MICROSTRUCTURE OF NI AND X-750 IRRADIATED AT LOW AND HIGH TEMPERATURES

摘要

Nickel-based alloys have been widely used in nuclearapplications because of high-temperature strength,toughness and corrosion properties. Inconel X-750 is anickel-chromium alloy precipitation-hardened byadditions of aluminum and titanium to form gamma prime(γ’) precipitates. It is used as spacer material in the fuelchannels of CANDU® 1 (CANada Deuterium Uranium)reactors, to separate hot pressure tubes (250-300 °C) andcold calandria tubes (60-80 °C). Understanding themicrostructural stability at both low and high operatingtemperatures are important for evaluating materialintegrity and predicting in-reactor performance. In thispaper, the microstructures of pure Ni and Inconel X-750irradiated in the National Research Universal (NRU)reactor at 60 °C and 300 °C were studied. The resultsshowed that dislocation loops, small dot defects andcavities were induced at both temperatures; their sizesincreased with temperature whereas their densitiesdecreased with temperature. Frank loops were created atboth temperatures, but the pure Ni contained a muchlower density of loops compared to Inconel X-750 underthe same irradiation conditions. The higher density ofFrank loops in Inconel X-750 was because of its lowerstacking fault energy due to the addition of alloyingelements such as Ti. The ’ precipitates in Inconel X-750were disordered at 60 °C but ordered at 300 °C. Nanosizecarbide precipitates were observed at 300 °C but notat 60 °C. In summary, a clear temperature effect on themicrostructural evolution, due to neutron irradiation at60 and 300 °C, was observed, which is expected to lead todifferences in performance for the materials at low andhigh temperatures.