Study of Process-Structure-Property Relationships in Stainless Steel 316L Made by Powder Bed Fusion

O'Brien, John

Study of Process-Structure-Property Relationships in Stainless Steel 316L Made by Powder Bed Fusion

Open Access

Author:: O'Brien, John
Graduate Program:: Additive Manufacturing and Design
Degree:: Master of Science
Document Type:: Master Thesis
Date of Defense:: June 08, 2020
Committee Members:: Allison Michelle Beese, Thesis Advisor/Co-Advisor
Timothy W. Simpson, Thesis Advisor/Co-Advisor
Guhaprasanna Manogharan, Committee Member
Timothy W. Simpson, Program Head/Chair
Keywords:: Additive Manufacturing
316L
3D Printing
L-PBF
Machine Learning
Statistics
Process control
Abstract:: This thesis aims to identify important links in the process-structure-property relationships in 316L Stainless Steel manufactured by laser powder bed fusion (L-PBF) additive manufacturing. The ultimate aim is to generate a model that can predict mechanical properties, including Ultimate tensile strength, based on laser power, scan speed, and hatch spacing parameter settings for the L-PBF process. The relationship between these parameters, microstructural features, and mechanical properties is investigated using the Advanced data SCiENce toolkit for Non-Data Scientists (ASCENDS). The microstructure of the built parts was examined using electron backscatter diffraction in order to quantify grain sizes, crystallographic orientations of grains, and grain morphologies. The length scale of the cellular solidification structure, on the order of 0.5-1 um, was also investigated as this relates to both volumetric energy density input and strength. Scanning electron microscopy was used to measure the size of the solidification cells. It was found that the interplay between these three process parameters is more complex than initially anticipated, and multi-variable experimentation failed to produce a useful predictive model. However, important links between microstructural features and process parameters were established, providing an increased understanding of the impacts of laser power, scan speed, and hatch spacing on grains and solidification cells.

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