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Instruments / Technical Area	Publication Details	Published
I12-JEEP: Joint Engineering, Environmental and Processing	Effects of melt pool flow on porosity levels in arc welding F. Wu , K. V. Falch , M. Drakopoulos , W. U. Mirihanage Iop Conference Series: Materials Science And Engineering 1274 6th International Conference on Advances in Solidification Processes (ICASP-6) DOI: 10.1088/1757-899X/1274/1/012011 Diamond Proposal Number(s): [20611] Open Access Show Abstract ▼ Abstract: Arc welding is one of the widely used approaches for joining metals. During the arc welding process, an electric arc creates intense heat to fuse metals that forms the melt pool between the parts to be welded together. Intensive flow fields are observable within the fusion weld pools as a result of multiple driving forces. The flow patterns within the melt pool significantly determine the shape of the weld joint and other attributes of the solidified joint, such as microstructure and defects. Porosity is one of the solidification-related defects that can bring a detrimental impact. During the formation and solidification of weld pools, gas bubbles that are formed can be driven in or out from the pool by the flow. In this work, employing in situ synchrotron X-rays, we have observed how different flow conditions and air-liquid interface are contributed to retaining and releasing the gas bubbles that formed during the arc welding. The results suggest that underpinning driving forces, such as electromagnetic forces, act on molten metal to retain the pores inside the weld joints; but, gravity-driven effects can contribute to reduce the porosity, with appropriate process conditions	Jan 2023
I12-JEEP: Joint Engineering, Environmental and Processing	X-ray imaging of complex flow patterns during tungsten inert gas welding F. Wu , K. V. Falch , S. Ramachandran , M. Drakopoulos , W. U. Mirihanage Journal Of Materials Engineering And Performance 559 DOI: 10.1007/s11665-022-07042-6 Diamond Proposal Number(s): [20611] Open Access Show Abstract ▼ Abstract: Fusion welding techniques such as tungsten inert gas (TIG) welding process have been widely used in industrial and construction applications. The molten metal flow in the weld pool has a major impact on the microstructure evolution, chemical element distribution and defects formation during solidification, which subsequently determines the performance of the welds. However, limited real-time experimental data availability of internal flow behavior has been considered as a major barrier to achieve a thorough understanding and development of accurate weld pool prediction models. In situ x-ray imaging with the tracking particles facilitated us to visualize the flow evolution during the solid–liquid–solid transformation. Experimental results indicated the flow patterns are progressively becoming complicated with the expansion of the melt pool. The shape of the melt pool also changed according to this flow evolution. Our analysis of flow patterns concerning the underlying variation of the driving forces suggests that gravity-derived buoyancy has a considerable effect on determining fluid flow at the melt pool periphery compared to other regions.	Jun 2022
I12-JEEP: Joint Engineering, Environmental and Processing	Mapping flow evolution in gas tungsten arc weld pools Fan Wu , Thomas F. Flint , Ken Vidar Falch , Michael C. Smith , Michael Drakopoulos , Wajira Mirihanage International Journal Of Heat And Mass Transfer 179 DOI: 10.1016/j.ijheatmasstransfer.2021.121679 Diamond Proposal Number(s): [20611] Open Access Show Abstract ▼ Abstract: The complex flow within the molten metallic pool, during advanced manufacturing and joining processes such as welding and additive manufacturing, directly affects the performance of the final components; through the generation of various microstructures and strain gradients. Understanding of the flow within such melt pools can enhance the predictability of the final microstructures and therefore component performance. In situ synchrotron X-ray imaging is employed to observe and map the evolving flow patterns within gas tungsten arc weld pools using tracking particles. The experimentally observed flow patterns are compared with numerical simulations to gain additional insights on accurate predictability in relevance to the physical driving forces within the flow. The spatio-temporal distribution of the flow using the mapped data is analyzed by considering the evolution of driving forces acting throughout the weld pool. The results demonstrate quantitative benchmark flow mapping with confirmation of the overall mechanisms of weld pool flow.	Nov 2021
I12-JEEP: Joint Engineering, Environmental and Processing	In situ X-ray observations of transient states in arc weld pools F. Wu , K. V. Falch , M. Drakopoulos , W. U. Mirihanage Iop Conference Series: Materials Science And Engineering 861 MCWASP XV 2020 DOI: 10.1088/1757-899X/861/1/012071 Diamond Proposal Number(s): [20611] Open Access Show Abstract ▼ Abstract: Metallic alloys coalesce via extremely rapid melting and subsequent solidification to form fusion welded joints. The melt pool evolution in melting and solidification sequences during the welding process determines the formation of the final weld joint shape, microstructure and defects. The scientific insight on weld pool evolution and related phenomena can be a key contribution to enhance structural integrity and resilience of the welded structures or components. However, inherent complexity with multi-physics phenomena, associated high temperatures and the rapidness of the processes make direct experimental investigation of welding is extremely demanding. Thus, internal flow behaviour during welding or other melt-pool-based metal processing such as additive manufacturing remains unclear and hinders progression to process optimisation. In this contribution we report the observation of melt pool dynamics that take place during electric arc welding, obtained through in situ synchrotron imaging at millisecond scale. The analysis flow patterns along with the quantified weld pool surface dynamics revealed us to how different contributing forces dictate the flow conditions over the distinct durations of the relatively short existence of the liquid phase. Our preliminary results suggest the existence of arc, surface tension and gravity dominant regimes during the evaluation of the weld pool. Further, we present our observations on how different welding parameters influence these regimes and develop into different transient conditions.	May 2020
B16-Test Beamline I12-JEEP: Joint Engineering, Environmental and Processing	Time evolved force domination in arc weld pools Fan Wu , Ken Vidar Falch , Da Guo , Paul English , Michael Drakopoulos , Wajira Mirihanage Materials & Design DOI: 10.1016/j.matdes.2020.108534 Diamond Proposal Number(s): [20611, 19595] Open Access Show Abstract ▼ Abstract: The flow within the melt pool during welding is a major factor that dictates the formation of the final fusion zone shape, solidification microstructure and defects. In this paper, we report the evolution sequence of the arc weld pool flow that observed via fast in-situ synchrotron X-ray imaging. Varying flow regimes attribute to the dominance of characteristic forces within the weld pool during rapid solid-liquid-solid phase transformation. Our analysis indicates the general sequence in the arc, surface tension and gravity driven force domination. Welding process parameters appear to influence significantly in determining the domination interval and the intensity of individual force. In some instances, arc and surface tension driven forces can prevent pores, which causes porosity in final welded structures, escaping from the melt pool. Preliminary relations between power input levels, diffract force domination regimes, flow patterns and pool surface changes in fusion welds are suggested by considering the behavior of multiple weld pools.	Feb 2020

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