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Wall, Andrew

University of British Columbia

Additive manufacturing (AM) is an emerging manufacturing technique in which parts are ‘printed’ one layer at a time, which presents many unique opportunities for innovative and sustainable manufacturing, but also presents many challenges. By example, solidification cracking (SC) is a metallurgical defect that occurs during the solidification of alloys in processes such as welding, casting, and AM. SC can cause significant mechanical deterioration in parts in which it occurs, and SC remains a significant hurdle for AM processes. Research into the causes, effects, and mitigation strategies of SC in AM is ongoing, however strategies of analysing and quantifying SC is inconsistent across studies. This thesis presents a novel test for SC susceptibility in AM processes. A benchmark specimen has been produced in order to assess the viability of a self-restraint test that can promote cracking in a repeatable and quantifiable manner. The design aims to be simple, yet robust, in order to be applicable to a range of AM processes. Samples were printed by laser directed energy deposition using Inconel 625 powder for repeatability analysis, and a sample was produced using Inconel 718 powder as a comparative analysis to assess the ability to distinguish SC susceptibility between material compositions. It was found that the initial design was capable of producing cracks with repeatable results, and cracks formed in the Inconel 718 sample were less severe than the cracks produced in the Inconel 625 samples. However, the cracks were determined to be ductile fractures that initiated in the solid-state rather than SC. A redesign of the specimen is presented to address the issues facing the initial design. Changes to dimensions were made to improve printability and reduce stress concentrations in order to reduce the likelihood of solid-state cracking in favour of promoting SC initiation modes. The results provide a foundation for standardisation of SC in AM. Standardised testing is a necessary step for widespread adoption of AM, and this first step may be used for further test development as the presented design may also serve as a basis for non-SC fracture modes, such as the solid-state cracking observed in the initial samples.

Text

2023-09-12

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/85892

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/