Metastable phases of the Zr-Al system obtained by mechanical attrition and rapid soldification

Abstract

The equilibrium phase diagram of the Zr-Al system, shows the existence at room temperature of the L1{sub 2} line compound Zr{sub 3}Al. The peritectoid reaction which leads to its formation, starting from the mixture {alpha}Zr + Zr{sub 2}Al, was thoroughly investigated. Apart from the interesting technological aspects several researchers have been concerned with the disordering, i.e., destruction of the long-range crystalline order, and amorphization of this intermetallic compound. Probably because of the links with nuclear reactors, the first experiments in this field involved electron and ion irradiation. More recent experiments using Kr{sup +} ions extended the early findings. In this paper, amorphization was observed and instability deduced from measurements of the shear modulus. For this reason, a parallel was drawn between this solid-state reaction and melting. Another factor considered necessary to a successful amorphization is the increase in the free energy of the system caused by the reduction of long-range order. A critical value of the long-range order parameter, S, measured from the intensity of the electron diffraction spots, of 0.2 has been reported as necessary to the appearance of the first amorphous regions.