Impurity and surface condition effects on pore formation at Al_2O_3/FeAL interfaces

摘要

Interfacial pores are commonly observed at the scale/alloy interface in NiAl and FeAl alloys after high temperature oxidation. The pores are often an order of magnitude larger than the oxide grains, and many are formed during the initial stage of oxidation. In order to better understand the development of these pores, the effects of pre-oxidation surface condition and surface impurities on pore formation at the oxide/alloy interface in Fe-40at percent Al are investigated. Surface conditions included polishing to 4000 grit with SiC and polishing to 1 mum with diamond suspension. Surface impurities included a number of nitrate salts dissolved in water. Pore number distribution in each case was determined and related to the treatment effects. Testing was also performed on an Hf-containing Fe-40Al to evaluate the effect of adding a reactive element. It was found that surface roughness and the presence of impurities, even residues from water drops, increased the number of interfacial pores. Hf addition made the alloy more resistant to pore formation, but large pores developed under heavy salt deposits.