Phase transformations in alloys of the Ni–Cr system

Microstructure of the alloys Ni40Cr60 and Ni68Cr32 heat treated at different temperatures has been investigated by means of the electron diffraction method. It is shown that the grains of the Cr2Ni chemical compound with an orthorhombic lattice are formed in the liquid solution of the Ni40Cr60 alloy as a result of a tendency to ordering. The rest of the liquid solution solidifies at the solidus temperature. At lowering the temperature below 1200 °C the fragmentation of the Cr2Ni grains occurs and the high-dispersed particles of the Ni2Cr3 chemical compound precipitate in the solid solution surrounding the Cr2Ni grains. The tendency to ordering at high temperatures is observed in the Ni68Cr32 alloy as well. This tendency is responsible for the formation of Cr-enriched clusters which can be considered as nuclei of the Cr2Ni phase. The Ni2Cr phase is not revealed in the Ni68Cr32 alloy at aging temperatures. It may be inferred that the experimental results obtained with the help of the TEM method doesn’t do not completely coincide with the Ni–Cr phase diagram. Causes of initiation of that situation are discussed.

► In all the studied alloys of the Ni–Cr system, there exists a tendency to ordering.
► Grains of the Cr2Ni chemical compound (orthorhombic lattice) are formed in liquid Ni40Cr60 alloy.
► With a decrease of the temperature to 550 °C, fragmentation of the Cr2Ni grains takes place in Ni40Cr60 alloy.
► At 500 °C aging and below, no precipitates of the Ni2Cr phase were found in the Ni68Cr32 alloy.