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Cold-spray,Cool Coating without Dangers.SOLUTIONS with Effective, Practical Advice
Cold-spray was introduced to our readers in short notes published along the years in the periodic publication Practical Welding Letter, distributed at no cost to subscribers.
In particular, references can be found in the following issues: PWL#022, #034, #036, #054, #061, #067, #068.
Cold Spray, or Gas Dynamic Cold Spray, is a materials deposition process developed in the mid-1980s in the Soviet Union. It consists in exposing a metallic or dielectric substrate to a high velocity (300–1200 meters per second) stream of small size (1–50 microns) particles accelerated by a supersonic jet of compressed gas.
The success of this process is based on the critical selection of the best combination of particle temperature, velocity, density and size that allows spraying at the lowest possible temperature. Similar in principle to other thermal spray methods, it follows the trend of increasing particle spray velocity and reducing particle temperature. It is the next progressive step in the development of high kinetic energy coating processes. In this process, powder particles are accelerated by the supersonic gas jet at a temperature that is always lower than the melting point of the material. This results in coating formation from particles that remain all time in the solid state. Therefore harmful effects are minimized or eliminated. Those common problems for traditional thermal spray methods are high-temperature oxidation, evaporation, melting, crystal formation, residual stresses, debonding, gas release, and more.
In Cold spray, high temperatures and their effects are absent from coatings and substrates. This fact offers significant advantages and makes cold spray promising for many industrial applications. The nozzle is moved along the substrate to obtain a uniform coating. Metals, polymers, and composite materials can be deposited using Cold-spray. The Cold-spray process uses the energy stored in high pressure compressed gas, usually helium or nitrogen, to propel fine powder particles at very high velocities. The gas is fed, via a heating unit to avoid expansion freezing, to a Laval type convergent-divergent nozzle, emerging therefrom at very high speed. Powder material is introduced into the high velocity gas jet by a secondary stream of compressed gas through the high pressure powder feeder. The accelerated powder particles impact at high speed onto the substrate, where they undergo plastic deformation, and bond to the surface in a dense layer, creating a Cold-spray coating. The solid state of the particles is not altered by the process as they remain relatively cold. In Cold spray, the kinetic energy (particle velocity) is increased and the thermal energy reduced. In this way it is possible to produce coatings virtually free of oxides. Cold-spray bonding is well adherent, with low shrinkage on cooling. The high strain induced on impact tends to stress the coatings in compression, thereby improving their properties. The original powder chemistry and phases present in the coating are retained during the process due to the low temperatures. Only their shape is changed by impact deformation and cold working. Laboratory investigations show that cold spray coating have extremely high bond strengths and are exceptionally dense. Cold-spray Process Advantages:
aerospace, automotive, biomedical, chemical, electronics, mineral processing, printing, oil and gas, glass and many others. Besides the main use as a coating process, Cold-spray has been already applied successfully for free forming processes, called rapid prototyping, building selected areas layer by layer, to generate complex tridimensional bodies. Find here one book on Cold Spray
See also the following: MIL-STD-3021 An Article on Direct Write Technology was published (11) in Issue 136 of Practical Welding Letter for December 2014>. An Article on High Pressure Cold Spray was published (7) in Issue 142 of Practical Welding Letter for June 2015. An Article on Acoustic Imaging for process quality control was published (3) in Issue 143 of Practical Welding Letter for July 2015. An Article on Aluminum Filler Metal for High Pressure Cold Spray of Magnesium Castings was published (4) in Issue 151 of Practical Welding Letter for March 2016. An Article on Cold Spray Repairs was published (2) in Issue 154 of Practical Welding Letter for June 2016. An Article on Cold Spray Characterization was published (7) in Issue 156 of Practical Welding Letter for August 2016. An Article on New issue of iTSSe was published (2) in Issue 165 of Practical Welding Letter for May 2017.
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To reach a Guide to the collection of the most important Articles from Past Issues of Practical Welding Letter, click on Welding Topics.
Cold welding
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