Abstract
Si-Y2O3 co-deposition coatings on an Nb-silicide-based ultrahigh temperature alloy were prepared by pack cementation processes at 1050, 1150 and 1250°C for 5, 10, 15 and 20 h, respectively. The coating structure, phase constituents and compositional distribution were investigated by SEM, EDS and XRD. Both the formation mechanism and growth kinetics of coatings and the catalysis mechanism of Y2O3 were discussed. The results show that all Si-Y2O3 co-deposition coatings are composed of a (Nb, X)Si2 (X represents Ti, Hf and Cr elements) outer layer and a (Nb, X)5Si3 transitional layer. Some thin discontinuous (Cr, Al)2(Nb, Ti) Laves precipitates form between the substrate and (Nb, X)5Si3 transitional layer. The distribution of Y in the coatings is not uniform. The content of Y in (Nb, X)Si2 and (Nb, X)5Si3 phases is about 0.46%-0.57% (molar fraction) while that in (Cr, Al)2(Nb, Ti) is about 0.94%. With increasing co-deposition temperature, the content of Y increases obviously, while it increases slightly with the prolonging co-deposition time. The addition of Y2O3 in the pack mixtures not only refines the microstructure of the coatings, but also obviously catalyzes the coating growth.
Original language | English |
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Pages (from-to) | 1822-1828 |
Number of pages | 7 |
Journal | Zhongguo Youse Jinshu Xuebao/Chinese Journal of Nonferrous Metals |
Volume | 19 |
Issue number | 10 |
State | Published - Oct 2009 |
Keywords
- Nb-silicide-based ultrahigh temperature alloy
- Pack cementation process
- Si-YO co-deposition coatings
- Structure formation
- YO