Date on Master's Thesis/Doctoral Dissertation

12-2018

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)

Hsu, Keng

Committee Member

Hsu, Keng

Committee Member

Gupta, Gautam

Committee Member

Kate, Kunal

Author's Keywords

laser-powder bed fusion; 420 stainless steel; microstructure; UTS; martensite; corrosion

Abstract

Laser-powder bed fusion (L-PBF) is an additive manufacturing technique for fabricating metal components with complex design and customized features. However, only a limited number of materials have been widely studied using L-PBF. AISI 420 stainless steel, an alloy with a useful combination of high strength, hardness, and corrosion resistance, is an example of one such material where few L-PBF investigations have emerged to date. In this dissertation, L-PBF experiments were conducted using 420 stainless steel powders to understand the effects of chemical composition, particle size distribution and processing parameters on ensuing physical, mechanical and corrosion properties and microstructure in comparison to wrought and metal injection molding (MIM). The density of the fabricated specimens increased, and their surface roughness decreased as the layer thickness and median particle size was decreased and energy density was increased. Following heat treatment, the ultimate tensile strength and elongation of L-PBF specimens with Nb (1.2 %) and Mo (0.57 %) improved to 1750 ± 30 MPa and 9.0 ± 0.2 %, which were higher than the previously reported values in L-PBF, MIM and wrought 420 stainless steel. Tempering of martensite during heat treatment and nanoscale NbC precipitation were consistent with improvement in properties. L-PBF specimens fabricated with deagglomerated fine powder (D50: 12 µm) exhibited similar spreadability, mechanical properties and microstructure to specimens fabricated with coarse powder (D50: 28 µm). In the presence of Nb (1.2 %) and Mo (0.57 %), corrosion properties improved over wrought 420 stainless steel.

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