Effect of Palladium and Chromium Additions on the Oxidation Behaviour of beta-NiAl Alloys

摘要

Isothermal oxidation behaviour of a Pd and (Pd + Cr) beta-NiAl alloyed phase has been studied between 900 and 1200deg C. The main effect of noble metal addition is the improvement of Al diffusion rate, as compared to binary beta-NiAl alloy. This modification leads to an increase of k_p related to growth of alpha-Al_2O_3 and to a decrease of the initial transitory periods where metastable Al_2O_3 are formed. Alloying of the beta-(NiPdAl) with chromium suppresses the initial transition step at 1200deg C, because hexagonal (Cr, Al)_2O_3 nuclei promote probably alpha-Al_2O_3 formation.