Abstract

The present work correlates quasi-static, tensile mechanical properties of additively manufactured Ti-6Al-4V (Grade 23) alloy to the phase constituents, microstructure and fracture surface characteristics that changed with post-heat treatment of stress relief (670 °C for 5h) and hot isostatic pressing (HIP with 100MPa at 920 °C for 2h). Ti-6Al-4V alloy tensile specimens in both the horizontal (i.e., X and Y) and vertical (Z) directions were produced by laser powder bed fusion (LPBF) technique. Mechanical properties were determined using quasi-static, tensile testing for both the as-stress-relieved (ASR) and HIP specimens. For the ASR and HIP samples built in X, Y and Z directions, density by Archimedes principle and image analysis, phase constituents by X-ray diffraction and Rietveld technique, microstructure and fracture surface by optical and electron microscopy, and microhardness by Vickers were examined. Higher yield strength (1141 MPa), higher tensile strength (1190 MPa), but lower elongation at fracture (6.9 %) along with a mechanical anisotropy were observed for ASR samples. After HIP, an isotropic mechanical behavior was observed with a slight reduction in yield strength (928 MPa) and tensile strength (1003 MPa), but with a significant improvement in elongation at fracture (16.1%). These properties satisfy the industry specification. Phase constituents of acicular a' phase in ASR and lamellar a + ß phases in HIP samples were consistently observed to substantiate the reduction in strength, but the anisotropic variation in elongation at fracture observed for the ASR samples was related to the presence of "lack-of-fusion" flaws.

Notes

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Graduation Date

2020

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

CFE0008585; DP0024261

URL

https://purls.library.ucf.edu/go/DP0024261

Language

English

Release Date

2-15-2021

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

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