Al 확산 침투 처리된 니켈기 초내열 합금의 고온 산화 특성

Abstract

Alloy 617, Ni-base superalloy, has widely been used such as High Temperature Gas Reactor (HTGR), Intermediate Heat Exchanger (IHX), and hot gas duct. It is very important to study about the high temperature oxidation behavior considering the maintenance environment of Alloy 617. In this study, Al pack cementation on high temperature oxidation behavior of Inconel 617. Al-pack cementation process was conducted on the surface of Alloy 617. Aluminide layer and inter-diffusion zone were formed by 1hr aging at 1000oC after Al-pack cementation. In the Aluminide layer, Ni2Al3 which is metastable phase transformed to NiAl which is stable phase at high temperature. It was also confirmed that M23C6 phase was formed at the upper part and σ phase was formed at the lower part of inter-diffusion zone. The difference of hardness value was small, but coating layer showed higher value than the matrix. In the case of high temperature cyclic oxidation test, it could be hardly observed the oxidation behavior at the coated layer and it was confirmed that the Ni2Al3 phase transformed to NiAl phase by XRD and EPMA analysis. Besides, internal oxidation layer was not formed because of the formation of NiAl coating layer. In addition, Molybdenum disilicide (MoSi2) is a possible structural material for high-temperature application like furnace components or aircraft turbine engines due to its high melting point of 2030oC combined with its moderate density which is much lower than the density of other high temperature structural materials like nickel base alloy. Furthermore, molybdenum disilicide shows an excellent high temperature oxidation resistance. molybdenum disilicide (MoSi2) coating process was investigated by hydrogen reduction and Si-pack cementation. At first, the metallic Mo coating was carried out by hydrogen reduction of MoO3 powder at 750oC for various holding time (1, 2, 3 h) in hydrogen atmosphere. A 4.3 ㎛ thick metallic molybdenum thin film was formed for 3 h. MoSi2 was obtained by Si-pack cementation on molybdenum thin film through hydrogen reduction processed. It was carried out using Si : Al2O3 : NH4Cl = 5 : 92 : 3 (wt.%) packs at 900°C for various holding time (30, 60, 90 min) in Ar atmosphere. Holding time was 90 min, MoSi2 layer was coated successfully and the thickness was observed 15.4 ㎛.