• Analytical Science and Technology
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• v.5 no.1
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• pp.143-152
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• 1992

Corrosion resistances in various acids and high temperature oxidation properties have been investigated for the Ni-base superalloy KM 1557. Corrosion tests were performed in $H_2SO_4$, HCl, $HNO_3$, $H_3PO_4$ and $CH_3COOH$. Oxidation tests were carried out in air for 20 and 110hrs at $900^{\circ}C$, $950^{\circ}C$ and $1050^{\circ}C$. Hot corrosion tests were done in salt bath of 75% $Na_2SO_4-25%$ NaCl at $900^{\circ}C$ for 20hrs. After the tests, the samples were observed by optical microscopy and analysed by EPMA and X-ray mapping in order to investigate the distribution of composition. It was shown that corrosion resistances in various acids and hot salt bath were proven to be excellent. It was suggested that the amounts of oxides were determined mainly by the depth of internal and intergranular $Al_2O_3$ oxide layers.

• Analytical Science and Technology
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• v.6 no.2
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• pp.167-180
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• 1993

The effects of coating variables on the formation of aluminide coating layer with good oxidation resistance on the strongest hot-forged superalloy in the world, KM 1557 developed at KIST by pack cementation process were studied. Pack aluminizing were performed by high-activity process with pure aluminium powders and by low-activity process with codep powders. For high-activity process, Al deposition rate, growth rate of coating layer, and cross-sectional microstructures were influenced by the species and additive amounts of activators and the additive amounts of pure aluminium powders. For low-activity process, Al deposition rate, growth rate of coating layer, and the cross-sectional microstructures were not influenced by the species but additive amounts of activators. Surface structures of coating layer were influenced by the species of activators. Regardless of aluminium activity, Al deposition rate was proportional to the square root of time and parabolic rate constants were different with the species of activators. The activation energy for deposition of aluminium was different with the species of activators for high-activity process. Regardless of the species of activators, the activation energy for deposition of aluminium was 12~14 Kcal/mole for low-activity process.