Fig. 1. (a) Fiber-like Ni2Si intermetallic compounds were precipitated discontinuously during aging throughout the matrix of Cu-Ni-Si alloy. (b) Fiber-like Ni2Si precipitates with an average diameter of 13.7 nm were selectively extracted by acid treatment from the Cu-Ni2Si matrix. The alloy bulk was plastically elongated up to 95% by mechanical drawing at room temperature. (c) Fibers of Ni2Si intermetallic were uni-directionally aligned along the direction of drawing, and the average diameter of fibers became 6.7 nm. (d) Plastically elongated nano-fibers of Ni2Si intermetallic could also be extracted by acid treatment from the matrix.

Fig. 2. (A) The major slip direction/plane in pure copper, and (B) the general stacking fault energy (GSFE) associated with it, where a step represents the shortest distance between two atoms divided by 10 along slip direction. (C) The slip direction/plane of Ni2Si matrix which corresponded to those of (A), and (D) the GSFE of Ni2Si intermetallic on the (C). The atomic arrangements of Cu along six slip directions are equivalent, while there are two different slip directions in Ni2Si. (2 for 〈100〉 direction, 4 for <$2\bar{3}6$> direction) The blue, white, red balls and complete arrows in (A) and (C) denote Cu, Ni, Si atoms and the Burgers vectors for each slip system, respectively.

Fig. 3. (A) High resolution TEM image showing a fiber of Ni2Si intermetallic compound precipitated discontinuously in the Cu matrix during aging. The Ni2Si intermetallic fiber in Cu-Ni2Si alloy was plastically deformed by drawing at room temperature up to (B) 50%, (C) 90% and (D) 95%, respectively, in terms of the reduction of area. Insets in each figure represent the fast Fourier transformation images showing the relevant planes of Cu and Ni2Si having a coherent orientation relationship.

Fig. 4. (A) The atomic structure of strained Ni2Si intermetallic that is coherently bonded to the matrix of Cu (to which all the Ni2Si lattices are fixed to those of copper). (B) The general stacking fault energies (GSFE) of strained Ni2Si intermetallic along major slip directions are compared with those of the unstrained counterpart. (C) The atomic structure and (D) the GSFE of the newly formed interface of slipped Ni2Si fibers in the Cu matrix, as shown in Fig. S9. (E) The change in intrinsic stacking fault (ISF) energy (ISFE) from ① to ⑥ in (B) of Ni2Si intermetallic with three different conditions: monolithic, strained by copper matrix and after atomic relaxation. Atomic relaxation is simulated under a constraint with fixed lattices. (F) Un-relaxed and relaxed structures of ISF of ③ in (E). The blue, white and red balls in (A), (C) and (F) denote Cu, Ni and Si atoms, respectively.