Alexandria Digital Research Library

Design and characterization of high-strength bond coats for improved thermal barrier coating durability

Author:
Jorgensen, David John
Degree Grantor:
University of California, Santa Barbara. Materials
Degree Supervisor:
Tresa M. Pollock
Place of Publication:
[Santa Barbara, Calif.]
Publisher:
University of California, Santa Barbara
Creation Date:
2016
Issued Date:
2016
Topics:
Engineering and Materials science
Keywords:
Bond Coats
Thermal Barrier Coating
Thermal Cycling
Rumpling
Ni3Al Gamma Prime
Platinum Aluminide
Genres:
Dissertations, Academic and Online resources
Dissertation:
Ph.D.--University of California, Santa Barbara, 2016
Description:

High pressure turbine blades in gas turbine engines rely on thermal barrier coating (TBC) systems for protection from the harsh combustion environment. These coating systems consist of a ceramic topcoat for thermal protection, a thermally grown oxide (TGO) for oxidation passivation, and an intermetallic bond coat to provide compatibility between the substrate and ceramic over-layers while supplying aluminum to sustain Al2O 3 scale growth. As turbine engines are pushed to higher operating temperatures in pursuit of better thermal efficiency, the strength of industry-standard bond coats limits the lifetime of these coating systems. Bond coat creep deformation during thermal cycling leads to a failure mechanism termed rumpling. The interlayer thermal expansion differences, combined with TGO-imposed growth stresses, lead to the development of periodic undulations in the bond coat. The ceramic topcoat has low out-of-plane compliance and thus detaches and spalls from the substrate, resulting in a loss of thermal protection and subsequent degradation of mechanical properties. New creep resistant Ni3Al bond coats were designed with improved high-temperature strength to inhibit this type of premature failure at elevated temperatures. These coatings resist rumpling deformation while maintaining compatibility with the other layers in the system. Characterization methods are developed to quantify rumpling and assess the TGO-bond coat interface toughness of experimental systems.

Cyclic oxidation experiments at 1163 °C show that the Ni3Al bond coats do not experience rumpling but have faster oxide growth rates and are quicker to spall TGO than the (Pt,Ni)Al benchmark. However, the Ni3Al coatings outperformed the benchmark by over threefold in TBC system life due to a higher resistance to rumpling (mechanical degradation) while maintaining adequate oxidation passivation. The Ni3Al coatings eventually grow spinel NiAl2O4 on top of the protective Al2O3 layer, which leads to the detachment of the ceramic topcoat. Furthermore, bilayer Ni3Al+NiAl architectures have been investigated to improve the oxidation performance of the monolithic Ni 3Al coatings while maintaining their high strength. These bilayer architectures are shown to improve the cyclic oxidation performance of the monolithic layers and increase the TBC system life. The design, characterization, and experimentation of these coatings is discussed and related to the development of high-strength coatings.

Physical Description:
1 online resource (301 pages)
Format:
Text
Collection(s):
UCSB electronic theses and dissertations
ARK:
ark:/48907/f36w9b6v
ISBN:
9781369341102
Catalog System Number:
990047189470203776
Rights:
Inc.icon only.dark In Copyright
Copyright Holder:
David Jorgensen
File Description
Access: Public access
Jorgensen_ucsb_0035D_13208.pdf pdf (Portable Document Format)