Papers by Keyword: Bridgman Method

Abstract: Large size Gasar ingots have the advantage of cost saving and productivity improvement, while little attention has been paid to the preparation of large size ingots, especially those with high structural quality. Bridgman method was introduced to fabricate large size Gasar metal ingot. High quality Gasar Cu cylinder sample of 150 mm in diameter and about 200 mm in height (weighing about 20 kg) was obtained at a proper withdrawing velocity. Pore structure distribution at different heights and radii in the sample was measured and analyzed in detail using the image analyzing software. The results showed that the pore aspect ratio changed slightly along the sample height. All the other structure parameters including porosity, penetrative porosity, penetrative pore area and number ratio, pore diameter, pore length and the pore aspect ratio kept almost constant at heights of over 65 mm, while they all varied little along the sample radius. Most of the pores were straight and round. The results suggested that Bridgman method was feasible for the fabrication of large size high quality Gasar metal ingots. This would promote the commercial application of Gasar metals, such as Gasar Cu for micro-channel heat sinks.

Abstract: Composition profiles of eutectic alloy Pb_25.9Sn_74.1 atomic % grown by the normal and inverted Bridgman methods are presented and the study of the solute alloy redistribution is made. The inverted vertical Bridgman method, where the solidification occurs from the top to the bottom of the melt under a destabilizing thermal gradient, allows the growth of crystals with buoyancy-driven convection different from that with the usual vertical Bridgman configuration. The scope of this work is to study the influence of the gravity acceleration in the convection process.

Abstract: In this work, Ga₂S₃ crystals were obtained by vertical Bridgman method. The presence of cracks in the grown crystals was interpreted as a result of phase transition into monoclinic structure during cooling. This suggests the use of another approach for the growth of high quality samples, e.g. chemical transport method or melt-solution method. Maximal transparency range of 0.48-22.5 μm and at least 10 times higher damage threshold to that for GaSe render anisotropic Ga₂S₃ crystal among the most prospective crystals for nonlinear applications.

Abstract: Single crystals of Magnesium alloys such as Mg-1Zn-0.5Y, Mg-0.1Y, and Mg-0.1Ce alloys were fabricated in this study by employing the modified Bridgman method. To determine the exact orientation of crystals, pole figure measurement using X-ray diffraction was carried out on each single crystal. Hardness and compression tests were conducted followed by subsequent recrystallization annealing. Recrystallization behavior of Mg alloy single crystals has also been investigated. Fabricated single crystals were deformed in compression mode by 30% reduction. Annealing treatment has been conducted on these samples at temperatures of 300°C for various times from 1 to 20 mins. The microstructure observation and hardness measurement conducted on the recrystallized specimens revealed that static recrystallization of ternary alloy single crystal was very slow, while recrystallization behavior of binary alloy single crystals appeared to be very fast.

Abstract: This paper presents the results of analysis of superalloys microstructures with different structures: polycrystalline nickel-based superalloy René 80, Mar-M 200Hf directionally solidified with columnar grains and single crystal CMSX-4. Microstructure studies were performed using a scanning electron microscope Hitachi FE-SEM SU-70 and S-3400N equipped with a Thermo Scientific Noran System for analysis of chemical composition by X-ray dispersion. Metallographic microsections of the rods before and after heat treatment was performed, which were electrolytically etched using different reagents. The morphology of γ phase precipitates in the interdendritic areas and dendritic cores was analyzed. Single crystal rods of nickel superalloy CMSX-4 were cast by Bridgman technique in a vacuum furnace of ALD Vacuum Technologies. Rods were withdrawn with rate: 1mm/min and 5mm/min. EDS X-ray microanalysis showed significant differences in chemical composition between the cores dendrites and eutectic regions. Significant differences in the number of dendrites, the shape and length of the arms were observed. A lower speed rate causes that amount of eutectic is lower but value of primary dendrite arm spacing is higher, while a higher withdraw rate increases the amount of eutectic and decreases primary dendrite arm spacing.

Abstract: The nonlinear optical properties of a novel AgGa_1-xIn_xSe₂ crystal were investigated. Its absorption coefficients and band gap were determined at wavelength 0.8-19 μm. The coefficients of its Sellmeier dispersion equations were calculated by using linear interpolation based on the Sellmeier equations of pure AgGaSe₂ and AgInSe₂. The corresponding phase matching curves for the second harmonic generation (SHG) of CO₂ laser radiation were calculated and plotted. The walk-off angle and accept angle curves were also determined and plotted. The measured phase matching angle θ_m and acceptance angle δθ·L are 68.5° and 3.66°·cm respectively for sample AgGa_1-xIn_xSe₂ (x=0.2).

Abstract: The article presents the comparison of two methods: classical X-ray topography and the modern automatic X-ray OD-EFG diffractometer. Both methods were applied to study the crystal orientation of turbine blades of single crystal nickel-based superalloys. The solidification of a hollow assembly structure for 5 various blades was carried out by the Bridgman method at the Research and Development Laboratory for Aerospace Materials at Rzeszow University of Technology using an ALD Vacuum Technologies vacuum furnace. Ceramic moulds made of Al2O3 were used. The alloy temperature during casting into the mould amounted to 1550°C. The specimens for Laue method tests were cut out from the blades at withdrawal rates of 1, 2, 3, 4, and 5 mm/min.

Abstract: The paper attempts to determine the changes in the γ’ lattice orientation of aircraft engine turbine blades made of the CMSX-4 single crystal nickel superalloy. The solidification of a hollow assembly structure for 2 various blades was carried out by the Bridgman method at the Research and Development Laboratory for Aerospace Materials at Rzeszow University of Technology using an ALD Vacuum Technologies vacuum furnace. Ceramic moulds made of Al2O3 were used. The alloy temperature during casting into the mould amounted to 1550°C. The specimens for Laue method tests were cut out from the blades at withdrawal rates of 3 and 4 mm/min.

Abstract: The composites of Al₆₁Cu₂₇Fe₁₂ alloys containing quasicrystalline and crystalline phases (CQ composites) were obtained by the Bridgman method. The morphology of composites crystallized with different solidification rates was studied. The solidification rate influence on fibrous reinforcement morphology was analyzed. The microsections for analysis were prepared parallel and perpendicular to the direction of crystallization. The optical and the scanning electron microscope were used for metallographic observation. Obtained composites were examined by X-ray powder diffraction and reflective X-ray topography. The Laue method enabled to conclude that the matrix is singlecrystalline. The different level of structural perfection of reinforcement fibres was presented at various solidification rates.

Abstract: Lead tungstate, PbWO₄ single crystals co-doped with Mo⁶⁺ and Sb³⁺ ions were grown using the modified Bridgman method. The X-ray powder diffraction, optical transmission, X-ray excited luminescence, photoluminescence, light output and decay time have been investigated. Compared to non-doped PbWO_4, the co-doped PbWO₄:(Mo,Sb) crystals exhibit improved transmittance in the short wavelength region. Luminescence and light output measurements demonstrated that Mo⁶⁺ and Sb³⁺ co-doping could enhance the luminescence of PbWO₄ and increase the light output to about 7.0% of Bi₄Ge₃O₁₂ crystal. Doped Mo⁶⁺ and Sb³⁺ ions in PbWO₄ were tentatively considered to occupy W and Pb sublattice sites mostly. The second excitation peak at 385 nm, which is the second effective excitation for the enhanced blue-green emission in as-grown PbWO₄:(Mo,Sb) crystal, should be related to [MoO₄]^2- group and oxygen vacancy.