Papers by Author: Kang Rae Lee

Abstract: Ti-Al intermetallic compounds are regarded as promising materials for the hightemperature structural and coating applications. We focused on the joining of Al casting alloy with Ti-Al intermetallic compounds by in-situ combustion synthesis to improve the surface properties of Al casting components. Microstructures and phase formation behavior of Ti-Al based intermetallic compounds synthesized by combustion reaction were analyzed using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectroscopy (EDS) and x-ray diffractometer(XRD) in Ti-Al intermetallic compounds. Three kinds of titanium aluminides of Ti3Al, TiAl and TiAl3 were synthesized by the heat from the Al molten metal and a coating layer of intermetallic phase were formed simultaneously on solidifed Al alloy surface. The shapes and microstructures of reacted compacts were varied by mixing ratio of elemental powders. The TiAl3 intermetallic compound was observed in the compacts regardless of the mixing ratio of elemental powders. And the unreacted Ti powders were remained in the reacted compacts due to the big size of Ti powder and low exothermic heat of reaction between Ti and Al powders. The zone that poured Al alloy diffused into the reacted Ti-25at.%Al compact of about 200 μm thickness was formed at the interface by the reaction between liquid molten Al alloy and solid Ti powders in green compact.

Abstract: We focused on the surface reinforcement of ligth weight casting alloys with Ni3Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of nonferrous casting components. In the present work, by setting the mixture of elemental Ni and Al powders in a casting mold, the powder mixture reacted to form Ni3Al intermetallic compound by SHS reaction ignited by the heat of molten AZ91D Mg alloy and simultaneously bonded with the Mg casting alloy. The AZ91D Mg alloy bonded with the Ni3Al intermetallic compound was sectioned and observed by optical microscopy and scanning electron microscopy(SEM). The chemical composition of intermetallic compounds and diffusion layer formed around bonding interface were identified by energy dispersive spectroscopy(EDS), X-ray diffraction analysis(XRD) and electron probe micro analyzer(EPMA). The main intermetallic compound was Ni3Al phase and a little Ni2Al3 intermetallic compound was formed from the Ni and Al powder mixtures. Residual pores were observed in the synthesized intermetallic compound. The AZ91D Mg alloy and Ni3Al intermetallic compound were bonded very soundly by the interdiffusion of Mg, Ni and Al elements, but some cracks were observed around the bonded interface on the interdiffusion layer. The diffusion length formed between AZ91D Mg alloy and Ni3Al was different depending on the diffusivity of Ni and Al elements into the molten Mg alloy. Ni was more deeply diffused into the Mg alloy than Al. The diffusion layer was about 200
m thickness and various phases were formed by the interdiffusion of Mg, Ni and Al. From this challenge we have successfully produced a coating layer based on nickel aluminide on ligth weight Mg alloy using molten metal heat without any additional process. On the basis of the results obtained, it is concluded that near-net shaped nickel aluminide coating layer can be formed using this unique process.

Abstract: We focused on the surface reinforcement of Al casting alloys with Ni-Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of Al casting components. Microstructure and phase formation behavior of Ni-Al based intermetallic compounds synthesized by combustion reaction were investigated in terms of thermal and phase analysis using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectrometer (EDS) and x-ray diffractometer(XRD) in Ni-Al intermetallic compounds. Three kinds of nickel aluminides, NiAl3, NiAl and Ni3Al, were synthesized by emission heat from the Al molten metal in order to form a coating layer of intermetallic phase simultaneously on the solidifed Al alloy surface. The synthesized shapes and microstructures of nickel aluminides were varied by casting temperature, Si contents, and the mixing ratio of elemental powders. The synthesized reaction products formed in nickel aluminides were observed to be different depending on the mixing ratio of elemental powders. The reaction layer of about 25
m thickness was formed at the interface, and it mainly consisted of NiAl3 phase by the reaction between liquid molten Al alloy and solid Ni powders in green compact. With this information, we successfully produced a coating layer of Ni3Al intermetallic compound onto the casting Al alloy surface using molten metal heat without any additional process. These findings led us to conclude that a near-net shaped nickel aluminide coating layer can be formed using this unique process.