Microstructure evolution in MA956 neutron irradiated in ATR at 328 °C to 4.36 dpa

Abstract

MA956 is an iron-chromium-aluminum (FeCrAl) based oxide dispersion strengthened (ODS) alloy produced by mechanical alloying. The alloy was irradiated in the Advanced Test Reactor (ATR) at 328 °C up to 4.36 dpa with both thermal and fast neutrons. The microstructures before and after irradiation were investigated by various TEM techniques. The size and number density of dislocation loops, voids, and oxides were analyzed. The results showed that both 1/2<111> and <100> loops were generated in irradiated materials. The number density of dislocation loops reached up to 7.17 × 1021/m3. Cavities/voids were formed during irradiation. Argon bubbles were observed in unirradiated materials attached to the surface of oxide particles. The swelling rate was estimated to be 0.08% without subtracting pre-existed Ar bubbles. The oxide particles could maintain crystal structure during irradiation. The oxides had small decrease in size but half reduction in number density after irradiation. Calculation estimated that <100> loops and dislocation lines contributed most to hardening. Alpha prime precipitates were suggested to be formed by comparing to the calculated hardening. Dislocation lines are demonstrated not forming tangles in irradiated specimens.