表面涂覆技术概述.ppt

High velocity oxyfuel(HVOF) spraying the versatile, high deposition rate thermal spraying process for dense, high performance coatings Principle: The Detonation gun basically consists of a long water cooled barrel with inlet valves for gases and powder. Oxygen and fuel (acetylene most common) is fed into the barrel along with a charge of powder. A spark is used to ignite the gas mixture and the resulting detonation heats and accelerates the powder to supersonic velocity down the barrel. A pulse of nitrogen is used to purge the barrel after each detonation. This process is repeated many times a second. The high kinetic energy of the hot powder particles on impact with the substrate result in a build up of a very dense and strong coating. Detonation Thermal Spraying Process Cold spray coating process Dr Antolli Papyrin and colleagues at the Russian Academy of Sciences were the first to demonstrate the cold spray process in the mid-1980s.Principle: The Cold Spray process basically uses the energy stored in high pressure compressed gas to propel fine powder particles at very high velocities (500 - 1500 m/s). Compressed gas (usually helium) is fed via a heating unit to the gun where the gas exits through a specially designed nozzle (laval type mostly) at very high velocity. Compressed gas is also fed via a high pressure powder feeder to introduce powder material into the high velocity gas jet. The powder particles are accelerated? and moderately heated to a certain velocity and temperature where on impact with a substrate they deform? and bond to form a coating. As with the other processes a fine balance between particle size, density, temperature and velocity are important criteria to achieve the desired coating. Characteristics of cold spray process The particles remain in the solid state and are relatively cold, so the bulk reaction on impact is solid state only. The process imparts little to no oxidation to the spray material, so surfaces stay clean which aids