LATTICE-RELAXATION AROUND NONBASAL PLANE STACKING DEFECTS IN 2H MARTENSITE

Stacking faults produced in the spontaneous martensitic transformation of 2H Cu-Zn-Al alloys have been studied by means of transmission electron microscopy. They were found to lay in basal and inclined {231}-type planes, forming a domain-like structure. Since the extinction criterion was not followed by all the faults, image simulations based on the dynamical theory in the two-beam approximation were performed. The displacement vectors were determined by comparison between experimental and calculated images. The basal fault displacement vector was found to be R = [+/- (1/3 + delta)1/2,1/2] where delta takes into account the orthorhombic distortion of the unit Cell. Further relaxations around the inclined faults were observed, giving rise to two types of fault F1 and F2, having additional displacement vectors, epsilon1 = [-0.03, 0.03, -0.16] and epsilon2 = [-0.28, 0.03, -0.16] respectively, depending on the way that they are connected to the basal fault. The difference between displacement vectors of connected faults implied the presence of partial dislocations at the intersections of faults.