gas temperature the main gas temperature is defined as the temperature of heated high pressure gas at the inlet to the nozzle 54 since these temperatures are chosen so that they heat the particles to a temperature that is less than the melting temperature of the particles even upon impact there is no change in the solid phase of the original particles due to transfer of kinetic and thermal energy and therefore no change in their original physical properties the particles themselves are always at a temperature below their melt temperature the particles exiting the nozzle 54 are directed toward a surface of a substrate to coat it upon striking a substrate opposite the nozzle 54 the particles flatten into a nub like structure with an aspect ratio of generally about 5 to 1 when the substrate is a metal and the particles are a metal the particles striking the substrate surface fracture the oxidation on the surface layer and subsequently form a direct metal to metal bond between the metal particle and the metal substrate upon impact the kinetic sprayed particles transfer substantially all of their kinetic and thermal energy to the substrate surface and stick if their yield stress has been exceeded as discussed above for a given particle to adhere to a substrate it is necessary that it reach or exceed its critical velocity which is defined as the velocity where at it will adhere to a substrate when it strikes the substrate after exiting the nozzle 54 this critical velocity is dependent on the material composition of the particle in general harder materials must achieve a higher.