Synthesis and Thermal Stability of the Multielement Carbide (TaZrHfNbTi)С5

Abstract

The multielement carbide (TaZrHfNbTi)С5 has been synthesized via two-step high-energy mechanical processing (HEMP). We have optimized mechanical processing parameters for the formation of the TaZrHfNbTi high-entropy alloy (HEA)—as a precursor for the synthesis of the mixed carbide—from a metal powder mixture. HEMP of a mixture of Ta, Zr, Hf, Nb, and Ti powders in an AGO-2 planetary mill for 15 min at 90g leads to the formation of a TaZrHfNbTi HEA with an imperfect crystal structure. The time needed for obtaining the multielement carbide (TaZrHfNbTi)С5 by milling a mixture of the metallic HEA and carbon black is 30 min. The thermal stability of the resultant carbide has been studied by high-temperature X-ray diffraction. The results demonstrate that the multielement carbide (TaZrHfNbTi)С5 is stable in the range 800–1200°C at an isothermal holding time of 5 h, without precipitation of individual carbide phases. Exposure to temperatures above 1000°C under dynamic vacuum leads to partial oxidation of (TaZrHfNbTi)С5.