[PO-C1] Poster Session 1

[P1-09] Structural and magnetic properties of long-period stacking ordered (LPSO) structure of iron; A first-principles study

^○Takao Tsumuraya¹, Ikumu Watanabe², Takahiro Sawaguchi² (1.Magnesium Research Center/POIE, Kumamoto Univ., Japan, 2.Research Center for Structural Materials, National Institute for Materials Science, Japan)

Fe-Mn-Si based alloys is known to exhibit a shape-memory effect associated with deformation-induced martensitic transformation from face-centered cubic (fcc) γ-austenite to hexagonal closed packed (hcp) ε-martensitic phase. The Fe-Mn-Si-based alloys with modified chemical compositions appeared to have outstanding properties of low-cycle fatigue lives, and a Fe-15Mn-10Cr-8Ni-4Si (mass%) alloy developed is practically used in a seismic damping component of architectural constructions. Recently, under cyclic push-pull loading of Fe-Mn-Si-based alloys, a new phase different from ε-phase was found by transmission electron microscopy. The new phase shows electron diffraction spots at the 1/3 position of the {10-11} spots of the ε-phase, which suggests the existence of a long-period stacking ordered (LPSO) structure. In 1960s, a similar phase was reported after several times of thermal cycles of γ-ε phase phase transitions in Fe-Mn-C alloys. However, actual stacking sequence of the LPSO phase and relative stability with γ and ε-phases still remain unclear. To understand these issues, we proposed several structural models of LPSO structure of pure Fe, such as 4H, 6H₁ and 6H₂, and discuss structural and magnetic stabilities among the candidate of LPSO structures with first-principles calculation methods. [1] L. I. Lysak, and B. I. Nikolin, Fiz Met. Mettaloved 20, 547 (1965), ibid. 23, 93 (1967).