Neutron irradiation and stress-induced creep rafting of α′ phase in Fe-Cr-Al alloy: Crystal plasticity multi-phase-field simulation

Abstract

Servicing as the nuclear power plant structural materials, the ferrite stainless steels suffer the high irradiation and stress in working. Driven by the creep strain energy and neutron irradiation dose rate (DR), the Cr-enriched α′ phase will be rafted via elemental diffusion in Fe-Cr-based ferrite steels; the rafting of the α′ phase has great effects on the creep properties of the alloys. By coupling the rate theory and crystal plasticity model, the multi-field coupling phase-field modeling is performed to investigate the morphology and evolution kinetics of Cr-enriched α′ phase in Fe-35Cr-10Al (at.%) alloy under different neutron irradiation DRs with creep strains, the elements directional diffusions between the α/α′ phases are revealed by the diffusion potential. As the DR increases from 10⁻¹² to 10⁻⁷ dpa (displacements per atom)/s, the concentration of vacancies increases, accelerating the diffusion of solute atoms, and the rafting degree of α′ phase becomes more evident during the creep process. The rafting shows a wave shape for the concentration of equivalent strain in the narrow α-matrix channel, which produces a higher strain than inside of α′ phases and other regions of the α-matrix channel. In the initial stage, rapid increases in the partition coefficient of Cr and rapid decreases in Al between α and α′ phases indicate that the formation of α′ phase is dominant, and the obvious rafting happens at this stage. The multi-filed effects in diffusion time and nano length scale reveal the essential diffusion rafting of α′ phase in creep and irradiation states.