EFFECT OF La AND Hf DOPANT ON THE HIGH TEMPERATURE OXIDATION OF CoNiCrAl ALLOYS
SONG Peng 1,2, LU Jiansheng 1, ZHANG Defeng 1, L¨U Jianguo 3, LI Dejiang 4
1. Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093
2. Forschungszentrum Juelich, IEK–2, Juelich 52425, Germany
3. Faculty of Applied Technology, Kunming University of Science and Technology, Kunming 650093
4. School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240
Cite this article:
SONG Peng LU Jiansheng ZHANG Defeng LU Jianguo LI Dejiang. EFFECT OF La AND Hf DOPANT ON THE HIGH TEMPERATURE OXIDATION OF CoNiCrAl ALLOYS. Acta Metall Sin, 2011, 47(6): 655-662.
Abstract CoNiCrAl alloys are widely used as bond coats for thermal barrier coating (TBC) at high operating temperature for energy conversion systems, especially turbine. However, the effect of reactive element (RE) on the oxidation behavior of CoNiCrAl alloys is still not uniform, thereby limiting the usage of the alloys. To study the effect of co–doped RE, the polished cast CoNiCrAlLa, CoNiCrAlHf and CoNiCrAlLaHf alloys were oxidized at 1100 ℃ in vacuum. Growth kinetics and adherence of oxide scales formed on above alloys were studied through comparing mass dynamics curves and tracer oxidation of the alloys. SEM, TG and XRD as well as secondary neutrals mass spectrometry (SNMS) were employed to study the microstructure and growth mechanism of the oxide layers. The results showed that a protective Al2O3 scale formed on the surface of CoNiCrAlLaHf alloy, and the Al2O3 scale showed a good adherence due to a pinning effect of the internal oxidation and less Ni(Co)Al2O4 formation. The Hf could suppress La enrichment at the oxide/alloy interface for the co–doped alloy. Oxygen inwards–diffusion along the oxide, which mainly controlled oxide scale growth, was observed when these three alloys oxidized in the atmospheres including tracer 18O. Enrichment of Cr, Co and Ni occurred at the outer part of oxide scale, and then decreased to a low level within the oxide layer. These Cr, Co and Ni enrichments could promote the Ni(Co)Al2O4 formation at the top of oxide scale for the single–doped alloys, which was detrimental to Al2O3 adherence properties.
