136 



ROYAL SOCIETY OF CANADA 



a parallelism exists between the crystallographic structure of the Heusler 

 alloys and the physical properties displayed by. them. 



'As one of the most interesting and instructive ways of studying 

 these phase (Changes it was. decided to begin an investigation of the 

 iiiicrostructure of the alloys in the hope of throwing some light on their 

 magnetic and other properties, and/in the following note an account 

 is given of some of the results obtained in the investigation up to the 

 present. 



The method employed was that of examining under the microscope 

 a polished surface of the metal, suitably etched by a reagent. This 

 mode of procedure was initiated by Sorby in the study of the micro- 

 structure of iron and steel as far back as ^1864, and has been developed 

 more recently in the case of alloys with signal success by Eosenhain and 

 Ewing, Haycock and Neville, Osmond, Stead, and others. 



Before taking up the Heusler alloys a specimen of steel and also one 

 of iron were examined to gain some experience in work of this kind, and 

 results were obtained similar to those of other experimenters. Tliis 

 was then followed by an examination of the constituents of the alloys 

 aluminium, manganese, copper, and Figs. 1, 2 and 3 give typical illus- 

 trations of their respective appearances under the microscope. A study 

 of the alloys was then taken up. 



Eight samples which had been cast in the form of rods were 

 examined, representing four ditïerent percentage compositions as fol- 

 lows : — 



Designation. 



la 



2, '2a . . 



3, 3a, 3b 



4, 4a. . . 



Percentage. 



Al. 



9.7 

 14.3 

 15.9 



Mn. 



32.1 

 25.6 

 28.6 

 23.9 



Cu. 



59.8 

 64.6 

 57.1 

 60.3 



Atomic ratio of 



Al to Mn. 



.51 



.77 



1.01 



1.392 



Polished sections were made along and perpendicular to the axis 

 of the rods, and these were examined under the microscope after being 

 suitably etched. 



The microstructure of the specimens shewed considerable variations 

 with the percentage composition, and hence with their magnetic pro- 

 perties. Those having the same composition, however, were fairly 

 uniform. 



