THE REFINING OF TITANIUM BY CRUCIBLELESS ZONE MELTING METHOD

The physical substantiation of titanium refining by crucibleless electron beam zone melting (ZM) method in vacuum was presented. Calculations of the equilibrium, limiting and effective distribution coefficients for impurity elements in the base metal were carried out. The refining of titanium was studied experimentally, and samples with a purity of 99.92 wt.% were received. The total content of impurities was reduced by a factor of 1.5 (from 0.12 to 0.08 wt.%). The concentration of interstitial impurities was significantly reduced (oxygen – by 1.3; carbon – by 2; nitrogen – by 2.5 times). The structure and microhardness were investigated.

Impact of interstitial impurities on the trapping of dislocation loops in tungsten

Ab initio simulations are employed to assess the interaction of typical interstitial impurities with self-interstitial atoms, dislocation loops and edge dislocation lines in tungsten. These impurities are present in commercial tungsten grades and are also created as a result of neutron transmutation or the plasma in-take process. The relevance of the study is determined by the application of tungsten as first wall material in fusion reactors. For the defects with dislocation character, the following ordering of the interaction strength was established: H < N < C < O < He. The magnitude of the interaction energy was rationalized by decomposing it into elastic (related to the lattice strain) and chemical (related to local electron density) contributions. To account for the combined effect of impurity concentration and pinning strength, the impact of the presence of these impurities on the mobility of isolated dislocation loops was studied for DEMO relevant conditions in the non-elastic and dilute limit.

THE INFLUENCE OF INTERSTITIAL IMPURITIES IN THE Zr–Y TARGET ALLOYS ON THE HEAT RESISTING CERAMIC COATING QUALITY

The influence of interstitial impurities in the Zr–Y target alloys (manufactured by two different techniques) on the quality of thermal barrier ceramic layers of heat resisting coating are studied in this work. The heat resisting ceramic coating manufactured in the UOKS-2 devices by magnetron medium-feculence plasma–chemical deposition on the surface of components that are used at the high temperatures (above 1150 °C). It was found that when the content of interstitial impurities in the target alloy is more than 0,1% (1000 ppm), the rate of the coating process decreases and has to be maintained by increasing the energy of argon ions. This leads to overheating of the target alloy and the surface of the parts (substrate) which impairs the adhesion of the deposited atoms.

Zone Recrystallization of Zirconium and Hafnium

The work studied the possibility of obtaining of the high-purity samples of zirconium and hafnium by the method of zone recrystallization of round rods with electron-beam heating in a vacuum of 1∙10-4 Pa. Some meltings were carried out in a constant electric field with the variability of its connection. It is shown that the simultaneous passage of several refining processes (evaporation of highly volatile metallic impurities, zone recrystallization with directional displacement of impurities to the end of the sample, electrotransport) made it possible to efficient refining of zirconium both from metallic impurities and from interstitial impurities. The best degree of purification was achieved when zone melting carrying out in an electric field directed opposite to the zone movement. In this case, the displacement of interstitial impurity ions coincided with the direction of movement of the liquid zone. Samples of zirconium with a purity of 99.89 wt. % were obtained (the concentration of aluminum was reduced by 5, iron - 11, copper - 45, chromium - 75, silicon - 10, titanium - 2.5, oxygen - 3.3, nitrogen - 3, carbon - 2 times). The hafnium samples refined by the zone recrystallization method were characterized by a purity of 99.85 wt. %. The concentrations of both all metal impurities and interstitial impurities were significantly reduced (concentration in wt% oxygen was 0.011, carbon - 0.0018, nitrogen - 5∙10-5). A study of gas evolution from samples of iodide hafnium and refined hafnium was carried out. It was found that the maximum gas release peak fell on the temperature range of 500 ... 550 °C. The use of an integrated approach, including high-temperature heating, stages of zone melting at different rates, and thermal cycling in the range of the polymorphic transformation temperature, made it possible to obtain single-crystal hafnium samples. According to X-ray diffraction data, the parameters of the hafnium crystal lattice were determined: а = (0.31950 ± 5·10-5) nm and с = (0.50542 ± 5·10-5) nm (at 298 K), which corresponds to the density ρ = 13.263 g/cm3 and axial ratio с/a = 1.5819.

Research Progress in Preparation and Purification of Rare Earth Metals

The purity of rare earth metals is one of the most important factors to research and develop high technique materials. However, high purity rare earth metals are not easily achieved. This review summarizes the preparation and purification methods of rare earth metals. First, the preparation principle and process of molten salt electrolysis and metal thermal reduction are introduced. The main sources of metallic impurities and interstitial impurities in rare earth metals as well as the action mechanism of reducing the concentration of different impurities are analyzed and summarized. Then, the purification principle and process of vacuum distillation, arc melting, zone melting, and solid state electromigration are also discussed. Furthermore, the removal effect and function rule of metallic impurities and interstitial impurities in rare earth metals are outlined. Finally, the crucial issues in the development of high purity rare earth metals are put forward, and the development direction of high purity rare earth metals in future are pointed out on this basis.

ZONE REFINING OF ZIRCONIUM IN AN ELECTRIC FIELD

The physical grounds and an experimental study of the efficiency of applying the zone recrystallization method in an electric field for zirconium refining from metal and gas-forming impurities are presented. The changes in the elemental composition, microhardness, and structure of the obtained ingots was investigated. It is shown that the application of the method can significantly reduce the content of interstitial impurities. Zirconium samples with a purity of 99.91 wt.% were obtained.

Study of Interstitial Impurities Influence on Properties of Titanium Alloy Ti-5Al-5V-5Mo-3Cr-1Zr

The effect of different interstitial impurities content (oxygen, carbon) on β - transus temperature and complex of properties in the heat-strengthened condition of the Ti-5Al-5V-5Mo-3Cr-1Zr (VST55531) titanium alloy has been studied. The possibility of determining alloy β - transus temperature by the differential scanning calorimetry method with accuracy comparable with the test quenching method is shown in this paper. It is shown that under identical aging regimes an increase of oxygen content from 0.176 to 0.25 wt.% and carbon content from 0.009 to 0.025 wt.% in VST55531 alloy results in higher strength, plastic characteristics and lower ductility, toughness characteristics, especially those which related to the crack propagation.