In contrast to conventional thermal spray processes, in cold gas spraying coatings are produced without melting of the powder particles. A fundamental precondition for the bonding is a certain ductility of the spray material. The bonding of the particles is based on plastic deformation of the particles at impact and the heat generated thereby. It occurs when a minimum critical particle velocity is reached. This critical velocity does not only depend on the particles´ temperature but mainly on their mechanical and physical properties like density and melting temperature. Due to their high melting temperature and due to the fact that their ductility is essentially impaired by gaseous impurities most refractory metals are comparatively difficult to be applied by cold gas spraying.