Phenomenological analysis of densification mechanism during spark plasma sintering of MgAl2O4

TL;DR

This study investigates the densification mechanism of MgAl2O4 during spark plasma sintering, revealing grain-boundary sliding facilitated by interface reactions and vacancy annealing challenges as key factors.

Contribution

It provides a phenomenological analysis of the densification process during SPS of MgAl2O4, highlighting the role of interface reactions and vacancy dynamics.

Findings

Densification involves grain-boundary sliding and interface reactions.

A zero-densification-rate period is observed due to vacancy annealing difficulties.

Atomic ledges and stoichiometry modifications are linked to vacancy behavior.

Abstract

Spark plasma sintering (SPS) of MgAl2O4 powder was investigated at temperatures between 1200 and 1300{\deg}C. A significant grain growth was observed during densification. The densification rate always exhibits at least one strong minimum, and resumes after an incubation period. Transmission electron microscopy investigations performed on sintered samples never revealed extensive dislocation activity in the elemental grains. The densification mechanism involved during SPS was determined by anisothermal (investigation of the heating stage of a SPS run) and isothermal methods (investigation at given soak temperatures). Grain-boundary sliding, accommodated by an in-series {interface-reaction/lattice diffusion of the O$^2$-anions} mechanism controlled by the interface-reaction step, governs densification. The zero-densification-rate period, detected for all soak temperatures, arise from the difficulty of annealing vacancies, necessary for the densification to proceed. The detection of atomic ledges at grain boundaries and the modification of the stoichiometry of spinel during SPS could be related to the difficulty to anneal vacancies at temperature soaks.