Ordering–separation phase transition: The fate of the existing phase diagrams

Abstract

Co₂V and Co₃V alloys are used as examples to discuss the principles of creating modern phase diagrams to take into account the discovery of an ordering–separation phase transition in alloys. The results of electron-microscopic studies of the Co₂V alloy after heat treatment at various temperatures are presented. A comparison of these results with the conclusions based on the existing Co–V phase diagram demonstrates their disagreement. This disagreement is explained in this work. It is concluded that the ordering–separation phase transition should be taken into account in plotting modern phase diagrams. The Fe–Cr and Ni–Cr phase diagrams are considered with allowance for the ordering–separation phase transition in them. A technique is described to determine the ordering–separation phase transition temperature by transmission electron microscopy. The introduction of the concept of the ordering–separation phase transition is shown to change the principles used by researchers to construct phase diagrams.