CC BY
29ISHS 2019 Moscow, Russia
REACTION SPARK PLASMA SINTERING OF BINARY AND
HIGH-ENTROPY CARBIDES
D. O. Moskovskikh*" and A. S. Mukasyan0
aNational University of Science and Technology MISiS, Moscow, Russia
bUniversity of Notre Dame, Notre Dame, USA
*e-mail: mos@misis.ru
DOI: 10.24411/9999-0014A-2019-10102
The work describes the production of bulk ceramic materials by spark plasma sintering (RSPS). The proposed method allows one to manufacture bulk ceramics based on SiC, B4C, HfC, AhO3-SiC, and equiatomic Hf0.2Ta0.2Ti0.2Nb0.2Zr0.2C and Hf0.2Ta0.2Ti0.2Nb0.2Mo0.2C high-entropy ultra-high temperature carbides in one step. By short-term high-energy ball milling (HEBM) of mixtures of metal and carbon powders, we were able to produce nanostructured composite particles with elements mixed at the submicron level. The small size of the reagent particles and the large surface area of contact between them can significantly accelerate the reaction and the consolidation processes during the SPS, leading to the formation of low-porosity ceramics (< 5%) with fine (~ 5 p,m) carbide grains and good mechanical properties. For example, optimization of HEBM + RSPS conditions allows rapid (less than 30 min of SPS) fabrication of B4C ceramics with porosity less than 2%, the hardness of ~ 35 GPa and fracture toughness of ~ 4.5 MPa m1/2 as well as fabrication of SiC ceramics with a hardness of ~ 24 GPa and fracture toughness of ~ 5 MPa m1/2
High-entropy ceramics were prepared in two steps. First, metallic high-entropy alloys Hf0.2Ta0.2Ti0.2Nb0.2Zr0.2 and Hf0.2Ta0.2Ti0.2Nb0.2Mo0.2 were produced by HEBM, then graphite powder was added to the alloy and mixture was milled for another 5 minutes. By the SPS of the resulting mixture, samples with the relative density up to 96%, hardness up to 33 GPa and Young modulus up to 570 GPa were produced. The composition Hf0.2Ta0.2Ti0.2Nb0.2Zr0.2C with the higher entropy-forming ability (100 (eV/atom)-1) was resistant against selective oxidation and formation of oxide phases during the sintering, whereas the composition Hf0.2Ta0.2Ti0.2Nb0.2Mo0.2C with lower entropy-forming ability (83 (eV/atom)-1) was prone to extensive formation of HfO2 under the same processing conditions.
The RSPS method allows one to produce ceramics with at least comparable in properties with SPS counterparts, with greater energy efficiency and skipping the stage of the ceramic powder synthesis.
D. O. Moskovskikh and A. S. Mukasyan
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