Revealing flow patterns in fusion welding with stereo X-ray imaging.

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Fusion welding is one of the most widely used and prominent joining methods for metallic alloys. It is well accepted that flow within the weld pool significantly influences weld region shape, microstructure, defect and resulting residual stress formation during solidification. However, there are no reliable experimental data on flow within metallic alloy weld pools and scientific understanding is reliant on simplified models and simulations that lack proper validation. Hence, the objective of this proposal is to acquire 3D visualisation in real time (i.e. 4D) quantification of the liquid metal flow to analyse evolving flow in weld pools. The results will guide, validate and qualify weld pool modelling and the scientific understanding will enable improvements in the weld processes. A unique and novel experimental configuration is proposed to realise time-resolved stereo X-ray imaging for in situ weld simulation experiments at the Diamond Light Source, UK. An experimental configuration, with two mutually inclined X-ray beams, which are obtained through splitting the regular synchrotron beam using X-ray optics, will be instrumental in realising the stereo imaging capability. Small, high X-ray attenuating particles embedded in the weld materials (in weld pool) will serve as markers to track the evolving fluid flow patterns. Combining the two sets of time-resolved images recorded in this stereo configuration, via bespoke image processing and analysing procedures will render 4D visualisation and spatio-temporal quantification of flow, enabling analysis of flow in evolving weld pools.