Atomic Configuration Determined by ALCHEMI and X-ray Diffraction of the L21 Type Parent Phase in a Cu-Au-Zn Shape Memory Alloy

Abstract

The atomic configuration in a & beta; phase Cu-21 Au-45Zn (at%) shape memory alloy with the L21 structure has been investigated by means of electron channelling enhanced microanalysis (ALCHEMI) utilizing an analytical electron microscope, and powder X-ray diffractometry. ALCHEMI has been successfully applied for determination of site occupancies of the constituent atoms, especially, of Cu and Zn atoms, which is difficult to be determined by conventional X-ray diffraction method, and thus had remained unclear to date. ALCHEMI showed that Zn atoms were located at the body-center sites, while Cu atoms were at the corner sites, referring to the fundamental bcc lattice. The crystal structure thus identified was in agreement with that formerly proposed by Duggin and Rachinger. On the other hand, X-ray diffraction revealed that the L21 ordering was completed in the present alloy during quenching even when rapidly quenched. This is consistent with the fact that Ms temperature of the present alloy is almost the same between specimens quenched into iced water and into boiling water, and with the fact that the transformation temperature is almost unchanged during aging at room temperature. © 1990, The Japan Institute of Metals. All rights reserved.