those ratios. It is found that the cleotron-atom ratio in the s e v e r a l-P ^ s can be used to explain many o f these phenomena, and then we have somethi^« ^ than an empirical record o f hardness; we have a means o un kind we shall happening. I think that in a short time, with information o f that kind, we shal be able to predict accurately what will bo the properties o f a given ternary
I would commend a study o f the very im portant papers which Dr.
and others have been publishing, largely under the inspiration °*
W L. Bragg. Thev really do lay a new foundation for the study o f C0®P‘“
alloys o f this kind. The subject o f metallography is undergoing a changewhich will enable it to progress much more rapidly in the next few years, and ™at of the kind given in this paper will then be re-interpreted with,, I think, verj valuable results. That is not, o f course, in the least to depreciaibe th® ' a}“ ® “ the authors' results; I merely suggest that they will have to be t r a n s l a t e d « t e a somewhat different form before they can have the general value which should like them to have.
Dr. H . W . B kow ssdon * (Vice-President): After the investigations that- we carried out several years ago on the effect o f adding nickel and copper in e 1 Jj proportions to copper and copper-rich alloys, we realized hat a more: d e t a i l studv of the copper-nickel-aluminium system than was then possible in ou laboratory' would be o f general interest, and we were fortunate in hndt r authors willing to undertake this further work.
It is gratifying to note that one o f our more important early observations relating to the nickel aluminium ratio giving optimum temper harc emng pi - perties! has been confirmed, and agrees with that indicated by the line Ji i m 1 1,_It may not be generally realized how very considerable was the am ount of work involved in preparing, in wire form , the alloys listed m Table I, and 1^sho like to thank those o f my colleagues who helped m their preparation an . y .
Although primarily o f scientific interest, this contribution has a very deti bearing onthe development o f new alloys o f commercial value.
Professor D . HiSSOS.t D.Sc. (Vice-President): Dr.
petent to deal with the technical discussion, but I should like to thank Messrs.
I C I Metals, Ltd., for making this investigation possible. I believe tha arose from a remark which I made in the discussion on a paper f r o m their laboratories, when the practical results of the heat-treatment of these allojs . first presented to us. Arising out o f those remarks, Dr. Brownsdon su^es that we should undertake the investigation o f some o f t h e s c i e n t i f i c problems connected with those alloys. W e have been very interested to do this, a n d 1 believe that the firm has benefited from this joint effort. It has been a ] effort; although the paper is published in our names, a very great amou preliminary work was carried out. by LC.L Metals-, Lt^ - ; / “ ^ u n i t i e s materials and in helping us at various stages. I hope that further opportu will arise for this kind o f co-operative effort between an industrial firm ancU scientific laboratory and that advantage will be taken o f these opportum , because this is a research which Universities would have the very greatest eti culty in carrying out unaided, even if they could do it at all, because the p paration o f the materials in a suitable form would be beyond their resources.
Dr. Al e x a n d e r(in reply) ■ At first I thought that D r. Desch referred simply to plotting the properties o f the a. solid solution in atomic percentages, w e
* Research Manager. I.C.I. Metals, Ltd., Birmingham, t Professor of Metallurgy, The University, Birmingham.
that, and did not obtain any linear relationships in the properties with com
position. From his subsequent remarks, however, I gather that Dr. Desch was referring to the electron-atom ratios o f the compounds concerned. We also thought o f that and tested it on a number o f ternary alloys, and obtained interesting results.
CORRESPONDENCE.
D r. A. J. Br a d l e y* (Member) and Mr. H. Lipsoir,* M.Sc. : This paper is o f special interest to us as wo have been working on the copper-nickel-aluminiuin system by X-rays. Our powder photographs o f slowly-cooled alloys give a general survey o f the phases throughout the system. From this, we ea.n interpret some of the results given by the present authors.
Fig. A shows the following phases:
a—face-centred cubic.
ccj— face-centred cube with superlatticc.
—body-centred cube with supcrlattiee.
The boundary o f the a-phase in the neighbourhood o f copper follows the trend of the dotted lines in Figs. 6 and 1. The resistivity measurements show beautifully the cusp o f the a-phase, where it comes into contact with the three- phase area (a 4- ¡32). The dotted lines from the cusp to number 14 in Figs.
6 and 7 probably lie within the three-phase areas at 400° and 600° C „ respectively.
It would be interesting if a closer examination o f the resistivity data should show the boundaries of the three-phase area separately.
The lower dotted line (X Y in Fig. 6) is not a phase boundary, but probably corresponds to a tie-line in the two-phase area a + a,. An alloy on this line breaks up as follow s: the a. constituent has a composition given by the point
; the constituent has a composition about midway between Ni3Al and CuNijAl, which are at the extremities o f the a! phase. It is probable that the conductivity is chiefly due to the a constituent. This has the lowest resistivity at the point X . Consequently, all alloys on the tie-line X Y will have a minimum resistivity.
* National Physical Laboratory, Teddington.
The Au t h o r s (in reply) : The results o f Dr. Bradley and Mr. Lipson’s X -ray observations on these slowly-cooled ternary alloys are known to us, and confirm what we had already determined microscopically. W e hope shortly to communicate to the Institute a paper dealing with the constitution of these alloys at all temperatures. W o also agree with the interpretation oi the line X Y (o f alloys having minimum resistivity) as a tie-lme between a and Ni3Al solid solution.