Isothermal Oxidation Behavior of Dysprosium/S-Doped β-NiAl Alloys at 1200°C

A β-NiAl alloy with normal purity, a S-doped and a Dy and S co-doped b-NiAl alloys were prepared by arc-melting and their corresponding S contents were less than 20×10 6, 33×10-6 and 22×10-6, respectively. The isothermal oxidation behavior of the alloys at 1200° C was investigated and the extent of S segregation at the scalee alloy interface was determined by scanning Auger microscopy. S-doping had no significant effect on the phase transformation rate from q- to a-Al2O3, while the addition of Dy retarded this process. For the Sdoped alloy, scale rumpling occurred only after 2 h thermal exposure and numerous large voids were observed at the scalee alloy interface where S segregated. In contrast to this, the oxide scale formed on the Dy and S co-doped alloy still remained flat even after 50 h isothermal oxidation and only small voids existed at the interface where S segregation was not detected.