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Understanding the Impact of Post Heat Treatments on the Mechanism of Annealing Twin Formation in 316L Stainless Steel 3D Printed Components

Zhou, Yu (2020) Understanding the Impact of Post Heat Treatments on the Mechanism of Annealing Twin Formation in 316L Stainless Steel 3D Printed Components. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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The fabrication of 316L stainless steel via selective laser melting (SLM) has been developed in the past decade due to the convenience of the complex geometry design, faster manufacturing times and fine microstructure. However, several problems such as porosity, residual internal stresses and anisotropic properties, make it necessary to heat treat the components to modify their microstructure and improve their performance. This post heat treatment leads to the loss of the initial fine microstructure and hence the high strength.
The goal of this dissertation is to provide an alternative approach for the post heat treatments of SLM fabricated 316L stainless steel. One of these approaches is the use of high energy systems, i.e. induction rapid heating. The application of fast heating rate is expected to promote the formation of annealing twin boundaries, which is a strengthening mechanism of this face centered cubic (FCC) materials. 316L stainless steel fabricated via SLM process using gas atomized powders was used as the base material in this study. A continuous induction heating laboratory simulator (CAL-30KW) was used to provide various heating rates during the post heat treatments. The microstructure of both as-fabricated specimens and post heat-treated specimens was characterized. Of particular interest in this study was to examine the role of rapid heating on the formation of annealing twin boundaries (coherent and incoherent) formation and the area density evolution. The influence of processing parameters, such as reheating temperature, heating rate and holding time, on the annealing twin density were investigated. The resulting microstructures were analyzed using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Back-scattered Diffraction (EBSD), and Transmission Electron Microscopy (TEM). The formation of twin boundaries during recrystallization was assessed. The mechanism of annealing twin boundaries formation of SLM fabricated SS316L during induction rapid heating is a combination of growth accident and grain boundary dissociation. The results are presented and discussed in this dissertation.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Zhou, Yuyuz54@pitt.eduYUZ54
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Thesis AdvisorGarcia, C. Isaaccigarcia@pitt.educigarcia
Committee MemberWang, Qing-Mingqiw4@pitt.eduqiw4
Committee MemberMao, Scott X.sxm2@pitt.edusxm2
Committee MemberTan, Sushengsut6@pitt.edusut6
Committee MemberCho, Sung Kwonskcho@pitt.eduskcho
Date: 28 September 2020
Date Type: Publication
Defense Date: 24 July 2020
Approval Date: 28 September 2020
Submission Date: 24 July 2020
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 138
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: Rapid heating, Additive manufacturing, Selective laser melting, Annealing twin boundaries.
Date Deposited: 28 Sep 2020 20:28
Last Modified: 28 Sep 2020 20:28

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