Development of Oxidation-Resistant Hafnium Alloys
Final rept. 1 Sep 1969-31 Aug 1970
IIT RESEARCH INST CHICAGO IL
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The objective of the program was to investigate oxidation-resistant hafnium-base alloys as cladding for columbium- and tantalum- base alloys. Oxidation behavior of other combinations of Group 4B-5B alloys was also studied. Clad composites consisting of Cb-752 and Ta-10W cald with Hf-Ta-Cr-B-Al and Hf- Ta-Cr-Si alloys were exposed at 2200, 2500, and 2700F. Oxidation life varied from about 100 hr at 2200F to 25 hr at 2700F. Failure of the composites generally occurred at edges between the picture frame and substrate. The Hf-Ta- Cr-B-Al alloy indicated greater tolerance to surface defects than the Hf-Ta-Cr- Si alloy. Oxidation studies of modified Group 4B-5B alloys at 2000-2500F showed that oxidation resistance could be developed in several systems. The minor alloying additions employed were chromium, boron, columbium, silicon, yttrium, vanadium, and combinations of these elements. Chromium-silicon additions were the most effective in improving oxidation resistance in nearly all systems, although Cr-Al-Si combinations were also effective in Cb-Ti alloys. X-ray diffraction examination of oxides developed in oxidation-resistant hafnium-base alloys suggested that the oxide structures, probably a complex HfTa oxide, were similar for all alloys. A model for the oxidation resistant obtained in Hf-Ta alloys is proposed.
- Properties of Metals and Alloys