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Understanding the influence of process parameters on the mechanical properties of alumina formed through lithography-based additive manufacturing
Boardman, Sarah V.
Boardman, Sarah V.
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2023
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Lithography-based ceramic manufacturing (LCM) is a developing additive manufacturing (AM) technology used to fabricate technical ceramics using layer-by-layer forming. However, studies assessing the impacts of processing parameters on the fundamental driving forces for failure of LCM-formed alumina are extremely limited. This thesis provides novel insight into the structure-property-processing relationships in LCM-formed alumina by evaluating the influence of thermal and print-based process parameters on the density, flexural strength, and flaw populations.
This thesis begins with the development of a multi-step thermal treatment to fully densify LCM-formed alumina. Attaining fully dense specimens is a prerequisite to flexural strength characterization as density and strength are directly correlated. The effect of thermal treatment is assessed via flexural strength and density measurements as well as the resultant grain size and grain morphology. The thermal processing study identified a set of conditions in which specimens are fully dense and also have a grain size, characteristic strength, and Weibull modulus comparable to conventionally-processed alumina from a round robin study.
Next, this work examines the impact of multiple LCM print parameters (including orientation, layer height, and energy) on the flexural strength, Weibull modulus, and flaw population of LCM-formed alumina. The findings reveal orientation and layer height print parameters do have a meaningful impact on the characteristic strengths, Weibull moduli, and flaw populations. Fractography reveals different print parameters lead to different strength-limiting defects, and all strength-limiting defects originate from the printing process. Finally, flaw populations are evaluated in a complex specimen geometry, finding the same type of print-based flaws responsible for failure.
This work determines characteristic strengths of AM alumina are near or above conventionally processed alumina. Additionally, under many print conditions Weibull moduli are near or above conventionally processed alumina but underperforms conventional alumina in the vertical orientation. Delamination defects are the most detrimental defect to Weibull moduli in vertically oriented specimens. Print-based flaws are evident in all configurations but not all flaws are significantly detrimental to performance when compared with conventional material. The analysis shown in this thesis provides a framework which enables future studies of other LCM-formed technical ceramics.
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