MAGNETIC ALLOYS OF IRON, NICKEL, AND COBALT 443 



front of the first maximum in the nickel-iron series. If you follow the 

 coordinate from 40 per cent nickel, you will note an elevation between 

 the 700 and 1,000 permeability contour lines. The ternary alloys of 

 this region are remarkable, not because of their high permeabilities 

 although they are higher than for the surrounding region, but because 

 of the constancy of permeability and low hysteresis loss at low 

 magnetizing forces. 



Another region of interest is located in the iron-cobalt plane between 

 40 per cent and 70 per cent iron. This is the plane in the figure on 

 which the iron percentages are marked. The initial permeability for 

 the highest point is over 600, more than twice the initial permeability 

 of Armco iron. 



When the alloys are air quenched, the initial permeabilities change 

 in some regions very materially and give us an entirely different 

 looking solid diagram as shown in Fig. 4. Because of the very high 

 values of the permeabilities a different scale was used in this figure 

 from that used in Fig. 3. It is interesting to note how the rapid 

 cooling has affected some of the binaries in the iron-nickel plane. 

 The rise in permeability begins at about 28 per cent, the same as for 

 the annealed alloys, and the initial permeabilities are substantially 

 the same, up to about 45 per cent nickel. Between 45 per cent and 

 about 90 per cent nickel, the permeabilities have increased to a 

 remarkable degree. The valley we saw in the region 45-75 per cent 

 nickel for the annealed alloys has disappeared, and from 55 per cent 

 upward there is a rapid increase reaching a peak value of approxi- 

 mately 8,000 for the composition containing 78^ per cent nickel, an 

 increase of over four times the permeability of the annealed alloy of 

 the same composition. 



Air quenching also increases the initial permeabilities of the group 

 of ternary alloys which in the annealed condition showed a maximum 

 characterized by a low hysteresis loss and a substantially constant 

 permeability. This increase in permeability, however, is accompanied 

 by a material increase in the hysteresis loss at low flux densities and a 

 decrease in the constancy of permeability. 



In contrast to the alloys just discussed, the iron-cobalt series in 

 the neighborhood of 50 per cent iron gives a lower permeability upon 

 rapid cooling. In this respect they behave the same as iron and 

 cobalt. 



The maximum permeabilities for the annealed alloys shown in 

 Fig. 5 give a surface very similar to that for the initial permeabilities. 

 The most interesting difference is the rapid decrease in permeability 

 of iron as indicated at the left-hand corner of the diagram by the 



