Scale mass gain, morphology and phase composition of air and steam oxidized electron beam melted and cast Ti–48Al–2Nb-0.7Cr-0.3Si alloys. (June 2022) - Dudziak, T.
Abstract: Oxidation resistance of γ - TiAl alloy RNT650 exposed to air and steam at 650 °C for 1000 h is reported. The samples were prepared either by conventional casting (CM) or electron beam melting (EBM). The materials were analysed using XPS, XRD, SEM and STEM/EDS techniques. Mass gains in both alloys were comparable and relatively small for air oxidation, but for steam treatment the mass increase in the EBM alloy was up to 50% more than in the CD material. Mass gain showed a faster growth of the scale in the steam treated material. The oxidized materials developed thin nano-crystalline scales predominantly of aluminium and titanium oxides arranged in TiO2 +Al2 O3 /TiO2 /Al2 O3 sublayers. Whiskers were detected sticking above the scale surfaces, with density much higher in steam treated specimens. Graphical abstract: Image 1 Highlights: Mass gain of air oxidized alloys were similar, the steam oxidized EBM was 50% higher. Only a few samples showed parabolic mechanisms of the scale formation. Phase constituents in both type of alloys were similar based on XRD investigations. More porous oxide scale were formed in steam than in air based on TEM observations. Always a very thin Al2 O3 layer at the scale – substrate interface was observed.