Flash sintering produces eutectic microstructures in Al₂O₃–LaPO₄ versus conventional microstructures in 8YSZ–LaPO₄

Abstract

Flash sintering is a novel manufacturing technique that applies an electrical field across a ceramic green body, while heating it in a furnace. [1][2][3] As the material sinters, the current induces joule heating, which assists in fast densification or enhanced reaction mixing. Over the past decade, flash sintering has shown promise in reducing sintering costs, increasing densification efficiency, promoting reaction sintering, etc. 4 In the current era of energy conservation to preserve the environment, it is important to find a way to reduce energy consumption for material processing. 5,6 Due to its nature of fast transformation and densification, flash sintering can induce non-equilibrium transitions and lead to unconventional microstructures which may have interesting thermal and mechanical properties. 1,7,8 The prerequisite conditions and phenomena of flash sintering are material specific. 1,9,10 8 mol% Y 2 O 3 -stabilized ZrO 2 (8YSZ) has been well established to flash sinter easily at low temperatures and low voltages. 1,11 The presence of 8YSZ can assist flash sintering for other materials in a

Reactive Flash Sintering of Ceramics: A Review

“…As an example, Figure shows reactive flash sintered Al 2 O 3 –LaPO 4 composites which display eutectic microstructures in the current‐localized region. [ 88 ] This work also demonstrated that Al 2 O 3 –LaPO 4 is a eutectic forming system, however, mechanical properties were not reported.…”

“…The first eutectic composition processed via RFS was Al 2 O 3 –Y 2 O 3 to achieve Al 2 O 3 –Y 3 Al 5 O 12 (YAG) ceramics, but eutectic microstructures were not reported. [ 83 ] Later, eutectic microstructures were found in this same Al 2 O 3 –YAG system, [ 84,85 ] and also in Al 2 O 3 –ZrO 2 , [ 86 ] Al 2 O 3 –GdAlO 3 –ZrO 2 , [ 87 ] LaPO 4 –Al 2 O 3 , [ 88 ] and 3YSZ–Al 2 O 3 . [ 89 ] In the case of Al 2 O 3 –YAG, Liu et al [ 84 ] reported that the RFSed specimens exhibited better mechanical properties (e.g., hardness of 18.5 ± 0.3 GPa, and toughness of 4.3 ± 0.2 MPa m 1/2 ) than materials made by traditional directional solidification.…”

“…Reproduced with permission. [88] Copyright 2021, John Wiley and Sons. SEM micrographs were presented, showing highly dense microstructures.…”

“…Eutectic microstructures of reactive flash sintered Al 2 O 3 -LaPO 4 composite system under 1100 V cm À1 and 25 mA mm À2 . Reproduced with permission [88]. Copyright 2021, John Wiley and Sons.…”

Formation of Al2O3–GdAlO3 eutectic ceramics with a fine anisotropic structure in a flash event

“…Therefore, with the flash event, the eutectic reaction would proceed even at a furnace temperature lower than the eutectic temperature because of the increase in specimen temperature. For example, Al 2 O 3 –LaPO 4 , Al 2 O 3 –GAP–ZrO 2 , and Al 2 O 3 –Y 3 Al 5 O 12 ceramics with eutectic microstructure were consolidated from raw powder mixtures at eutectic compositions using flash sintering 10–12 …”