The oxidation behaviour of an aligned Ni-Al-Cr3-C2 eutectic alloy under isothermal and thermal cycling conditions
✍ Scribed by Dr. J. G. Fountain; Prof. G. C. Wood; Dr. F. H. Stott
- Publisher
- John Wiley and Sons
- Year
- 1979
- Tongue
- German
- Weight
- 848 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0947-5117
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✦ Synopsis
The isothermal and thermal cycling oxidation behaviour of a directionally solidified Ni-Al-Cr3C2 eutectic alloy at temperatures from 800" to 1200 OC in flowing air have been investigated using several physical techniques. A t all temperatures an initial, protective, external layer of a-A12 O3 develops on the alloy surface. However, this breaks down mechanically during thermal cycling, enabling a less protective Cr203-rich scale to form. decreases with increasing temperature, failing after between 30 min and 2 h at 1100" and 1200 "C. However, if platinum metal is introduced into the hot zone at these temperatures, this period is increased to about 48 h.
Following formation of the external Cr2 O3 scale, internal oxide penetration into the alloy can be considerable, involving preferential oxide penetration down the alloy/carbide fibre interfaces. Thermal cycling does not influence markedly the oxidation behaviour, although it does result in formation of a greater quantity of nickel-rich oxide nodules on the scale surface following crack development in the Cr2 03-rich scale. This crack development is assisted by differential thermal contraction stresses.