Cracking and healing of oxide scales on Ti-Al alloys at 900 C
- Lurgi Oel Gas Chemie GmbH, Frankfurt/Main (Germany)
- Karl-Winnacker-Inst. der DECHEMA e.V., Frankfurt/Main (Germany)
This behavior of oxide scales on Ti-50Al and Ti-50Al-2Nb (at.%) was investigated in constant strain-rate tensile tests at 900 C in air. The strain rates ranged between 1 {times} 10{sup {minus}9} sec{sup {minus}1} and 3 {times} 10{sup {minus}4} sec{sup {minus}1}. The tests were accompanied by acoustic-emission measurements in order to detect scale-cracking processes during deformation. The critical strains to scale cracking amounted to 0.12-0.5% for the scales on TiAl and 0.17--0.58% for Ti-50Al-2Nb. These values were found to depend strongly on the size of the pores in the scales and, by using a fracture mechanics-based model, the results for the critical strains could be condensed into a narrow scatterband, which is independent of the applied strain rate. Healing of scale cracks was found for strain rates below 1.5 {times} 10{sup {minus}6} sec{sup {minus}1} (Ti-Al) and 1.9 {times} 10{sup {minus}4} sec{sup {minus}1} (Ti-Al-Nb), respectively. It turned out that the healing process is dominated by TiO{sub 2} growth. In a later healing stage, the original Al{sub 2}O{sub 3} barrier is, however, restored in the scale on Ti-50 Al. For Ti-50Al-2Nb, an Al{sub 2}O{sub 3} layer is found on the former scale-crack contours. The healing process is also described by a quantitative model. As a general conclusion from the investigations, it turned out that critical strains to oxide-scale cracking can be estimated from just simple oxidation experiments without sophisticated mechanical testing if the microstructural parameters of the scale are determined quantitatively as a function of oxidation time by metallographic means.
- OSTI ID:
- 679201
- Journal Information:
- Oxidation of Metals, Vol. 52, Issue 3-4; Other Information: PBD: Oct 1999
- Country of Publication:
- United States
- Language:
- English
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