Abstract

The microstructural development of 316L stainless steel (316L SS) was investigated over a wide range of systematically varied laser powder bed fusion (LPBF) parameters, such as laser power, laser scan speed, hatch distance, and volumetric energy density. The use of volumetric energy density between 46 and 127 J/mm3 produced samples with relative density above 99.8% demonstrating that even in the optimized range of processing parameters the pores are unavoidable. Shifting from this range through a variation of laser scan speed produced two types of flaws, lack of fusion (LoF) and keyhole (KH) porosity leading to a decrease in the relative density targeted to higher than 97 %, and about 98 %, and 99 %. The specific mechanism behind the formation of these flaws influences the appearance of the individual pores characterized by circularity, size, and aspect ratio from extensive image analysis of optical micrographs. The samples were tested in uniaxial tension to correlate the flaw characteristics with yield strength (YS), ultimate tensile strength (UTS), and elongation at failure (EL%). As laser scan speed was increased, the flaw circularity increased in the KH domain while decreased in the LoF domain. The opposite trend was followed by the flaw size and aspect ratio. Additional to the influence of the density, the YS and UTS of the samples showed more sensitivity to the LoF than KH, while the EL% was comparable between the two types of flaws when the porosity is below 2%. The difference in mechanical properties for the 316L SS samples containing KH and LoF flaws with similar density was minimal because of the intrinsically high ductility of the alloy.

Notes

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Graduation Date

2022

Semester

Summer

Advisor

Sohn, Yongho

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Materials Science and Engineering

Degree Program

Materials Science & Engineering

Identifier

CFE0009164; DP0026760

URL

https://purls.library.ucf.edu/go/DP0026760

Language

English

Release Date

August 2022

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

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Included in

Metallurgy Commons

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