Chapter 3 - Gas-dynamics of cold spray

Abstract

This chapter discusses the gas-dynamics and thermal effects associated with a supersonic jet exhausting from the nozzle and its interaction with the substrate in the cold spray method. To accelerate particles, two types of nozzles are used—nozzles with circular and rectangular sections. The chapter investigates the gas-dynamics of jets exhausting from conical nozzles with circular cross sections—symmetrical-axis flows. An analysis of the features of such jets, as applied to the cold spray method, reveal that the use of nozzles with rectangular cross sections is also significant. With the same ratio of the nozzle-exit and throat cross sections, nozzles with a rectangular section can provide a wider spray beam in the direction of the smaller size of the section and a narrower beam in the direction of the larger size of the section. Such nozzles can also decrease the effect of particle deceleration in the compressed layer in front of the substrate by decreasing the thickness of the layer itself. The issues of acceleration of finely dispersed particles in supersonic nozzles and formation of flat and comparatively thin two-phase jets, which ensure high deposition efficiency over the area, are of significant interest in the process of cold spray. The chapter concludes that the particle velocity reached immediately before the impact on the substrate plays the most important role in deposition of coatings by cold spray method.