Stability of External α-Al2O3 Scales on Alloy 602 CA at 1100–1200 °C
An external ultrathin α-Al2O3 scale grown on the Ni-base alloy 602 CA during air oxidation at 800 °C was characterized by means of high-resolution TEM/EDX and electron diffraction. Alloy samples pre-oxidized at 800 °C were subsequently exposed at 1100, 1150 and 1200 °C for up to 100 h. Whereas the external alumina remained stable at 1100 °C, with the increasing exposure temperature, the pre-grown alumina scale tended to break down resulting in an external chromia scale accompanied by internal alumina precipitation. The transition from external to internal Al oxidation was investigated using SEM/EDX/EBSD. The critical Al depletion at the scale-alloy interface during the post-exposure at 1100–1200 °C was modeled using the CALPHAD-based thermodynamic-kinetic approach.
KeywordsAlloy 602 CA Internal oxidation Alumina scales Depletion Breakaway Pre-oxidation
The authors are grateful to Dr. H. Hattendorf from VDM Metals (Werdohl, Germany) for providing a batch of 602 CA. Mr. H. Cosler is kindly acknowledged for carrying out oxidation tests.
- 1.V. D. M. ThyssenKrupp, Nicrofer® 6025 HT—alloy 602 CA, Material Data Sheet No. 4137, 2007.Google Scholar
- 2.U. Brill, Metall 46, 778 (1992).Google Scholar
- 3.U. Brill and J. Klower, Metall 51, 263 (1997).Google Scholar
- 4.A. P. Fraas, Heat Exchanger Design, (Wiley, New York, 1989).Google Scholar
- 5.H. R. N. Jones, The Application of Combustion Principles to Domestic Gas Burner Design, (Spon, London, 1989).Google Scholar
- 6.Haynes, Haynes 214—Material Data Sheet, (Haynes International, Kokomo, 2011).Google Scholar
- 7.P. J. Maziasz, I. G. Wright, J. P. Shingledecker, R. R. Gibbons and R. R. Romanosky, in Advances in Materials Technology for Fossil Power Plants; the Fourth International Conference, eds. R. Viswanathan, D. Gandy and K. Coleman (ASM International, Hilton Head Island, South Carolina, 2005), pp. 602–622.Google Scholar
- 12.V. P. Deodeshmukh, S. K. Srivastava, in: Superalloys 2008, Vol. 2008, p. 689.Google Scholar
- 14.Haynes, Haynes 224—Material Data Sheet, (Kokomo, Haynes International, 2011).Google Scholar