Structure and properties of ZrB2- and HfB2– based ultrahigh temperature ceramics sintered under high pressure
PRIKHNA T. 1,4, LOKATKINA A. 1, KARPETS M. 1,2, HABER R. 3, BÜCHNER B. 4, JOCHEN W. 4, HUFENBACH J. 4, KLUGE R. 4, MOSHCHIL V. 1, BARVITSKYI P. 1, BONDAR A. 5, BORIMSKYI O. 1, DEVIN L. 1, PONOMARYOV S. 6
1 V. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine, Avtozavodska Str., 2, Kyiv 04074, Ukraine, Kyiv, Ukraine; 2 National Technical University of Ukraine «Igor Sikorsky Kyiv Polytechnic Institute”, Peremogy Avenue 37, 03056 Kyiv, Ukraine, Kyiv, Ukraine; 3 Department of Materials Science and Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA, Piscataway, United States; 4 Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden e. V. Helmholtzstraße 20, 01069 Dresden, Germany, Dresden, Germany; 5 Frantsevich Institute for Problems of Material Sciences of the National Academy of Sciences of Ukraine, Krzhizhanovsky Str., 3, 03142 Kyiv, Ukraine, Kyiv, Ukraine; 6 Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine , 41, Nauky Ave., 03028 Kyiv, Ukraine, Kyiv, Ukraine
The study of the structure; mechanical characteristics and high temperature stability in vacuum (using Pirani – Alterthum technique) and in air (by DTA and TG measurements up to 1600 oC) of sintered under high quasihydrostatic pressure (at 4.1 GPa, 4 min heating up to 1800 oC and 4 min holding at 1800 oC,) and by hot pressing (at 30 MPa) ZrB2- and HfB2 – based materials without and with SiC and Si3N4 additions showed that the use of high pressures at comparatively low temperatures and short sintering time makes it possible to obtain mentioned materials with improved mechanical properties as compared to the materials obtained by other known methods. In the case of SiC-added composites, this is attributed to the diffusion of some C and Si in the ZrB2 or HfB2 matrix and Zr and Hf in SiC grains. The Auger and EDS quantitative study and mapping confirm these conclusions. For ZrB2 and HfB2 without additives this can be due to high connectivity between grains and a higher density of defects such as twins, dislocations and stacking faults (as TEM study showed). The stability in vacuum of pure ZrB2 and HfB2 occurred to be essentially higher than that of the materials with SiC additions (the beginning of melting of the materials with additions observed at 2150-2160 °C, while the materials without them did not melt up to 2970 °C). The composite material prepared from HfB2-30 wt.% SiC mixture demonstrated high mechanical characteristics (density r=6.21 g/cm3, microhardness Hv(9.8 N) = 38.1±1.4 GPa, HV(49 N) = 27.7±0.24 GPa,, HV(98 N)=26.3±2.03 and fracture toughness K1C(9.8 N) = 8.2±0.2, MN•m0.5, K1C(49 H)=6.8±0.6 MN•m0.5, K1C(98 N) = 6.4 ±0.11 MH•m0.5) which are essentially higher than that of pure HfB2 sintered in the same conditions (r=10.79 g/cm3, Hv(9.8 N)=21.3±0.84 GPa, HV(49 N)=19.3±1.34 GPa,, HV(98 N)=19.2±0.5 and fracture toughness K1C (49 N)=7.2±0.9 MH•m0.5, K1C=5.7 ±0.3 MN•m0.5, Young modulus E=984 GPa, Poisson ratio µ=0.146). The mechanical characteristics of high pressure sintered material from ZrB2+20 wt.% SiC (r=5.04 g/cm3, Hv(9.8 N)=24.2±1.0 GPa, HV(49 N)= 17.6±0.7, HV(98 N)=16.73±1.1 GPa, K1C (49 H)=7.21±1.55 MN•m0.5, K1C=6.2 ±1.24 MN•m0.5, E=386 GPa, µ=0.093) are higher than that sintered by hot pressing at 30 MPa, 1900 oC for 1 h from ZrB2+30 wt.% SiC (r=5.25 g/cm3, Hv(9.8 N)=22.95±1.0 GPa, K1C ((9.8 H)=3.44±0.22 MN•m0.5)..
The availability of large-volume high-pressure apparatuses and the level of technology development make method of high pressure-high temperature sintering promising for industrial application.