Detection of phase separation of neutron-irradiated Fe–Cr binary alloys using positron annihilation spectroscopy

Abstract

Phase separation in Fe–Cr binary alloys irradiated with neutrons at 473 K and 573 K was investigated using positron annihilation spectroscopy. Using positron annihilation coincidence Doppler broadening (CDB) measurements, the phase separation progress was observed in neutron-irradiated samples at 473 K and 573 K. Vacancy clusters were detected in Fe–xCr (x = 0, 9, 15, 30, 45, 50, and 100) during 473 K irradiation using positron annihilation lifetime measurements, but were not detected in Fe–xCr (x = 70, 85, and 91) irradiated at 473 K or in any samples irradiated at 573 K. Additionally, in Fe–xCr (x = 70, 85, and 91) irradiated at 473 K, all positrons were annihilated with core Fe electrons as determined from CDB ratio curves. Thus, vacancy clusters were not detected in the Fe-rich phase. There was a possibility that vacancy clusters are formed in the Cr-rich phase, but they were not detected by the PAS. Therefore, another method is necessary to investigate this further. Vickers hardness tests indicated that neutron-irradiated samples were harder than unirradiated samples. The contribution of phase separation and neutron-irradiation defects to increased hardness was dependent on the irradiation conditions including temperature and dose. Keywords: Fe–Cr binary alloys, Neutron irradiation, Positron annihilation, Hardness, Phase separation