Abstract
Discussion of the requirements for the placement of ZrO 2 powder in the cathode, which must be taken into account in the production of ODS steel by vacuum-arc remelting in order to provide the high level of homogenization of the oxide particle is presented. The description of the experimental setup and the cathode structure for vacuum arc remelting of steel, alloyed with oxide nano-powder is given. The role of convective processes in the homogenization of nano-particles in the production of ODS steel is highlighted. The convective flow of liquid metal captures ZrO 2 powder particles and carries them throughout its volume. The use of the elementary convective cell with free boundary conditions is proposed for the description of homogenization of the oxide particles. The structure and spatial distribution of the convective mass transfer in the elementary convective cell with the non-planar bottom profile are provided. Spatial distribution of convective flow in the cell is described by the Stokes lines, which are concentrically arranged smooth closed lines, which indicates the formation of convective flow in the form of a single vortex in the cell with free boundary conditions. Near the bottom, the Stokes lines reflect the curved cosine bottom profile. The scenario of vacuum arc melting and convective mixing of ZrO 2 nano-particles is formulated. Drops of the material of the cathode with ZrO 2 nano-particles fall to the central vertical flow of the ECC. Here, the particles are subjected to the action of the convective flow, which will result in the impact of multidirectional forces: Archimedes force (always directed upwards); gravity force (always directed downwards); friction force (Stokes force) (directed along the liquid velocity vector) on these particles. The Archimedes force depends on the volume, i.e. size, of the particle. Thus, the less the nano–particle size, the lower the buoyancy force. The criterion of overcoming the Archimedes force allows determining the sizes of the particle at which their uniform distribution in the cell volume is possible. It is necessary to provide such conditions: – the deeper the drops get into the cell, the more evenly ZrO 2 particles are distributed in the cell volume; – even distribution of ZrO 2 particles in the sample volume should be observed for sizes less than 80–100 nm.
Highlights
Powder metallurgy (PM) is the area of theoretical and practical knowledge, which describes methods of the key components manufacturing such as metal powders, alloys and metallic compounds, semi-finished products and their products as well as non-metallic powder production without melting the main component [1, 2].PM includes the following main groups of operations: production of the starting metal powders and batch preparation; compacting powders in the preforms; sintering the resulting pieces.The materials formed by the PM methods are called powder materials
The method of vacuum-arc remelt on the example of 08Х18Н10Т steel with addition of ZrO2 [8] is the alternative technology of obtaining the oxide dispersion strengthened (ODS) steels which is under development in the last time
Close to the upper boundary of the cell, due to the radial flux, nanoparticles are flowing to the crystallizer walls, where by means of Stokes forces and gravity forces are directed to the bottom of the cell. If these forces overcome the Archimedes force, nano-particles get into the closed convective flux and will be subject to convective mixing inside of elementary convective cell (ECC), which is equal to their even distribution over the volume of the ODS steel sample
Summary
Powder metallurgy (PM) is the area of theoretical and practical knowledge, which describes methods of the key components manufacturing such as metal powders, alloys and metallic compounds, semi-finished products and their products as well as non-metallic powder production without melting the main component [1, 2]. PM includes the following main groups of operations: production of the starting metal powders and batch preparation; compacting powders (or mixtures thereof) in the preforms; sintering the resulting pieces. The materials formed by the PM methods are called powder materials. These materials can be divided into the following types associated with their performance: structural, tribological, filtering, hard alloys, high temperature, electrical etc. Прикладная физика of the dioxide-based powders, carbides, uranium nitrides and powders of refractory compounds of other transuranic elements [3] are made of them
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