Papers by Keyword: Remelting

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Authors: Stephen P. Midson, David J. Browne
Abstract: The CDC (Cast-Decant-Cast) Process is novel semi-solid processing method for joining two alloys, allowing the production of components from two or more alloys. The process produces a functionally gradient material (FGM) which, instead of having a sharp interface between the two alloys, features a transition region exhibiting a smooth gradient in concentration, microstructure and properties. Functionally gradient materials provide engineers with the flexibility to design components with different material properties at different locations. The details of the CDC Process are described. This paper, for the first time, provides information regarding the fabrication of functionally gradient castings from steels, cast irons and cobalt alloys. The first example involves the production of functionally gradient castings from a Ni-Hard cast iron + mild steel. The second example describes the production of functionally gradient castings from Stellite + mild steel. Processing parameters are documented and microstructures of the castings described.
Authors: Leszek Adam Dobrzański, Mirołsaw Bonek, Marek Piec, Ewa Jonda
Abstract: The objective of the present work was to study the modification of the microstructure of hot-work tool steels X40CrMoV5-1 and X38CrMoV5-3 during the surface modifying by means of laser technology. This treatment aims to harden and alloy the steel surface which had been previously coated with tungsten carbide (WC) and were introduced using the rotor conveyer to improve the properties of the surface layer. The fine grained, dendritic structure occurs in the remelted and alloyed zone with the crystallization direction connected with the dynamical heat abstraction from the laser beam influenced zone. The fine grained martensite structure is responsible for the hardness increase of the alloyed layer.
Authors: Markus Rettenmayr, O. Warkentin, M. Rappaz
Authors: J. Dahlström, Hasse Fredriksson
Authors: David J. Browne, M. Scanlan, A. Bates
Abstract: A novel technique for the production of functionally gradient materials, developed by the authors, is presented. The process is known as the Cast-Decant-Cast or CDC process, and involves a partial solidification step. This process takes expensive and time-consuming factors out of the production of functionally gradient materials by enabling utilisation of standard foundry equipment, and the process is carried out in a single multi-step casting operation. The CDC process involves simultaneous but separate melting of two alloys of different composition in order to produce a gradient in material properties. Details of the process are presented. It is shown that the outcome depends on partial local remelting and alloy mixing, which results in a gradual change or gradient between the first and second alloys in the as-cast condition, hence producing a functionally gradient material. The process has been adapted to conventional casting methods such as gravity casting and low pressure casting. It is the method of decanting the first material from the mould that differentiates the process variants. The decanting step for the low pressure method is controlled by pressure application and release on the molten alloys within their respective, but separate, sealed holding chambers. Decanting for the gravity casting method began as a physical inversion of the mould and is now at the point of autodecanting through careful design of an innovative gating system. The CDC process has been proven by means of metallographic study of microstructure to produce functionally gradient materials. Adapting the CDC process to conventional casting methods has made it a potentially commercially viable option for numerous applications. The results of recent research on the process are presented in summary form, including multi-alloy experiments, observations on the influence of timing and thermal control, and FGM manufacture using MMCs and joining dissimilar metals.
Authors: Ewa Jonda, Krzysztof Lukaszkowicz
Abstract: The paper presents the effect of alloying with WC and TaC powders on structure and mechanical properties of the X40CrMoV5-1 steel surface layer using the HPDL (High Power Diode Laser). The metallographic investigations on light microscope show that during alloying the X40CrMoV5-1 hot work tool steel with the WC and TaC powder the obtained run face is characteristic of the high roughness, multiple pores, irregularity, and flashes at the borders. The changes of the surface layers hardness formed as a result of alloying with ceramic powders containing carbides are accompanied with the increased tribological properties. The microstructure of the alloyed layers which were formed on the surface of the investigated hot work steel was examined using optical microscope. The tribological wear relationships using pin-on-disc test were specified for surface layers subject to laser treatment, determining the friction coefficient, and mass loss of the investigated surfaces.
Authors: Abdellah Kharicha, Wolfgang Schützenhöfer, Andreas Ludwig, Gerhard Reiter
Abstract: The Electro-Slag-Remelting (ESR) is an advanced technology for the production of components of e.g. high quality steels. In the present study a comprehensive computational model using the VOF technique for the prediction of the slag/pool interface is presented for axisymmetric and steady state conditions. In this model the distribution of the electric current is not constant in time, but is dynamically computed according to the evolution of the slag and steel phase distribution. The turbulent flow, created by the Lorentz and buoyancy forces, is computed by solving the time-averaged mass and momentum conservation equations. The turbulence effect is modelled by using a k-model. Two numerical simulations were performed, one assuming a flat interface, and a second leaving the interface free to find an equilibrium shape. The results are then analysed and compared for both cases.
Authors: Veronika Řičánková, Ladislav Čelko, Jiří Švejcar
Abstract: The specimens in the present study were prepared by air plasma spraying of NiCrAlY coatings onto the INCONEL 713LC nickel-based superalloy substrate surface. Subsequently an aluminium sheet was cladded onto the coating surface by means of uniaxial cold pressing. After that the specimens were annealed at temperatures of 650, 850 and 1000°C for two hours in argon-flow atmosphere. The remelted NiCrAlY coating specimens were annealed at a temperature of 800°C for fifty hours in ambient atmosphere. A scanning electron microscope was used to record the changes in the modified coating microstructure. Chemical composition was measured by means of energy dispersive microanalysis. Qualitative and quantitative x-ray diffraction analysis was used for the final determination of phases. The microhardness of remelted air-plasma-sprayed NiCrAlY coatings before and after short thermal exposure was also measured.
Authors: Marek Piec, Leszek Adam Dobrzański, Krzysztof Labisz, Ewa Jonda, Andrzej Klimpel
Abstract: Investigations include alloying the X38CrMoV5-3 hot-work tool steel surface layer with the tungsten carbide, using the high power diode laser (HPDL). The tungsten carbide ceramic particles of the medium grain size according to FSSS = 50 /m were introduced using the rotor conveyer to improve the properties of the surface layer. The powder feed rate was set at the steady level of 8.64g/min. Remelting and alloying were carried out several times in the laser power range of 1.2 – 2.3 kW in the remelting/alloying, alloying/remelting sequences. The structural mechanism was determined of gradient layer development, effect was studied of alloying parameters, gas protection method, and powder feed rate on its mechanical properties, and especially on its hardness, abrasive wear resistance, and roughness. Structure changes were revealed consisting, in particular, in its refining, and also hardness and microhardness changes in comparizon to the nonremelted steel. Examination results obtained with the EDX microanalysis, surface and linear analysis of the chemical composition, as well as the X-ray qualitative phase analysis are presented.
Authors: Wan Wu Ding, Jiang Tao Zhu, Wen Jun Zhao, Tian Dong Xia
Abstract: The regular pattern of evolution of TiC and TiAl3 during the remelting process of Al-Ti-C alloy wires was analyzed and the impact mechanism was discussed. The results show that: when the temperature of the remelting mass is at 730°C, with the increase of the heat preservation time of remelting, the degree of agglomeration of the original dispersed TiC will increase, and they are pushed toward crystal boundaries by α-Al during the solidification process, while TiAl3 will dissolve, aggregate, and grow. When the remelting temperature is at 1000°C, as the heat preservation time increases, not only the agglomeration degree of TiC increases significantly compared to that at 730 °C and the sizes and shapes of TiAl3 change significantly as well. The morphology of TiAl3 will change from being lump-and-short-rod-like to needle-and-flake-like. Before and after remelting, the Al-Ti-C alloys are both composed of TiAl3 and TiC, with no other phases formed.
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