Transmission Electron Microscopy Observations of the Phase Separation of D0₃ Precipitates in an Elastically Constrained Fe–Si–V Alloy

Abstract

When Fe–16.2mol%Si–13.3mol%V alloy is homogenized at 1473 K for 7.2×10³ s and then quenched into iced brine, D0₃ (ordered bcc) particles appear in the A2 (disordered bcc) matrix. The D0₃ particles are cuboidal because of the influence of elastic energy which arises from the lattice mismatch between the A2 matrix and the D0₃ particle. When the two-phase microstructure of A2+D0₃ is aged at 923 K, the phase separation of D0₃ precipitate takes place and fine A2 particles appear in each cuboidal D0₃ particle. In the course of further ageing at 923 K, the A2 particles coarsen to become plates in the D0₃ particles as a result of elastic energies, then the A2 plates elongate along {100} to reach the A2 matrix surrounding the D0₃ particles, and finally the split of D0₃ particles is realized. Such a split phenomenon takes place throughout the microstructure to bring the refinement or at least the decelerated coarsening of two-phase microstructure, which is a result of not only the elastic energies but also the chemical free energy.