The stress-strain state of ZrB2-SiC ultra-high-temperature ceramics, produced using commercial powders with different impurity levels, was investigated by X-ray diffraction. Upon analysis of ZrB2 and ...SiC diffraction lines shift, the level of thermal stresses (strains) of the different phases was determined. An increase of internal stresses in ceramics with rising viscous-brittle transition temperatures, Tve, was attributed to increased grain boundary strength. Ceramics, for which high Tve and high level of internal stresses were estimated, exhibited high strength, up to 700 MPa at 1400 °C. A field of compressive thermal stresses in the matrix phase resulted to be necessary for achieving high strength at low-temperatures. On the contrary, the presence of low-melting impurities at the grain boundaries negatively impacted on the stress level in ZrB2 boundaries in the high temperature regime.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The correlations between structures and mechanical characteristics of α-AlB12-, AlB12C2-, B4C-based lightweight ceramics and composites synthesized or sintered by hot pressing (at 30 MPa) and ...SiC-based ceramics obtained by reactive sintering are compared. The effect of C, TiC and SiC additions on the properties of the resultant composites and the particularities of the ceramics destruction under shock loading are discussed. Ballistic tests performed on 10 mm thick plates fabricated from the developed ceramics (2.63 g/cm3 density; 78 wt% B4C and 22 wt% SiC composition according to X-ray diffraction analysis; B3.64CSi0.01 and SiC1.07 stoichiometry according to SEM microprobe X-ray analysis), showed that the material could withstand a 10 m distance shot using a bullet with initial kinetic energy of 3.7 kJ.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The effect of amorphous a-SiOxCy(:Er) layers on the oxidation behavior of ZrB2-SiC composite ceramics has been studied. ZrB2–15%SiC composite samples were obtained by hot pressing of ZrB2+15%SiC ...powder at 1850оС and 48MPa. Amorphous a-SiOxCy:(Er) thin films (1μm thick) were deposited on ZrB2-SiC specimens at a temperature of 200°C by reactive RF-magnetron sputtering of SiC/Er target in argon/oxygen flow. Coated ZrB2-SiC samples were exposed to a high-temperature oxidation at 1400°C for 1h at atmospheric pressure. Structure and phase composition were examined by optical microscopy, X-ray diffraction, SEM and EDS. It was demonstrated that a-SiOxCy coating noticeably enhances the oxidation resistance of the surface. Further development of the oxidation resistance was observed in Er-incorporated a-SiOxCy coating. Along with the improvement of the antioxidation resistance the deposition of a-SiOxCy(:Er) coatings resulted in increasing of bending strength of ZrB2-SiC samples in comparison to uncoated samples. The enhancement of surface stability and strengthening by a thin a-SiOxCy(:Er) coating is discussed in terms of the effects of dense coating by itself and the modification of a surface silica layer by erbium incorporation as well.
•SiOC(:Er) coating by RF magnetron sputtering on ZrB2–15%SiC strongly improves the antioxidation resistance of ceramics at 1400 °C.•One micrometer thick SiOC(:Er) coating increase bending strength of the 3 mm thick ceramics blocks in the range of 5-100 %.•Er incorporation play a key role in development of antioxidation resistance but not in the mechanical strengthening.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The effect of preliminary mechanical activation on the structural and physical state of the starting reagents, phase formation, and structure of sintered 80 vol.% ZrB
2
–15 vol.% SiC–5 vol.% B
4
C ...ceramics was studied. The starting powders were mechanically activated in steel drums of an AIR water-cooled high-energy ball mill at a rotation speed of 1440 rpm in an argon atmosphere. The mechanical activation lasted 15, 30, 60, and 120 min. The samples were produced by hot pressing using an SPD-120 pilot plant with induction heating in graphite dies in a CO–CO
2
atmosphere. The particle-size distribution was determined by laser diffraction. Metallographic studies were conducted using a Superprobe 733 electron microscope (Japan). The mechanical activation of ultrahigh-temperature ceramics was found to influence the compaction kinetics of the samples. When mechanical activation time increased from 15 to 120 min, the sample density increased by 10% in the hot pressing process at 2150
°
C (15 min). The samples had 5–10 μm particles. During hot pressing, the ZrB
2
matrix phase acquired a skeletal structure: the SiC phase in an amount of 15 vol.% acted as reinforcement in partial dissociation and B
4
C in an amount of 5 vol.% acted as a boron and carbon donor. Preliminary mechanical activation of the 80 vol.% ZrB
2
–15 vol.% SiC–5 vol.% B
4
C powder mixture intensified sintering in the temperature range 2100–2150°C, featuring the formation of secondary phases and recrystallization (at 2150°C), and promoted high density and low porosity of the hot-pressed ceramics. The studies showed that the densest samples were sintered from the powder mixture mechanically activated for 120 min. The density of the samples hot-pressed at 2100°C (5 min) and 2150°C (15 min) increased.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The interaction in the ZrB
2
–Ni system with change in the ZrB
2
content from 3.5 to 75 wt.% has been studied. It is shown that the process occurs through the contact melting mechanism, leading to ...the formation of a liquid phase, wetting the substrate with a contact angle of about 50°, even at 1250°C. The liquid phase interacts with the substrate and crystallizes with time as more refractory compounds are formed. The structure and phase composition of the reaction products are determined by the ratio of alloy components, representing double, triple, and more complex compounds based on the crystalline lattices of Zr–Ni intermetallides. The eutectic point is found at 13% ZrB
2
in the alloy. The eutectic nature of the ZrB
2
–Ni quasibinary phase diagram restricts the upper temperature limit for application of the alloys and associated materials in friction joints of fuel equipment. Considering that they may undergo solid-phase interaction, the upper temperature limit is 1000°C.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Zirconium boride–nichrome (Ni–20 Cr) interaction at zirconium boride concentration in the charge varying from 3.6 to 60% and at annealing temperatures of 1100–1850°C has been studied. It is shown ...that the interaction begins at 1200°C as a solid-phase reaction to form nickel borides. At 1300–1350°C, contact melting that is characteristic of eutectic systems follows the solid-phase interaction. The eutectic liquid appears and wets zirconium boride with a contact angle of 0° at 1500°C. The eutectic melting point is 1320 ± 20°C at a zirconium boride concentration of 11–13% in the alloy. The phase composition of the interaction products depends on the ratio of alloy components and temperature. It is represented by binary and ternary compounds in the Ni–Cr–B–(in part) C system formed from chromium and nickel boride crystal lattices. The main part of zirconium in the alloy is concentrated in the formed intermetallides. Thus, the contact pairs made of zirconium boride –nichrome materials can operate only at temperatures below 1200°C.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Ultrahigh-temperature ZrB
2
-based ceramics with different sintering additions was developed for extreme conditions. Its strength characteristics, phase composition, and structure were examined. The ...ceramics was oxidized in air at 1250 and 1550°C. In addition, the most stable composites were subjected to temperature cycling in a flow of aviation fuel combustion products in a temperature range of 1400–1500°C. All materials show high oxidation resistance. The method used to produce samples influences their oxidation behavior: materials produced by vacuum hot pressing show higher oxidation resistance than those produced by hot pressing in a CO–CO
2
atmosphere, probably because of their higher final density. The best results were obtained when ZrB
2
sintering was combined with introduction of MoSi
2
and CrB
2
.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The effect of amorphous a-SiOxCy(:Er) layers on the oxidation behavior of ZrB2-SiC composite ceramics has been studied. ZrB2–15%SiC composite samples were obtained by hot pressing of ZrB2 + 15%SiC ...powder at 1850оС and 48 MPa. Amorphous a-SiOxCy:(Er) thin films (1 μm thick) were deposited on ZrB2-SiC specimens at a temperature of 200 °C by reactive RF-magnetron sputtering of SiC/Er target in argon/oxygen flow. Coated ZrB2-SiC samples were exposed to a high-temperature oxidation at 1400 °C for 1 h at atmospheric pressure. Structure and phase composition were examined by optical microscopy, X-ray diffraction, SEM and EDS. It was demonstrated that a-SiOxCy coating noticeably enhances the oxidation resistance of the surface. Further development of the oxidation resistance was observed in Er-incorporated a-SiOxCy coating. Along with the improvement of the antioxidation resistance the deposition of a-SiOxCy(:Er) coatings resulted in increasing of bending strength of ZrB2-SiC samples in comparison to uncoated samples. The enhancement of surface stability and strengthening by a thin a-SiOxCy(:Er) coating is discussed in terms of the effects of dense coating by itself and the modification of a surface silica layer by erbium incorporation as well.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The galaxy Mrk 501 has been monitored with the GT-48 Cherenkov telescope at the Crimean Astrophysical Observatory for 14 years (1997–2010). Very-high-energy (VHE) gamma-ray photons have been recorded ...from Mrk 501 with a total significance of 15σ. The arrival directions of VHE gamma-ray photons have been mapped. They have been identified with Mrk 501. The TeV fluxes from Mrk 501 are shown to be highly variable. The light curves from the data of Cherenkov telescopes and the telescopes that observed Mrk 501 at high energies (MeV and GeV) and in the X-ray and optical bands are presented. Based on the GT-48 observations, we have constructed a TeV spectrum and determined the differential spectral index. The fluxes and spectral characteristics of Mrk 501 inferred from the GT-48 observations are consistent with the data of the MAGIC and H.E.S.S. Collaborations, respectively.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
To improve the corrosion resistance of the ZrB
2
–15 vol.% SiC composite, SiC, SiOC, and SiO
2
–Er
2
O
3
coatings were deposited on its surface by magnetron sputtering. The surface modification of ...the ZrB
2
–15 vol.% SiC ceramics improves their corrosion resistance through the development of a dense layer consisting of high-temperature phases formed in the oxidation process. In addition, the mechanical properties become twice as high (bending strength of the coated samples is 803–875 MPa). X-ray diffraction and scanning electron microscopy were used to examine the phase composition of the oxidation products and the structure of the resultant oxide film.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
