With 36 alloys selected from indications provided first by differential thermal analysis and by other methods of analysis and physical measurements, it has been possible to specify accurately the Fe-Ni-Al ternary diagram. This research enabled us to : 1. Give a better definition of the solid/liquid state limits, α and γ phases existence fields, miscibility-gap extent, Curie temperature variations in relation with the alloy composition, 2. Prove that for some ternary alloys, there does appear a miscibility gap related to the

reaction. The three phases having very close lattice parameter are b.c.c., α
2phase being an ordered phase (superstructure). 3. Show that, for an alloy in the miscibility gap, the α
1and α
2phase compositions at room temperature are not constant.