Maris-Sida, Monica C
(2005)
EFFECTS OF WATER VAPOR ON THE HIGH TEMPERATURE OXIDATION OF ALUMINA-FORMING COATINGS AND NI BASE SUPERALLOYS.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Oxidation studies were performed at 1100°C, 900°C and 700°C in dry air and air containing fixed partial pressures of water vapor on specimens of Ni base superalloys and coatings on these alloys that form α-alumina scales under oxidizing conditions. The materials studied included René N5, PWA1484, CMSX4, diffusion aluminide coatings (with or without Pt addition) on René N5, Thermal Barrier Coatings on René N5, and a Ni-8wt%Cr-6wt%Al model. All of these alloys and metallic coatings are normally α-alumina-formers under oxidization conditions. The observed important effects of water vapor include: • Increased severity of cracking and spalling of α-alumina scales in wet environments especially for those systems with alumina only moderately adherent in dry air; • Water vapor affects the nucleation and growth of α-alumina scales - the growth rate of α-alumina is increased in water vapor conditions; • Thicker oxides form during oxidation in wet air than dry air. The transient oxidation phenomenon is affected by the presence of water vapor due to more rapid growth of NiO during the transient period. The selective oxidation of aluminum is inhibited in water vapor conditions; even more adverse effects of water vapor are observed as the oxidation temperature is lowered. • Spinel phase forms on top of the alumina scales during long term oxidation. Current results indicate that nickel diffusion at alumina grain boundaries significantly contributes to the formation of new spinel phase at the oxide/gas interface and water vapor is found to enhance this process. Mechanisms for these observations are proposed.
Share
| Citation/Export: |
|
| Social Networking: |
|
Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
31 January 2005 |
| Date Type: |
Completion |
| Defense Date: |
5 October 2004 |
| Approval Date: |
31 January 2005 |
| Submission Date: |
11 October 2004 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Materials Science and Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
water vapor; alumina; oxidation |
| Other ID: |
http://etd.library.pitt.edu/ETD/available/etd-10112004-152721/, etd-10112004-152721 |
| Date Deposited: |
10 Nov 2011 20:02 |
| Last Modified: |
15 Nov 2016 13:50 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/9454 |
Metrics
Monthly Views for the past 3 years
Plum Analytics
Actions (login required)
 |
View Item |
![[feed]](/images/feed-icon-32x32.png){kind=icon}