抄録
The antiphase domain (APD) structure and the chemical composition of α1 bainite plates which form in a Cu-26.7 mass% Zn-4.0 mass% Al alloy during isothermal aging at 423 K have been studied by TEM dark field imaging and thin foil energy dispersive X-ray (EDX) microanalysis, respectively. At early stages of the transformation, both nearest-neighbor (NN) and next-nearest-neighbor (NNN) APD structures of the β3 parent phase are inherited by the α1 plate having an M18R structure. The EDX microanalysis indicates that a composition difference exists between the α1 plate and the β3 parent phase. With increasing aging time, the α1 plate thickens in a manner that only the NN APD structure remains inherited the thickened layers which become NNN disordered while both NN and NNN order and their APD structures remain inherited in the plate tip. In addition, solute rich composition profiles are present in the parent phase adjacent to the interface. Local solute depletion is also observed at dislocations in the parent phase. It is suggested that solute depleted defects act as nucleation sites for the formation of the α1 bainite plate which lengthens through a shear mechanism. Subsequent plate thickening is then controlled by a diffusional process. This model is consistent with the transformation kinetics, crystallography and microchemistry of the α1 plates.
