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In situ - Investigation of kinetics and stresses in alumina scales on NiAl during the phase transformation theta to alpha

: Eisenreich, Norbert; Fietzek, Harald; Garcia-Vargas, M.J.; Juez-Lorenzo, Maria; Kolarik, V.

Volltext urn:nbn:de:0011-n-1703519 (1.0 MByte PDF)
MD5 Fingerprint: 6e89f4d68dbfc4794635ef23170a2d2f
Erstellt am: 12.11.2014

Journal of Corrosion Science and Engineering : JCSE. Online resource (Nicht mehr online verfügbar) 6 (2003), Preprint 102, 14 S.
ISSN: 1466-8858
International Symposium on Corrosion Science in the 21st Century <2003, Manchester>
Zeitschriftenaufsatz, Konferenzbeitrag, Elektronische Publikation
Fraunhofer ICT ()

NiAl pure and NiAl doped with Hf were oxidised in air for 100 h at 950°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°C and cooled again. The residual stresses were measured every 200°C and plotted as a function of temperature. In the first 45 h for NiAl and 35 h for NiAl+Hf -Al 2O3 is observed, which transforms into -Al 2O3. In this time interval compressive stresses of -200 MPa were measured, and after the disappearance of the -Al 2O3 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 t he stresses decreased again to +500 MPa as before cooling. On the second cooling again a compressive stress of -1500 MPa was found.