Grain growth kinetics and densification mechanism of (TiZrHfVNbTa)C high-entropy ceramic under pressureless sintering.

• The grain growth kinetics and densification mechanism of (TiZrHfVNbTa)C high-entropy carbide ceramic under pressureless sintering are first investigated. • The compositional complexity results in sluggish diffusion effect and consequently improves the activation energy threshold of lattice diffusion in the main densification stage. • The solid solution formation procedure is accompanying and promotes the densification process. The grain growth kinetics and densification mechanism of (TiZrHfVNbTa)C high-entropy carbide ceramic are investigated in this work. A single phase carbide with a rock-salt structure is formed until 2300 °C, below which an apparent aggregation of V, Zr and Hf exists. It is associated with the slow diffusion rate of V element as well as the relatively poor solubility of VC in HfC (as well as ZrC). The grain growth mechanism gradually changes from surface diffusion to volume diffusion and then grain boundary diffusion with increasing sintering temperature. This is attributed to the variation of activation energy of grain growth. The densification mechanism is principally dominated by the mass transport through lattice diffusion with the activation energy of 839 ± 53 kJ/mol. Through the design of two-step sintering, it is verified that the solid solution formation can effectively promote the densification process. [Display omitted] [ABSTRACT FROM AUTHOR]