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Flash sintering produces eutectic microstructures in Al 2 O 3 –LaPO 4 versus conventional microstructures in 8YSZ–LaPO 4
Author(s) -
Yang Yingjie,
Mumm Daniel R.,
Mecartney Martha L.
Publication year - 2021
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.17786
Subject(s) - microstructure , eutectic system , materials science , flash (photography) , sintering , lamellar structure , scanning electron microscope , transmission electron microscopy , composite material , metallurgy , nanotechnology , optics , physics
While monazite (LaPO 4 ) does not flash sinter even at high fields of 1130 V/cm and temperatures of 1450°C, composite systems of 8YSZ–LaPO 4 and Al 2 O 3 –LaPO 4 have been found to more readily flash sinter. 8YSZ added to LaPO 4 greatly lowered the furnace temperature for flash to 1100°C using a field of only 250 V/cm. In these experiments, α ‐Al 2 O 3 alone also did not flash sinter at 1450°C even with high fields of 1130 V/cm, but composites of Al 2 O 3 –LaPO 4 powders flash sintered at 900‐1080 V/cm at 1450°C. Alumina–monazite (Al 2 O 3 –LaPO 4 ) composites with compositions ranging from 25 vol% to 75 vol% Al 2 O 3 were flash sintered with current limits from 2 to 25 mA/mm 2 . Microstructures were evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A eutectic microstructure was observed to form in all flash sintered Al 2 O 3 –LaPO 4 composites. With higher power (higher current limits), eutectic structures with regular lamellar regions were found to coexist in the channeled region (where both the current and the temperature were the highest) with large hexagonal‐shaped α ‐Al 2 O 3 grains (up to 75 μ m) and large irregular LaPO 4 grains. With lower power (lower current limits), an irregular eutectic microstructure was dominant, and there was minimal abnormal grain growth. These results indicate that Al 2 O 3 –LaPO 4 is a eutectic‐forming system and the eutectic temperature was reached locally during flash sintering in regions. These eutectic microstructures with lamellar dimensions on the scale of 100 nm offer potential for improved mechanical properties.