Oxidation of β‐NiAl, undoped and doped with Ce, Y, Hf

Abstract

Abstract The high temperature oxidation of β‐NiAl, undoped and doped with Ce, Y and Hf was studied in situ by thermogravimetry in He with p(O 2 ) = 5·10 −6 bar at 1000°C and by high temperature X‐ray diffraction at 950 and 1000°C in air. After the in situ experiments the samples were analysed by optical microscopy and SEM with EDX. It was observed by thermogravimetry that the weight gain for β‐NiAl+Hf is lower than for undoped β‐NiAl, whereas the weight gain for β‐NiAl+Y was similar to that for β‐NiAl. For β‐NiAl+Ce an enhanced increase of mass gain was observed. The in situ X‐ray‐experiments show that in the first hours of the oxidation process the metastable Θ‐Al 2 O 3 is formed, which transforms to the protective α‐Al 2 O 3 after different periods of time, depending on the dopant element and the temperature. The analysis of the samples shows that the ternary phases along the grain boundaries were oxidized, whereas the ternary phase precipitates within the grains remained unoxidized. The extend of the grain boundary oxidation increases from β‐NiAl+Hf and β‐NiAl+Y to β‐NiAl+Ce.