Abstract

Laser Powder Bed Fusion (LPBF) is an additive manufacturing technique with growing relevance in industry. However, alloys with a high susceptibility to micro-cracking during solidification cannot be feasibly manufactured through LPBF, such as in selected high-strength Al-alloys. The cracking susceptibility (CS) of Al-alloys varies with composition, so modeling CS with respect to composition is crucial in designing compatible alloys for LPBF. In a theoretical modeling of solidification cracking based on the Scheil equation, the relative CS is taken as the maximum value of |dT/d(fs^1/2)| when solidification is near completion. However, experimental observations of the crack density in Al-alloys suggest that the composition at which the crack density is maximum occurs at a higher solute concentration than predicted. This shift in the maximum CS can be observed in the theoretical model when a back-diffusion Fourier number was incorporated into the Scheil equation to account for solid-state diffusion during solidification. This shift can also be observed by increasing the partition coefficient above its equilibrium value, which is expected during rapid solidification due to solute trapping. A computational study was conducted on the CS of Al-Cu binary alloys with compositions ranging from 0 to 10 wt.% Cu, in which the Fourier number was varied from 0 to 0.3, and the partition coefficient was varied from its equilibrium value, 0.173, to 0.5. This was then compared to experimental crack density measurements taken for Al-Cu binary alloys with compositions of 1.5, 3, 4.5, 6, and 10 wt.% Cu manufactured through LPBF using gas atomized alloy powders. Increases in Fourier number and/or partition coefficients were both effective in conforming to the experimental results. Increasing the partition coefficient was found to be more effective at shifting the CS towards higher solute concentrations, while increasing the Fourier number was more effective at lowering the magnitude of CS.

Notes

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Graduation Date

2021

Semester

Summer

Advisor

Sohn, Yongho

Degree

Master of Science in Materials Science and Engineering (M.S.M.S.E.)

College

College of Engineering and Computer Science

Department

Materials Science and Engineering

Degree Program

Materials Science and Engineering

Format

application/pdf

Identifier

CFE0008707;DP0025438

URL

https://purls.library.ucf.edu/go/DP0025438

Language

English

Release Date

August 2021

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

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