It may be said first, in order to avoid any misunderstanding, that the exposed idea oŁ homogeneous structure must not be considered in an absolute but in a practical manner. The homo-geneity which is admitted as being the practical one is that which can be deducted from the largest microscopical enlargements for the time being (500 to 1000 diameters). It Is said that an alloy is practically homogeneous when, seen under such enlargements, it does not show any structural heterogeneousness.
I have found that the phenomenon of melioration of the nickel-beryllium alloys must not be considered exclusively as being due to the reprecipitation of the hardening constituent but, already from the beginning, to a diffusion of the beryllium atoms into the elemental cell of the nickel and to the subsequent formation of elemental particles of the hardening constituent Ni-Be. The dimensions of these groups increase in such a manner that greater and greater stresses are exerted upon the reticle of the solid solution of nickel up to a limit which can not be exceeded without the expulsion of the said cristalline groups out of the rectile of the solid solution taking place, and it Is in this manner that the re-precipitation takes place. In correspondence with the reality of the phenomena one has in the first phase an increase of the resistance to deformation and, parallelly to this, an increase of the electric resistance and in the second phase a concomitant diminution of the electric resistance and of the mechanical strength. I do not intend to give more details which would not be in their place here, but I shall add that, always guided by this analogy, 1 have admitted that the phenomenon of the badly bound hardening constituents is due to the fact that the reticular surface arrangement is much more altered than the internal arrangement; what amounts to admitting the presenee of fine heterogeneous interpositions between the hardening constituents.
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