Zheng, Chuyuan
(2022)
A Densified Binder-jet Printed Powder System Via Viscous-Rearrangement Assisted Sintering.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
This is the latest version of this item.
Abstract
Binder jet 3D printing (BJ3DP) is a non-beam based additive manufacturing technology that can fabricate stress-free metal and ceramic parts with great production efficiency. One of the major challenges for BJ3DP is the consolidation of as-printed green bodies. In preliminary work, gas-atomized Inconel 625 alloy was binder-jetted and isothermal sintered under subsolidus and supersolidus temperatures. Quantitative analyses on 2D sections suggested that under supersolidus sintering, rapid particle rearrangement occurred with the help of a viscous liquid phase, which collapsed large printing defects and facilitated densification. Based on the preliminary results, a new two-step viscous liquid rearrangement assisted (VRA) sintering process was proposed to efficiently densify printed 625 alloy while preventing heavy elemental segregations caused by liquid phase formation in supersolidus sintering. Three-dimensional analyses were performed using X-ray micro-computer tomography (μCT) to quantify the evolution of the microstructure during sintering. This revealed pore defect structures that were attributed to both powder spreading and jetting of the binder. Subsolidus sintering was able to remove those defects attributed to jetting but not all the defects attributed to powder spreading. In contrast, supersolidus sintering in the first step of the VRA process was able to remove all the defects. However, the second step of the VRA process was not able to fully prevent the formation of grain boundary phases on cooling. To further support the attribution of the pore structures to powder spreading and binder jetting, “skin” structures were printed. These samples contained a “core” in which the powder was spread but not jetted surrounded by a “skin” that was both spread and jetted. μCT analysis revealed differences in densification behavior between the “skin” and the “core” that resulted in differential sintering. The microstructure heterogeneity caused by differential sintering could also be repaired by supersolidus sintering.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
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| ETD Committee: |
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| Date: |
10 June 2022 |
| Date Type: |
Publication |
| Defense Date: |
4 April 2022 |
| Approval Date: |
10 June 2022 |
| Submission Date: |
10 April 2022 |
| Access Restriction: |
1 year -- Restrict access to University of Pittsburgh for a period of 1 year. |
| Number of Pages: |
140 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Materials Science and Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Binder-jet printing; Inconel 625; Microstructure analysis; Computer tomography; Sintering |
| Date Deposited: |
10 Jun 2022 19:31 |
| Last Modified: |
10 Jun 2023 05:15 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/42571 |
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A Densified Binder-jet Printed Powder System Via Viscous-Rearrangement Assisted Sintering. (deposited 10 Jun 2022 19:31)
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