Microstructures Responsible for the Invar and Permalloy Effects in Fe-Ni Alloys

摘要

The experimental studies of Fe_(68)Ni_(32) and Fe_(23)Ni_(77) alloys by transmission electron microscopy and X-ray electron spectroscopy show that the ordering-separation phase transition in these alloys occurs in a temperature range near 600°C. At temperatures higher than the transition temperature, the ordering energy of the alloy is positive, and the structures contain clusters enriched in one of the components. After heat treatment at the temperatures where the invar effect in the Fe_(68)Ni_(32) alloy is maximal, a modulated microstructure forms. Below the transition temperature, the ordering energy is negative, which provides a tendency to formation of chemical compounds. After aging at these temperatures (where the Fe_(23)Ni_(77) alloy exhibits high permalloy properties), highly dispersed completely coherent particles of the FeNi_3 phase with structure Ll_2 precipitate in a solid solution.