Alloy 617 and Alloy 230 are lead structural materials for next generation nuclear power plant (NGNP). Both alloys possess good corrosion resistance and exceptional high-temperature strength. In order to gain a better understanding of the high-temperature degradation process of these materials, long-term (up to 10000 hours) aging experiments have been carried out to investigate the microstructural evolution and mechanical property development for both alloys. In the present study, focus is placed on the alloys aged for 10000 hours. Tensile and hardness tests were conducted. EDS coupled SEM and EBSD techniques were applied to reveal microstuctural characters of both alloys. Tensile tests were performed at strain rate of 10-3/s and in temperature range from room temperature to 1000oC. The Portevin-LeChatelier effect was observed and strain-rate sensitivities were studied. The tensile tests at room temperature show that both alloys softened significantly after aging at 1000ºC for 10000 hours, and the strength of both alloys was improved when aging at 900ºC. However, both long-term aged alloys, especially Alloy 230, exhibit high strength at high temperature. Carbide particle (mainly M23C6 and M6C) growth is known to be a dominant microstructual feature during long-term aging at elevated temperatures. The evolution of the carbide structure is also the major contributor to dislocation pile-up enhancement, dynamic recrystallization (DRX) area fraction increase and fracture mechanisms change, which in turn influence mechanical properties.
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High temperature aging study on long-term aged Alloy 617 and Alloy 230
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