The nature of dislocations and effect of order in rapidly solidified Fe-(5.5-7.5)wt.%Si alloys

Abstract

The results of an investigation on the nature of dislocations in rapidly solidified Fe-(5.5-7.5)wt.%Si has been presented as a function of the ordered state achievable during rapid solidification processing. The comparative study involves three rapid solidification processing routes for each alloy: melt spinning, planar flow casting and twin rolling. It is shown that for Fe-5.5wt.%Si alloy, ordering can be completely suppressed, while, in Fe-6.5wt.%Si alloy, the B2 ordering cannot be suppressed. The DO₃ state is present in twin-rolled Fe-wt.%Si alloy while, in rapidly solidified Fe-7.5wt.%Si alloy, it is the predominant ordered state. The disordered Fe-5.5wt.%Si alloy contains dislocation dipoles and vacancy loops, while rapidly solidified samples of Fe-6.5wt.%Si composition exhibit B2 order with a₀/2<111>type superdislocations where ain0 is the DO₃ lattice parameter. The paper reports the first observation of a four dislocation set in Fe-Si alloys with the superdislocation burgers vector a₀<111>. They are predominantly of mixed type, with some in edge orientation. Analysis of the experimental superdislocation separations in terms of existing models of interaction energies is presented. It is shown that separations reflect the non-equilibrium order parameters prevalent in the alloy. Furthermore it is pointed out that the dislocation separations observed in the DO₃-ordered state cannot be explained by the existing models.