Gas dynamic cold spray is a coating deposition method developed in the mid-1980s in the Soviet Union in The Institute of Theoretical and Applied Mechanics by Papyrin and his team. The solid powders (1 to 50 micrometers in diameter) are accelerated in supersonic gas jets to velocities up to 500–1000 m/s. During impact with the substrate, particles undergo plastic deformation and adhere to the surface. To achieve a uniform thickness the spraying nozzle is scanned along the substrate. Metals, polymers, and composite materials can be deposited using cold spraying. The kinetic energy of the particles, supplied by the expansion of the gas, is converted to plastic deformation energy during bonding. Unlike thermal spraying techniques e.g, plasma spraying, arc spraying, flame spraying, high velocity oxygen fuel (HVOF) the powders are not melted during the spraying process.
Contents |
The most prevailing bonding theory in cold spraying is attributed to "adiabatic shear instability" which occurs at the particle substrate interface at or beyond a certain velocity called critical velocity. When a spherical particle travelling at critical velocity impacts a substrate, a strong pressure field propagates spherically into the particle and substrate from the point of contact. As a result of this pressure field, a shear load is generated which accelerates the material laterally and causes localized shear straining. The shear loading under critical conditions leads to adiabatic shear instability where thermal softening is locally dominant over work strain and strain rate hardening, which leads to a discontinuous jump in strain and temperature and breakdown of flow stresses. This adiabatic shear instability phenomena results in viscous flow of material at an outward flowing direction with temperatures close to melting temperature of the material. This material jetting is also a known phenomenon in explosive welding of materials.[1] [2] [3]
Today, cold spray technology is used in a wide range of surfacing applications. In addition to repair and remanufacturing for aerospace and industrial components, the latest applications include rapid manufacturing and microsystems. A list of original cold spraying equipment manufacturers includes :
Other companies involved in the research and development of cold spraying:
GP LTD. Eqipment for Cold Gas Dynamic Metallization in Europe