The Vacancy Cluster Tubes Formation and Metal Properties Changes After Dynamic Centrifugal Casting

Abstract

Presents experimental results of Al and Pb metals crystallization carried out under high intensity plastic deformation (HIPD) [e′ = (102–104) sec-1] reaching the level of so called «solid-liquid» state in the new type of centrifugal casting device at rotor speeds of up to 2000 rpm. Using the method of atomic force microscopy (AFM), vacancy cluster tubes (VCT) with average diameters of 39 nm for Al and 25 nm for Pb have been detected in the crystallized volume of Al and Pb metals. Physical model of the formation of a new substructure within the metals in the form of vacancy cluster tubes, received in the process of high-intensive plastic deformation (HIPD) during the process of mass crystallization of Al and Pb melts, and, also the changes in the mechanical, magnetic and superconducting properties of the above metals, which followed this process. When crystallizing Al and Pb under high-intensive plastic deformation (HIPD) of e′ = (102–104) per second type, in high-speed centrifugal casting devices, specially selected modes of metal crystallization are being chosen and special conditions are being created to achieve the dimensional effect of dynamic (shift) re-crystallization. Shift deformation during centrifugal crystallization is caused primarily by a large incline of the temperature field from the periphery (relative to the cold wall of the rotor) to the molten central part of the rotor. The difference in the angular movement velocities of the already-frozen part of the metal (adjacent to the outer surface of the rotor wall) and the central part, where the metal still remains in the molten state, leads to a high-intensity deformation [e′ = (102–104) sec-1] of the crystallized metal melt solidified phase. Since the grain sizes at the crystallized phase initially comprise around tens of nano-meters (approximately crystal nucleation size), it becomes possible to achieve the dimensional effect of the dynamic re-crystallization of a «nanocrystalline» solidified metal at high shift of strain velocities. The «non-equilibrium vacancies» formed this way condense into vacancy clusters, which are formed in the centrifugal force field in the form of vacancy-shaped cluster tubes stretched out to the center of rotation of the rotor. The process undergoes conditions that are considerably different from the «equilibrium» conditions as compared to the ordinary metal crystallization from the melt. Such processes can lead to the formation of highly ordered non-equilibrium states characteristic of non-equilibrium open systems.