Directionally solidified sample of Fe-Fe3C eutectic alloy were produced under an argon atmosphere in a vacuum Bridgman-type furnace to
study the eutectic growth with v = 167 μm/s pulling rate and constant temperature gradient G = 33.5 K/mm. Since how the growth texture
of eutectic cementite is related to its growth morphology remains unclear, the current study aims to examine this relationship. The technique
such as X-ray diffraction, have been used for the crystallographic analysis of carbide particles in white cast irons.
It is well-known that the better the control of the liquid aluminium allows obtaining of better properties. One of the most important defects
that is held responsible for lower properties has been the presence of porosity. Porosity has always been associated with the amount of
dissolved hydrogen in the liquid. However, it was shown that hydrogen was not the major source but only a contributor the porosity. The
most important defect that causes porosity is the presence of bifilms. These defects are surface entrained mainly due to turbulence and
uncontrolled melt transfer. In this work, a cylindrical mould was designed (Ø30 x 300 mm) both from sand and die. Moulds were produced
both from sand and die. Water cooled copper chill was placed at the bottom of the mould in order to generate a directional solidification.
After the melt was prepared, prior to casting of the DC cast samples, reduced pressure test sample was taken to measure the melt quality
(i.e. bifilm index). The cast parts were then sectioned into regions and longitudinal and transverse areas were investigated
metallographically. Pore size, shape and distribution was measured by image analysis. The formation of porosity was evaluated by means
of bifilm content, size and distribution in A356 alloy.
A eutectic reaction is a basic liquid-solid transformation, which can be used in the fabrication of high-strength in situ composites.
In this study an attempt was made to ensure directional solidification of Fe-C-V alloy with hypereutectic microstructure. In this alloy, the
crystallisation of regular fibrous eutectic and primary carbides with the shape of non-faceted dendrites takes place. According to the data
given in technical literature, this type of eutectic is suitable for the fabrication of in-situ composites, owing to the fact that a flat
solidification front is formed accompanied by the presence of two phases, where one of the phases can crystallise in the form of elongated
fibres.
In the present study an attempt was also made to produce directionally solidifying vanadium eutectic using an apparatus with a very high
temperature gradient amounting to 380 W/cm at a rate of 3 mm/h. Alloy microstructure was examined in both the initial state and after
directional solidification. It was demonstrated that the resulting microstructure is of a non-homogeneous character, and the process of
directional solidification leads to an oriented arrangement of both the eutectic fibres and primary carbides.
Directional solidification of the Fe - 4,3 wt % C alloy was performed with the pulling rate equal to v=83 μm/s. Sample was frozen during
solidification to reveal the shape of the solid/liquid interface. Structures eutectic pyramid and spherolitic eutectic were observed. The
solidification front of ledeburite eutectic was revealed. The leading phase was identified and defined.
Directional solidification of ledeburite was realised out using a Bridgman’s device. The growth rate for movement sample v=83.3 μm/s
was used. In one sample the solidification front was freezing. The value of temperature gradient in liquid at the solidification front was
determined. Interfacial distance λ on the samples was measured with NIS-Elements application for image analysis.
In a vacuum Bridgman-type furnace, under an argon atmosphere, directionally solidified sample of Fe - C alloy was produced. The pulling
rate was v = 83 μm/s (300 mm/h) and constant temperature gradient G = 33,5 K/mm. The microstructure of the sample was examined on
the longitudinal section using an Optical Microscope and Scanning Electron Microscope. The X-ray diffraction and electron backscatter
diffraction technique (EBSD) have been used for the crystallographic analysis of carbide particles in carbide eutectic. The
X-ray diffraction was made parallel and perpendicular to the axis of the goniometer. The EBSD shows the existence of iron carbide Fe3C
with orthorhombic and hexagonal structure. Rapid solidification may cause a deformation of the lattice plane which is indicated by
different values of the lattice parameters. Such deformation could also be the result of directional solidification. Not all of the peaks in
X–ray diffractograms were identified. They may come from other iron carbides. These unrecognized peaks may also be a result of the
residual impurity of alloy.
Twinned dendrites in Al-Zn alloy with high Zn content (40% wt.%) were successfully prepared by directional solidification. At different directional solidification rates (1000 and 1500 μm/s), microstructures and growth orientation variations of Al twinned dendrite and non-twinned dendrite were characterized. By using the inverted trapezoidal graphite sleeve at 1000 μm/s, Al twinned dendrite were formed to developed feather crystal structures in longitudinal section. Its primary and secondary twinned dendrite were grew along [110] direction. Moreover the deviation angle between [110] direction of Al twinned dendrite and the heat flow direction was about 27.15°. While not using the inverted trapezoidal graphite sleeve at 1000 and 1500 μm/s, Al dendrite was the non-twinned dendrite and the twinned dendrite was not appeared. The experimental results showed that the higher temperature gradient, a certain pulling rate and convection environment were the formation conditions of twinned dendrites.
In order to determine the leading phase of the Fe - 4.25% C eutectic alloy, the method of directional crystallization, which allows to study the character of the solid / liquid growth front, was used. Examined eutectic was directionally solidified with a constant temperature gradient of G = 33,5 K/mm and growth rate of v = 125 μm/s (450 mm/h). The Bridgman technique was used for the solidification process. The sample was grown by pulling it downwards up to 30 mm in length. The alloy quenched by rapid pulling down into the Ga-In-Sn liquid metal. The sample was examined on the longitudinal section using a light microscope and scanning electron microscope. The shape of the solid/liquid interface and particularly the leading phase protrusion were revealed. The formation of the concave – convex interface has been identified in the quasi-regular eutectic growth arrested by quenching. The cementite phase was determined to be a leading phase. The total protrusion d is marked in the adequate figure.
Cu-2wt%Ag alloy with diameter of 10 mm was fabricated by induction heating directional solidification (IHDS). The effect of different mold temperatures on microstructure of IHDS Cu-2wt%Ag alloy was investigated. The results show that IHDS Cu-2wt%Ag alloy is mainly composed of coarse columnar grains at mold temperature of 1075°C. While the mold temperature is at 1100°C, 1150°C and 1200°C, respectively, the IHDS Cu-2wt%Ag alloy is composed of columnar grains and equiaxed grains and the number of grains increases. Meanwhile, the growth direction of columnar grains in the edge of alloys deviates from the direction of continuous casting to form “V” shape. While the mold temperature is controlled at high temperature, the induced current increases, which leads to the enhancement of eddy current in the mold. Therefore, the dendrites fall off to form new grains under the effect of eddy stirring, resulting in an increasing in the number of grains.
Directional solidification technique is an important research instrument to study solidification of metals and alloys. In the paper the model
[6,7,8] of directional solidification in special Artemis-3 facility was presented. The current work aimed to propose the ease and efficient
way in calibrating the facility. The introduced M coefficient allowed effective calibration and implementation of defined thermal
conditions. The specimens of AlSi alloys with Fe-rich intermetallics and especially deleterious β-Al5FeSi were processed by controlled
solidification velocity, temperature gradient and cooling rate.
Solidification of AlSiFe alloys was studied using a directional solidification facility and the CALPHAD technique was applied to calculate
phase diagrams and to predict occurring phases. The specimens solidified by electromagnetic stirring showed segregation across, and the
measured chemical compositions were transferred into phase diagrams. The ternary phase diagrams presented different solidification paths
caused by segregation in each selected specimen. The property diagrams showed modification in the sequence and precipitation
temperature of the phases. It is proposed in the study to use thermodynamic calculations with Thermo-Calc which enables us to visualize
the mushy zone in directional solidification. 2D maps based on property diagrams show a mushy zone with a liquid channel in the
AlSi7Fe1.0 specimen center, where significant mass fraction (33%) of β-Al5FeSi phases may precipitate before α-Al dendrites form.
Otherwise liquid channel occurred almost empty of β in AlSi7Fe0.5 specimen and completely without β in AlSi9Fe0.2. The property
diagrams revealed also possible formation of α–Al8Fe2Si phases.
Fe - 4,25% C alloy was directionally solidified with a constant temperature gradient of G = 33,5 K/mm and growth rate of v = 83,3 μm/s (300 mm/h) using a vacuum Bridgman-type crystal growing facility with liquid metal cooling technique. To reveal more detailed microstructure, the deep etching was made. This was obtained in the process of electrolytic dissolution. The microstructure of the sample was examined on the longitudinal and transverse sections using an Optical Microscope and Scanning Electron Microscope. Using the Electron Backscattered Diffraction technique, phase map and analysis of phase were made. In this paper the analysis of Fe-C alloy eutectic microstructure is presented. Regular eutectic structure was obtained. The fracture surfaces show lamellar structure. Microscopic observation after electrolytic extraction indicates that the grains of longitudinal shape of eutectic cementite have been obtained. These grains are characterized by layered construction with many rounded discontinuities.