Structural transitions in complexly alloyed melts

Abstract

The possibility of structural transitions in the metal melts is discussed based on analysis of the temperature dependences of their viscosity, electrical resistance, and surface tension. Mechanism of structural transitions in complexly alloyed melts consists in destruction of microinhomogeneity not only of the structure, but also of the chemical composition. Anomalies in the temperature and concentration dependences of the structurally sensitive properties of metal melts - viscosity, density, electrical resistance, and surface tension - are caused by a change in the melt structure. Branching of the temperature dependences of the structurally sensitive properties of such melts is explained by an irreversible violation of the microinhomogeneous state inherited from the initial multiphase chemically inhomogeneous ingot. Microinhomogeneities that arise due to the predominant interaction of singlesort or not single-sort atoms correspond to short-range order violation in atomic arrangement (SRO) and to a range of 2 - 5 Å. Microinhomogeneous state of the metal melts is caused by the segregation of atoms of fluctuation nature without clear interphase boundaries (by clusters), and is associated with violation of the middle order (MRO) and with a range of 5 - 20 Å. Microheterogeneous state of the melt, which is characterized by the presence of dispersed particles enriched by one of the components suspended in an environment of a different composition and separated from it by a interfacial surface, corresponds to the long-range order (LRO) and to a range of more than 20 Å. Structural transitions in metal melts can also be understood as "liquid - liquid" phase transitions in terms of competition between two homogeneous liquid phases, which differ in the magnitude of the enthalpy, which varies with increasing temperature. Liquid - liquid phase transitions are observed depending on the temperature background of the melt. Branching of the temperature dependences of viscosity, density, and surface tension, measured during heating and subsequent cooling of the melt, is also the result and evidence of the liquid-liquid phase transition. The author proposes an algorithm for a priori analysis of the temperature dependences of viscosity, electrical resistance, and surface tension of complexly alloyed melts based on their structure. © 2020 National University of Science and Technology MISIS. All rights reserved.