Orientation in Peritectic Structures

Abstract

PRELIMINARY results from an X-ray study of the peritectic reaction + liquid in the Cu-Zn system prove that the orientations assumed by the -phase are definitely related to the orientation of the -phase. Specimens suitable for accurate orientation studies (by means of back-reflection Laue patterns) were prepared by solidifying a pure -alloy (52 per cent copper) under a uniform temperature gradient, and seeding the crystallisation with a copper single crystal. The resulting specimens then consist (in order, from bottom to top) of (a) copper crystal seed, (b) primary crystallised -phase having the same orientation as the copper seed, (c) large -grains (2–5 mm.), the nuclei of which originated in the peritectic reaction +liquid; these -grains have a narrow rim of segregated -phase. This sequence of crystallisation is made possible, as was expected, by the diffusion of copper into the liquid -brass adjacent to the solid copper crystal.