Strength of additively manufactured alumina with different debinding and sintering heat treatments

Abstract

Lithography-based ceramic manufacturing (LCM) utilizes slurries with low solids loading, which makes pressureless sintering to full density especially difficult. A further compounding issue in sintering to full density and establishing structure-property-processing relationships for LCM alumina is the fact that the current literature lacks consensus on heat treatments to achieve full densities. Treatment specifics that are recorded are frequently ambiguous and insufficiently detailed. In this work, temperatures and times for debinding and sintering schedules were varied to characterize the influence of heat treatment parameters on density, microstructure, and flexural strength of high-purity, LCM-formed alumina. Removing the bisque-fire from debinding and fine-tuning sintering parameters produced parts with full densities, high flexural strengths, and Weibull moduli that match or exceed the values documented in a round robin study of traditionally processed alumina.

Linking flexural strength and strength‐limiting flaws in additively manufactured alumina with print parameter variations

“…The two datasets corresponding to 25‐ and 50‐μm layer sizes in the Flatwise orientation with 125 mJ/cm 2 energy were previously published in ref. [12]. The same data are also included in this publication in the context of other orientations and with the addition of fractography and surface roughness characterization.…”

“…varied print layer height and curing energy simultaneously in their study, finding no impact on characteristic strength or modulus in samples of 96%−98% density when using the ball on three balls test method. In our earlier publication focusing on thermal treatment of high‐purity LCM alumina, we indicated an impact of the printed layer height on flexural strength 12 using 4‐point flexural strength testing of bars sized 3 mm × 4 mm × 45 mm, adhering to the ASTM C1161 testing protocol 14 . Bars formed with 25 versus 50‐μm layers in the flatwise orientation had statistically significant differences in Weibull modulus and characteristic strength at a level of 90% confidence, despite identical curing energy and heat treatment, and no differences in density.…”

“…To remove organics and sinter the alumina bars, a two‐step postprocessing heat treatment was completed in air. Our earlier publication outlines the development of this heat treatment, and identical experimental procedures to the expedited heat treatment with a 16 h sinter at 1500°C were implemented in this study 12 . Debinding was the first step, with a duration of 1.9 days and a maximum temperature of 600°C with a 1 h dwell.…”

“…Our earlier publication outlines the development of this heat treatment, and identical experimental procedures to the expedited heat treatment with a 16 h sinter at 1500 • C were implemented in this study. 12 Debinding was the first step, with a duration of 1.9 days and a maximum temperature of 600 • C with a 1 h dwell. This step contained multiple dwells at lower temperatures within the 120−430 • C range.…”

“…[5][6][7][8][9][10] Thermal processing can significantly impact strength and microstructure of high purity LCM alumina; conditions that result in full density can result in Weibull modulus and characteristic strength comparable to values for alumina reported in a well-regarded round robin study. 12,13 Advancing LCM for structural ceramics requires a comprehensive understanding of how processing conditions influence the strength-controlling defect population.…”