintering into one operation, the densification effect is much more pronounced and it is possible to produce fully-dense compacts by this method when the same result cannot be achieved by cold-pressing and sintering. Undoubtedly the major effect arises from the increased plasticity of the particles concerned at elevated temperatures. This allows considerable deformation to occur during pressing so that greatly increased areas of contact between individual particles are obtained when compared with cold pressing. This increased area of contact is accompanied by much surface shearing action so that surface films and oxides are disrupted mechanically and new “clean” surfaces are generated.
Metal Matrix, Ceramic Matrix, and Carbon/Carbon Composites
Published in Manoj Kumar Buragohain, Composite Structures, 2017
In the powder metallurgy methods, powders of the matrix material are blended with reinforcements [8]. The reinforcements are taken in the form of particles, short fibers, or whiskers and the blending process results in a homogeneous mix. The mix is then cold pressed followed by sintering. The cold-pressed green compact mass is a porous structure containing water vapor and volatile contaminants such as lubricants of mixing and blending additives. In the first stage of sintering, the water vapor and volatile contaminants are removed by a process of degassing. The second stage of the sintering process involves the consolidation of the green compact part at high temperature during which the particles diffuse to the powder matrix. As an alternative to the cold pressing and sintering route, the homogeneous mix of matrix and reinforcement is hot pressed. (Cold pressing is a process of consolidation at low temperature without simultaneous sintering. On the other hand, hot pressing is the process of powder consolidation at high temperature with simultaneous sintering.) In the secondary processing, the cold-pressed and sintered or hot-pressed MMC part is extruded, forged, or rolled to obtain the final finished product. Figure 13.1 schematically shows the powder metallurgy methods of MMC manufacture.
Polycrystalline Iron Disilicide as a Thermoelectric Generator Material
Published in D.M. Rowe, CRC Handbook of Thermoelectrics, 2018
Ulrich Birkholz, Erwin Groβ, Ulrich Stöhrer
Experimental procedure — FeSi2 can be uniaxially hot pressed in a graphite die at a maximum pressure of 50 MPa. The hot pressing temperature is in the range between 800 and 1200°C. Figure 2 shows the densification of sprayed powder during hot pressing at 880°C. In the semilogarithmic presentation two straight lines are observed corresponding to a fast densification process (plastic flow) and a nearly constant density after some minutes, when only diffusion takes place. At 37.5 MPa a density of 95% and at 50 MPa a density of 97% can be obtained.
Fabrication and Characterization of Zirconium Silicide for Application to Gas-Cooled Fast Reactors
Published in Nuclear Technology, 2022
George M. Jacobsen, Hangbok Choi, James A. Turso, Amanda M. Johnsen, Andrew J. Bascom, Xialu Wei, Eugene A. Olevsky
Arc melting of 99.9% purity Si and Zr granules was performed by ACI Alloys (San Jose, California) using conditions developed to minimize the presence of zirconium-rich or silicon-rich phases such as Zr5Si4, Zr5Si3, and Zr2Si. The bulk ingot was broken into pieces of 1 cm or less and then ball milled (Jar Mill, US Stoneware) using silicon carbide balls to form micron-sized to submicron-sized powders. The ball-milled powder was placed into graphite dies with a grafoil release layer and cold pressed to 10 to 15 MPa. Hot pressing was performed (50-ton Vacuum Hot Press, OXY-GON Industries Inc.) at temperatures above 1200°C and pressures ranging from 50 to 150 MPa, depending on the part shape and processing temperatures. The exact conditions were dependent on the size and shape of the coupon being manufactured and were chosen to avoid phase transformation during processing and that yield dense Zr3Si2 pellets. After sintering, any adhered grafoil was gently removed using a 30-µm Dia-Grid Grinding Disk (Allied High Tech).
Micro-end milling of biomedical Tz54 magnesium alloy produced through powder metallurgy
Published in Machining Science and Technology, 2020
Ali Erçetin, Kubilay Aslantas, Özgür Özgün
Among the production techniques for biomedical materials, the most commonly used method is continuous casting and powder metallurgy. Although powder metallurgy is an easy method to control the content of the alloy, the grain size, forming pressure and sintering temperatures affect the strength of the material significantly. In this study, TZ54 alloy was produced by the hot-pressing method and sintered at 635 °C under a constant pressure of 50 MPa for 30 min. The reason why the hot-pressing technique is preferred is that it achieves a denser, fine-grained microstructure and superior mechanical properties. For the TZ54 alloy produced, Scanning Electron Microscopy (SEM) analysis, X-ray diffraction (XRD) and Energy Distribution Spectroscopy (EDS) analysis results are given in Figure 2. No pore formation was observed in the microstructure. Tensile strength tests were performed using standard tensile samples prepared after production. In addition, Vickers hardness and corrosion rate measurement results are given in Table 1.
High-performance hybrid composites made of recycled Nomex, Kevlar, and polyester selvages: mechanical property evaluations
Published in The Journal of The Textile Institute, 2019
Yu-Chun Chuang, Limin Bao, Ching-Wen Lou, Jia-Horng Lin
This study investigates the high-performance hybrid composites in terms of characterizations and mechanical properties based on the constituent recycled staple fibers. The eco-friendly manufacturing design uses high performance of recycled Nomex, Kevlar, and PET selvages. The recycled fibers take up 50, 70, and 90 wt% of the hybrid composites, and corresponding LPET fibers account for 50, 30, and 10 wt%. When base weight is excluded from consideration, K9 of the control groups has the optimal mechanical properties, and likewise P9 of the experimental groups has the optimal mechanical properties. The satisfactory test results are ascribed to the high performance of the recycled staple fibers and the reinforcement of LPET fibers. In particular, the combination of recycled PET fibers and LPET fibers has a synergistic effect in stabilized structure and mechanical improvement. In this study, the influence of a specified temperature of hot pressing of 130 °C on different properties is discussed. On the other hand, the influences of hot pressing in terms of temperature and pressures of hot pressing are not discussed in this study, and thus provide opportunities for the future studies to carry on the further investigation examining whether these parameters are related to the reinforcement of high performance hybrid composites.