CC BY
42iSHS 2019
Moscow, Russia
SPARK PLASMA SINTERING AND SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OF ULTRA-HIGH TEMPERATURE
CERAMICS Hf-C-N
V. S. Buinevich*", A. A. Nepapushev", G. V. Trusov", D. O. Moskovskikh",
A. S. Rogachevfi, and A. S. Mukasyanc
aNational University of Science and Technology MISiS, Moscow, 119049 Russia bMerzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of
Sciences, Chernogolovka, Moscow, 142432 Russia ^Department of Chemical and Biomolecular Engineering, University of Notre Dame,
Notre Dame, IN, 46556 USA *e-mail: [email protected]
DOI: 10.24411/9999-0014A-2019-10025
The future of the aerospace industry is directly related to the development and modernization of the heat-loaded components of hypersonic aircraft: jet engines, nose tips and sharp leading edges of the wings, which are required to withstand ultrahigh temperatures (above 2000°C) caused by aerodynamic heating. The greatest practical interest for the aerospace industry is centered around ultra-high temperature ceramics based on borides, nitrides, carbides, carbonitrides and double transition metal carbides [1-4]. These materials have unique physical and chemical properties. They are characterized by unparalleled combination of heat resistance, thermal conductivity, refractoriness (melting points above 3000°C), hardness, as well as electrical and thermal properties close to those of metals [5-9]. According to recent publications, hafnium carbonitride of optimum composition not only has good mechanical properties and high thermal conductivity, but also is believed to have the highest melting point (above 4200°C) among all currently existing systems. This peak refractoriness is explained by several factors affecting the melting point: the presence of point defects in the crystal lattice and strong covalent and ionic bonds in the system.
Synthesis of carbonitrides with optimal composition is complicated by the high melting points of the main components and the difficulty of controlling the carbon-nitrogen ratio in the compound. Traditional methods of production, such as high-temperature diffusion saturation, require extensive and expensive high-temperature annealings. Moreover, the resulting carbonitrides often deviate from the composition with the maximum melting point (HfC0.3N0.5). Alternative "nonequilibrium" synthesis methods include mechanochemical synthesis and self-propagating high-temperature synthesis (SHS). These approaches allow one to obtain the material of the desired composition in a short period of time. Correspondingly, the purpose of this work was to obtain a new promising ultrahigh-temperature ceramic material based on hafnium carbonitride powders produced by the mechanochemical synthesis or SHS, followed by spark plasma sintering (SPS).
The synthesis of carbonitride was carried out according to the following schemes:
a) mechanochemical processing of powders of hafnium and graphite in a nitrogen atmosphere in a planetary ball mill (PBM) "Activator 2S" during 30 min at a jar gas pressure of 0.4 MPa;
b) mechanical activation of mixture of hafnium and graphite in PBM for 5 min, followed by SHS in a laboratory reactor at a nitrogen pressure of 0.8 MPa.
Ball milling was carried out at a 20:1 ball-to-mixture mass ratio, rotation frequency 694 rpm and rotation ratio k = 1.0. The synthesized powders were studied by X-ray phase analysis (XRD)
XV International Symposium on Self-Propagating High-Temperature Synthesis
and scanning electron microscopy (SEM). Sintering was carried out on a Spark Plasma Sintering Labox 650 unit at a 100°C/min heating ratio in temperature range 1900-2200°C, with a dwelling time 0-10 min at a pressure of 50 MPa. As a result, hafnium carbonitride powders of different composition were obtained and sintered into dense ceramics. The maximum density (98.7%) was observed in the sample obtained using the SHS method, along with the highest hardness (21.3 GPa) and crack resistance (4.7 MPa m1/2) among all samples.
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