Date on Master's Thesis/Doctoral Dissertation

8-2018

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Mechanical Engineering

Degree Program

Mechanical Engineering, PhD

Committee Chair

Atre, Sundar V.

Committee Co-Chair (if applicable)

Berfield, Thomas A.

Committee Member

Berfield, Thomas A.

Committee Member

Yang, Li

Committee Member

Kate, Kunal H.

Author's Keywords

laser-powder bed fusion; 17-4 PH stainless steel; hot isostatic pressing; heat treatment; mechanical properties; microstructure; corrosion; gas- and water-atomized powders

Abstract

17-4 PH stainless steel is commonly used in medical, tooling, automotive, chemical and aerospace industries due to its excellent strength and corrosion properties. Additive manufacturing processes such as laser-powder bed fusion (L-PBF) have gained attention and importance due to the potential to produce complex-shaped three-dimensional parts for various industries. In order to manufacture three-dimensional components from 17-4 PH stainless steel powder using L-PBF, it is critical for design and manufacturing engineers to have an awareness of various material options and corresponding processing and post-processing conditions to obtain useful mechanical properties from the process. The goal of this dissertation is to establish a fundamental understanding of the material-process-property relationships of 17-4 PH stainless steel processed by laser-powder bed fusion (L-PBF). The investigation was carried out to understand the effects of post-processing treatment cycles such as hot isostatic pressing (HIP) on the densification, mechanical properties, corrosion properties and microstructures of L-PBF parts fabricated at various energy densities using 17-4 PH stainless steel gas- and water-atomized powders. The microstructure formation and its impact on mechanical and corrosion properties due to different HIP treatment cycles were studied for 17-4 PH stainless steel gas and water-atomized L-PBF parts at various energy densities. The most significant aspect of this work is that density, microstructures, mechanical and corrosion properties of 17-4 PH stainless steel can be vastly improved and reliable properties can be achieved irrespective of starting powder attributes and L-PBF process conditions by using HIP treatment. Further, the properties obtained after the HIP treatment was less sensitive to variations in powder characteristics (size distribution and shape) and energy density during processing and were superior to known reported properties of 17-4 PH stainless steel fabricated by L-PBF, powder metallurgy, metal injection molding, or wrought samples.

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