Formation mechanism of periodic layered structure between Fe–Cr–Si–B cast steel with high B content and molten Al

The periodic layered structures (PLSs) have been confirmed to be formed as the Fe–Cr–B cast steels containing about 3.0 wt% B were dipped into Al melt. However, there was no PLSs formed, in terms of a novel Fe–Cr–Si–B cast steel with B content much higher. The interfacial reaction between borides contained in this novel Fe–Cr–Si–B cast steel with 8.5 wt% B content and Al at 750 °C was studied using hot dip aluminizing, thermal diffusion treatment, and subsequent SEM, TEM, and 3DAP of the obtained specimens. The PLSs were formed in situ after a long period of incubation because of the high chemical stability induced by the overstoichiometric (Cr, Fe)2B. The formation of PLSs proceeded through an intermediate state which involved transformation from disordered particles to ordered Cr–Al–B intermetallic compound. Owing to the formation of the localized melt of FeAl3–Al eutectics, the understoichiometric Cr–Al–B intermetallic compound gradually drifted to agglomerate and grew under the effects of the driving force of the lamellar growth of MAB phase and the thermal flux, along with the drag of the overstoichiometric Cr–Al–B intermetallic compound due to the interlaced structure.