A study of the parameters affecting the particle velocity in cold-spray: Theoretical results and comparison with experimental data

Within coating applications, cold-spray is nowadays an extended technique commonly used in environments such as the additive manufacturing or repair industries. The differential factor that leads this approach to be chosen over others is its low deposition temperature. The need for ensuring the resistance and durability of the free-standing components has led to the development of models that can predict the kinetic energy of the particles, which is the main driving parameter affecting the deposit performance. In this study, an optimisation theoretical model, previously developed by the authors, is validated with the experimental exit particle velocity data taken from commercial geometries and using Fluent simulations available in literature. The aim of this work is to relate fundamental parameters in the cold-spray process such as the stagnation conditions, nozzle geometry, powder size or particle velocity. This objective is achieved by creating novel interdependent maps connecting these pivotal data by virtue of the model presented. Several graphs describing the final particle velocity depending on the stagnation pressure and temperature are obtained along with the optimal geometry for a wide range of materials (aluminium, titanium, steel, Inconel 625 and copper). In addition, the analytical model is able to hand over a deposition window of particle sizes and velocities that can be achieved using a specific cold-spray equipment. Both set of maps combined together can be a powerful tool which users and manufacturers can benefit from on the grounds that they do not only provide information about whether a deposition can be achieved or not with a cold-spray equipment but also about the stagnation conditions needed. The results obtained with this methodology reflect the limitations of low and medium-pressure equipment in terms of the maximum particle diameter that can be deposited and constitute a novel advance in the state of art of cold-spray. Moreover, the fundamental parameter regarding the geometry, namely the ratio between the nozzle exit and the nozzle throat diameters, is represented as a function of the above-mentioned parameters.