RESEARCH ON THE POSSIBILITY OF PRODUCING (Ta,Hf)C SINGLE-PHASE TANTALUM-HAFNIUM CARBIDE BY SHS

Abstract

The paper studies the effect of mechanical activation conditions (MA) on the microstructure and phase composition of Ta–Hf–C reaction mixtures and products derived from them by self-propagating high-temperature synthesis (SHS). The mechanical activation of Ta–Hf-C reaction mixtures was carried out in centrifugal planetary mills with different drum rotation speeds. It was found that an increase in the drum rotation speed from 250 to 900 rpm reduced the heterogeneity scale of the reaction charge, reduced the size of coherent scattering regions of tantalum and hafnium by an order of magnitude, and led to an increase in the strain degree of their crystal lattices by 1,5–2,0 times. It was experimentally established that initiation of the SHS reaction in the activated Ta–Hf–C mixture at an initial temperature Т 0 Т 0 = 800 K only, when the adiabatic combustion temperature reached 3274 K. The single-phase carbide (Ta,Hf)C with a lattice parameter а = 0,44787 nm corresponding to 18,0 at.% of HfC dissolved in TaC, was obtained from reaction mixtures activated under optimal regimes. The content of hafnium oxide in products does not exceed 1 %. The structure of samples is characterized by high porosity (more than 30 %) and a small carbide grain size (less than 10 μm), which made it possible to obtain the (Ta,Hf)C powder by milling the SHS product in a ball mill.