Sebastian Marussi’s research while affiliated with University College London and other places

To faithfully capture the laser-material interaction and subsequent process dynamics during the industrial laser powder bed fusion process, we developed a Quad-laser in situ and operando process replicator (or the Quad-ISOPR) – a physical twin that mimics the Renishaw plc.’s RenAM 500Q multi-laser additive manufacturing system that can be used in laboratories and synchrotron radiation facilities. The Quad-ISOPR allows users to take synchrotron X-ray measurements while collecting correlative high-speed optical and photodiode imaging within a 10 ns delay, mounted in-line with the scanning lasers. We have selected case studies to demonstrate: (i) multi-modal data acquisition; (ii) signal processing using continuous wavelet transform; (iii) the study of laser drilling with ultra high-speed X-ray imaging; (iv) process mapping of melting and defect modes in Ti-6Al-4V; and lastly, (v) we showcase the interaction between multi-lasers on a Ti-6Al-4V alloy. Our experimental approach allows end-users to explore the process-structure–property relationship in multi-laser material processing and to use such the physical twin to design new materials and processes.

Keyhole instability during laser welding and laser powder bed fusion (LPBF) can cause keyhole collapse and pore formation. Using high-speed x-ray imaging, we demonstrate that the flow vortex–induced protrusion on the rear keyhole wall is crucial in initiating keyhole instability. Applying a transverse magnetic field suppresses the keyhole instability by driving a secondary thermoelectric magnetohydrodynamics (TEMHD) flow that alters the net flow vortex. This minimizes protrusions and large-amplitude keyhole oscillations. The suppression effectiveness depends on the laser scanning direction relative to the magnetic field orientation because this controls the Seebeck effect–induced Lorentz force’s direction. We show that at LPBF length scales, electromagnetic damping is weak, and for alloys with a large Seebeck coefficient, TEMHD becomes the dominant mechanism controlling flow behind the keyhole.

Transitions between effusive and explosive styles at basaltic volcanoes are strongly dependent on how easily gas can decouple from magma during ascent. Stronger gas-melt coupling favours highly explosive eruptions, whereas a weaker coupling promotes lava fountaining and lava flows. However, the mechanism fostering the transition from closed- to open-system degassing is still poorly understood, due to a lack of direct observations of bubble dynamics under natural magma ascent conditions. A series of in-situ experiments were performed at Diamond Light Source (United Kingdom) combining X-ray synchrotron radiography with a novel high-pressure/high-temperature X-ray transparent Internally Heated Pressure Vessel apparatus to directly observe and quantify in 2D bubble growth and coalescence in a basaltic magma from 100 MPa to the surface, in real-time. This new study provides unique quantitative information on bubble growth, expansion and coalescence through time. We found that for low-viscosity basaltic magmas, bubbles coalesce and recover a spherical shape within 3 s, implying that, for lava fountaining activity, both gas and melt remain coupled during the ascent up to the last hundred metres of the conduit. For higher viscosity magmas, instead, the recovery time becomes longer, promoting connected bubble pathways leading to some degree of decoupling that we directly observed as bubbles expand until they connect to an open pathway and then contract as gas escapes. This new apparatus combined with X-ray synchrotron radiography is an invaluable tool to capture and quantify bubble kinetics in basaltic magmas at natural pre- and syn-eruptive conditions, which are fundamental to improve our understanding of magma behaviour and mitigating the volcanic risk associated with basaltic systems.

Lower back pain is linked to vertebral biomechanics, with vertebral endplates (VEPs) playing a key role in vertebral load transfer and distribution. Synchrotron computed tomography (sCT) allows for detailed visualisation of the microstructure of intact VEPs under near-physiological loads and, when coupled with digital volume correlation (DVC), can be used to quantify three-dimensional (3D) strain fields with nanoscale resolution. Herein, we spatially couple DVC data and an image-based finite element model (FEM) to determine the material properties of murine VEPs. This model was then extended to investigate VEP biomechanics under different motions and disease conditions to reveal that VEP protrusions are important for load absorption and redistribution under different motions and predicted that abnormal intervertebral disc (IVD) stress may underpin osteoporosis- and pycnodysostosis-related IVD degeneration. Our study validates the efficacy of using DVC to increase the accuracy of FEM predictions and highlights that these methodologies may be scalable to large animals and humans.

Transitions in eruptive style during volcanic eruptions strongly depend on how easily gas and magma decouple during ascent. Stronger gas-melt coupling favors highly explosive eruptions, whereas weaker coupling promotes lava fountaining and lava flows. The mechanisms producing these transitions are still poorly understood because of a lack of direct observations of bubble dynamics under natural magmatic conditions. Here, we combine x-ray radiography with a novel high-pressure/high-temperature apparatus to observe and quantify in real-time bubble growth and coalescence in basaltic magmas from 100 megapascals to surface. For low-viscosity magmas, bubbles coalesce and recover a spherical shape within 3 seconds, implying that, for lava fountaining activity, gas and melt remain coupled during the ascent up to the last hundred meters of the conduit. For higher-viscosity magmas, recovery times become longer, promoting connected bubble pathways. This apparatus opens frontiers in unravel-ing magmatic/volcanic processes, leading to improved hazard assessment and risk mitigation.

Crystallisation processes affect the rheological properties of magma and, hence, its ability to move and rise in the crust and erupt. Here we propose in situ crystallisation experiments to study for the first time crystal nucleation and growth in a tephritic magma at high pressure and high temperature under water saturated conditions. We combined fast synchrotron x-ray microtomography with a unique X-ray transparent Internally Heated Pressure Vessel (IHPV) apparatus to simulate magma storage conditions within the crust at pressures ≤100 MPa and temperatures ≤1200 °C in presence of volatiles (H2O). Through the experiments we investigated crystal and bubble nucleation and growth during single step and continuous cooling. At first we pressurised the system with gas (He), and then we heated up to 1140 °C. At this point we continued the experiments via (1) single step cooling (ΔT = 20 °C) at temperatures between 1140 and 1080 °C with a cooling rate of 45 °C/min between each step, and (2) continuous cooling at cooling rates of 0.5 and 1 °C/min. We worked at fixed pressures typical of shallow to intermediate crustal storage (P = 20-50 MPa, corresponding to a depth of ~1-2 km), under H2O-saturated conditions. We were able to directly observe and record vesiculation and crystallization kinetics in both experimental settings. This new apparatus in combination with fast synchrotron x-ray microtomography allow us to capture, visualize and quantify in 4D (3D + time) crystallisation and vesiculation kinetics in magmas at pre- and syn-eruptive conditions, which are fundamental to improve our understanding of magma behaviour and mitigate the volcanic risk associated with these systems. This apparatus, indeed, opens a new frontier in unravelling the processes which control volcanic eruptions, leading to improve the current numerical models by integrating new experimental constraints, and, in turn, hazard assessment and risk mitigation.

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.

Transitions in eruptive style during volcanic eruptions are strongly dependent on how easily gas can decouple from magma during ascent. Stronger gas-melt coupling favours highly explosive eruptions, whereas a weaker coupling promotes lava fountaining and lava flows. However, the mechanism fostering the transition from closed- to open-system degassing is still poorly understood, due to a lack of direct observations of bubble dynamics under natural magma ascent conditions. We combined X-ray synchrotron radiography with a novel high-pressure/high-temperature X-ray transparent Internally Heated Pressure Vessel apparatus to directly observe and quantify in 2D bubble growth and coalescence from 100 MPa to the surface, in real-time. We found that for low-viscosity basaltic magmas, bubbles coalesce and recover a spherical shape within 3 s, implying that, for lava fountaining activity, both gas and melt remain coupled during the ascent up to the last hundred metres of the conduit. For higher viscosity magmas, instead, the recovery time becomes longer, promoting connected bubble pathways leading to some degree of decoupling that we directly observed as bubbles expand until they connect to an open pathway and then contract as gas escapes. Together with degassing, also crystallisation processes play a key role in determining transitions in eruptive style by affecting the rheological properties of magma and, hence, its ability to move and rise in the crust and erupt. For this reason, we combined fast synchrotron x-ray microtomography with our X-ray transparent Internally Heated Pressure Vessel to simulate magma storage conditions within the crust at pressures ≤100 MPa and temperatures of ≤1200 °C in presence of volatiles (H2O). These experiments allowed us to capture, visualise and quantify in 4D (3D + time) crystallisation and vesiculation kinetics in a tephritic magma at pre and syn-eruptive conditions, which are fundamental to improve our understanding of magma behaviour and mitigating the volcanic risk associated with tephritic systems like the one that fed the 2021 Tajogaite eruption (Canary Islands). This apparatus opens a new frontier in unravelling the processes which control volcanic eruptions, leading to improve the current numerical models by integrating new constraints, hazard assessment and risk mitigation.