Structure and properties of rapidly solidifing foils Sn – 14 at.% In – 6.5 at.% Zn

Abstract

The results of studies of the effect of ultra-high cooling rates of the melt equal to 10 5 K/s on the phase composition, microstructure, grain structure and mechanical properties of the Sn – 14 at.% In – 6.5 at.% Zn alloy are presented. To prepare the samples, the rapid quenching from the melt technique was used. A drop of melt was injected onto the inner surface of a rapidly rotating copper cylinder and solidifing in the form of a foil with a thickness of 30–90 μm. Investigations of the phase composition, carried out by the method of Х-ray diffraction analysis, made it possible to establish that the foil consists of a solid solution of zinc in the γ -phase (Sn4In) and zinc. Observations of the microstructure of the foil using scanning electron microscopy showed that the decomposition of a supersaturated solid solution proceeds at room temperature with the release of dispersed zinc particles. The character of the grain structure and texture of the foil is studied by the electron backscatter diffraction technique. A mechanism of the formation of elongated grains is proposed, which consists in the fact that at a high solidification rate, comparable to the rate of movement of the melt over the surface of the mold, grain growth can occur not only in the direction opposite to the direction of heat removal, but also in the direction of movement of the spreading. The formation of the preferred growth of grains, in which the most closely-packed plane (0001) is parallel to the foil surface, provides the maximum rate of decrease in the enthalpy of the alloy during crystallization. The features of the influence of the microstructure and grain structure on the mechanical properties of the foil are revealed. The microhardness of the rapidly solidifing Sn – 14 at.% In – 6.5 at.% Zn alloy is 105 MPa. The stress–strain curve of the Sn – 14 at.% In – 6.5 at.% Zn foil, obtained at room temperature, has a shape specific for the stress–strain curve of metals at high temperatures, which is due to the low melting point of the γ-phase.