Phase transition ‘ordering-phase separation’ in alloys of Ni–Cr system

• Transition line ‘ordering-phase separation’ was constructed for Ni–Cr system.
• The chemical interaction energy sign changes with changes in Ni–Cr alloys composition.
• Method of determination of the ‘ordering-phase separation’ line is offered.

An electron microscopic study of the microstructure of the Ni46Cr54, Ni56Cr44 and Ni62Cr38 alloys after heat treatment at different temperatures has been carried out in order to determine the line of the phase transition ‘ordering-phase separation’ in the Ni–Cr system. The results have been compared with the data obtained previously for the Ni40Cr60 and Ni68Cr32 alloys. It has been shown that in the Ni46Cr54 alloy as in the Ni40Cr60 one, particles of the Ni2Cr chemical compound are formed in the entire temperature range, as a result of the tendency to ordering. Heating of the Ni56Cr44 and Ni62Cr38 alloys to certain temperatures leads to formation of phase separation microstructures, heating to others leads to the appearance of ordering microstructures. The obtained experimental results indicate that the position of the line separating the regions of ordering and phase separation in the phase diagram of Ni–Cr, in a greater degree depends upon changes in concentration than changes in temperature.