Micropillar compression tests made for each of the five intermetallic phases of the Fe-Zn system, which constitute the coating of galvannealed steels, have revealed that the Γ phase formed in direct contact with the steel substrate and the ζ phase formed on the outermost surface are ductile, sandwiching the other three brittle phases (Γ 1 , δ 1k and δ 1p). Compression deformability of these ductile phases is considered to mitigate the coating failure through sustaining ruptured fragments of the brittle phases during the forming process.

The deformation behavior of the ζ (zeta) phase in the Fe-Zn system has been investigated by micropillar compression tests at room temperature with the use of single crystals with thirteen 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 [ 3 05] where (100)[001] slip operates. The CRSS for {110}<112>

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The deformation behavior of the Γ (gamma) phase in the Fe-Zn system has been investigated via room-temperature compression tests of single-crystal micropillar specimens fabricated by the focused ion beam method. Trace analysis of slip lines indicates that {110} slip occurs for the specimens investigated in the present study. Although the slip direction has not been uniquely determined, the slip direction might be <111> in consideration of the crystal structure of the Γ phase (bcc).