I12-JEEP: Joint Engineering, Environmental and Processing
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Siyuan
Wei
,
Delvin
Wuu
,
Verner
Soh
,
Kwang Boon
Lau
,
Fengxia
Wei
,
Konstantinos A.
Liogas
,
Baicheng
Zhang
,
Qiang
Zhu
,
Chee Koon
Ng
,
Alexander M.
Korsunsky
,
Pei
Wang
,
Upadrasta
Ramamurty
Diamond Proposal Number(s):
[31917]
Abstract: The role of the nitrogen atmosphere on the microstructure and tensile properties of laser powder bed fused (PBF-LB/M) Fe-xCr (x=0, 5, 10, 15, 24 wt.%, mixed using elemental Fe and pre-alloyed Fe-46 wt.% Cr powders) binary alloys was investigated and compared with those fabricated under an inert (argon) atmosphere. Microstructural characterization reveals the variations of grain morphology with the chemical composition and the distinct effects of nitrogen on grain refinement and texture. Additionally, PBF-LB/M performed under the nitrogen atmosphere leads to the formation of Cr and Fe nitrides in the alloy. Significant enhancements in strength were observed in Fe, Fe-5Cr, and Fe-10Cr fabricated under nitrogen atmosphere due possibly to the solid solution and precipitation strengthening caused by dissolved nitrogen and the nitrides, respectively. However, the Fe-15Cr and Fe-24Cr alloys processed under the nitrogen atmosphere are brittle and crack upon PBF-LB/M due to the residual stresses. The findings in this work enrich the understanding of the effects of fabrication atmospheres in additive manufacturing, insights of which can be extended to diverse categories of alloys.
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Mar 2024
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B16-Test Beamline
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Diamond Proposal Number(s):
[30460]
Open Access
Abstract: Current experimental and numerical quantification methods are limited in their ability to full-field mapping of the unpredictable distribution of all residual stress and permanent plastic strain components in additive manufacturing parts with discontinuous processing properties. To address this limitation, a tomographic eigenstrain (inherent strain) reconstruction method, that merges eigenstrain reconstruction with diffraction strain tomography for mapping volumetric distribution of all components of eigenstrains and corresponding elastic deformations like residual stresses non-destructively using minimum amount of tomographic scans is presented through numerical experiments, and then applied to the analysis of a CM 247 LC superalloy additive manufacturing part using diffraction strain tomography data. The method reconstructs all eigenstrain and corresponding residual stress components, parallel to the build direction, aligned with the experimental data component accurately, demonstrating its potential in optimizing the performance and reliability of parts designed for high-tech industries such as aerospace. Subsequent validations using the X-ray diffraction and neutron diffraction strain scanning techniques confirm the method's reliability in reconstructing residual stress components parallel to the plane of powder bed that are different from the experimental data component. Furthermore, the novel findings of this study reveal a characteristic residual stress distribution pattern within additive manufacturing parts particularly those featuring rectangular shapes. Microstructural analysis also validates eigenstrain distribution in accordance with the findings on the characteristic distribution of residual stresses, highlighting the significance of this method in advancing materials research and development.
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Feb 2024
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[2370]
Open Access
Abstract: Surface roughness controls the mechanical performance and durability (e.g., wear and corrosion resistance) of laser powder bed fusion (LPBF) components. The evolution mechanisms of surface roughness during LPBF are not well understood due to a lack of in situ characterisation methods. Here, we quantified key processes and defect dynamics using synchrotron X-ray imaging and ex situ optical imaging and explained the evolution mechanisms of side-skin and top-skin roughness during multi-layer LPBF of Ti-6AI-4V (where down-skin roughness was out of the project scope). We found that the average surface roughness alone is not an accurate representation of surface topology of an LPBF component and that the surface topology is multimodal (e.g., containing both roughness and waviness) and multiscale (e.g., from 25 µm sintered powder features to 250 µm molten pool wavelength). Both roughness and topology are significantly affected by the formation of pre-layer humping, spatter, and rippling defects. We developed a surface topology matrix that accurately describes surface features by combining 8 different metrics: average roughness, root mean square roughness, maximum profile peak height, maximum profile valley height, mean height, mean width, skewness, and melt pool size ratio. This matrix provides a guide to determine the appropriate linear energy density to achieve the optimum surface finish of Ti-6AI-4V thin-wall builds. This work lays a foundation for surface texture control which is critical for build design, metrology, and performance in LPBF.
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Oct 2023
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B16-Test Beamline
I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[30460, 31917]
Open Access
Abstract: The formation of residual stresses is inevitable during the additive manufacturing of metallic parts due to thermo-mechanicals effects, but the chaotic nature of printing processes makes it impossible to have a comprehensive understanding about the magnitude and distribution of these residuals. The voxel-based eigenstrain (inherent strain) reconstruction method is capable of the full-field reconstruction of residual stresses in discontinuous processing bodies at a scale that depends on the resolution of experimental data without using simplifying assumptions and regularisation functions. This advanced method firstly maps the distribution of eigenstrains and then quantifies corresponding residual stresses, residual elastic strains, and displacements by a cost-effective linear elastic computational framework. The reliability of this process solely depends on the quality of experimental data and the availability of computational power. The motivation behind this study is the use of the voxel-based eigenstrain reconstruction method for the full-field mapping of complex residual stress fields, that cannot be predicted by regularizing assumptions, in discontinuous processing additive manufacturing parts. The height Digital Image Correlation (hDIC) technique satisfied the need for high-quality experimental data by calculating triaxial displacements, corresponding to the elastic response of CM 247 LC powder bed fusion (PBF) additive manufacturing part after changes in the boundary conditions due to separation from the base, using optical profilometry measurements at a resolution adjusted in a way to reconstruct Type I residual stresses. Three components of displacements calculated by the hDIC were used to map the distribution of three components of eigenstrains for the reconstruction of six residual stress, six residual elastic strain and three displacement components that belong to the before and after separating from the base states. The reliability of calculations has been validated by monochromatic synchrotron X-ray beams in powder diffraction mode from the same surface of optical profilometry measurements and in transmission mode from the sampling volumes.
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Sep 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[28804]
Open Access
Abstract: Melt flow is critical to build quality during additive manufacturing (AM). When an external magnetic field is applied, it causes forces that alter the flow through the thermoelectric magnetohydrodynamic (TEMHD) effect, potentially altering the final microstructure. However, the extent of TEMHD forces and their underlying mechanisms, remain unclear. We trace the flow of tungsten particles using in situ high-speed synchrotron X-ray radiography and ex situ tomography to reveal the structure of TEMHD-induced flow during directed energy deposition AM (DED-AM). When no magnetic field is imposed, Marangoni convection dominates the flow, leading to a relatively even particle distribution. With a magnetic field parallel to the scan direction, TEMHD flow is induced, circulating in the cross-sectional plane, causing particle segregation to the bottom and side of the pool. Further, a downward magnetic field causes horizontal circulation, segregating particles to the other side. Our results demonstrate that TEMHD can disrupt melt pool flow during DED-AM.
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Jun 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[28804]
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.
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Apr 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[20096]
Open Access
Abstract: Laser additive manufacturing is transforming several industrial sectors, especially the directed energy deposition process. A key challenge in the widespread uptake of this emerging technology is the formation of undesirable microstructural features such as pores, cracks, and large epitaxial grains. The trial and error approach to establish the relationship between process parameters and material properties is problematic due to the transient nature of the process and the number of parameters involved. In this work, the relationship between process parameters, melt pool geometry and quality of build measures, using directed energy deposition additive manufacturing for IN718, is quantified using neural networks as generalised regressors in a statistically robust manner. The data was acquired using in-situ synchrotron x-ray imaging providing unique and accurate measurements for our analysis. An analysis of the variations across repeated measurements show heteroscedastic error characteristics that are accounted for using a principled nonlinear data transformation method. The results of the analysis show that surface roughness correlates with melt pool geometry while the track height directly correlates with process parameters indicating a potential to directly control efficiency and layer thickness while independently minimising surface roughness.
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Mar 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Yuanbo T.
Tang
,
Chinnapat
Panwisawas
,
Benjamin M.
Jenkins
,
Junliang
Liu
,
Zhao
Shen
,
Enrico
Salvati
,
Yilun
Gong
,
Joseph N.
Ghoussoub
,
Stefan
Michalik
,
Bryan
Roebuck
,
Paul A. J.
Bagot
,
Sergio
Lozano-Perez
,
Chris R. M.
Grovenor
,
Michael P.
Moody
,
Alexander M.
Korsunsky
,
David M.
Collins
,
Roger C.
Reed
Diamond Proposal Number(s):
[23674]
Open Access
Abstract: A supersaturated phase microstructure is produced in Ni-based superalloys using laser powder bed fusion (L-PBF) – the cooling rate arising from the process is shown to suppress the solid-state precipitation of the phase. The response of the material to a heat treatment therefore requires new understanding at the fundamental level, since the first population of precipitate forms upon heating, in contrast to cooling from homogenisation above the solvus. Here, we have interrogated two new nickel-based superalloys designed for the L-PBF technology, both in situ and ex situ, at multiple length scales using advanced characterisation methods. First, we conducted in situ synchrotron X-ray diffraction during various heat treatments to trace the evolution of the volume fraction with temperature. The first structural changes were detected at an unexpectedly low temperature of 445 °C. Second, the temperature for nucleation and its sensitivity to heating rate was studied using an electrical resistivity method. Then, the composition upon heating, isothermal holding and cooling is analysed using atom probe tomography (APT), the result is rationalised by further scanning-transmission electron microscopy and nanoscale secondary ion mass spectroscopy. Finally, static recrystallisation during isothermal exposure was investigated, which occurs within minutes. This work sheds light on a new strategy of tailoring microstructure for additively manufactured superalloys by manipulation of the precipitate distribution upon heating.
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Jan 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[21946]
Abstract: The repeated localised heating-melting-cooling-solidification processes during laser beam powder bed fusion (PBF-LB) additive manufacturing (AM) induce intricate thermal residual stress (RS) in manufactured parts. Non-destructive characterisation using X-ray diffraction was used to measure the RS of Ti-6Al-4V square plates that were manufactured by using six different scanning strategies. Computational modelling was used to interpret the experimental stress measurement results. It was revealed that an inclined scanning strategy is beneficial for reducing the average through-thickness RS because the inclined scanning strategy can mitigate the non-uniform thermal profile and corresponding residual thermal stresses in successive layers of material. Among all the different scanning strategies that were analysed in this work, the 45° inclined 90° rotation scanning resulted in the lowest RS. The thicker parts have a greater gradient of RS than the thinner parts, after base plate removal. This research outcome can help the AM industry to design or optimise the process parameters of the PBF-LB aiming to minimise the RS of metal parts.
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Nov 2022
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[20096]
Open Access
Abstract: To prevent oxygen contamination, additive manufacturing (AM) techniques normally operate in an inert gas chamber (GC). An alternative method, useful for large builds and components repair, is the application of localised shielding gas (LSG). The effect of oxygen contamination on Ti6242 during directed energy deposition (DED) AM using an inert GC compared to LSG was investigated by in situ synchrotron X-ray experiments. When processing in LSG mode, the amount of oxygen absorbed from the atmosphere was sufficient to reverse the Marangoni flow leading to an alteration of the molten pool geometry and strongly influencing defect formation. Microstructural analysis reveals that, at high oxygen levels, the commonly developed α' martensitic microstructure was completely suppressed, forming precipitation of a tetra modal microstructure of α phase consisting of globular, primary and secondary lamellae (in colonies) and basketweave structure. These results help elucidate the influence of oxygen contamination in additively manufactured Ti alloys, potentially enabling improved industrial practices for AM of titanium alloy.
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Nov 2021
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