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

Catchpole-Smith, Sam; Aboulkhair, Nesma T.; Parry, Luke A.; Tuck, Christopher; Ashcroft, Ian; Clare, Adam T.

doi:10.1016/j.addma.2017.02.002

Cited by 101 publications

(57 citation statements)

References 24 publications

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“…Laser additive manufacturing (AM) is an established technology for the direct fabrication of metal components with complex geometries using layer-by-layer powder deposition and a high-power laser [1] [2] [3]. A wide range of metallic materials can be successfully processed using laser AM, including steel [4], titanium [5] [6], aluminium [7][8] [9], nickel [10] [11] and various composites. A variety of powder bed characteristics are critical to achieving a quality process because they affect the dimensional accuracy and structural integrity of the fabricated parts.…”

Section: Introductionmentioning

confidence: 99%

Discrete element simulation of powder layer thickness in laser additive manufacturing

Han

Setchi

2019

Powder Technology

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The optimisation of the laser additive manufacturing (AM) process is a challenging task when a new material is considered. Compared to the selection of other process parameters such as laser power, scanning speed and hatch spacing, optimisation of powder layer thickness is much more time-consuming and costly because a new run is normally needed when the layer thickness value is changed. In practice, the layer thickness is fixed to a value that is slightly higher than the average particle size. This paper introduces a systematic approach to layer thickness optimisation based on a theoretical model of the interactions between the particles, the wiper and the build plate during the powder deposition. The focus is on a systematic theoretical and experimental investigation of the effect of powder layer thickness on various powder bed characteristics during single-layer and multi-layer powder deposition. The theoretical model was tested experimentally using Hastelloy X (HX) with an average particle size of 34.4 µm. The experimental results validated the simulation model, which predicted a uniform powder bed deposition when employing a 40 µm layer thickness value. Lower (30 µm) and higher (50 µm) layer thickness values resulted in large voids and short-feed defects, respectively. The subsequent optimisation of the scanning speed and hatch spacing parameters was executed using a 40 µm layer thickness. The optimum process parameters were then used to examine the microstructure and tensile performance of the as-fabricated HX. This study provides an improved understanding of the powder deposition process and offers insights into the selection of suitable powder layer thicknesses in laser AM.

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Section: Introductionmentioning

confidence: 99%

Discrete element simulation of powder layer thickness in laser additive manufacturing

Han

Setchi

2019

Powder Technology

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“…In particular, AM has a powerful capacity in changing the process parameters to effectively vary the thermal parameters of the melt pool from location to location within layers and from layer to layer, enabling the tailoring of the material microstructure to specific locations to achieve desired mechanical properties [23][24][25] . In addtion, it is important to highlight the influential role of scan strategy in controlling preferred texture and minimising columnar grains, residual stresses and cracking behaviour in built parts to achieve desired mechanical properties 17,24,[26][27][28] . The opportunities of using scan strategies to tailor microstructure, thereby mechanical behaviour, reiterate the need of studying the detail of the crystal orientation, morphology, spatial distribution and length-scale of microstructure during epitaxial growth from single tracks to multi-track layers of deposition under the variation in scan strategy.…”

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confidence: 99%

The role of side-branching in microstructure development in laser powder-bed fusion

et al. 2020

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In-depth understanding of microstructure development is required to fabricate high quality products by additive manufacturing (for example, 3D printing). Here we report the governing role of side-branching in the microstructure development of alloys by laser powder bed fusion. We show that perturbations on the sides of cells (or dendrites) facilitate crystals to change growth direction by side-branching along orthogonal directions in response to changes in local heat flux. While the continuous epitaxial growth is responsible for slender columnar grains confined to the centreline of melt pools, side-branching frequently happening on the sides of melt pools enables crystals to follow drastic changes in thermal gradient across adjacent melt pools, resulting in substantial broadening of grains. The variation of scan pattern can interrupt the vertical columnar microstructure, but promotes both in-layer and out-of-layer side-branching, in particular resulting in the helical growth of microstructure in a chessboard strategy with 67°rotation between layers.

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“…In order to have sufficient creep resistance, the superalloys are expected to have a high g 0 volume fraction. Some studies related AM processes for non-weldable superalloy have been reported, which revealed the printability of those superalloys by refining the AM printing strategy [11] or tune the composition [12]. While the high-temperature mechanical properties of g 0 containing Nickelbase superalloy processed by AM have not received much attention, the major studies are limited to the cracking susceptibility [13], powder characteristics [14], microstructures [15] or postprocess effects [16].…”

Section: Introductionmentioning

confidence: 99%

Short-Term Creep Behavior of an Additive Manufactured Non-Weldable Nickel-Base Superalloy Evaluated by Slow Strain Rate Testing

Gruber

Deng

et al. 2019

SSRN Journal

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a b s t r a c tAdditive manufacturing (AM) of high g 0 strengthened Nickel-base superalloys, such as IN738LC, is of high interest for applications in hot section components for gas turbines. The creep property acts as the critical indicator of component performance under load at elevated temperature. However, it has been widely suggested that the suitable service condition of AM processed IN738LC is not yet fully clear. In order to evaluate the short-term creep behavior, slow strain rate tensile (SSRT) tests were performed. IN738LC bars were built by laser powder-bed-fusion (L-PBF) and then subjected to hot isostatic pressing (HIP) followed by the standard two-step heat treatment. The samples were subjected to SSRT testing at 850 C under strain rates of 1 Â 10 À5 /s, 1 Â 10 À6 /s, and 1 Â 10 À7 /s. In this research, the underlying creep deformation mechanism of AM processed IN738LC is investigated using the serial sectioning technique, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM). On the creep mechanism of AM polycrystalline IN738LC, grain boundary sliding is predominant. However, due to the interlock feature of grain boundaries in AM processed IN738LC, the grain structure retains its integrity after deformation. The dislocation motion acts as the major accommodation process of grain boundary sliding. Dislocations bypass the g 0 precipitates by Orowan looping and wavy slip. The rearrangement of screw dislocations is responsible for the formation of subgrains within the grain interior. This research elucidates the short-creep behavior of AM processed IN738LC. It also shed new light on the creep deformation mechanism of additive manufactured g 0 strengthened polycrystalline Nickel-base superalloys.

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

Cited by 101 publications

References 24 publications

Discrete element simulation of powder layer thickness in laser additive manufacturing

Discrete element simulation of powder layer thickness in laser additive manufacturing

The role of side-branching in microstructure development in laser powder-bed fusion

Short-Term Creep Behavior of an Additive Manufactured Non-Weldable Nickel-Base Superalloy Evaluated by Slow Strain Rate Testing

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