Papers by Keyword: Solidification

Abstract: This paper deals with the formation of sulphides in as-cast grain-oriented electrical steel (GOES) thin strip during solidification and subsequent cooling through the (δ + γ) field. Chemical composition of the strip was as follows, in mass %: 0.034 C, 2.81 Si, 0.06 Mn, 0.024 S, 0.20 Cr, 0.15 Cu, 0.055 Ni, 0.0011 Ti, 0.0056 N and 0.002 Al. It was found out that chemical composition of coarse sulphides, formed in the area of final solidification, was very different from the composition of fine sulphides precipitated in the two-phase region. Coarse sulphides were rich in iron. Fine complex sulphides were identified as the Cr₂CuS₄ phase. The effect of fine sulphides on the austenite decomposition at the end of the (δ + γ) field was studied.

Abstract: The foundry casting process is complex and takes various stages to produce the desired component; as a result, simulation is necessary before manufacturing. Hot spots are areas that become thermally isolated and take the longest to cool, resulting in cavities during the solidification of the casting. So it is important to know about the hot spot location and size so that any casting designer can identify the hot spot behaviours before the casting. To predict the initiation of the hot spot, a 3D aluminium permanent mould casting model has been developed by Ansys Fluent. The suitable boundary and initial conditions such as temperature, pressure, convectional heat transfer coefficient, etc. are reasonably established in the simulation of Ansys Fluent. The simulation has been performed for varied pouring parameters i.e. pouring velocity and pouring temperature, to examine the beginning of hot spots. This study can predict the position and approximate size of the hot spots for various pouring conditions and it is found that a hot spot is commonly located below the riser.

Abstract: Accumulation of spent garnet the world over poses a threat to the environment as it can cause water pollution when it enters waterways during flooding or runoff. This study summarizes potential solidification of spent garnet in concrete and the use of magnesia cement to stabilize the heavy metals in the concrete. The concrete will then be able to be used for construction purposes. The research was conducted in two phases. The first phase was preparing different percentages of spent garnet mortar at 0%, 10%, 20% and 30% and cured for 28 days. The compressive strength and density of the spent garnet mortar in 100x50 mm samples was compared against those of sand mortar. 10% application obtained the highest strength of 15.97N/mm². The second phase was preparing another set of mortar mix with 10% spent garnet and 5%, 10%, 15% of magnesia cement. The mortars were cured in distilled water and the results shown that 28 Days strength for 90:10, OPC: MgO ratio was able to achieve 21.4 N/mm². This ratio also shown recommendable low leaching of heavy metals.

Abstract: The present investigation attempted to explore the effect of stirring during solidification of Aluminum A356 alloy, mainly focusing on the change from dendrite to globular structure. For this purpose samples of A356 alloy were melted in the electrical resistance furnace and cooling curves were recorded for each level agitation. The experimental curves were numerically processed by calculating first and second derivatives. From these were determined temperatures and times of start nucleation of alpha solid and eutectic reaction.

Abstract: In order to predict the effect of the Marangoni convection and the morphology of melted stainless steel powder, during the selective laser melting (SLM) process, a transient three-dimensional numerical model is developed at the mesoscale. The evolution of the temperature and velocity fields’ is then studied. The initial powder bed distribution is obtained by the discrete element method (DEM) calculation, and the temperature distribution and the molten pool shape deformation are calculated and analyzed by the Ansys-Fluent commercial code. The molten pool shape is obtained by considering the influence of Marangoni convection on the internal flow behavior. The recoil force was not considered in our calculation. As main results, a slight deviation between the position of the maximum temperature of the molten pool and the center of the laser spot is observed. The direction of the heat diffusion is more likely to be horizontal and the flow centrifugal, which causes the melt track to be wide. Finally, the Marangoni convection is the main driver of the flow.

Abstract: The objective of presented research was to verify and evaluate whether the treated hazardous waste (HW) can be used as filler in polymer coatings based on epoxy (EP) and polyurethane resin (PUR). The end product created by the incineration of municipal waste and cement dusts from cement kiln bypasses were chosen for solidification. The hazardous waste used was solidified by a homogenisation method using filter fly ash from fluidized bed combustion of lignite and silica flour as the solidifying agents. The aim was to use as much hazardous waste as possible and incorporate it into the polymer matrix of the coatings. The usability of the filler prepared in this way was verified by testing the tensile properties of polymer coatings, the surface hardness and the adhesion to the concrete. The cohesion of the coatings with concrete was observed using a digital optical microscope. It has been found that the PUR-based coatings with HW content show better properties than the coatings containing only the silica flour as a filler.

Abstract: To obtain an A356 aluminum alloy casting with a uniform structure and no internal shrinkage defects, ProCAST software is used to set different filling and solidification process parameters for an A356 aluminum alloy casting with large wall thickness differences, And multiple simulations are conducted to obtain optimized casting process; then, based on the process, the microstructure of the thickest and thinnest part of the casting are simulated. The size, morphology, and distribution of the simulated microstructure of the thinnest part and the thickest part of the casting are very similar. The simulated microstructure is similar to that of the actual casting. This shows that castings with uniform structure and no internal shrinkage defects can be obtained through the optimized casting process .

Abstract: RETRACTED ARTICLE: Bulk metallic glasses (BMGs) and their composites (BMGMCs) have emerged as competitive materials for structural engineering applications exhibiting superior tensile strength, hardness along with very large elastic strain limit. However, they suffer from lack of ductility and subsequent low toughness due to the inherent brittleness of the glassy structure which makes them amenable to failure without appreciable yielding. Various mechanisms and methods have been proposed to counter this effect out of which, recently Additive Manufacturing has gained widespread attention. It is proposed that additive manufacturing can overcome these difficulties in single step due to inherent existence of very high cooling rate in the process which is essential for glass formation. This, when coupled with careful selection of alloy chemistry is proposed to be the best solution to fabricate near net shape parts in a single step with excellent properties. In this report, an effort has been made to describe one possible route to achieve this. Solidification processing employing carefully selected inoculants based on edge to edge matching technique along with the carefuly controlled inoculation procedure is proposed to reflect upon enhanced mechanical properties. It is hypothesized that number density, size and distribution of ductile crystalline phase would best be able to improve microstructure and hence properties. This is meant to be controlled by manipulating type, size and the amount of inoculants. The proposed methodology is claimed to bear maximum potential.

Abstract: The most popular aluminium alloy used for the automotive applications is the wrought-Al alloy, where its popularity arises from its intrinsic characteristics such as, excellent formability, crash resistance, corrosion resistance and excellent specific strength. In the coming decades the use of aluminium alloys is expected to increase within automotive and aerospace industries, where this will source for an upsurge in Al recycling. Problems arise during Al recycling, where there is a steady build-up of Fe content, as this is recognised as being an impurity element. Fe has very little solubility in Al in its solid state and precipitation of these Fe intermetallics (IMC), in the Al matrix decrease mechanical properties, due to the Fe IMC brittle nature. These Fe-rich IMC also have very little cohesion to the Al matrix and can separate from the Al matrix resulting in the development of voids, where the initiation of microcracks becomes ostensible when subjected to thermomechanical processing. In order to curtail the damaging effect of the Fe IMC it so of importance to alter the nucleation and growth characteristic of the Fe rich IMC during solidification. Addition of trace elements and the manipulation of cooling rates have shown to be an effective technique to alter the Fe IMC morphology. In order observe the morphological evolution of the Fe IMC, various experiments were conducted using Al-1Si-1Mg-1Fe alloy with the addition of Mn and TiB₂-based commercial grain refiner. Microstructural analysis of the primary α-Al and Fe IMC are observed and the morphological evolution of the Fe IMC is analysed with respects to the addition of Mn and TiB₂. How the addition of these trace elements influence the growth characteristics and chemistry of the Al melt is also presented in this work.

Abstract: MoSi₂/Mo₅Si₃ eutectic composites have been considered as one of the promising candidates for ultra-high temperature structural applications owing to their high melting point, good oxidation resistance, and low mass density. Their mechanical properties can be improved by controlling the eutectic structure (i.e. script lamellar structure) in directional solidification. It is important to elucidate the dominant factors underlining the unique pattern formation. We conducted a comprehensive phase field study to examine the influence of various factors on the MoSi₂/Mo₅Si₃ eutectic microstructure with complicated morphology. First, the inclined lamellae have been attributed to the minimization of elastic strain energy due to the lattice mismatch between MoSi₂ and Mo₅Si₃, which are partially relaxed by forming semi-coherent phase boundaries. Second, the maze-like pattern on the horizontal cross-section appeared when a two-fold anisotropy of interfacial energy is superimposed on the MoSi₂/Mo₅Si₃ boundary. Third, the random and intersected lamellae have been obtained by assuming the instability of the solid-liquid interface and introducing successive nucleation of Mo₅Si₃ phase. These findings provide guidance for manipulating the eutectic structure and act as footsteps for further theoretical investigation.