March 31, 19 10] 



NATURE 



141 



where results of practical interest were to be anticipated. 

 As regards the heavy alloys, consisting principally of 

 copper, important results were to be sought only in alloys 

 containing more than 85 per cent, of copper, while at the 

 aluminium end of the series only alloys containing more 

 than 95 per cent, of aluminium could be expected to yield 

 results of practical value. The study of the constitution 

 of the alloys has, however, been pushed beyond these 

 limits in order to render the data obtained over the 

 " useful " range more intelligible. 



Fig. I.— Model of the liqaidus surface of ternary alloys of copper with alnminum and manganese. 



The report therefore includes a model of the " liquidus 

 surface " of the ternary system over a range of alloys con- 

 taining less than 11 per cent, of alimiinium and less than 

 10 per cent, of manganese. This model is constructed on 

 the well-known principle of trilinear coordinates, in which 

 the range of compositions of ternary alloys is represented 

 by an equilateral triangle ; the liquidus surface is con- 

 structed by erecting a vertical ordinate representing the 



copper side) are homogeneous, while those to the left are 

 duplex. A comparison of the model with the mechanical 

 properties of the alloys further indicates that in the 

 ternary alloys, just as in the binary copper-aluminium 

 series, the presence of the second phase to the left of the 

 minimum renders the alloys stiffer, stronger, and less 

 ductile. 



Throughout the range covered by this model (which 

 represents the data obtained from more than 100 different 

 alloys) no new phase resulting from the presence of man- 

 ganese can be detected. This re* 

 suit is of special interest, because 

 some of the alloys included in this 

 group, viz. those lying towards the 

 left-hand corner of the model, are 

 distinctly magnetic, their permea- 

 bility increasing towards the 

 extreme left-hand corner of the 

 figure. If, therefore, the magnetic 

 properties of these alloys (which 

 approach the type of some of the 

 well-known Heussler alloys) are 

 due to the existence of a magnetic 

 metallic compound, this compound 

 must be soluble in either or both 

 the phases found in these alloys. 



K photomicrograph topical of 

 the structure of alloys in this 

 region is reproduced from Fig. 75 

 of the report (Fig. 2), representing 

 the structure of an alloy contain- 

 ing 856 per cent, of aluminium, 

 477 per cent, of manganese, and 

 8667 per cent, of copper in the 

 sand-cast condition. The effects- 

 of heat-treatment on the micro- 

 structure of these alloys are very 

 marked. Thus Fig. 122 of the re- 

 port (Fig. 3) shows the structure 

 of another alloy of this t>-pe after annealing at 900° C.,. 

 both these photographs being taken at the same magnifi- 

 cation (150 diameters). Quenching the same alloy from 

 900° C. produces a totally different structure, reproduced' 

 from Fig. 129 of the report (Fig. 4), and this .change 

 renders the alloy hard and brittle. 



-As regards alloys at the light end of the series, the- 

 introduction of manganese is found to give rise to the- 



Fig. 2.— Mi^rc-;,:iuc;u:e of ...l^y u^ ^ijt ;:. sacu. 



temperature of initial freezing, on the points representing 

 the alloys examined. A photograph of the model, upon 

 which contour lines representing e.-ich 10° C. have been 

 drawn, is reproduced in Fig. i. The well-marked mini- 

 mum of the copper-aluminium series, occurring at a con- 

 centration of about 8^ per cent, aluminium, is continued 

 into the ternary system in the form of a valley in the 

 liquidus surface, and microscopic examination has shown 

 that alloys to the right of this valley (i.e. nearer the 



NO. 2109, VOL. 83] 



Fig. 3. — Micro-sttucture of alloy after long anneaiing at 900 C. 



formation of a definite compound, AljMn, which tends tch 

 render the alloys hard and brittle. If present in large- 

 proportions, this compound appears to undergo a more or 

 less gradual change, which leads to the spontaneous dis- 

 integration of the alloys containing it ; an ingot consist- 

 ing of 65 per cent, aluminium and 35 per cent, manganese 

 is a hard, metallic mass when first cooled, but falls to a 

 fine crystalline powder in the course of six or eight hours, 

 and this process appears to be independent of oxidation.. 



