Effect of Heat Treatment of a Liquid Alloy on Its Properties in the Molten State and after Amorphization

Based on the earlier reported conceptions about the possibility to control the structure of liquid alloys by varying the heating temperature, we think that the use of optimized heat treatment of staring melts shows promise for stabilizing the properties of advanced liquid-metal coolants of nuclear reactors. This idea is confirmed by the results of studying the binary lead–bismuth, lead–tin, and gallium–indium liquid eutectics. Evidence about their metastable microheterogeneity, which can be retained in wide temperature ranges for a long time after melting a coolant, is obtained experimentally. Changing the preparation method of the melt is shown to weakly affect the degree of its heterogeneity and the temperature of transition into a homogeneous state. The main ways of eliminating the effect of the above microheterogeneity on the safe operation of a reactor are determined. The possibility to improve the quality of amorphous ribbons prepared by melt quenching and bulk amorphous alloys as a result of application of optimized temperature conditions of their melting is discussed. The effect of heat treatment of a starting melt on the structure and properties of amorphous samples prepared by traditional melt spinning is shown by examples of a number of systems. Heating of a liquid metal above the boundary of a metastable microheterogeneity is found to favor the formation of amorphous structure, which is more disordered as compared to that obtained by traditional melting technology, and to allow the concentration range of liquid metal amorphization to be substantially widened. Heating of a microheterogeneous melt to the temperatures of its intermediate structural transformations within two microheterogeneous states is also shown to be efficient not only in terms of laboratory experiments but also for full-scale production of amorphous ribbons. To understand the causes of the formation of bulk amorphous alloys, the correlation between the heating temperature of a starting melt and its capability toward deep supercooling is of key importance. The following specific temperature range is detected: after heating in this range, a melt can be subjected to deep supercooling, and the rate of decrease of the viscosity with increasing temperature and the activation energy of viscous flow decrease substantially in this temperature range. Our understanding of the causes of the correlation is reported.