2. Gas Flow, Particle Acceleration and Heat Transfer in Cold Spray Additive Manufacturing

In CSAM, successful particle deposition requires the particles to achieve a higher velocity than critical velocity. Therefore, a thorough understanding of particle acceleration and heating behavior inside and outside a cold spray nozzle is critical for developing high-performance cold sprayed deposits. Over the years, much effort has been devoted to investigate the supersonic gas flow and the consequent particle acceleration and heating behavior inside and outside the nozzle. Experimental investigation is the most direct way to clarify these physical phenomena involved in cold spray process. However, the relatively high money- and timing- cost, especially the infeasibility to capture all the flow features (e.g. flow velocity, temperature, density and turbulence properties) inside and outside the nozzle significantly limits the wide application of experimental approach. To deal with this problem, analytical and numerical modeling were developed and employed in many studies. In the early stage, various analytical models were developed to predict the gas flow properties and particle velocity. These analytical models, mainly one-dimensional (1D) model, normally introduced assumptions and simplifications to the real physical problems, thus the prediction accuracy may be not satisfactory. Thanks to the rapid growth of the computer power, computational fluid dynamics (CFD) technique has become a popular approach to predict the gas flow properties and particle velocity in cold spray. It is highly flexible to simulate the gas flow at different working conditions and costs less than experiment. This chapter provides a comprehensive introduction on the gas flow, particle acceleration, and heat transfer behavior in cold spray.