MAGNETIC MATERIALS IN RELATION TO STRUCTURE ZZ 



temperature during which precipitation occurs, or a quench followed by 

 an aging treatment at a lower temperature to produce the precipitation. 

 Examples of alloys of this type are the iron-nickel-aluminum alloys, 

 which have been described by Mishima,'"' and the iron-cobalt-molyb- 

 denum and iron-cobalt-tungsten alloys, which have been described by 

 Seljesater and Rogers ^^ and Koster.''^ 



Iron- Nickel- Aliuninum Alloys 



A representative composition of the alloys described by Mishima '"' 

 consists of 65 per cent iron, 25 per cent nickel and 10 per cent aluminum. 

 The composition may be further modified by the addition of manganese, 

 vanadium, cobalt, chromium, tungsten, molybdenum, or copper. 



For the simple ternary alloy in the cast condition a coercive force of 

 240 oersteds and a residual induction of 9600 gauss have been reported 

 by Mishima.^" By slight modifications in compositions, coercive 

 forces of over 500 oersteds in combination with residual inductions of 

 approximately 9500 gauss are reported. Values for three Mishima 

 alloys, presumably of different composition, have been reported recently 

 by Steinhaus and Kussman ^^ and are given below. 



Type of Coercive Force Residual Induction 



Misliima Alloy Oersteds Gauss 



MKl 660 7,600 



MK3 440 9,800 



MK5 130 10,800 



Koster ^" has investigated the ternary equilibrium conditions for the 

 iron-nickel-aluminum alloys. In the range of compositions of interest 

 for magnet purposes, a surface of solubility varying with the tempera- 

 ture exists. It would be expected, therefore, that these alloys would 

 be amenable to age hardening treatment. This has actually been 

 demonstrated by Koster for the alloys of iron-nickel-aluminum. The 

 curves shown in Fig. 14 are reproduced from his published data and will 

 be recognized as demonstrating typical age hardening phenomena. 

 The optimum aging temperature appears to be 700° C. 



The fact that Mishima obtained high permanent magnet quality in 

 specimens in the cast condition can be explained in that the precipita- 

 tion of the second phase occurs during the simple cooling of the casting. 

 It would be expected, therefore, that the magnet properties obtained 

 would depend upon the casting dimensions and the rate of cooling. If 

 this is true, it might be desirable in some magnet structures to subse- 

 quently heat treat the material to obtain uniform and reproducible 

 results. 



The fact that precipitation occurs is indicated more completely by 

 examination of the photomicrographs in Figs. 15 and 16 of a typical 



