Date of Award

Fall 2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering - (Ph.D.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

N. M. Ravindra

Second Advisor

Eon Soo Lee

Third Advisor

Siva P.V. Nadimpalli

Fourth Advisor

Michael Jaffe

Fifth Advisor

Stacey Clark

Sixth Advisor

Donald Skelton

Abstract

The US Department of Defense is interested in developing, understanding, and optimizing process parameters for low alloy (4340/4140 steel) for the powder bed fusion process. Low alloy steel is used in parts where high strength and toughness are required. During parameter optimization, several aspects of the process are investigated. Powder size and morphology optimization is important for manufacturability because adequate packing is required to produce full density components. Microstructure evaluation is used in order to provide insight into parameters that lead to optimal mechanical performance and recoating performance. Influence of residual stress is evaluated with this process. Large thermal stress can lead to high distortion and deflection. A general corrosion study is conducted on direct metal laser sintered parts in order to evaluate the factors which lead to corrosion. The main objectives of this effort are to produce mechanical properties of steel that are comparable to wrought 4340 and to understand the factors which influence the qualification of the powder bed fusion process.

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