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In situ correlative observation of humping-induced cracking in directed energy deposition of nickel-based superalloys

DOI: 10.1016/j.addma.2023.103579 DOI Help

Authors: Tristan G. Fleming (Queen's University) , David Tien Rees (University College London; Research Complex at Harwel) , Sebastian Marussi (University College London; Research Complex at Harwell) , Thomas Connolley (Research Complex at Harwell) , Robert C. Atwood (Research Complex at Harwell) , Martyn A. Jones (Rolls-Royce plc) , James Fraser (Queen's University) , Chu Lun Alex Leung (University College London; Research Complex at Harwell) , Peter D. Lee (Research Complex at Harwell)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Additive Manufacturing , VOL 119

State: Published (Approved)
Published: April 2023
Diamond Proposal Number(s): 28804

Open Access Open Access

Abstract: Directed energy deposition (DED) is a promising additive manufacturing technique for repair; however, DED is prone to surface waviness (humping) in thin-walled sections, which increases residual stresses and crack susceptibility, and lowers fatigue performance. Currently, the crack formation mechanism in DED is not well understood due to a lack of operando monitoring methods with high spatiotemporal resolution. Here, we use inline coherent imaging (ICI) to optically monitor surface topology and detect cracking in situ, coupled with synchrotron X-ray imaging for observing sub-surface crack healing and growth. For the first time, ICI was aligned off-axis (24° relative to laser), enabling integration into a DED machine with no alterations to the laser delivery optics. We achieved accurate registration laterally (<10 µm) and in depth (<3 µm) between ICI measurements and the laser beam position using a single-element MEMS scanner and a custom calibration plate. ICI surface topology is verified with corresponding radiographs (correlation >0.93), directly tracking surface roughness and waviness. We intentionally seed humping into thin-wall builds of nickel super-alloy CM247LC, locally inducing cracking in surface valleys. Crack openings as small as 7 µm were observed in situ using ICI, including sub-surface signal. By quantifying both humping and cracking, we demonstrate that ICI is a viable tool for in situ crack detection.

Journal Keywords: Inline coherent imaging; Directed energy deposition; synchrotron X-ray imaging; humping and cracking defects; in situ monitoring

Diamond Keywords: Additive Manufacturing; Alloys

Subject Areas: Materials, Engineering

Instruments: I12-JEEP: Joint Engineering, Environmental and Processing

Added On: 01/05/2023 09:13


Discipline Tags:

Materials Engineering & Processes Materials Science Engineering & Technology Metallurgy

Technical Tags:

Imaging Tomography