Fractal scan strategies for selective laser melting of ‘unweldable’ nickel superalloys

By S. Catchpole-Smith, N. Aboulkhair, L. Parry, Christopher John Tuck, Ian Ashcroft, A. Clare. 2017

210 citations recorded by the source corpus.

The high thermal gradients experienced during manufacture via selective laser melting commonly result in cracking of high γ/γ′ Nickel based superalloys. Such defects cannot be tolerated in applications where component integrity is of paramount importance. To overcome this, many industrial practitioners make use of hot isostatic pressing to ‘heal’ these defects. The possibility of such defects re-opening during the component life necessitates optimisation of SLM processing parameters in order to produce the highest bulk density and integrity in the as-built state. In this paper, novel fractal scanning strategies based upon mathematical fill curves, namely the Hilbert and Peano-Gosper curve, are explored in which the use of short vector length scans, in the order of 100 μm, is used as a method of reducing residual stresses. The effect on cracking observed in CM247LC superalloy samples was analysed using image processing, comparing the novel fractal scan strategies to more conventional ‘island’ scans. Scanning electron microscopy and energy dispersive X-ray spectroscopy was utilised to determine the cracking mechanisms. Results show that cracking occurs via two mechanisms, solidification and liquation, with a strong dependence on the laser scan vectors. Through the use of fractal scan strategies, bulk density can be increased by 2 ± 0.7% when compared to the ‘island’ scanning, demonstrating the potential of fractal scan strategies in the manufacture of typically ‘unweldable’ nickel superalloys.

Subfields: Industrial and Manufacturing Engineering, Mechanical Engineering, Mechanics of Materials

View Paper: https://www.semanticscholar.org/paper/e89e8291c9aa4d95fa6f00e372cec5a58e21a4f3

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In Industrial and Manufacturing Engineering

In Mechanical Engineering

In Mechanics of Materials

Citations in the corpus

Manufacturability of AlSi10Mg overhang structures fabricated by laser powder bed fusion (2018, background): “A wide range of metallic materials have been successfully processed using LPBF in the past few years, including aluminium [3-5], titanium [6,7] and nickel [8-10] and these elements’ alloys and composites.”
A Novel Strategy to Additively Manufacture 7075 Aluminium Alloy With Selective Laser Melting (2021, methodology): “The relative density and crack fraction in SLM-fabricated samples were examined through image analysis using the ImageJ software as per the procedure outlined in [38].”
3D printing of Aluminium alloys: Additive Manufacturing of Aluminium alloys using selective laser melting (2019, methodology): “Besides being used for porosity evaluation, cross-sectioning, X-ray CT, and SRAS have also been used to investigate the presence of cracks, especially their density and orientations [90,93,267].”