Effect of test atmosphere composition on high-temperature oxidation behaviour of CoNiCrAlY coatings produced from conventional and ODS powders. (4th May 2018)

• Record Type: Journal Article
• Authors: Huang, T.; Bergholz, J.; Mauer, G.; Vassen, R.; Naumenko, D.; Quadakkers, W. J.
• Is Part Of: Materials at high temperatures. Volume 35:Number 1/2/3(2018)
• Page Start: 97
• Page End: 107
• Publication Date: 2018-05-04
• Subjects: Oxidation -- alumina scale -- oxygen diffusion -- ODS coating; Materials at high temperatures -- Periodicals; High temperatures -- Periodicals; 620.1121705
• DOI: 10.1080/09603409.2017.1389422
• Languages: English
• ISSNs: 0960-3409

Abstract

Abstract: The oxidation behaviour of free-standing CoNiCrAlY coatings produced by low-pressure plasma spraying using conventional powder and oxide dispersion strengthened (ODS) powder containing 2 wt. % Al-oxide dispersion was investigated. Thermogravimetric experiments at 1100 °C in Ar-20%O2 and Ar-4%H2 -2%H2 O showed lower oxidation rates of the ODS than the conventional coating. In the latter material the scale growth was enhanced by extensive Y-incorporation of Y/Al-mixed oxide precipitates in the scale and apparently by Y-segregation to oxide grain boundaries. In the ODS coating the alumina dispersion bonded Y in the form of Y-aluminate thereby effectively suppressing scale 'overdoping'. SEM/EBSD studies of all alumina scales revealed a columnar grain structure with the lateral grain size increasing approximately linearly with depth from the oxide/gas interface. For both coatings the alumina scale growth was slower in Ar–H2 –H2 O than in Ar–O2 . The result is believed to be related to a lower oxygen potential gradient and to slower grain boundary diffusion in the scale forming in H2 /H2 O containing gas.