7o 



NA TURE 



[November 16, 1905 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, July 20. — "The Influence of Phase 

 Changes on the Tenacity of Ductile Metals at the Ordinary 

 Temperature and at the Boiling Point of Liquid Air." 

 By G. T. Beilby and H. N. Beilby, B.Sc. Communicated 

 by Prof. J. Larmor, Sec.R.S. 



The observations recorded in this paper are intended to 

 prepare the way for a more direct attack on the problems 

 of molecular cohesion by the establishment of clearer views 

 as to the influence of changes of phase on the tenacity of 

 ductile metals at various temperatures. 



^OT&3:^v 



According to thi phase theory of the hard and soli states 

 in metals which was lirsi developed by one of the authors 

 more than a year ago, the changes of state from hard to 

 soft and from soft to hard were shown to be due to the 

 changes of phase brought about, in the one case by heat, 

 and in the other bj mechanical deformation or How. In 

 the ductile metals the crystalline is the mechanically un- 

 stable phase, while the amorphous only becomes thermally 

 unstable when a definite temperature is reached. 



NO. l88 I , VOL. 73] 



The comparative mechanical instability of the two phases- 

 is well illustrated in the stretching of wires under tension. 

 Annealed wires, which are in the C phase, stretch when 

 they arc stressed beyond the yield point ; hardened wires, 

 which are partly in the A phase, do not stretch — they break 

 without extension when their limit of tenacity is reached. 



The homogeneous C phase in ductile metals has no true 

 breaking point — it yields and stretches when stressed 

 bevond the elastic limit, and in so doing it passes partly 

 into the A phase, and rupture occurs at the breaking point 

 of tin- mixed structure. The tenacity of the mixed struc- 

 ture approaches, but never quite reaches, that of the 

 homogeneous A phase. For the purpose the authors had 

 in view it was necessary to obtain the metals as nearly as 

 possible in this homogeneous condition. 



Wire drawing was the means employed for the break- 

 ing down of the C phase. Alter a wire had been stretched 

 to four or five limes its original length bv drawing it 

 through the holes of a wire plate, all the ordinary traces 

 of crystalline structure disappeared, but it still consisted of 

 minute 'granules of the C phase embedded in a matrix of 

 the A phase. Further drawing at the same temperature 

 alters the mixed structure only slightly; for each tempera- 

 ture there appears to be a certain mechanical equilibrium 

 between the phases. By lowering the temperature of 

 drawing, the C phase is further broken down into still 

 smaller granules, and the mixture approaches more nearly 

 to the homogeneous A state. 



(a) Fig. 1 is a photograph of a gold wire which has 

 been etched alter drawing The How lines near the surface 

 consist of rows of granules. (/>) On the same photograph, 

 shows the effect of heating another piece of the same- wire 

 to about 400 . Removal of the surface by etching now 

 <lisi loses the fully developed crystalline grains with their 

 differently oriented lamella?. The thermal transformation 

 from A to c has taken place, and the wire is restored to 

 the soft condition. Figs. 2 and 3 are photomicrographs 

 at higher magnifications, which show the details of struc- 

 ture ulcere fully. Fig. 2 is the granular structure by oblique 

 light at a magnification c,l 250, and Fig. 3 is the crystal- 

 line structure' bv normal light at a magnification of 700. 



the observations were made on wires which had been 

 as completely as possible converted into the A phase by 

 wire drawing at the ordinary temperature, and in every 

 case the tenacity observed was higher than any which had 

 been recorded by previous observers for ci 

 metals. 



pure 



Gold. Purity — 9,997 per 10,000 



Tenacity at 2SS° absolute 115' C. ) ... 

 53° •• (-lSo°C.) 

 Silver. Purity — 10,000 per 10,000 



Tenacity at 288° absolute (15 C. ) . . . 

 53° ,. (-1S0 C.) 

 Copper. Purity— 9,996 per 10,000 



Tenacity at 288° absolute (15° C ) . 

 53° ,, (-i8o°C.) 



The wiies broken at the ordinan temperature showed 

 no general stretching. There was a slight extension of 

 from .y per cent, to 1 per cent., due entirely to a sharp 

 reduction of diameter at the actual point of rupture. At 

 the boiling point of liquid air all the wires stretched from 

 11 per cent, to 12 per cent. This stretching was uniform 

 over the whole length between the grips. This was con- 

 firmed by exact measurements of the diameter at a number 

 of points. 



The appearance of the fractured ends revealed several 

 points of interest. In every case the copper wires showed 

 the cupped formation at the extreme end. This formation 

 is evidently due to the lower tenacity of the central core, 



due tO the pies, nee of g.ls bubbles which ll.lVe been clraWIl 



out into long tubes or cells. The silver wires occasionally 

 showed a slight cupped formation, but in this case the 

 gas bubbles to which it was due were globular, as if they 

 had been evolved at the moment of fracture-. The gold 

 wins were practically free from sponginess, and the frac- 

 tures wore almost perfectly viscous (Fig. 4). 



By drawing wires at the lowest possible temperatures 

 the authors hope to obtain the ductile metals in their 

 condition of maximum tenacity, and from the- tigun-s then 



