Papers by Keyword: Solidification

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Authors: Henri Nguyen-Thi, Jiang Wang, Georges Salloum-Abou-Jaoude, Guillaume Reinhart, Imants Kaldre, Nathalie Mangelinck, Zhong Ming Ren, Leonids Buligins, Andris Bojarevics, Yves Fautrelle, Olga Budenkova, Tamzin Lafford
Abstract: It is well known that the application of a magnetic field during the growth process can have pronounced effects on cast material structures and their properties, so that magnetic fields have been widely applied since the 1950s. In the case of a permanent magnetic field, some recent results revealed a dual effect on the liquid metal flow. 1: the magnetic field has a selective damping action on the flow at the scale of the crucible, due to the Lorentz force; 2: the interaction of thermo-electro-magnetic (TEM) currents in the close vicinity of the solid-liquid interface with the applied magnetic field leads to the generation of electromagnetic forces, which act both on the liquid and on the solid at the scale of the microstructure. We present an experimental investigation of the TEM forces induced by a permanent magnetic field during columnar and equiaxed solidification of Al-4wt%Cu. In situ visualization was carried out by means of synchrotron X-ray radiography, which is a method of choice for studying dynamic phenomena. It was shown that the TEM forces were at the origin of a motion of dendritic particles, perpendicular to the direction of gravity. A heuristic analysis allowed us to estimate the fluid velocities and the velocities of the solid particles, and a good agreement was achieved with the experimental data. Similar observations were also made during equiaxed growth in a temperature gradient. The in situ observation of the grain trajectories for various values of the temperature gradient demonstrated that gravity and TEM forces were the driving forces which controlled the grain motion.
Authors: Yuichi Komizo, Hidenori Terasaki
Abstract: Time-resolved X-Ray Diffraction (TRXRD) experments were carried out to identify the phase transformation during welding in-situ. For the martensitic steel weld with different chemical compositions, the solidification behavior was directly analyzed in the time-resolution of 0.01 seconds. The halo pattern from the weld pool gives basis to observe the phase transformation during solidification process of weld. Furthermore, the latest development of TRXRD system was outlined. The importance of detector area was discussed and brand-new TRXRD system in real and reciprocal lattice space was presented.
Authors: Jean Marie Drezet, Bastien Mireux, Guven Kurtuldu
Abstract: During solidification of metallic alloys, coalescence corresponds to the formation of solid bridges between grains when both solid and liquid phases are percolated. As such, it represents a key transition with respect to the mechanical behaviour of solidifying alloys and to the prediction of solidification cracking. Coalescence starts at the coherency point when the grains begin to touch each other, but are unable to sustain any tensile loads. It ends up at the rigidity temperature when the solid phase is sufficiently coalesced to transmit macroscopic tensile strains and stresses. This temperature, also called mechanical or tensile coherency temperature, is a major input parameter in numerical modelling of solidification processes as it defines the point at which thermally induced deformations start to generate internal stresses in a casting. The rigidity temperature has been determined in Al Zn alloys using in situ X-ray diffraction (XRD) during casting in a dog bone shaped mould. This set-up allows the sample to build up internal stress naturally as its contraction is prevented. The cooling on both extremities of the mould induces a hot spot at the middle of the sample which is irradiated by X-rays. Diffraction patterns were recorded every 0.5 s using a detector covering a 426 x 426 mm2 area. The change of diffraction angles allowed us to observe agglomeration/decohesion of growing grain clusters and to determine a solid volume fraction at rigidity around 98 % depending on solidification time for grain refined Al 6.2 wt% Zn alloys.
Authors: D.M. Stefanescu
Abstract: This paper is a review of the marvelous development of mathematical and computer models that describe the fundamentals of microstructure evolution during the solidification of cast alloys, from the 1966 seminal paper by Oldfield, the first to attempt computational modeling of microstructure evolution during solidification, to the current prediction of mechanical properties. The latest analytical models for irregular eutectics such as cast iron, as well as numerical models with microstructure output, to include cellular automaton, will be discussed. Phase field models will not be discussed because of their inapplicability to casting solidification at the present time.
Authors: Hamid Reza Zareie Rajani, Andre Bernard Phillion
Abstract: Meso-scale modeling through the use of a granular-type model is a key new tool for predicting solidification-related defects. In the present study, the application of a granular-type model to welding microstructure is presented, along with application challenges and solutions. This new model can simulate the solidification of a weld pool at the mesoscale, i.e. both solid grains and liquid are included. Consequently, the behaviour of the semisolid structure within the weld pool can be studied. By means of this 3D meso-scale model, the continuous network of liquid channels that forms at the last stages of solidification have been investigated, allowing for prediction of the variation in the distribution of liquid channel width as a function of welding parameters.
Authors: D. Ruvalcaba, Dmitry G. Eskin, Laurens Katgerman
Abstract: In the present investigation, serial sectioning and 3D reconstructions are made on samples quenched at selected temperatures during unconstrained solidification in order to observe the evolution in morphology of coarse dendrites in 3D. The 3D microstructure reconstruction during the solidification of an Al−7 wt.% Cu alloy allowed the identification of a complex coarse morphology of dendrites. High-ordered branches present different morphologies at different temperatures and locations in the microstructure due to coarsening and coalescence. 3D visualization of complex dendritic structures is discussed in the present investigation.
Authors: D. Ruvalcaba, Dmitry G. Eskin, Laurens Katgerman
Abstract: In the present research the possibility of studying the solidification of aluminum alloys by using the quenching technique is analyzed. Since the quenching technique does not provide reliable information (i.e. due to an overestimation of solid fraction) when measuring the solid fraction over 2D images from samples quenched at high temperature, the overestimation problem is investigated by analyzing 3D reconstructed microstructures from quenched samples. The 3D reconstructed microstructure may provide better understanding about the cause of overestimation of solid fraction when quenching at high temperatures. Consequently, the reconstruction of the microstructure that has existed before quenching may be possible after identifying and removing the solid phase that develops during quenching. In the present research, binary aluminum alloys are solidified and quenched at different temperatures, and then 3D reconstructed images are analyzed. The possibility of reconstructing the microstructure that develops during solidification before quenching is discussed.
Authors: David H. St. John, Mark A. Easton, Peng Cao, Michael Bermingham, Ma Qian
Abstract: The development of grain refinement technologies began in the 1930s in response to the need to improve the mechanical properties of as-cast components. Commercial grain refining technologies were developed by industrial and experimental trials often with good success including the production of effective master alloys. In parallel, researchers developed theories to explain the mechanisms of refinement in order to improve the efficiency of refiners and develop new better performing grain refining master alloys. This research continues today. Here we briefly present the history of these developments. It is shown that many developments in our understanding were based on assumptions arising from experimental and industrial observations and the prevailing solidification theories of the time.
Authors: Xin Lin, Lei Wei, Meng Wang, Wei Dong Huang
Abstract: A modified cellular automaton model for describing the dendritic solidification of pure substance was developed. Instead of using the high mesh-induced anisotropy capture rules, such as Von Neumann’s and Moore’s method, a new capture rule---random zigzag method was developed, which greatly reduced the mesh-induced anisotropy in crystallographic orientation. The calculation method for the solid/liquid interface curvature was also improved. The effect of interfacial energy anisotropy on the dendritic growth behavior was analyzed.
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