|Adam Kurzawa, Jacek W. Kaczmar
The paper presents the results of investigations into the microstructures of composite materials produced by pressure infiltration of preforms of ceramic α-Al2O3 particles with aluminium alloy EN AW-2024. In particular, the quality of the bonds at the interphase boundaries of matrix-ceramic particles was evaluated using microscopy investigations. It was found that silica (SiO2) used for bonding alumina particles in the preform causes an enrichment of the matrix in silicon (Si), which partly diffuses to aluminium alloy, yet remains in the matrix in the form of SiO2 concentrations, especially within ceramic particles with a high degree of agglomeration. The infiltration of open pores of ceramic preforms with EN AW-2024 alloy of limited flowing power hinders the infiltration process, resulting in local porosity. The propagation of cracks in the composite material after tests for mechanical properties occurs mainly along the interphase boundaries of the matrix-particle, especially in places with an increased residual amount of silica (SiO2) in the matrix. On the surfaces of the fractures ceramic particles of the α-Al2O3 reinforcement are observed, they form a strong adhesive bond with the matrix and crack during the formation of scrap metal.
Keywords: composite materials, pressure infiltration, ceramic preform,
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Wojciech Leśniewski, Piotr Wieliczko, Marek Wawrylak
This article presents a method of melting zirconium alloy in an induction vacuum furnace using a thermally insulated graphite crucible. The design of the Supercast Titan induction centrifugal furnace allows for the quick melting of metal alloys in ceramic crucibles. The ceramic crucible used for melting is separated from the induction coil by a quartz glass casing. The maximal temperature of heating the alloy in the melting ceramic crucible is limited by the permissible operating temperature of quartz casing seals and the furnace chamber. The design of the furnace also allows for melting of titanium in disposable alumina-based crucibles. The melting point of the zirconium, 1859°C, which does not allow for melting in the alumina-based crucible. The problem was solved by using a graphite crucible thermally insulated from a ceramic crucible. The batch of the zirconium alloy 702 after melting in the graphite crucible was poured, using centrifugal force into a rotating horizontal graphite mold. The metallographic structures were determined for both the batch material and the casting. The cast material was subjected to hot isostatic pressing (HIP). The densities of the batch material, casting and cast material subjected to the HIP process were determined. The hardness of the cast material was compared to the hardness of the batch material.
Keywords: zirconium alloys, centrifugal casting, hot isostatic pressing,
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Piotr Dudek, Jerzy J. Sobczak
The article presents the history and current state of the technology of external pressure casting in the case of High Pressure Die Casting (HPDC) and Squeeze Casting (SC). The similarities and differences between the two technologies and the common areas that were used in the construction of modern hybrid machines combining the features of HPDC and SC were shown. Recent years have seen the development of pressure machine designs that have enabled the hybridisation of technologies with high flexibility of the process, consisting in the choice of such a method of applying external pressure in which its influence can be more effectively used as a thermodynamic factor. The following experiments were presented in the field of liquid and solid-liquid casting, obtained from research conducted at the Foundry Research Institute in Kraków.
Keywords: High Pressure Die Casting, Squeeze Casting, aluminum alloys, magnesium alloys, metal matrix composites,
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The paper presents laboratory test results for an assessment of the binding characteristics of two grades of calcium bentonite compounds for casting moulds. The bentonite compounds were chemically modified with sodium carbonate at several different percentage ratios of the modifier. Samples were selected as the specimens and assessed for certain physical and chemical characteristics, including compressive strength, swelling factor, and montmorillonite content. The test results allowed the so-called bentonite activation curves to be plotted. Some of the specimens had their physical and chemical characteristics tested at high temperatures. The entirety of the laboratory tests of bentonite activation and heat resistance enabled an optimised selection of the sodium carbonate percentage fraction for a bentonite compound modification which would produce the best binding properties of foundry bentonite.
Keywords: bentonite, heat resistance; activation curve,
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Marcin Małysza, Zbigniew Stefański
Ductile iron castings are widely used in many industrial branches because of their mechanical properties. The production process of such a grade of cast iron requires the maintenance of the technological regime and the purity of initial charge material. For this reason, methods of manufacturing and controlling materials are constantly being developed. This publication presents a new method of modification and spheroidization in the mould. The innovation of this method is the use of specially developed construction of the reaction chamber. Simulation studies were conducted to analyze the flow profile of liquid metal in the developed shapes of the chamber. Subsequently, the changes in the geometry of the chamber were made and analyzed under the same boundary conditions. The result of the study is the designation of a structure that will provide the appropriate flow characteristics to achieve good quality castings.
Keywords: computer simulation, modification and spheroidization in the form, ductile iron, casting technology,
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