A magnetic study of the two-phase iron-nickel alloys

Abstract

The iron-rich alloys of iron and nickel resemble pure iron in that they undergo a phase change from body-centred cubic ( α ) structure to face-centred cubic ( γ ) structure on heating. On cooling the alloys, however, the return to the original state takes place at a much lower temperature, and on account of this thermal hysteresis the alloys are known as irreversible. A magnetic investigation of these alloys has been made by Peschard (1925), who measured the variation of the saturation intensity of the alloys with temperature. The change from the α to the γ lattice is accompanied by a decrease of the saturation intensity of the alloy, since the γ phase is non-magnetic at the temperature of the change. Curves showing the variation of intensity with temperature are very useful in the study of these alloys, since they give visual evidence of the irreversibility. The relation of the irreversible changes to the equilibrium phase diagram is not clearly understood. Recently, however, equilibrium diagrams of the iron-nickel system, determined by means of X-ray data, have been published by Bradley and Goldschmidt (1939) and Owen and Sully (1939).