Experimental investigation of the bond coat rumpling instability under isothermal and cyclic thermal histories in thermal barrier systems

Panat, Rahul Padmakar; Hsia, K. Jimmy

Permalink

https://hdl.handle.net/2142/292 Copy

Description

Title

Experimental investigation of the bond coat rumpling instability under isothermal and cyclic thermal histories in thermal barrier systems

Author(s)

• Panat, Rahul Padmakar
• Hsia, K. Jimmy

Issue Date

2003-05

Keyword(s)

• experimental solid mechanics
• fracture
• micromechanics
• plasticity

Abstract

"Reliable life prediction models for the durability of thermal barrier coatings require the identification of the relative importance of various mechanisms responsible for the failure of the coatings at high temperatures. Studies of these mechanisms in sub-systems of thermal barrier coatings can provide valuable information. In the present work, we undertake an experimental study of ""rumpling"", or progressive roughening of the bond coat surface in the bond coat-superalloy systems upon high temperature exposure. Thermal cycling and isothermal experiments are carried out on a platinum-aluminide bond coat and on a NiCoCrAlY bond coat deposited on a Ni-based superalloy in air and in vacuum. The cyclic experiments are conducted in air from 200°C to 1200°C for different levels of initial roughness of the bond coat surfaces. Isothermal experiments are carried out at various temperatures, ranging from 960°C to 1200°C. The bond coat surfaces in cyclic experiments rumple to a similar characteristic wavelength of about 60-100 µm and an amplitude varying from 2 µm to 5 µm. Additional small scale fluctuations are seen to develop between the thermally grown oxide (TGO) and the bond coat surface with a wavelength of about 3-5 µm. Smooth initial bond coat surfaces (fluctuations in tens of nanometers) are seen to have rumpled, indicating that significant initial flaws are not required for rumpling to occur. Observations of the rumpled bond coat edges are shown to indicate that bond coat stresses play a dominant role during the rumpling process. On comparing the experimental observations with existing rumpling models in literature, it is concluded that the TGO and the microstructural changes in the bond coat have a rather limited role in inducing rumpling. Diffusion driven by thermal mismatch stress in the bond coat is likely to be the dominant mechanism during rumpling."

Publisher

Department of Theoretical and Applied Mechanics (UIUC)

Series/Report Name or Number

TAM Reports 1022

ISSN

0073-5264

Type of Resource

text

Language

en

Permalink

http://hdl.handle.net/2142/292

Owning Collections