Direct observation of higher order atomistic structure in TiNiFe at lower temperature phase

TiNiFeの低温相における高次構造の直接観察

Hu, W.; 林 好一*; 八方 直久*; 細川 伸也*; 寺井 智之*; 福田 隆*; 掛下 知行*; 高橋 正光

Hu, W.; Hayashi, Koichi*; Happo, Naohisa*; Hosokawa, Shinya*; Terai, Tomoyuki*; Fukuda, Takashi*; Kakeshita, Tomoyuki*; Takahashi, Masamitsu

The Ti-Ni series shape memory alloys shows novel phase transition behaviours depending on the concentrations of doped third element Fe and only the precursor phenomena are observed when more than 6 at.% of Fe atoms are substituted for Ni. In the present work, we have focused on TiNiFe, which exhibits only a second-order-like parent (P) - incommensurate (IC) - commensurate (C) transition, and investigated the local structure around Fe and Ni by the X-ray fluorescence holography (XFH). We successfully obtained 3D real space local structures at both the P- and C-phases. Cluster-like structure appears around Fe and the direct evidence of the existence of supperlattice structure at C-phase appears around Ni. We discuss structural changes by comparing the microstructures obtained around Fe and Ni at two phases. The results provide hints on the lattice modulation related to precursors of the martensitic transition and direct evidence of superlattice phenomena.