Phase-field simulation of - phase separation in nuclear Fe-Cr-Al-based alloys induced by chemical composition and irradiation

The present work applied the phase-field (PF) method to comprehensively investigate the effects of chemical composition and irradiation on the alpha-alpha ' phase separation in nuclear Fe-Cr-Al-based alloys since it is difficult to be clarified by experiments alone. Three series of alloys were designed by changing the amount of Cr, Al, and Mo in sequence, being Fe-xCr-9.375Al, Fe-15.625Cr-xAl, and Fe-(15.625-x)Cr-9.375Al-xMo (at%). The PF simulation was based on the Cahn-Hilliard equation, in which a radiation-enhanced model was embedded to consider the atomic mobility of alloying elements under irradiation. The results indicated that the Cr element can accelerate the alpha-alpha ' phase separation, as demonstrated by the increase in volume fraction (5.1% in 15Cr and 12.6% in 40Cr) and the reduction in incubation time of alpha ' nanoprecipitates (5000 h in 15Cr and 200 h in 28Cr) during aging at 573 K, while Al and Mo inhibit the phase separation effectively due to an obvious extension of the incubation time (5x104 h in 1.7Mo). Coupled with the irradiation, the phase separation will be speeded up significantly with a severe shrinkage of the incubation time to 2 - 388 h (0.14 - 0.5 dpa) in 15Cr. The mechanisms on the alpha-alpha ' phase separation were then discussed from both thermodynamic and kinetic viewpoints, in which the incubation time is closely related to the driving force of alpha ->(alpha+alpha ') and the atomic mobility of Cr. The present PF simulation can provide an important method to predict the alpha-alpha ' phase separation in novel nuclear Fe-Cr-Al-based alloys.