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 elec tron microscopy. They were found to lay in basal and inclined {231}-ty pe planes, forming a domain-like structure. Since the extinction crite rion was not followed by all the faults, image simulations based on th e dynamical theory in the two-beam approximation were performed. The d isplacement 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 th e 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, dependi ng on the way that they are connected to the basal fault. The differen ce between displacement vectors of connected faults implied the presen ce of partial dislocations at the intersections of faults.