Selective laser flash sintering of 8‐YSZ

Abstract

Flash sintering of ceramics is characterized by rapid sintering during simultaneous application of electric field and heat. Previous studies of flash sintering have been conducted in furnace environments, where sample temperatures are approximately uniform. In this work, we use highly dynamic heating from a scanning laser to initiate flash sintering while simultaneously applying a DC electric field. Onset of flash sintering is determined by a measurable increase in current through the sample. Our results show that stage I and stage II flash sintering can be initiated by laser heating. At low‐to‐moderate combinations of laser energies and applied electric fields, measured current rises slightly when the laser is scanned completely across the specimen from the positive to the negative electrodes. Microstructures for these samples show that powder consolidation is minimal in this regime (stage I flash sintering), and thus the observed current is likely due to onset of neck growth between powder particles rather than densification. At higher laser energies and fields, current rises steeply and microstructures show significant consolidation (stage II flash sintering). The demonstration that flash sintering occurs when ceramic is heated by laser‐scanning supports future utilization of selective laser flash sintering as an additive manufacturing process.

Onset of selective laser flash sintering of AlN

“…Current conducted through the sample during the experiment was measured with a precision of 1 µA at a frequency of 500 Hz using a data acquisition system (CompactRIO, National Instruments). 5…”

“…The field was applied to the top surface of the pellet, between the silver‐painted electrodes, and was varied from 0 to 3000 V/cm. Current conducted through the sample during the experiment was measured with a precision of 1 µA at a frequency of 500 Hz using a data acquisition system (CompactRIO, National Instruments) 5 …”

“…According to the chemical composition, these clayey materials are characterized by high iron contents whose the effect on the color of the ceramic materials is well known, and the attendance of fluxing agents as alkali and alkaline earth elements which are necessary for low temperatures firing. Mineralogically, considered materials consist entirely of kaolinite rich clays containing impurities, mostly illite, calcite, feldspar, and iron, which serve as fluxing agents to improve densification at low temperature [3][4][5][6] and appeared helpful in improving the physical and mechanical properties of the manufactured ceramic materials.…”

“…This is unlike YSZ, which has a much lower bulk thermal conductivity (1.5 W/m⋅K for YSZ vs. 320 W/m⋅K for AlN) and flashes after a single scan. 5,12 The low heat dissipation rate is a significant factor in the rapid onset of SLFS for YSZ.…”

“…The SLFS process has been previously demonstrated using 8%mol yttria-stabilized zirconia (8-YSZ). 5 It was shown that a combination of laser heating and electric field can be used to initiate SLFS, and its subsequent progression can be controlled by adjusting the laser power and electric field strength. Although SLFS has not been demonstrated on any other ceramics to date, a large number of oxide [5][6][7] and carbide ceramics 8,9 have previously been conventionally flash sintered using a furnace, suggesting that other ceramics may also be candidates for SLFS.…”