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Powder bed binder jet 3D printing of Alloy 625: Microstructural evolution, densification kinetics and mechanical properties

Mostafaei, Amir (2018) Powder bed binder jet 3D printing of Alloy 625: Microstructural evolution, densification kinetics and mechanical properties. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Abstract

Binder jet 3D printing (BJ3DP), a non-beam based, additive manufacturing (AM) method, refers to the technology in which powdered material is deposited layer-by-layer and selectively joined in each layer with binder and then densified through sintering or infiltration. Binder jetting of metals holds distinctive promise among AM technologies due to its fast, low-cost manufacturing; stress-free structures with complex internal and external geometries; and the isotropic properties of the final parts. Also, by taking advantage of traditional powder metallurgy, BJ3DP machines can produce prototypes of metal parts in which material properties and surface finish are similar to those achieved with metal injection molding or traditional powder metallurgy. Therefore, a comprehensive overview of the fundamental science of metallurgical structure after sintering and post heat-treatment steps are provided in this work to understand the microstructural evolution and properties of BJ3DP parts. Further, to determine the effects of the BJ3DP process on metallurgical properties, an empirical framework to describe the role of particle size, morphology and powder size distribution, and sintering followed by a post heat-treatment is discussed. With the growth of AM and the need for post-processing in BJ3DP parts, an understanding of the microstructural evolution is necessary, and in this work sintering steps and mechanisms are explained and aligned with the BJ3DP process.
Nickel-based alloy 625 was BJ3DP from water- and gas-atomized powders for a detailed comparative study on densification behavior, microstructural evolution and mechanical properties in terms of hardness, tensile strength and fatigue life. Then, gas-atomized alloy 625 powders of three different powder size distributions were printed and sintered in order to extend existing knowledge of sintering of alloy 625 to binder jetted parts. Sintering was evaluated in the context of microstructural evolution, using grain and pore intercept length, pore separation, surface area per unit volume and number of pore sections per unit area. The results suggest that particle size distribution is a determining factor for densification kinetic and final microstructure, if printing parameters such as layer thickness, binder saturation and drying time are similar.


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Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Mostafaei, Amiramm397@pitt.eduamm397
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairGleeson, Bgleeson@pitt.edu
Committee CoChairNettleship, Inettles@pitt.edu
Committee MemberRollett, Arollett@andrew.cmu.edu
Thesis AdvisorChmielus, Mchmielus@pitt.edu
Date: 25 September 2018
Date Type: Publication
Defense Date: 20 July 2018
Approval Date: 25 September 2018
Submission Date: 18 July 2018
Access Restriction: 2 year -- Restrict access to University of Pittsburgh for a period of 2 years.
Number of Pages: 189
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: Additive manufacturing; Sintering; porosity; Phase formation; Mechanical properties
Date Deposited: 25 Sep 2018 16:20
Last Modified: 25 Sep 2018 16:20
URI: http://d-scholarship.pitt.edu/id/eprint/34920

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