252 



BELL SYSTEM TECHNICAL JOURNAL 



composition or structure, which are stable at the temperatures and com- 

 positions indicated. The a phase has the body-centered-cubic crystal struc- 

 ture characteristic of iron. At 910°C it transforms into the face-centered 

 phase 7, and at 1400° into the 5 phase, which has the same structure as the 

 a phase. At about 400°C cobalt transforms, on heating, from the e phase 

 (hexagonal structure) into the 7 phase. 



2 4 6 8 10 12 14 16 18 20 



FIELD STRENGTH, H, IN OERSTEDS 



Fig. 1 — Effect of mechanical and heat treatment on the magnetization curve of 70 

 permalloy (70% Ni, 30% Fe). 



Table I 



Properties Commonly Sensitive or Insensitive to Small Changes in Structure, and Some of the 

 Factors which Effect Such Changes 



The dotted lines indicate the Curie point, at which the material becomes 

 non-magnetic. 



In between the areas corresponding to the single phases a, 7, 8 and e 

 there are two-phase regions in which two crystal structures co-exist, some 

 of the crystal grains having one structure and others the other. Such a two- 

 phase structure is usually evident upon microscopic or X-ray examina- 



