The influence of microstructure on environmentally assisted cracking of alloy 718. Final report
- Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Nuclear Engineering
The goal of this project was to understand the effects of microstructure on the behavior of alloy 718 in aqueous environments. To achieve this goal the microstructure and resultant environmental properties of modified heat treatments were characterized. The role of grain boundary microstructure was emphasized. The performance of alloy 718, in both conventional and modified heat treatments, is also compared to existing data for the behavior of alloy X-750 in light water reactor environments. These comparisons were made with the goal of understanding the effects of alloy microstructure on performance. Four thermal treatments were investigated. Each condition was given an identical aging treatment (720 C/8h, furnace cool, 620 C/8h) to maintain equivalent precipitation of the strengthening precipitate, {gamma}{prime}. Annealing treatments were varied to control grain boundary precipitation. Stress corrosion cracking (SCC) resistance was determined using fatigue pre-cracked, bolt loaded specimens in high purity, deaerated water at 288 C. Reduced grain boundary precipitation substantially increases resistance to SCC for both grain sizes. The ADA condition showed no evidence of SCC for the environmental conditions studied. Alloy 718 direct aged (DA) also has superior SCC resistance relative to alloy X-750, an alloy more commonly used in light water reactor applications today. In corrosion fatigue crack growth experiments in high purity, deaerated water it was found that under all conditions studied the crack path was transgranular. Alloy 718 is not susceptible to accelerated, intergranular, corrosion fatigue crack growth at temperatures near 100 C as is alloy X-750 in some thermal treatments. This is most likely due to superior resistance to hydrogen embrittlement.
- Research Organization:
- Electric Power Research Inst., Palo Alto, CA (United States); Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Nuclear Engineering
- Sponsoring Organization:
- Electric Power Research Inst., Palo Alto, CA (United States)
- OSTI ID:
- 251386
- Report Number(s):
- EPRI-TR--104927
- Country of Publication:
- United States
- Language:
- English
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