A SISF formation mechanism in Ni3Al

Abstract

In the ordered Ll2 structure, the superlattice intrinsic stacking fault (SISF) has often been observed to be formed through two steps, the formation of antiphase boundary (APB) by dissociation of superlattice dislocation at first and then the conversion of the APB to the SISF(1,2). The present paper studied the SISF in NijAl by TEM and found that the SISF can also be formed by superlattice dislocation dipoles.The tensile deformation of the directionally solidified Ni3Al (of composition in wt% of 82.88Ni, 8.5A1, 0.8Zr, 7.8Cr, and 0.02B) specimens was performed at room temperature. Thin foils were made normal to the specimen axis (parallel to [001]) and studied at 200 kv in H-800.As shown in Fig.l, a SISF is formed at the end of a superlattice dislocation dipole, according to the SISF-type dissociation [10] =1/3 [11]+1/3[2l] on (111) plane. In Fig.2, a superlattic dislocation dipole is moving away from a SISF.