Micropillar compression deformation of single crystals of the intermetallic compound ς-FeZn₁₃

The deformation behavior of the f phase in the Fe-Zn system has been investigated by micropillar compression tests at room temperature with the use of single crystals with 13 different crystal orientations prepared by the focused ion beam method. Two different slip systems, {110}〈112〉 and (100)[001], are observed to operate. The critical resolved shear stresses (CRSS) value for {110}〈112〉 slip is more than three times smaller than that for (100)[001] slip. From the anisotropy in CRSS for these two slip systems, {110}〈112〉 slip is predicted to operate for most crystal orientations, except for a narrow orientation region around [305] where (100)[001] slip operates. The CRSS for {110}〈112〉 slip shows an inverse power-law scaling against the specimen size with an exponent of -0.517. The bulk CRSS value for {110}〈112〉 slip is estimated to be 62-76 MPa by taking into account the specimen size effects of CRSS. The reasons why {110}〈112〉 slip with a rather long Burgers vector (0.7700 nm) is selected as the easiest slip system are discussed in terms of the nature of atomic bonding in the crystal structure, especially the rigid atomic bonding within an Fe-centered Zn₁₂ icosahedron (for slip plane selection), and the energetic barrier height along the slip direction and the resultant possible dissociation schemes (for slip direction selection). Some implications are made on how the deformability of the ς phase can be improved in the textured coating layer in galvannealed steels based on the results obtained.