In order to contribute to a better understanding of the processes, which occur in the
structure of FeCrAl alloys during oxidation, in situ – studies by two-dimensional high temperature
X-ray diffraction (2D-XRD) using a global area detector and grazing incidence with a
monocapillary have been performed. The 2D-XRD yields simultaneously with the identification of
the oxides and their formation kinetics information about the grain size, grain shape, stresses,
texture as well as grain movements during the oxidation process of both oxide and metal.
Two commercial FeCrAl alloys with different reactive element additions were investigated
in the temperature range of 850°C to 1100°C. In the range of 1100°C already in the first 5 min the
alloy grains become coarse and appear as single spots along the lateral profile in the 2D-XRD
pattern. Dynamic displacement of these spots along the 2θ – axis during the exposure indicates the
formation of stresses, which differ from grain to grain. Initially, re-crystallisation and grain growth
dominate and grains disappear and new grains appear. On further exposure the grains twist
continuously with 1° to 3° per hour, depending on the alloy. The “dancing grain” effect of the alloy
is probably related with growth stresses in the oxide scale and influenced by the bulging of the foil.
Simultaneously, α-Al2O3 is detected from the first pattern after 5 min and shows an
enhanced formation rate in the first 15 min of the oxidation. The α-Al2O3 grains are with 0.3 to 0.4
4m extremely fine and, a dense well adherent scale is observed even after 1 h.
In-Situ X-ray Diffraction Measurement for Pure Niobium Metal in High Temperature Hydrogen Atmosphere