Oxidation of Aluminides

摘要

In the recent years the oxidation of NiAl, FeAl and TiAl and alloys of these intermetallics have been investigated extensively. For NiAl and FeAl selective Al_2O_3 formation occurs but at lower temperatures metastable modifications are formed. The nucleation, morphologies, trans-formations and growth rates of these modifications and of alpha-Al_2O_3 are described and also the ef-fects of alloying additions on their occurrence. Depending on temperature and stoichiometric com-position, marked Al-depletion and cavity formation are observed upon oxidation of NiAl and FeAl. Under certain conditions intergranular and internal oxidation of NiAl is reported. The mechanisms of these phenomena have been elucidated and described. During oxidation of TiAl generally mixed layers of Al_2O_3 and TiO_2 are grown, due to the similar oxygen affinity of Ti and Al. Different forms of scale structure are observed for oxidation in oxygen. Various conditions are reported which effect the oxidation resistance. For example, the presence of nitrogen and water vapour deteriorate the resistance, and surface finish (grinding) and certain alloying elements (Nb) improve the resistance.