Abnormal grain growth in DC flash sintered 3‐mol% yttria‐stabilized zirconia ceramics

Abstract

The origin of nonuniform microstructure and abnormal grain growth (AGG) was investigated in flash sintered 3 mol% yttria‐stabilized zirconia (3YSZ) ceramics. The microstructural homogeneity decreased with increasing direct current (DC) density and with dwell time in a flash state, eventually resulting in AGG in the specimen core, the first observation of AGG in 3YSZ. Abnormal grains up to 100 μm in size emerged when the DC density was ≥160 mA/mm2, and the specimen's density exceeded 99% of theoretical, starting from the cathode and propagating toward the anode. The results are discussed by comparison with established mechanisms and previous experimental evidence concerning AGG in oxides, focusing on the possible effects of the electrochemical reduction at the cathode end of the specimen.

Promoting effects of alternating current and input power on grain growth behavior of cubic ZrO2 polycrystals

“…The acceleration of the grain growth under an electric field was explained in terms of the segregation of $$Y_{Zr}^\prime $$ along the grain boundaries and the generation of space‐charge layers due to oxygen vacancies. Other studies have indicated that the grain growth is enhanced during the flash event as a result of the generation of defects such as oxygen vacancies 28–31,34,36,38,39,45 . In contrast, opposite results stating that the electric field and current suppress the grain growth have also been reported 33,35,40,43,44 .…”

“…To clarify the athermal effects on the diffusion phenomena during a flash event, the effects of the electric field and current on the microstructures have been investigated in the flash sintering of zirconia systems 27,29–31,33–45 . However, conflicting results have been described even for the same zirconia system.…”

“…In the previous studies, several factors prevented revealing the effects of electric field and current on the grain growth. First, as the grain growth was examined during the flash sintering, the pure intrinsic grain growth behavior was not evaluated; the intrinsic grain growth component might be masked by the grain coarsening occurring during densification in the sintering process 33–41,45 . Second, the thermal and electric field/current effects on the grain growth during the flash event were not evaluated separately from the experimental results; the effect of the electric field strength and current density on the grain growth was investigated at different temperatures 33,35,37,41 .…”

Unraveling the electric field effect on the grain‐boundary migration in alumina through phase field modeling

“…Moreover, the field-assisted sintering and annealing of ceramics had demonstrated that an electric field can promote neck formation and refine grains. [8][9][10] Noticeably, it was directly observed that the electric field can drive directional movement of GBs in ceramics, such as alumina (Al 2 O 3 ) 11 and strontium titanate. 12 In addition, ceramics can be used to make key components in microelectronic packages and integrated circuits 13 ; recently, there has been extensive attention to the material reliability of ceramics, including grain morphology and distribution characteristics, especially the anisotropic properties of ceramics are in dependence on orientation and grain size.…”

“…For instance, stress 6 and thermal gradient 7 can be the driving force for GB migration and grain evolution, accompanied by the capillary driving force influence. Moreover, the field‐assisted sintering and annealing of ceramics had demonstrated that an electric field can promote neck formation and refine grains 8–10 . Noticeably, it was directly observed that the electric field can drive directional movement of GBs in ceramics, such as alumina (Al 2 O 3 ) 11 and strontium titanate 12 .…”