Structural evaluation and deformation features of polycrystalline BCC Fe with carbides during creep process

Abstract

Creep deformation of polycrystalline BCC Fe, with and without carbides, is investigated at various temperatures and different levels of applied stress through molecular dynamics. As creep curves reveal, samples with carbides show a little higher creep strain than samples without carbides. As temperature and applied stress increase, creep strain also increases at the same creep time. As the diameter of carbides increases, the creep life decreases, which is due to the brittle interface between carbides and the matrix Fe. Microstructure evolution of samples with 1 nm diameter of carbides and those without carbides, during creep deformation, is also analyzed. Phase transformation more likely occurs at higher temperatures and applied stresses, where, the fraction of BCC atoms decreases and that of HCP atoms increases as creep strain increases. The dislocation density of both samples, with and without carbides, shows a general descending trend during creep deformation. Grain boundary slip and rotation lead to the formation of the twin structure. Deformation twinning structure is considered as the main mechanism during creep deformation rather than dislocation evolution. Compared with pure polycrystalline, the samples with carbides form twinning structure more easily.