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Instruments / Technical Area	Publication Details	Published
I12-JEEP: Joint Engineering, Environmental and Processing	Towards the equiaxed grain microstructure in CrMnFeCoNi high‐entropy alloy fabricated by directed energy deposition Minsoo Jin , Yunhui Chen , Bogdan Dovgyy , Peter Lee , Minh-Son Pham Advanced Engineering Materials DOI: 10.1002/adem.202301969 Diamond Proposal Number(s): [20096] Open Access Show Abstract ▼ Abstract: The columnar grains in additively manufactured alloys increase tendency to form solidification cracks and cause anisotropy. Studying the effect of process parameters on microstructure development helps to guide the manufacturing of the equiaxed grain microstructure. We firstly studied the effect of process condition on the melt pool dimensions using in-situ synchrotron X-ray imaging; and thermal profile and solidification condition using finite element simulation and calculation of thermodynamics phase diagrams of CrMnFeCoNi High-Entropy Alloy (HEA) fabricated by directed energy deposition (DED). Increasing the laser power reduced the thermal gradient to solidification rate ratio, pushing the solidification closer to the columnar-equiaxed transition. Nevertheless, the simulations still indicated the columnar microstructure for all scan conditions in contrast to experimental observation that showed single-wall samples built at 200 W consisted of dominantly equiaxed grains, whereas columnar grains were dominant in samples built at 100 W. It was believed that in addition to the effect of thermal gradient and solidification rate, the chemical segregation (Mn and Ni) during solidification might promote dendrite detachment, hence assisting the transition to equiaxed grains. The multi-track deposition results in more solid beneath a new melt pool, increasing the thermal gradient that promotes more columnar grains in comparison to single-tracks.	Jun 2024
	Pore evolution mechanisms during directed energy deposition additive manufacturing Kai Zhang , Yunhui Chen , Sebastian Marussi , Xianqiang Fan , Maureen Fitzpatrick , Shishira Bhagavath , Marta Majkut , Bratislav Lukic , Kudakwashe Jakata , Alexander Rack , Martyn A. Jones , Junji Shinjo , Chinnapat Panwisawas , Chu Lun Alex Leung , Peter D. Lee Nature Communications 15 DOI: 10.1038/s41467-024-45913-9 Open Access Show Abstract ▼ Abstract: Porosity in directed energy deposition (DED) deteriorates mechanical performances of components, limiting safety-critical applications. However, how pores arise and evolve in DED remains unclear. Here, we reveal pore evolution mechanisms during DED using in situ X-ray imaging and multi-physics modelling. We quantify five mechanisms contributing to pore formation, migration, pushing, growth, removal and entrapment: (i) bubbles from gas atomised powder enter the melt pool, and then migrate circularly or laterally; (ii) small bubbles can escape from the pool surface, or coalesce into larger bubbles, or be entrapped by solidification fronts; (iii) larger coalesced bubbles can remain in the pool for long periods, pushed by the solid/liquid interface; (iv) Marangoni surface shear flow overcomes buoyancy, keeping larger bubbles from popping out; and (v) once large bubbles reach critical sizes they escape from the pool surface or are trapped in DED tracks. These mechanisms can guide the development of pore minimisation strategies.	Feb 2024
I12-JEEP: Joint Engineering, Environmental and Processing	Sinter formation during directed energy deposition of titanium alloy powders 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 International Journal Of Machine Tools And Manufacture 8 DOI: 10.1016/j.ijmachtools.2022.103887 Diamond Proposal Number(s): [20096] Open Access Show Abstract ▼ 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	Oxidation induced mechanisms during directed energy deposition additive manufactured titanium alloy builds Caterina Iantaffi , Chu Lun Alex Leung , Yunhui Chen , Shaoliang Guan , Robert C. Atwood , Jedsada Lertthanasarn , Minh-Son Pham , Martina Meisnar , Thomas Rohr , Peter D. Lee Additive Manufacturing Letters 143 DOI: 10.1016/j.addlet.2021.100022 Diamond Proposal Number(s): [20096] Open Access Show Abstract ▼ 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
I12-JEEP: Joint Engineering, Environmental and Processing	Variance stabilised optimisation of neural networks: A case study in additive manufacturing Scott V. Notley , Yunhui Chen , Peter D. Lee , George Panoutsos 2021 International Joint Conference on Neural Networks (IJCNN) DOI: 10.1109/IJCNN52387.2021.9533311 Diamond Proposal Number(s): [20096] Show Abstract ▼ Abstract: A new framework is presented for training neural networks that is based on the characterisation and stabilisation of measurement variations. The framework results in a number of useful properties that maximises the use of data as well as aiding in the interpretation of results in a principled manner. This is achieved via variance stabilisation and a subsequent standardisation step. The method is a general approach that may be used in any context where repeatability data is available. Standardisation in this manner allows goodness of fit to be quantified and measurement data to be interpreted from a statistical perspective. We demonstrate the utility of this framework in the analysis of advanced manufacturing data.	Sep 2021
I12-JEEP: Joint Engineering, Environmental and Processing	Correlative synchrotron X-ray imaging and diffraction of directed energy deposition additive manufacturing 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 Acta Materialia 21 DOI: 10.1016/j.actamat.2021.116777 Diamond Proposal Number(s): [20096] Show Abstract ▼ 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	Synchrotron X-ray imaging of directed energy deposition additive manufacturing of titanium alloy Ti-6242 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 Additive Manufacturing 92 DOI: 10.1016/j.addma.2021.101969 Diamond Proposal Number(s): [20096] Show Abstract ▼ 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
E01-JEM ARM 200CF	Evaluation and realization of safer Mg-S battery: the decisive role of the electrolyte Lin Sheng , Zhangxiang Hao , Junrun Feng , Wenjia Du , Manxi Gong , Liqun Kang , Paul R. Shearing , Dan J. I. Brett , Yunhui Huang , Feng Ryan Wang Nano Energy 334 DOI: 10.1016/j.nanoen.2021.105832 Diamond Proposal Number(s): [20643] Show Abstract ▼ Abstract: The magnesium–sulfur (Mg-S) battery may be a safer alternative for the lithium-sulfur battery because Mg plating usually proceeds without dendrite formation. Here, we correlate the thermal runaway of Mg-S battery with the associated change of electrolyte vapour pressure via battery testing calorimetery. Over-pressure builds up along with the programmed heating of the cell, and as a result, the thermal runaway is triggered at 20 to 45 K over the electrolyte boiling point, corresponding to 70 to 150 kPa pressure difference between the cell and the environment. The distinct performance-safety-cost behaviours of three ether type of electrolytes stems from the different CH2CH2O chain lengths. Such molecular insight will serve as a fundamental guideline in choosing and designing the desired electrolyte that simultaneously achieves a high explosion limit and good electrochemical performance.	Jan 2021
I12-JEEP: Joint Engineering, Environmental and Processing	In situ X-ray quantification of melt pool behaviour during directed energy deposition additive manufacturing of stainless steel Yunhui Chen , Samuel J. Clark , Yuze Huang , Lorna Sinclair , Chu Lun Alex Leung , Sebastian Marussi , Thomas Connolley , Oxana V. Magdysyuk , Robert C. Atwood , Gavin J. Baxter , Martyn A. Jones , Iain Todd , Peter D. Lee Materials Letters DOI: 10.1016/j.matlet.2020.129205 Diamond Proposal Number(s): [20096] Open Access Show Abstract ▼ Abstract: The Directed Energy Deposition Additive Manufacturing (DED-AM) of SS316L was studied using in situ and operando synchrotron X-ray imaging to quantitively understand the effect of processing parameters on the melt-pool morphology and surface quality. It was found that surface roughness of DED-AM builds can result from melt pool surface perturbations caused by changes in the melt flow and build stage motion perturbations. Process maps are developed that quantitatively correlate build quality to process parameters including powder feed rate, laser power and traverse speed. How the AM process parameters control build efficacy is clarified, and the processing conditions required to dampen surface perturbations leading to roughness were determined.	Dec 2020
I12-JEEP: Joint Engineering, Environmental and Processing	Melt pool morphology in directed energy deposition additive manufacturing process Y. Chen , S. Clark , A. C. L. Leung , L. Sinclair , S. Marussi , R. Atwood , T. Connolley , M. Jones , G. Baxter , Peter Lee Iop Conference Series: Materials Science And Engineering 861 MCWASP XV 2020 DOI: 10.1088/1757-899X/861/1/012012 Diamond Proposal Number(s): [20096] Open Access Show Abstract ▼ Abstract: Directed Energy Deposition Additive Manufacturing (DED-AM) is one of the principal AM techniques being explored for both the repair of high value components in the aerospace industry as well as freeform fabrication of large metallic components. However, the lack of fundamental understanding of the underlying process-structure-property relationships hinders the utilisation of DED-AM for the production or repair of safety-critical components. This study uses in situ and operando synchrotron X-ray imaging to provide an improved fundamental understanding of laser-matter interactions and their influence on the melt pool geometry. Coupled with process modelling, these unique observations illustrate how process parameters can influence the DED-AM melt pool geometry. The calibrated simulation can be used for guidance in an industrial additive manufacturing process for microstructure and quality control.	May 2020

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