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Periodic Report Summary 1 - SSAM (The development of advanced numerical tools to study and control supersonic particle beams in Cold Spray)

Current methods for the manufacturing of metallic coatings onto non-metallic surfaces are slow, limited in size and to a small range of feedstock materials. Also, they require time-consuming masking steps or complex etching procedures, have low bond strengths, and are coming under very strong pressure to limit their environmental impact through the elimination of toxic waste products.
This project investigates the revolutionary powder-based technology Cold Spray (CS). The deposit formation is completely solid-state (free of melting), and it is possible through the acceleration of the feedstock powders up to supersonic velocities in a nozzle and their high-energy impact onto the substrate. This programme, Supersonic Spray Advanced Modelling – SSAM – will generate the required computational tools to study and control the particle acceleration process, and will set the ground for further research and development.
In this regard, a novel Computational Fluid Dynamics (CFD) simulation tool was developed to accurately predict the particle dynamics in supersonic CS-nozzles. The core of this model is the interaction between the gas phase and the powder particles within the nozzle flow. State-of-the-art simulations are based on the assumption that the volume occupied by particles and their interaction with the gas is low enough to neglect any feed-back on the gas phase. It was shown that this is not justified in many circumstances. The underlying mathematical models were extended by additional force components and the direct gas-solid coupling. The validation procedure against particle velocity measurements using Particle Image Velocimetry (PIV) revealed experimentally that the particle feed rate has a significant effect on the final particle velocity; it decreases as the amount of powder increases. This observation, considered unimportant in previous studies, can lead to drastic reduction of the deposition efficiency. The developed type of model was shown to work well for variable particle feed rates with spherically shaped powders. The behaviour of irregular particles is more challenging to calculate and can be kept within errors of ca. 10%. Moreover, the distribution of particles and their velocity is affected. In order to amend the manufacturing process, the aim is to fully understand and enable simulation of this particle behaviour. Consequently, a high precision particle spray beam can be generated and manipulated based on this knowledge.
Further improvement of the current version of the model will enable the design of a device for mask-free, environmentally friendly and low-cost deposition by means of high precision control of the particle beam. In this regard, the CS-site at Trinity College Dublin will be a precursor facility for research in the field of additive manufacturing of complex geometries using metallic coatings onto non-metallic surfaces, which will influence high-tech industries, such as aerospace, automotive, energy systems and many more. This long term goal will strengthen the status of the Department of Mechanical and Manufacturing Engineering at Trinity College Dublin in Europe as a top-ranked education and research institution and establish the Cold Spray research group within the field.

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Life Sciences
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