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New alloy process development emphasizing high-strength low-alloy steels in laser powder-feed directed energy deposition

thesis
posted on 2023-09-27, 16:11 authored by Jose LoliJose Loli

This work focuses on process development in metals additive manufacturing, specifically investigating high-strength low alloy (HSLA) steels in a directed energy deposition (DED) system. The study examines the effect of process parameters, including laser power, scan speed, and powder feed rate, on melt pool characteristics for 4130 steel. Relationships between independent parameters and single track characteristics such as added material dimensions, powder capture efficiencies, and substrate dilution are established through single track measurements. Layer heights and hatch spacings for multilayer builds are determined based on these findings. This work further compares the impact of open air versus inert argon environments on builds using 4340 steel. It is observed that for the same build parameters, open air builds exhibit overbuilding, while inert argon builds show underbuilding due to lower powder capture efficiency. Adjustments in layer heights and hatch spacings address these issues. Pore and composition analysis of builds with HSLA 4340 and a new higher Cr-content steel reveals the influence of environmental reactions and composition on porosity. Because of this, build environment is then added as another factor influencing single track characteristics. The methodology I propose is material-agnostic. A custom scan strategy is suggested to optimize deposition rates and minimize idle movement of the deposition head. The framework presented offers the potential for high-throughput single track experiments to determine desirable process parameters. Additionally, a separate framework is also reported for new alloy development. Three oxidation resistant alloys are manufactured.

History

Date

2023-08-22

Degree Type

  • Dissertation

Department

  • Mechanical Engineering

Degree Name

  • Doctor of Philosophy (PhD)

Advisor(s)

Maarten de Boer, Jack Beuth

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