The effect of high-temperature oxidation on the creep behavior of a superalloy (NIMONIC-105)
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RODUCTION
SUPERALLOY-BASED components are exposed to corrosive and oxidizing environments during operation. Studies of varying nature have been conducted to understand the effect of environment on the performance of the superalloys. The effect of prior exposure to high temperatures in oxidizing environment on the creep properties has been one such aspect of investigation.[1,12] Bricknell and Woodford[4] exposed the IN*-738 alloy in various gaseous environments at elevated temperatures and showed that oxygen degraded the subsequent creep properties most severely. INCONEL* *IN and INCONEL are trademarks of INCO Alloys International, Inc., Huntington, WV.
600 and INCONEL X-750 exhibited embrittlement during creep testing at lower temperatures following exposure to air at 1000 ⬚C and 1050 ⬚C.[7,8,9] However, no embrittlement was observed when the exposure temperatures were increased to 1120 ⬚C and 1150 ⬚C.[10,11] Pandey et al.[13] proposed, based on the electron probe microanalysis (EPMA), that kinetics of formation of a protective oxide layer were faster than that of inner oxygen diffusion at high temperatures. At lower temperatures, the trend was reversed. Dyson and Osgerby[14] concluded that this behavior is due to the lower activation energy for oxygen diffusion compared to that of oxide layer formation. This is explained schematically in Figure 1. Both depth of oxide layer and oxygen penetration can be represented by the Arhenius type of relation. For a given time interval, the slope of ln (depth of oxide layer) or ln (depth of oxygen penetration) vs 1/T is the activation energy of oxide layer formation or oxygen penetration, respectively. As shown in Figure 1, at higher temperatures, the process with high activation energy (oxide formation) dominates, and at lower temperature, the process with lower activation energy (oxygen diffusion) dominates.
D.V.V. SATYANARAYANA and D.V. KOLLURU, Scientists, are with the Defence Metallurgical Research Laboratory, Kanchanbag, Hyderabad500058, India. Manuscript submitted August 31, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
Osgerby and Dyson[15] have shown that prior exposure of a NIMONIC*-105 alloy in air at 1000 ⬚C resulted in no *NIMONIC is a trademark of INCO Alloys International, Inc., Huntington, WV.
embrittlement. They proposed that NIMONIC-105 can readily form protective oxide layers at all temperatures as it contains much higher aluminum than INCONEL alloys. Hence, it is immune to oxygen-induced embrittlement resulting from high-temperature exposure. However, investigations by Pandey et al.[16] revealed that solution treatment of a NIMONIC-105 alloy in air at 1050 ⬚C led to significant embrittlement during creep testing at 750 ⬚C. Presently, the authors are working toward understanding the oxygen induced damage as a function of various parameters such as prior exposure temperature, creep testing temperature, and chemical composition. The current report details a part of that work concentrating on the creep embrittlement observed in the NIMONIC-105 between 650
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