THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Wednesday, October 3, 2018

1:00 PM
in Love 210

will be held the

DISSERTATION DEFENSE

for

Xinyi Gong

"High throughput assays for exploring materials space for additive manufacturing"

Committee Members:

Prof. Surya R. Kalidindi, Advisor, MSE

Prof. David McDowell, MSE

Prof. Preet Singh, MSE

Prof. Hamid Garmestani, MSE

Prof. Richard W. Neu, ME

Abstract:

Recent advances in additive manufacturing (AM) offer exciting opportunities to build materials with novel internal structures combined with intricate part geometries that cannot be achieved by traditional manufacturing approaches. The large space of potential material chemistries combined with process parameters in AM presents a significant challenge for a systematic exploration of the materials’ microstructures along with their final properties. In order to form a “design allowable” property data package, the current experimental assays require major investments either of time and effort on highly customized samples or of cost on large sample volumes.

The goal of this work is to establish practically useful high throughput (HT) experimental assays that matches characteristics of AM, delivers abundant and reliable dataset on microstructure and mechanical properties and creates meaningful process-structure-property (P-S-P) linkages with relatively small sample volumes. Spherical indentation protocols are extended for HT assays, taking advantage of its flexibility on sample shapes and small sample volumes. Various microstructure characterization techniques including SEM (BSE), EDS and EBSD are introduced to the assays along with quantification methods for microstructure statistics (e.g., phase volume fractions, chord length distributions). AM Titanium alloys are chosen because of their potential of displaying novel microstructure/mechanical properties that cannot be achieved by conventional case/wrought approaches. In collaboration with external partners, laser engineered net shaping (LENS) and electron beam melting (EBM) were selected to represent two different types of AM (direct energy deposition (DED) and powder bed fusion (PBF)). Due to LENS’s capability of changing powder composition and the post build heating requirement on its final parts, it was employed to explore the effect of chemical composition and post build heat treatment on Ti-Ni and Ti-Mn alloys. A second case study explored the thermal history induced within build variance on Ti64 manufactured by EBM. The results of HT screening and systematic study of material chemistry and process space will be presented and discussed along with demonstration of extracting practically useful S-P/P-S-P linkages to build materials knowledges for accelerating alloy development.