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VASYLKIV, Oleg
Address
305-0047 1-2-1 Sengen Tsukuba Ibaraki JAPAN [Access]

Research

Keywords

materials science, ceramic engineering, nano-engineering, nano-composites, electric current assisted sintering techniques (ECAST: SPS, reaction-driven spark plasma sintering (RD-SPS), 'flash sintering, 'flash'-SPS), nano-powders, nano-ceramic & composites, hard ceramic, tough ceramic, flexural strength behavior, ultra-high temperature ceramic (UHTC), ultra-high elevated temperature strength, superplasticity of brittle hard ceramics, dynamic toughness, highly ordered nano-scale structures, self-assembled magnetite-chitosan nanostructures, boron carbide, boron suboxide, titanium diboride, tantalum boride, tantalum carbide, niobium boride, niobium carbide, zirconium boride, hafnium boride, silicon carbide,vanadium diboride, zirconium oxide, energetic materials, nano-explosive synthesis, multication nanopowders, etc.

The request in new multipurpose ultra-high temperature ceramics (UHTC), able to act as plasma-facing parts in fusion reactors, special engine & vehicle protection as far as ceramic segmented leading edge components for aerospace, ceramic parts for solar towers used for gas turbine operation in a combine cycle power plants (grids, superheaters, reheaters, evaporators, stream turbines, condensers and chimneys) cause the worldwide demand in new class of light-weight ceramic composites with incredibly high strength, sufficient balance between high toughness & hardness, ultra-hardness and high-modulus. Currently Dr. Oleg Vasylkiv conducting research in chemical and structural engineering of deformation-resistant carbides, borides, and nitrides of Me(IV–V) ceramic composites with superior hardness, toughness and flexural strength up to 2000°C. Simultaneously Oleg studying the mechanisms of high-temperature (HT) flexural strengthening, and HT plasticity (change in the deformation mechanism from brittle fracture to plastic deformation) of usually brittle MeIV–V carbides, borides, and nitrides. Few current studies: (1) Ultra-high temperature flexure and strain driven amorphization in bulk polycrystalline boron carbide. At temperatures above 2000 °C, boron carbide showed an ultrahigh flexural strength exceeding 1.8 GPa which was accompanied by a change in the deformation mechanism from brittle fracture to plastic deformation. The amorphization occurs inside of the severely deformed grains. The results at 2000 °C suggest that the magnitude of the tensile stresses imposed on the B4C grains during deformation in flexure and the total strain transferred to a ceramic during the deformation process play the dominant role in the crystalline-amorphous transformation. (2) We report the formation of a Zr-Ta multimoride ceramic composite with an artificially created hierarchical superstructure. Such a composite was formed during the reaction-driven consolidation process using a mixture of ZrB2, Ta, and amorphous boron powders. The homogeneity of the reaction between these powders allowed the forming of a highly reproducible and repetitive superstructure where Ta3B4 forms a chain-like mesh which entraps the ZrB2, ZrB, TaB and (Zr,Ta)B2 phases. The multiboride ceramic composite exhibited extremely superhardness: 28.6±3.2 GPa (at 98 N), and 22.6±0.6 GPa (at 196 N). The primary reason for the superhardness of Zr, Ta multiboride ceramic composite was considered to be the formation of the (Zr,Ta)B2 solid solution. The main phase of multiboride ceramic was the solid-solution of Zr and Ta diborides which improve the flexural strength up to 2000 °C. At 2000 °C, the multiboride composite showed a strength of nearly 400 MPa and fractured in an elastic manner at the loading rate of 2.5 mm/min. This level of strength is usual for the bulk zirconium diboride at room temperature. (3) A long-term dream of producing bulk additive-free polycrystalline alpha-SiC been accomplished. Bulk silicon carbide showed ultra-high hardness of 29 GPa at 196 N. The super-strength exceeding 2 GPa observed using the strain rate of 2.5 mm/min. at 2000 °C. The increase in strength with increase in temperature was accompanied with a sufficient increase in the stacking faults density inside the SiC grains suggesting activation of a self-strengthening mechanism. (4) Bulk boron prepared by SPS of amorphous β-boron powder. It showed a steady increase in strength up to 1200 °C, which is 0.66 of the absolute melting point for boron. Despite showing clear signs of plastic deformation on the strain-stress curves, the yield strength of the monolithic boron ceramic exceeds 1.2 GPa at 1200 °C which surpasses the data currently available for boron carbide bulks. (5) Deformation- resistant Ta0.2Hf0.8C solid- solution ceramic with superior flexural strength at 2000°C. we explored the consolidation, solid- solution formation and high temperature properties of tantalum hafnium carbide with the 1 TaC:4 HfC ratio, that is, Ta0.2Hf0.8C. Tantalum hafnium carbide bulks can be consolidated using spark- plasma sintering only at temperatures exceeding 2200°C. Based on the three- point flexural tests, it was observed that the toughness and strength of Ta0.2Hf0.8C remained high at 2000°C (3.4 ± 0.4 MPa m1/2, 500 ± 20 MPa). At 2000°C, majority of carbides show a plastic behavior, but the strain- stress curves of the SPSed Ta0.2Hf0.8C ceramic were linear. (6) Consolidation and high-temperature strength of monolithic lanthanum hexaboride. Rare-earth hexaborides are excellent thermionic electron emitter materials. Among all the binary ceramic compounds ever fabricated, LaB6 shows the best figure of merit as a thermionic emission material. LaB6 was determined to have many advantageous properties, including a low electron work function and good chemical resistance. In this study we explored the densification, microstructure evolution, and high temperature properties of bulk lanthanum hexaboride. (7) Reactive consolidation and high-temperature strength of HfB2–SiB6. During theSPS, SiB6 decomposes into cubic SIC and B4C. For the HfB2-SiB6 ceramic improvement in hardness (24.5 ± 0.7 GPa) was attributed to the formation of the B12(C,Si,B)3. Fracture toughness by indentation (6.8 ± 2.4 MPa·m1/2), single-edge notched bend specimens (4.6 ± 0.4 MPa·m1/2) and room-temperature strength (513 ± 21 MPa) of the HfB2–SiB6 composite produced by SPS was higher as the HfB2–SiC ceramics. (8) Ternary single-phase high-entropy TaZrNb carbide was obtained using reaction driven-ECAST. Phase analysis and lattice parameter measurements using x-ray diffraction showed multi-stage formation of the single-phase high-entropy-type carbide with lattice parameter of 4.535 Å. This is expected to be also true for other multicomponent high-entropy carbides, as metal atoms have a different diffusivity in newly formed phases. Flexural strength of TaZrNb carbide showed a peak of strength at 1600 °C. Above this temperature, carbide phase fractured in a different manner and been accompanied with decrease in strength and elastic modulus. High-strength boron-based eutectic composites via in situ SPS. (9) High-temperature toughening in ternary medium-entropy (Ta, Ti, Zr)C carbide consolidated using SPS. Synthesis and HT properties of medium-entropy (Ti,Ta,Zr,Nb)C using the spark plasma consolidation of carbide powders. (10) B4C-TaB2 eutectic composites by spark plasma sintering. (11) High-strength TiB2-TaC ceramic composites prepared using reactive spark plasma consolidation. (12) Mechanical properties of SiC–NbB2 eutectic composites by in situ spark plasma sintering. (13) High-temperature reactive spark plasma consolidation of TiB2-NbC. (14) Synthesis of iron oxide nanoparticles with different morphologies by precipitation method with and without chitosan addition. (15) Flash spark plasma sintering of ultrafine yttria-stabilized zirconia ceramics. Hot-spots generation, exaggerated grain growth and mechanical performance of silicon carbide bulks consolidated by flash-SPS. (16) Nanoexplosion synthesis of multimetal oxide ceramic nanopowders. Nano-engineering of zirconia-noble metals composites. Nanoreactor engineering and SPS densification of multimetal oxide ceramic nanopowders. (17) Synthesis and magnetic properties of self-assembled magnetite-chitosan nanostructures. (18) Tough yttria-stabilized zirconia nanoceramic by low-temperature SPS. High-toughness tetragonal zirconia and zirconia/alumina nano-ceramics. Tough yttria-stabilized zirconia nanoceramic by low-temperature presureless consolidation. (19) Nanoblast synthesis and SPS of nanostructured oxides for SOFC.

PublicationsNIMS affiliated publications since 2004.

Proceedings
Presentations
Patents
  • No. 5024796 ナノサイズ粉体の製造方法 (2012)
  • No. 5713284 強磁界技術によって配向された高硬度B4C及びその製造方法 (2015)
  • No: 2012062210 強磁界技術によって配向された高硬度B4C及びその製造方法 (2012)
  • No: WO2006082844 ナノサイズ粉体の製造方法 (2006)

Society memberships

The Ceramic Society of Japan, The American Ceramic Society

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