X. L. Jiang, C. B. Liu, L. S. Yu, Central South University, Changsha, China
In this study, NiCoCrAlTaY bond coat on Ni substrate was deposited by low pressure plasma spray and nanostructured and conventional ZrO2+7-8wt.%Y2O3 top coat was deposited by air plasma spray. Agglomerated nano-powder calcinated at 1250oC was used as feedstock powder. Nanostructured and conventional TBCs samples were calcinated from 1050oC to 1250oC for 2-20 h. Experimental results indicate that monoclinic/tetragonal phases in the agglomerated nano-powder were transformed into cubic phase after calcination. The cubic phase content increases with increasing calcination temperature. High temperature calcination can make the yttria segregated at grain boundaries dissolve in zirconia. Different from the phase constituent of the as-sprayed conventional TBC which consists of diffusionless transformed tetragonal, the as-sprayed nanostrcutured TBC consists of cubic phase containing high yttria. No phase transformation in both nanostructured and conventional TBCs after calcination is found.
Summary: I am a professor of the Central South University in China. I have worked on thermal spray technology since 1991. The paper that will be presented in the ITSC-2009 reveals the following significant phenomenon. Monoclinic/tetragonal phase in nanocrystalline ZrO2-8wt.%Y2O3 powder was transformed into cubic phase when heat treatment was conducted. The content of cubic phase increases with increasing heat treatment temperature. When agglomerated nano-powder heat treated at 1250oC was used, the phase constituents in the nanostructured and conventional zirconia thermal barrier coatings deposited by air plasma spray are different.
