What is Particles

This chapter is focused on cold spray deposition of particles for surface modification. The method, which has been recently proven to have wide applicability in the domain of tribology and wear-resistant coatings, relies on supersonic gaseous jets to deposit the particle without phase change. The chapter aims at examining the influence of the unique gas dynamic characteristics of the high-speed jets on the deposition process. The general structure of the supersonic jets, including the velocity field, pressure gradients, and the impingement behaviour, is discussed with specific attention to the requirements of the sprays for tribological coatings. Results of detailed numerical simulation of the impingement process are made use of to demonstrate the parametric influence of the supersonic jet structure on critical spray characteristics, like the particle velocity. The study also examines various aspects of the energy conversion as applied to the basic nature of the supersonic jet as well as its interaction with the microparticles.