Atomistic Microstructures in Short-Range Ordered Alloys

摘要

Short-range order (SRO) in Ni-Mo alloys and their relatives has been controversial for decades, since it causes clearly diffraction intensity maxima at positions which do not coincide with the superlattice reflections in the long-range order (LRO) state. This paper gives an overview of recent studies on the structure of SRO and the transition from SRO to LRO in Ni-Mo alloys, including our results obtained in atomic level by combination of kinetic Monte Carlo simulation and semi-quantitative high-resolution transmission electron microscopy. It is rationalized in our results that the SRO state is set up by local ordering of A_4B, A_3B and A_2B types in sub-unit cell scale. The dispersed mixture of the sub-unit cell clusters gives diffraction intensity maxima at the particular positions. An LRO state is formed by selected growth of the A_4B, A_3B and A_2B type clusters into LRO domains depending on alloy-composition.