Browsing by Author "Markov M."

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    Electron beam melting efficiency at multiple hafnium e-beam processing
    (2024-01-01) Markov M.; Stefanova V.; Vutova K.; Vassileva V.; Tanaka T.; Kakugawa K.
    The method of electron beam melting and vacuum refining has clear advantages over other metallurgical methods since it enables manufacturing of refractory and chemically active metals. This study focuses on the efficiency of removing impurities from technogenic hafnium under multiple electron beam melting. Assessments are performed on the efficiency of double and triple e-beam melting processing of refractory metal hafnium. The influence of different e-beam melting technological modes on the refining effectiveness is investigated. A highest hafnium purity of 99.2% was achieved after double and triple e-beam refinements of the investigated materials, with the highest process efficiency reaching 61.58% and 51.07%, respectively.
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    Study of the Possibility of Recycling of Technogenic Hafnium during Electron Beam Refining
    (2022-12-01) Vutova K.; Stefanova V.; Markov M.; Vassileva V.
    The possibility of removing metallic (such as Zr, Fe, Cr, and Zn) impurities and non-metallic (such as [O] and C) impurities from technogenic hafnium through single and double refining in the conditions of electron beam melting (EBM) has been studied. The influence of thermodynamic and kinetic parameters on the degree of removal of these impurities from the base metal under vacuum conditions and within a temperature interval of 2500 K to 3100 K is defined. The relative volatility of metal impurities and the stability of the oxides and carbides present in the base metal are evaluated. The possibility for complete removal of Fe, Cr, Zn, [O], and C during EBM is shown. In the case of double refining, at a temperature of 2700 K for 20 min, the maximum degree of removal of Zr is 46.8%, the achieved highest hafnium purity is 99.004%, and the overall effectiveness of the refining of hafnium from impurities is 53%. There is a correlation between the degree of removal of Zr and the micro-hardness of the Hf ingots obtained after EBM. The weight losses vary in the ranges of 1.5–5.8% and 1–8% under the studied single and double refining processes, respectively.
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    Study on Hardness of Heat-Treated CoCrMo Alloy Recycled by Electron Beam Melting
    (2023-04-01) Vutova K.; Stefanova V.; Markov M.; Vassileva V.
    The hardness of heat (thermally) treated CoCrMo ingots, recycled by electron beam melting and refining (EBMR) of a technogenic CoCrMo material (waste from the dental technology) under different process conditions (temperature and residence time) is examined. The heat treatment consists of two-step heating up to temperatures of 423 K and 1343 K and retention times of 40 and 60 min, respectively. The influence of various loads (0.98 N, 1.96 N, 2.94 N, 4.9 N, and 9.8 N) on the hardness of the CoCrMo alloy, recycled by EBMR, before and after heat treatment is studied. It has been found that regardless of the EBMR process conditions, the obtained samples after heat treatment have similar hardness values (between 494.2 HV and 505.9 HV) and they are significantly lower than the hardness of the specimens before the heat treatment. The highest hardness (600 HV) is measured in the alloy recycled at 1845 K refining temperature for 20 min. This is due to the smaller crystal structure of the resulting alloy and the higher cobalt content. The results obtained show that the heat treatment leads to considerable changes in the microstructure of the CoCrMo ingots recycled by EBMR. With the increase of the e-beam refining temperature, after the heat treatment, the grains’ size increases and the grains’ shape indicates an incomplete phase transition from γ-fcc to ε-hcp phase. This leads to a slight increase in the hardness of the alloy.
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    THE EFFECTIVENESS OF ELECTRON BEAM MELTING FOR REMOVING IMPURITIES FROM TECHNOGENIC METAL MATERIALS
    (2024-01-01) Markov M.; Stefanova V.; Vutova K.
    Electron beam melting and vacuum refining (EBMR) is a modern metallurgical method that has proven advantages in terms of environmental sustainability and efficiency for recycling refractory and reactive metals and alloys with unique physical, chemical, and mechanical properties. In this work, the effectiveness for removing impurities from technogenic molybdenum, titanium, and hafnium metals using EBMR method is investigated. The thermodynamic and kinetic process conditions and their influence on the possibility of impurities’removal from the studied technogenic materials are discussed. It has been established that there are no thermodynamic limitations for the removal of silicon, antimony, iron, aluminum, and copper impurities at EBMR of molybdenum and the maximal overall removal efficiency is 58 %. In the case of titanium technogenic material, the highest refining efficiency and maximal overall impurity removal level of 99.97 % and 100 % for some inclusions (such as Fe, Cu, Ta, and Cd) are achieved. The studies show that impurities (metallic and non-metallic) can be effectively removed from technogenic hafnium using single e-beam refining processing and the highest refining effectiveness is 52.21 %. The obtained results allow formulating the conditions of the refining process aiming to obtain metal materials with high purity, better structures and properties and demonstrate high effectiveness of the EBMR method.