X-ray study of phase boundaries in thermal diagrams of alloy systems—cu-zn system

Abstract

Within the last 10 years, the study of the diffraction of X-rays by crystal units in metals and alloys has shown that X-ray analysis, apart from giving data on the form and dimensions of the crystalline units, is a powerful method with which to examine the thermal diagrams of alloy systems. Rosenhain has pointed out, however, that although the X-ray analysis of alloys yields valuable results as to structure and so on, the constitutional diagrams arrived at by this means must necessarily be incomplete, firstly because a very small amount of a second phase in a large mass of another phase cannot be detected by X-ray methods, and secondly, because the parameter measurements have not been accurate enough to determine definitely the boundaries of solid solubility. In view of this statement we felt it would perhaps serve a useful purpose to carry out a careful investigation into the reliability of accurate X-ray methods for establishing thermal equilibrium diagrams of alloy systems. An account of such an investigation is given in this paper, and it may be stated at the outset that, where X-ray data could be compared with data reliably established by other methods, the agreement is as good as, if not better than, that between the data of the various methods amongst themselves. It will be shown that a phase boundary can be determined by the X-ray method from parameter measurements alone, and that an accurate determination can be made irrespective of the amount of the second phase present. It will be necessary to go into the method of measurement and the heat treatment of the alloys in some detail. Precautions have to be taken in the preparation and analysis of the alloys to ensure that the parameter measured is that of the alloy in the equilibrium state, and that its composition is that corresponding to the alloy actually used in the measurement. The paper is therefore divided into two parts; the first part deals with the method of measurement and the preparation of the alloys, and the second part refers to the X-ray examination of the alloys with a view to determining the phase boundaries.