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Presence of Oxygen in Ti-Al-C MAX Phases-Based Materials and their Stability in Oxidizing Environment at Elevated Temperatures

100%

Prikhna T., Ostash O., Sverdun V., Karpets M., Zimych T., Ivasyshin A., Cabioc'h T., Chartier P., Dub S., Javorska L., Podgurska V., Figel P., Cyboroń J., Moshchil V., Kovylaev V., Ponomaryov S., Romaka V., Serbenyuk T., Starostina A.

Acta Physica Polonica A

2018

vol. 133

issue 4

789-793

The Ti₃AlC₂-, (Ti,Nb)₃AlC₂- and Ti₂AlC-based materials turned out to be more resistant than Crofer JDA steel in oxidizing atmosphere as 1000 h long tests at 600°C have shown. But the amounts of oxygen absorbed by the materials during testing were different. The Ti₂AlC-based material demonstrated the lowest oxygen uptake, (Ti,Nb)₃AlC₂-based absorbed a somewhat higher amount and the highest amount was absorbed by Ti₃AlC₂-based material. Scanning electron microscopy and the Auger study witnessed that amounts of oxygen in the MAX phases before the exposure in air were as well different: the approximate stoichiometries of the matrix phases of materials were Ti_{3.1-3.2}AlC_{2-2.2}, Ti_{1.9-4}Nb_{0.06-0.1}AlC_{1.6-2.2}O_{0.1-1.2} and Ti_{2.3-3.6}AlC_{1-1.9}O_{0.2-0.6}, respectively. The higher amount of oxygen present in the MAX phase structures may be the reason for higher resistance to oxidation during long-term heating in air at elevated temperature. The studied materials demonstrated high stabilities in hydrogen atmosphere as well. The bending strength of the Ti₃AlC₂- and (Ti,Nb)₃AlC₂-based materials after keeping at 600°C in air and hydrogen increased by 10-15%, but the highest absolute value of bending strength before and after being kept in air and hydrogen demonstrated the Ti₂AlC-based material (about 590 MPa).

Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines

73%

Prikhna T., Gawalek W., Savchuk Y., Sergienko N., Moshchil V., Sokolovsky V., Vajda J., Tkach V., Karau F., Weber H., Eisterer M., Joulain A., Rabier J., Chaud X., Wendt M., Dellith J., Danilenko N., Habisreuther T., Dub S., Meerovich V., Litzkendorf D., Nagorny P., Kovalev L., Schmidt C., Melnikov V., Shapovalov A., Kozyrev A., Sverdun V., Kosa J., Vlasenko A.

issue 1

7-14

Materials of the Y-Ba-Cu-O (melt-textured YBa_{2}Cu_{3}O_{7-δ}-based materials or MT-YBCO) and Mg-B-O (MgB_{2}-based materials) systems with high superconducting performance, which can be attained due to the formation of regularly distributed nanostructural defects and inhomogeneities in their structure can be effectively used in cryogenic technique, in particular in fault current limiters and electrical machines (electromotors, generators, pumps for liquid gases, etc.). The developed processes of high-temperature (900-800°C) oxygenation under elevated pressure (16 MPa) of MT-YBCO and high-pressure (2 GPa) synthesis of MgB_{2}-based materials allowed us to attain high superconductive (critical current densities, upper critical fields, fields of irreversibility, trapped magnetic fields) and mechanical (hardness, fracture toughness, Young modulus) characteristics. It has been shown that the effect of materials properties improvement in the case of MT-YBCO was attained due to the formation of high twin density (20-22 μm^{-1}), prevention of macrocracking and reduction (by a factor of 4.5) of microcrack density, and in the case of MgB_{2}-based materials due to the formation of oxygen-enriched as compared to the matrix phase fine-dispersed Mg-B-O inhomogeneities as well as inclusions of higher borides with near-MgB_{12} stoichiometry in the Mg-B-O matrix (with 15-37 nm average grain sizes). The possibility is shown to obtain the rather high T_{c} (37 K) and critical current densities in materials with MgB_{12} matrix (with 95% of shielding fraction as calculated from the resistant curve).

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Presence of Oxygen in Ti-Al-C MAX Phases-Based Materials and their Stability in Oxidizing Environment at Elevated Temperatures

Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines