How does cold sintering affect the microstructural evolution of high-entropy pyrochlore during pressureless sintering?

Abstract

The challenge of producing dense fine-grained high-entropy ceramics is hereby addressed by a combined cold and conventional pressureless sintering method for the first time. It provides nearly fully dense high-entropy pyrochlores with better microstructural homogeneity, and only half the grain size of conventional pressurelessly sintered samples with identical density. Both the finer and more homogeneous microstructures benefit better mechanical properties in hardness and reduced Young’s modulus. The kinetics and activation energies of both densification and grain growth were quantified and discussed to understand how cold sintering affects the microstructural evolution during the following pressureless sintering. More importantly, cathodoluminescence analysis suggested that cold sintering could cause more defects on the surface of the original particles, which could promote the grain boundary diffusion and have drag effects on grain boundary motion. The lessons learned here offer scientific understanding and technological guidance towards pressureless sintering of dense bulk high-entropy ceramics.