Transmission electron microscopic observation of thermally introduced planar faults in Fe-35 mol.% Al alloys

Thermally introduced planar faults are investigated both in an Fe-35 mol.%Al binary alloy and in B, Cr, Pd and W added ternary alloys using transmission electron microscopy. Air cooling of the alloys from 1273 K followed by annealing at 698 K for 120 h introduces two types of planar faults. One type is the antiphase boundary (APB), which is observed in all of the alloys. The other is the complex planar fault having both APB and stacking fault characters, which is observed in only the B-added alloy. The formation of the APBs is envisaged from a collapse of the lattice owing to vacancy condensation on triple layers of {111} planes. The size, distribution and planarity of the APBs are affected by ternary element addition.