In situ - Investigation of Kinetics and Stresses in Alumina Scales on NiAl during the Phase Transformation Theta to Alpha

NiAl pure and NiAl doped with Hf were oxidised in air for 100 h at 950 deg C. The residual stresses and the oxide scale growth were measured in situ by high temperature X-ray diffraction and evaluated as a function of time. A mathematical model was applied to describe the alumina growth during the t...

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Bibliographic Details
Published in:The journal of corrosion science and engineering 2003-01, Vol.6
Main Authors: Eisenreich, N, Fietzek, H, Garcia-Vargas, M J, Juez-Lorenzo, M, Kolarik, V
Format: Article
Language:English
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Summary:NiAl pure and NiAl doped with Hf were oxidised in air for 100 h at 950 deg C. The residual stresses and the oxide scale growth were measured in situ by high temperature X-ray diffraction and evaluated as a function of time. A mathematical model was applied to describe the alumina growth during the transformation and oxidation process. After the isothermal period the samples were cooled to room temperature, reheated to 950 deg C and cooled again. The residual stresses were measured every 200 deg C and plotted as a function of temperature. In the first 45 h for NiAl and 35 h for NiAl+Hf theta-Al2O3 is observed, which transforms into alpha-Al2O3. In this time interval compressive stresses of -200 MPa were measured, and after the disappearance of the theta-Al2O3 nearly constant tensile stresses of +500 MPa were detected. On cooling compressive stresses reaching -1500 MPa at room temperature were formed due to the different thermal expansion coefficients of the metal and the alumina. On reheating the stresses decreased again to +500 MPa as before cooling. On the second cooling again a compressive stress of -1500 MPa was found. [This is an unrefereed preprint].
ISSN:1466-8858
1466-8858