Dynamic modelling and validation of the metal/flux interface in continuous casting

This paper concerns the development and validation (using an oil/water system) of a finite volume computer model of the continuous casting process for steel flat products. The emphasis is on hydrodynamic aspects and in particular the dynamic behaviour of the metal/slag interface due to the momentum imparted by the submerged entry nozzle (SEN) jets that bring the metal into the mould. Instability and wave action encourage the entrainment of inclusions into the melt affecting product quality. To track the interface between oil and water a new implicit algorithm was developed, called the Counter Diffusion Method. To prevent numerical damping of low frequency waves, a time-filtered version of the k- model was incorporated in the model. The physics of the interface dynamics are affected by density stratification and surface interfacial tension, with additional source terms introduced in the turbulence model to account for the former effect. Gas bubbles were modelled using a Lagrangian tracking method. The model was validated against experimental measurements obtained in a water model apparatus at Arcelor Research. Silicon oil was used to represent the lighter layer whilst air was pumped through the SEN to represent the argon

The effects of Thermoelectric Magnetohydrodynamics in directional solidification under a transverse magnetic field

The mechanism of macrosegregation and modification to dendrite size and spacing from a transverse magnetic field has been modelled through direct numerical simulation. The primary driver for this mechanism was identified as a strong Lorentz force formed in the interdendritic region, which leads to a large scale flow circulation. The microstructure evolution is modified by convective transport of solute and the predicted morphological features compare favourably to experimental data in the literature. The numerical results also give an insight into the magnitude of flow velocities within the interdendritic region.</p

The integration of structural mechanics into microstructure solidification modelling

In situ structural mechanics are an often neglected area when modelling alloy microstructure during solidification, despite the existence of practical examples and studies which seem to indicate that the interaction between thermal or mechanical stresses and microstructure can have a significant impact on its evolution and hence the final properties at a macroscopic level. A bespoke structural mechanics solver using the finite volume method has been developed to solve the linear elasticity equations, with design choices being made to facilitate the coupling of this solver to run in situ with an existing solidification model. The accuracy of the structural mechanics solver is verified against an analytic solution and initial results from a fully coupled system are presented which demonstrate in a fundamental example that the interaction between structural mechanics and a solidifying dendrite can lead to a significant change in growth behaviour

Modulating Meltpool Dynamics and Microstructure using Thermoelectric Magnetohydrodynamics in Additive Manufacturing

Meltpool modulation in Selective Laser Remelting Additive Manufacturing via an oscillating magnetic field generates Thermoelectric Magnetohydrodynamics (TEMHD) flow. Numerical predictions show that the resulting microstructure can be significantly altered. A multi-scale numerical model captures the meso-scale melt pool dynamics coupled to microscale solidification showing the microstructure evolution and solute redistribution. The results highlight the complex interaction of the various physical phenomena and also show the method's potential to disrupt the epitaxial growth defect. The model predictions are supported by preliminary experimental results that demonstrate the dependency of the melt pool depth on magnetic field orientation. The results highlight how a time-dependent field has the potential to provide an independent control mechanism to tailor microstructures

Growth of β intermetallic in an Al-Cu-Si alloy during directional solidification via machine learned 4D quantification

Fe contamination is a serious composition barrier for Al recycling. In Fe-containing Al-Si-Cu alloy, a brittle and plate-shaped β phase forms, degrading the mechanical properties. 4D (3D plus time) synchrotron X-ray tomography was used to observe the directional solidification of Fe-containing Al-Si-Cu alloy. The quantification of the coupled growth of the primary and β phase (Al5FeSi) via machine learning and particle tracking, demonstrates that the final size of the β intermetallics was strongly influenced by the solute segregation and space available for growth. The temperature gradient direction controlled the β orientation. The work can be used to validate predictive models

Inhaled corticosteroids reduce senescence in endothelial progenitor cells from COPD patients

Cellular senescence contributes to the pathophysiology of chronic obstructive pulmonary disease (COPD) and cardiovascular disease. Using endothelial-colony-forming-cells (ECFC), we have demonstrated accelerated senescence in smokers and COPD patients compared to non-smokers. Subgroup analysis suggests that ECFC from COPD patients on inhaledcorticosteroids (ICS) (n=14; 8 on ICS) exhibited significantly reduced senescence (Senescence-associated-beta galactosidase activity, p21CIP1), markers of DNA damage response (DDR) and IFN-γ-inducible-protein-10 compared to COPD patients not on ICS. In vitro studies using human-umbilical-vein-endothelial-cells showed a protective effect of ICS on the DDR, senescence and apoptosis caused by oxidative-stress, suggesting a protective molecular mechanism of action of corticosteroids on endothelium

PEGylated Domain I of Beta-2-Glycoprotein I Inhibits Thrombosis in a Chronic Mouse Model of the Antiphospholipid Syndrome

Antiphospholipid syndrome (APS) is an autoimmune disorder in which autoantibodies cause clinical effects of vascular thrombosis and pregnancy morbidity. The only evidence-based treatments are anticoagulant medications such as warfarin and heparin. These medications have a number of disadvantages, notably risk of haemorrhage. Therefore, there is a pressing need to develop new, more focused treatments that target the actual pathogenic disease process in APS. The pathogenic antibodies exert their effects by interacting with phospholipid-binding proteins, of which the most important is beta-2-glycoprotein I. This protein has five domains, of which the N-terminal Domain I (DI) is the main site for binding of pathogenic autoantibodies. We previously demonstrated bacterial expression of human DI and showed that this product could inhibit the ability of IgG from patients with APS (APS-IgG) to promote thrombosis in a mouse model. Since DI is a small 7kDa protein, its serum half-life would be too short to be therapeutically useful. We therefore used site-specific chemical addition of polyethylene glycol (PEG) to produce a larger variant of DI (PEG-DI) and showed that PEG-DI was equally effective as the non-PEGylated DI in inhibiting thrombosis caused by passive transfer of APS-IgG in mice. In this paper, we have used a mouse model that reflects human APS much more closely than the passive transfer of APS-IgG. In this model, the mice are immunized with human beta-2-glycoprotein I and develop endogenous anti-beta-2-glycoprotein I antibodies. When submitted to a pinch stimulus at the femoral vein, these mice develop clots. Our results show that PEG-DI inhibits production of thromboses in this model and also reduces expression of tissue factor in the aortas of the mice. No toxicity was seen in mice that received PEG-DI. Therefore, these results provide further evidence supporting possible efficacy of PEG-DI as a potential treatment for APS

Modulating meltpool dynamics and microstructure using thermoelectric magnetohydrodynamics in additive manufacturing

Meltpool modulation in Selective Laser Remelting Additive Manufacturing via an oscillating magnetic field generates Thermoelectric Magnetohydrodynamics (TEMHD) flow. Numerical predictions show that the resulting microstructure can be significantly altered. A multi-scale numerical model captures the meso-scale melt pool dynamics coupled to microscale solidification showing the microstructure evolution and solute redistribution. The results highlight the complex interaction of the various physical phenomena and also show the method’s potential to disrupt the epitaxial growth defect. The model predictions are supported by preliminary experimental results that demonstrate the dependency of the melt pool depth on magnetic field orientation. The results highlight how a time-dependent field has the potential to provide an independent control mechanism to tailor microstructures

Ultrasound induced fragmentation of primary Al3Zr crystals

© The Authors, 2020. Ultrasonic cavitation melt treatment (UST) of aluminium alloys has received considerable attention in the metal industry due to its simple and effective processing response. The refined primary intermetallic phases formed in the treated alloys during controlled solidification, govern alloy structural and mechanical properties for applications in the automotive and aerospace industries. Since the UST is performed close to the liquidus temperatures of the alloys, understanding the refinement mechanism of the primary intermetallic phases has been beset by difficulties in imaging and handling of liquid metals. In this paper, the sonofragmentation behaviour of primary intermetallic Al3Zr crystals extracted from the matrix of an Al-3 wt% Zr alloy and fixed on a solid substrate was investigated. The intermetallics were exposed to cavitation action in deionized water at 24 kHz of ultrasound frequency. The fragmentation mechanism from the nearby collapsing cavitation bubbles was studied with in-situ high speed imaging. Results revealed that the main fragmentation mechanism is associated with the propagation of shock wave emissions from the collapsing bubble clouds in the vicinity of the crystal. The mechanical properties of the Al3Zr phase determined previously were used for the fracture analysis. It was found that an Al3Zr intermetallic undergoes low cycle fatigue fracture due to the continuous interaction with the shock wave pressure. The magnitude of the resulting shear stress that leads to intermetallic fragmentation was found to be in the range of 0.6 – 1 MPa

Revealing the mechanisms by which magneto-hydrodynamics disrupts solidification microstructures

A key technique for controlling solidification microstructures is magneto-hydrodynamics (MHD), resulting from imposing a magnetic field to solidifying metals and alloys. Applications range from bulk stirring to flow control and turbulence damping via the induced Lorentz force. Over the past two decades the Lorentz force caused by the interaction of thermoelectric currents and the magnetic field, a MHD phenomenon known as Thermoelectric Magnetohydrodynamics (TEMHD), was also shown to drive inter-dendritic flow altering microstructural evolution. In this contribution, high-speed synchrotron X-ray tomography and computational simulation are coupled to reveal the evolution, dynamics and mechanisms of solidification within a magnetic field, resolving the complex interplay and competing flow effects arising from Lorentz forces of different origins. The study enabled us to reveal the mechanisms disrupting the traditional columnar dendritic solidification microstructure, ranging from an Archimedes screw-like structure, to one with a highly refined dendritic primary array. We also demonstrate that alloy composition can be tailored to increase or decrease the influence of MHD depending on the Seebeck coefficient and relative density of the primary phase and interdendritic liquid. This work paves the way towards novel computational and experimental methods of exploiting and optimising the application of MHD in solidification processes, together with the calculated design of novel alloys that utilise these forces