Investigations on ordering and formation of antiphase domains in iron aluminides with chromium

The effect of chromium and nonequilibrium processing routes on the formatio n of B2 and DO3 ordering in Fe3Al(Cr) base alloys have been investigated. T hree selected iron aluminides, Fe70Al30, Fe60Al30Cr10 and Fe55Al22Cr23 (com positions in at.%), were processed by conventional ingot metallurgy. mechan ical milling (MA), and rapid solidification using planar flow casting (PFC) technique. The different processing routes and heat treatments influence s trongly the long range order (LRO) parameters, the lattice constants, and t he ordered B2 and DO3 structures in these aluminides. The ordered states pr ior to the A2 --> B2 and B2 --> DO3 phase transformations and after that we re imaged by transmission electron microscopy (TEM) and quantitatively eval uated by X-ray diffraction (XRD). All aluminides possess in the as-cast sta te the disordered A2 and ordered B2 structures. However, the Fe70Al30 and F e60Al30Cr10 aluminides show also the DO3 superlattice structure. After mech anically milling these alloys exhibit the disordered state in both composit ions. The highest value of the LRO parameter was achieved in melt spun ribb ons. The as-spun ribbons of the Fe70Al30, and Fe60Al30Cr10 aluminides posse ss large B2-antiphase domains (APDs) of the order of 5 to 10 microns and sm all DO3 domains of 2 to 5 nm in size whereas the Fe55Al22Cr23 aluminide rev eals only B2 nano-size domains.