Mapping of the transition 'ordering-phase separation' into phase diagrams

The article on the example of two alloys Co2V and Co3V discusses the principles of the modern phase diagram construction in connection with the discovery of the phase transition 'ordering-phase separation' in alloys. The results of electron microscopic studies of the Co2V alloy after heat treatment at different temperatures are presented. Comparison of the obtained data with the existing Co-V phase diagram shows that these results do not coincide with those that follow from this diagram. An explanation of why this discrepancy exists is presented. It is concluded that the phase transition 'ordering-phase separation' must be considered when creating modern phase diagrams. Phase diagrams of Fe-Cr and Ni-Cr, taking into account the existence of such a transition were presented as examples. Methodical instructions on how to determine the temperature of the phase transition “ordering-phase separation” using the method of transmission electron microscopy are given. It is concluded that the introduction of such a concept as the phase transition 'ordering-phase separation' will change in future the principles that guide researchers in creating phase diagrams.