Oxidation protection of Ti-aluminide orthorhombic alloys: An engineered multilayer approach
- UES, Inc., Dayton, OH (United States)
- Air Force Research Lab., Wright-Patterson AFB, OH (United States). Materials and Manufacturing Directorate
The lack of high-temperature environmental resistance is a major issue in the application of orthorhombic-based titanium aluminide alloys (O alloys) and their composites. Improvement in environmental capability can be achieved by applying diffusion barrier coatings to the surface of the orthorhombic matrix alloy. However, since thin coatings are prone to foreign-object damage, an approach based on thicker multilayer materials may be more prudent for fracture-critical applications. In the present study, foils of the orthorhombic alloy were diffusion bonded on either side with a {gamma} alloy, the latter used in an attempt to provide environmental protection. Mechanical tests suggested that the {gamma} alloy was successful in preventing degradation of the O alloy due to oxidation and interstitial embrittlement under thermal cycling conditions. Processing below the {beta} transus of the O alloy provided an improvement in the stress and strain to failure of the joined material compared to materials processed above the transus. However, in either case, the strengths of the joined materials were significantly lower than that of the uncoated O alloy with similar microstructures. Results suggest that the low strength of the joined materials may be due to cracking of the {gamma} alloy, resulting in premature failure of the O alloy. Finite element analysis (FEA) was performed to understand the stress distribution in the joined material and to investigate approaches for reducing the residual stress. Several approaches for improving the stress and strain to failure of the joined material are presented.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 616502
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 29, Issue 4; Other Information: PBD: Apr 1998
- Country of Publication:
- United States
- Language:
- English
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