Exothermic Synthesis of Binary Solid Solutions Based on Hafnium and Zirconium Carbides

Abstract

The paper presents the results of an experimental study into the possibility of producing ultrahigh temperature ceramics constituting solid solutions of HfC and ZrC carbides by the single-stage electrothermal explosion (ETE) method under pressure. Adiabatic flame temperature and phase composition of the equilibrium final product were calculated on the basis of thermodynamic data. It was shown that, when the ZrC content in the final product is less than 20 wt %, the adiabatic flame temperature reaches 3800–3900 K, and the combustion product contains hafnium and zirconium carbides. The effect of mechanical activation modes in an AGO-2 planetary centrifugal mill used for a reaction mixture containing Hf, Zr, and C powders on its properties, phase composition formation, and the microstructure of carbide solid solutions was studied. It was shown that high-energy mixing in hexane leads to the destruction of the crystal structure of Hf and Zr particles and the formation of amorphous composite particles. The synthesized samples of ultrahigh temperature ceramics were studied by X-ray diffraction and microstructure analyses. It was shown that exothermic synthesis leads to the formation of single-phase solid solutions of HfC and ZrC carbides with the average particle size of 1.5–0.2 µm. The residual porosity of the binary carbides obtained is 10–12%. It was found that, despite the high temperature of sample heating during ETE under pressure, the particle size of the resulting solid solutions is significantly (by an order of magnitude) smaller than the particle size of similar complex carbides (20–50 µm) obtained by other methods (SPS and hot pressing). This is associated with the rapidity of the exothermic interaction of the reagents (10–50 ms) during ETE.