P. S. Popel, V. E. Sidorov, M. Calvo-Dahlborg, U. Dahlborg, V. V. Molokanov.
ABSTRACT
The idea of using optimized heat treatment of initial melts in order to stabilize the properties of promising liquid metal coolants in nuclear reactors is formulated basing on the previously published statements about the possibility of regulating the structure of liquid alloys by varying their temperature. This idea is confirmed by the results for liquid binary eutectics leadbismuth, lead-tin and gallium-indium. The evidences for their metastable microheterogeneous structure in the wide temperature ranges and for a long time after the coolants melting were obtained experimentally. It was shown that the variations in melt preparation do not affect significantly the degree of its heterogeneity and the temperature of transition to a homogeneous state. The main ways to eliminate the influence of the indicated microheterogeneity on the safety of the reactor are determined. The possibility of improving the quality of amorphous ribbons obtained by rapid quenching and bulk amorphous alloysulation by optimization of smelting temperature regimes is discussed. The effect of melt heat treatment on structure and properties of amorphous samples obtained by the standard spinning method is shown using several examples. It has been established that overheating of liquid metal above the metastable microheterogeneous area promotes the formation of a more disordered amorphous structure compared with the standard smelting technology and thus allows one to expand significantly the concentration range of alloy amorphization. The efficiency of heating a microheterogeneous melt to temperatures of its intermediate structural rearrangements between two microheterogeneous states is shown and confirmed not only in laboratory experiments, but in industrial full-scale production of amorphous ribbons also. To understand the reasons for the formation of bulk amorphous alloys, the relation between heating temperature and melts tendency to deep supercooling is of key importance. It was found that there is a specific temperature range where the melt becomes prone to deep supercooling, and its rate of viscosity decrease with increasing temperature and the activation energy of the viscous flow are reduced significantly. The reasons for such a correlation are discussed.
KEYWORDS
melts, optimized heat treatment, liquid metal coolants, quenching rate, amorphous ribbons and bulk amorphous alloys, structure, properties
DOI: 10.31857/S023501062003007X