I12-JEEP: Joint Engineering, Environmental and Processing
|
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.
|
Jun 2023
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
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.
|
Apr 2023
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Chu Lun Alex
Leung
,
Matthew D.
Wilson
,
Thomas
Connolley
,
Stephen P.
Collins
,
Oxana V.
Magdysyuk
,
Matthieu N.
Boone
,
Kosuke
Suzuki
,
Matthew C.
Veale
,
Enzo
Liotti
,
Frederic
Van Assche
,
Andrew
Lui
,
Chun
Huang
Diamond Proposal Number(s):
[23400]
Open Access
Abstract: Increasing electrode thickness is gaining more attention as a potential route to increase energy density for Li ion batteries although the realizable capacity and rate capability are usually limited by Li+ ion diffusion during (dis)charge, especially at increased (dis)charge rates. It remains challenging to visualize and quantify the low atomic number Li+ chemical stoichiometry distribution inside the electrode within commercially standard battery geometry, e.g., coin cells with stainless steel casings. Here, we map the distribution of Li+ chemical stoichiometry in the electrode microstructure inside a working coin cell battery to show the amount of electrode materials contributing to energy storage performance using innovative in situ correlative full-field X-ray Compton scattering imaging (XCS-I) and X-ray computed tomography (XCT). We design and fabricate an ultra-thick (∼1 mm) cathode of LiNi0.8Mn0.1Co0.1O2 with a microstructure containing vertically oriented pore arrays using a directional ice templating method. This novel technique paves a new way to map low atomic number elements in 3D structures and study how the microstructure improves Li+ ion diffusivity and energy storage performance.
|
Dec 2022
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Diamond Proposal Number(s):
[16214]
Open Access
Abstract: Laser powder bed fusion (LPBF) can produce high-value metallic components for many industries; however, its adoption for safety-critical applications is hampered by the presence of imperfections. The interdependency between imperfections and processing parameters remains unclear. Here, the evolution of porosity and humps during LPBF using X-ray and electron imaging, and a high-fidelity multiphase process simulation, is quantified. The pore and keyhole formation mechanisms are driven by the mixing of high temperatures and high metal vapor concentrations in the keyhole is revealed. The irregular pores are formed via keyhole collapse, pore coalescence, and then pore entrapment by the solidification front. The mixing of the fast-moving vapor plume and molten pool induces a Kelvin–Helmholtz instability at the melt track surface, forming humps. X-ray imaging and a high-fidelity model are used to quantify the pore evolution kinetics, pore size distribution, waviness, surface roughness, and melt volume under single layer conditions. This work provides insights on key criteria that govern the formation of imperfections in LPBF and suggest ways to improve process reliability.
|
Oct 2022
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Chun
Huang
,
Matthew
Wilson
,
Kosuke
Suzuki
,
Enzo
Liotti
,
Thomas
Connolley
,
Oxana
Magdysyuk
,
Stephen
Collins
,
Frederic
Van Assche
,
Matthieu N
Boone
,
Matthew C.
Veale
,
Andrew
Lui
,
Rhian-Mair
Wheater
,
Chu Lun Alex
Leung
Diamond Proposal Number(s):
[23400]
Open Access
Abstract: The performance of Li+ ion batteries (LIBs) is hindered by steep Li+ ion concentration gradients in the electrodes. Although thick electrodes (≥300 µm) have the potential for reducing the proportion of inactive components inside LIBs and increasing battery energy density, the Li+ ion concentration gradient problem is exacerbated. Most understanding of Li+ ion diffusion in the electrodes is based on computational modeling because of the low atomic number (Z) of Li. There are few experimental methods to visualize Li+ ion concentration distribution of the electrode within a battery of typical configurations, for example, coin cells with stainless steel casing. Here, for the first time, an interrupted in situ correlative imaging technique is developed, combining novel, full-field X-ray Compton scattering imaging with X-ray computed tomography that allows 3D pixel-by-pixel mapping of both Li+ stoichiometry and electrode microstructure of a LiNi0.8Mn0.1Co0.1O2 cathode to correlate the chemical and physical properties of the electrode inside a working coin cell battery. An electrode microstructure containing vertically oriented pore arrays and a density gradient is fabricated. It is shown how the designed electrode microstructure improves Li+ ion diffusivity, homogenizes Li+ ion concentration through the ultra-thick electrode (1 mm), and improves utilization of electrode active materials.
|
Apr 2022
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Lorna
Sinclair
,
Yunhui
Chen
,
Samuel J.
Clark
,
Sebastian
Marussi
,
Saurabh
Shah
,
Oxana
Magdysyuk
,
Robert
Atwood
,
Gavin J.
Baxter
,
Martyn
Jones
,
Graham
Mccartney
,
Chu Lun Alex
Leung
,
Peter D.
Lee
Diamond Proposal Number(s):
[20096]
Open Access
Abstract: During directed energy deposition (DED) additive manufacturing, powder agglomeration and sintering can occur outside of the melt pool when using titanium alloy powders. Using in situ synchrotron radiography we investigate the mechanisms by which sintering of Ti6242 powder occurs around the pool, performing a parametric study to determine the influence of laser power and stage traverse speed on sinter build-up. The results reveal that detrimental sinter can be reduced using a high laser power or increased stage traverse speed, although the latter also reduces deposition layer thickness. The mechanism of sinter formation during DED was determined to be in-flight heating of the powder particles in the laser beam. Calculations of particle heating under the processing conditions explored in this study confirm that powder particles can reasonably exceed 700 °C, the threshold for Ti surface oxide dissolution, and thus the powder is prone to sintering if not incorporated into the melt pool. The build-up of sinter powder layer on deposit surfaces led to lack of fusion pores. To mitigate sinter formation and its detrimental effects on DED component quality, it is essential that the powder delivery spot area is smaller than the melt pool, ensuring most powder lands in the melt pool.
|
Apr 2022
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
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.
|
Nov 2021
|
|
I13-2-Diamond Manchester Imaging
|
Diamond Proposal Number(s):
[19354]
Open Access
Abstract: Laser powder bed fusion (LPBF) is a revolutionary manufacturing technology that fabricates parts with unparalleled complexity, layer-by-layer. However, there are limited choices of commercial powders for LPBF, constrained partly by the laser absorbance, an area that is not well investigated. Carbon additives are commonly used to promote near infra-red (NIR) absorbance of the powders but their efficiency is limited. Here, we combine operando synchrotron X-ray imaging with chemical characterisation techniques to elucidate the role of additives on NIR absorption, melt track and defect evolution mechanisms during LPBF. We employ a reduced graphene oxide (rGO) additive to enable LPBF of low NIR absorbance powder, SiO2, under systematic build conditions. This work successfully manufactured glass tracks with a high relative density (99.6%) and overhang features (> 5 mm long) without pre/post heat treatment. Compared to conventional carbon additives, the rGO increases the powder's NIR absorbance by ca. 3 times and decreases the warpage and porosity in LPBF glass tracks. Our approach will dramatically widen the palette of materials for laser processing and enable existing LPBF machines to process low absorbance powder, such as SiO2, using a NIR beam.
|
Jun 2021
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Yunhui
Chen
,
Samuel J.
Clark
,
David M.
Collins
,
Sebastian
Marussi
,
Simon A.
Hunt
,
Danielle
Fenech
,
Thomas
Connolley
,
Robert C.
Atwood
,
Oxana V.
Magdysyuk
,
Gavin J.
Baxter
,
Martyn A.
Jones
,
Chu Lun Alex
Leung
,
Peter D.
Lee
Diamond Proposal Number(s):
[20096]
Abstract: The governing mechanistic behaviour of Directed Energy Deposition Additive Manufacturing (DED-AM) is revealed by a combined in situ and operando synchrotron X-ray imaging and diffraction study of a nickel-base superalloy, IN718. Using a unique DAE-AM process replicator, real-space imaging enables quantification of the melt-pool boundary and flow dynamics during solidification. This imaging knowledge was also used to informed precise diffraction measurements of temporally resolved microstructural phases during transformation and stress development with a spatial resolution of 100 µm. The diffraction quantified thermal gradient enabled a dendritic solidification microstructure to be predicted and coupled to the stress orientation and magnitude. The fast cooling rate entirely suppressed the formation of secondary phases or recrystallisation in the solid-state. Upon solidification, the stresses rapidly increase to the yield strength during cooling. This insight, combined with the large solidification range of IN718 suggests that the accumulated plasticity exhausts the ductility of the alloy, causing liquation cracking. This study has revealed additional fundamental mechanisms governing the formation of highly non-equilibrium microstructures during DED-AM.
|
Mar 2021
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Yunhui
Chen
,
Samuel J.
Clark
,
Lorna
Sinclair
,
Chu Lun Alex
Leung
,
Sebastian
Marussi
,
Thomas
Connolley
,
Robert C.
Atwood
,
Gavin J.
Baxter
,
Martyn A.
Jones
,
Iain
Todd
,
Peter D.
Lee
Diamond Proposal Number(s):
[20096]
Abstract: Directed Energy Deposition Additive Manufacturing (DED-AM) is transformative for the production of larger, geometrically complex metallic components. However, the mechanical properties of titanium alloy DED-AM components do not always reach their full potential due to microstructural features including porosity and regions of lack of fusion. Using in situ and operando synchrotron X-ray imaging we gain insights into key laser-matter interaction and microstructural feature formation mechanisms during DED-AM of Ti-6242. Analysis of the process conditions reveals that laser power is dominant for build efficiency while higher traverse speed can effectively reduce lack of fusion regions. We also elucidate the mechanisms underlying several physical phenomena occurring during the deposition of titanium alloys, including the formation of a saddle-shaped melt pool and pore pushing. The findings of this work clarify the transient kinetics behind the DED-AM of titanium alloys and can be used as a guide for optimising industrial additive manufacturing processes.
|
Mar 2021
|
|
