Structure and oxidation behavior of Si–Y co-deposition coatings on an Nb silicide based ultrahigh temperature alloy prepared by pack cementation technique
✍ Scribed by Xiaodong Tian; Xiping Guo
- Publisher
- Elsevier Science
- Year
- 2009
- Tongue
- English
- Weight
- 762 KB
- Volume
- 204
- Category
- Article
- ISSN
- 0257-8972
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✦ Synopsis
In order to improve the oxidation resistance of silicide coatings on Nb silicide based alloys, Y-modified silicide coatings were prepared by co-depositing Si and Y at 1050, 1150 and 1250 °C for 5-20 h, respectively. It has been found that the coatings prepared by co-depositing Si and Y at 1050 and 1150 °C for 5-20 h as well as at 1250 °C for 5 h were composed of a thick (Nb,X)Si 2 (X represents Ti, Cr and Hf elements) outer layer and a thin (Nb,X) 5 Si 3 inner layer, while the coatings prepared by co-depositing Si and Y at 1250 °C for 10-20 h possessed a thin outer layer composed of (Ti,Nb) 5 Si 3 and Ti-based solid solution, a thick (Nb,X)Si 2 intermediate layer and a thin (Nb,X) 5 Si 3 inner layer. EDS analyses revealed that the content of Y in the (Nb, X)Si 2 layers of all the coatings was about 0.34-0.58 at.% while that in the outer layers of the coatings prepared by co-depositing Si and Y at 1250 °C for 10-20 h was about 1.39-1.88 at.%. The specimens treated by co-depositing Si and Y at 1250 °C for 10 h were selected for oxidation test. The oxidation behavior of the coating specimens at 1250 °C indicated that the Si-Y co-deposition coating had better oxidation resistance than the simple siliconized coating because the oxidation rate constant of the Si-Y co-deposition coating was lower than that of the simple siliconized coating by about 31%. The scale developing on the Si-Y codeposition coating consisted of a thicker outer layer composed of SiO 2 and TiO 2 and a thinner SiO 2 inner layer.