AN INNOVATIVE TECHNIQUE FOR THIN FILM INTERFACE TOUGHNESS RESEARCH
A material configuration of central importance in microelectronics, optoelectronics, and thermal barrier coating technology is a thin or thick film of one material deposited onto a substrate of a different material. Fabrication of such a structure inevitably gives rise to stress in the film due to lattice mismatch, differing coefficients of thermal expansion, chemical reactions, or other physical effects. Therefore, in general, the weakest link in this composite system often resides at the interface between the film and substrate. In order to make multi-layered electronic devices and structural composites with long-term reliability, the fracture behavior of the material interfaces must be known. Unfortunately, none of the state-of-the-art testing methods for evaluating interface fracture toughness is fully conformed to fracture mechanics theory, as is evident from the severe scatter in the existing data and the procedure dependence in film/coating evaluation methods. This project is intended to address the problems associated with this deficiency and offers an innovative testing procedure for the determination of interface fracture toughness applicable to coating materials in general. This new approach and the associated bi-material fracture mechanics development proposed for evaluating interface fracture toughness are described herein. The effort includes development of specimen configuration and related instrumentation set-up, testing procedures, postmortem examination, and analytical evaluation. A spiral notch torsion fracture toughness test system was utilized. The objective of the testing procedure described is to enable the development of new coating materials by providing a reliable method for use in assessing their performance. This innovative technology for measuring interface toughness was demonstrated for oxide scales formed on high-temperature alloys of MA956. The estimated energy release rate (in terms of J-integral) at the interface of the alumina scale and MA956 substrate is 3.7 N-m/m{sup 2}, and the estimated equivalent Mode I fracture toughness is 1.1 MPa {radical}m. This innovative technique is expected to greatly assist the development of coating materials with improved protective capabilities and provide a reliable method for use in assessing material performance.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 885569
- Report Number(s):
- ORNL/TM-2004/221; TRN: US200617%%53
- Country of Publication:
- United States
- Language:
- English
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