High-speed Synchrotron X-ray Imaging of Laser Powder Bed Fusion Process

Parab, Niranjan D.; Zhao, Cang; Cunningham, Ross; Escano, Luis I.; Gould, Benjamin; Wolff, Sarah; Guo, Qilin; Xiong, Lianghua; Kantzos, Christopher; Pauza, Joseph; Fezzaa, Kamel; Greco, Aaron; Rollett, Anthony D.; Chen, Lianyi; Sun, Tao

doi:10.1080/08940886.2019.1582280

Cited by 20 publications

(13 citation statements)

References 13 publications

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“…Ultrahigh-speed synchrotron X-ray imaging, such as available at the Advanced Photon Source (APS), IL, USA, the Stanford Synchrotron Radiation Lightsource (SSRL), CA, USA, and the Diamond Light Source, UK, has been used to study, e.g., powder scattering during SLM, [183] particle-scale powder spreading dynamics, [184,185] laser-matter interactions in AM, [186,187] melt pool dynamics, [188][189][190][191] metal spattering, [192] keyhole formation during laser melting, [189,193] as well as defect dynamics and pore formation. [188,192,[194][195][196] In situ diffraction and scattering have so far largely focused on the evolution of the materials' microstructure (i.e., phase transformations and precipitation reactions under simulated or real manufacturing conditions, new phase transformation pathways enabled by the unusually high cooling rates and complex temperature profiles, and microstructural stability of as-built parts) as well as the development of residual stresses during AM. [95,99,197] To address these research questions, a variety of setups differing in their constructional complexity and, hence, ranging from basic furnaces simulating AM temperature profiles to high-end setups based on industry-standard process chambers has been used.…”

Section: In Situ Studiesmentioning

confidence: 99%

Exploring Structural Changes, Manufacturing, Joining, and Repair of Intermetallic γ‐TiAl‐Based Alloys: Recent Progress Enabled by In Situ Synchrotron X‐Ray Techniques

et al. 2021

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Intermetallic titanium aluminides based on the ordered γ-TiAl phase fulfil many of the key requirements of lightweight high-temperature applications. In addition to a high melting point, high specific Young's modulus and strength at elevated temperatures, excellent creep properties, and a satisfactory oxidation and burn resistance, especially their low density of roughly 4 g cm À3 makes them a material of choice for challenging structural applications such as found, e.g., in environmentally friendly combustion engine options. [1][2][3][4] Capable of withstanding extreme conditions, γ-TiAl-based alloys have already entered service as low-pressure turbine blades in jet engines, such as the GEnx engine by GE Aviation, [5] the Geared Turbofan (GTF) engine by Pratt and Whitney, [6] as well as the LEAP engine by CFM International, a joint company between Safran Aircraft Engines and GE. [7,8] In these applications, γ-TiAl-based turbine blades substitute some of the blades made of twice as heavy Ni-base superalloys in a temperature range up to 750 °C. The implementation of the advanced, lightweight material, which is also attended by an adaptation of the design, entails a substantial reduction in weight, fuel consumption, and CO 2 and NO x emissions. [9] Apart from the aircraft engine industry, γ-TiAl-based alloys have also found applications in the automotive industry, e.g., as engine valves in sports and racing cars or as turbocharger turbine wheels. [1,3,[10][11][12][13][14] The past few decades have witnessed great efforts to develop intermetallic γ-TiAl-based alloy systems that are suitable for service in these demanding areas while being economically competitive at the same time. To this end, various alloy compositions and processing routes have been studied intensively. [1,[15][16][17][18][19][20][21] Recent progress has been reviewed, e.g., in the works by Appel et al., Clemens et al., and Mayer et al. [1,3,9,22] Due to the complexity of the intermetallic alloy system, which encompasses a multitude of phases and phase transformations, [23] purposeful alloy design requires the use of manifold characterization methods. Diffraction and scattering techniques, in particular, offer access to the atomic structure of the material and provide insights into a variety of microstructural parameters. [24][25][26][27] High-energy X-rays, such as available at today's synchrotron radiation sources, and recent developments in hardware technology nowadays allow to conduct so-called in situ experiments. Experiments of this kind reveal-at a high temporal resolution-the relationship between selected external

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Section: In Situ Studiesmentioning

confidence: 99%

Exploring Structural Changes, Manufacturing, Joining, and Repair of Intermetallic γ‐TiAl‐Based Alloys: Recent Progress Enabled by In Situ Synchrotron X‐Ray Techniques

et al. 2021

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“…The manufacturing of defect-free, high performance materials requires understanding of defect formation mechanisms and microstructural development as a function of process parameters. For that purpose, multiple in situ and operando techniques have been applied as for instance observation of sputter formation using a high speed camera 30 , IR imaging 31 , or two wavelength high speed-imaging thermography to measure operando thermal gradients and cooling rates during LPBF 32 .…”

Section: Introductionmentioning

confidence: 99%

“…Operando and in situ diffraction studies performed during LPBF allow for observation of phase transformations occurring prior and after melting and solidi cation as well as evaluation of temperature pro les and cooling rates 35 34,37,47 , while in situ X-ray radiography provides invaluable knowledge about melt pool dynamics [47][48][49][50] and formation of defects such as cracks 37,51 and porosity 49,52−54 . Thanks to the rapid progress in detector and synchrotron development, X-ray radiography bene ts from a high temporal resolution allowing frame rates up to 400 kHz 31,50 suitable for observing uctuations of the keyhole, sputtering or powder particles ejection 55 . For metals, high speed X-ray radiography studies, have shown that porosity formation mechanisms are strongly dependent on the melt pool dynamics.…”

Section: Introductionmentioning

confidence: 99%

Operando tomographic microscopy during laser-based powder bed fusion

Makowska

Verga

Pfeiffer

et al. 2022

Preprint

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Laser-based Powder Bed Fusion (LPBF) of oxide ceramics enables fabrication of objects with complex three-dimensional shapes, which are impossible to achieve using conventional manufacturing routes. However, mechanical properties of dense LPBF-manufactured ceramics are very poor due to large amount of structural defects. To acquaint deeper understanding of the underlying mechanisms, operando tomographic microscopy during LPBF of a magnetite-modified alumina using a pulsed, green laser has been carried out. Operando 3-dimensional information provides an insight into phenomena not accessible with other techniques. The effect of the laser energy density on the surface roughness, powder denudation zone and porosity formation mechanisms is investigated. Using increasing power results in significant increase of the melt pool width, but not of its depth and no melt pool depression is observed. For the investigated ceramic system, the forces due to the recoil pressure do not significantly influence the melt pool dynamics. Increasing power leads to avoid the lack of fusion porosity, but enhances formation of spherical porosity that is formed by either reaching boiling point of liquid alumina, or by introducing gas bubbles by injection of hollow powder particles into the liquid.

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“…Much of the porosity analysis work has been carried out by ex situ studies, supported by computational models, to investigate formation hypotheses. In situ experiments with synchrotron X-ray radiography can provide critical information to substantiate these models and theories [38] by observing process phenomena such as spatter [39], melt pool flow [37,40], melt pool size [34,41], keyhole melting [36,42] and porosity formation [32,[43][44][45] .…”

Section: Introductionmentioning

confidence: 99%

“…However, to date, most in situ synchrotron studies of the melt pool and pore formation in LPBF have involved the melting of a single layer of material. Experiments have been carried out on: a range of materials in overhang (melting onto powder) conditions [37,40,51]; a bare substrate without powder [34]; and on a substrate with a single layer of powder [32,36,[41][42][43][44].…”

Section: Introductionmentioning

confidence: 99%

In situ radiographic and ex situ tomographic analysis of pore interactions during multilayer builds in laser powder bed fusion

Sinclair

Leung

Marussi

et al. 2020

Additive Manufacturing

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Porosity and high surface roughness can be detrimental to the mechanical performance of laser powder bed fusion (LPBF) additive manufactured components, potentially resulting in reduced component life. However, the link between powder layer thickness on pore formation and surface undulations in the LPBF parts remains unclear. In this paper, the influence of processing parameters on Ti-6Al-4V additive manufactured thin-wall components are investigated for multilayer builds, using a custom-built process replicator and in situ highspeed synchrotron X-ray imaging. In addition to the formation of initial keyhole pores, the results reveal three pore phenomena in multilayer builds resulting from keyhole melting: (i) healing of the previous layers pores via liquid filling during remelting; (ii) insufficient laser penetration depth to remelt and heal pores; and (iii) pores formed by keyholing which merge with existing pores, increasing the pore size. The results also show that the variation of powder layer thickness influences which pore formation mechanisms take place in multilayer builds.High-resolution X-ray computed tomography images reveal that clusters of pores form at the ends of tracks and when variations in the layer thickness and melt flow cause irregular 2 remelting and track height undulations. Extreme variations in height were found to lead to lack of fusion pores in the trough regions. It is hypothesised that the end of track pores were augmented by soluble gas which is partitioned into the melt pool and swept to track ends, supersaturating during end of track solidification and diffusing into pores increasing their size.

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High-speed Synchrotron X-ray Imaging of Laser Powder Bed Fusion Process

Cited by 20 publications

References 13 publications

Exploring Structural Changes, Manufacturing, Joining, and Repair of Intermetallic γ‐TiAl‐Based Alloys: Recent Progress Enabled by In Situ Synchrotron X‐Ray Techniques

Exploring Structural Changes, Manufacturing, Joining, and Repair of Intermetallic γ‐TiAl‐Based Alloys: Recent Progress Enabled by In Situ Synchrotron X‐Ray Techniques

Operando tomographic microscopy during laser-based powder bed fusion

In situ radiographic and ex situ tomographic analysis of pore interactions during multilayer builds in laser powder bed fusion

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