Structural repair using cold spray technology for enhanced sustainability of high value assets

Abstract

Cold spray technology has been in significant development since the early 1990s, however, not until recently has it begun to approach near wrought like properties for metals and alloys of aluminum, copper, nickel, titanium, as well as steels, stainless steels, superalloys, and refractory metals like niobium and tantalum. These advancements have come through the use of high pressure cold spray equipment and a greater fundamental understanding of the process variables. As a result, numerous applications have been developed for repairing high cost and long lead time parts for the aerospace and defense market, as well as a broad range of commercial markets such as oil & gas, transportation, and heavy industry. In particular, parts with lead times in excess of 12 months have been successfully repaired and re-introduced into service. This saves not only the direct cost of the part, but also returns the system to service much sooner. Cold spray is an additive manufacturing technology that uses heated high-pressure inert gas to accelerate metal powders through a converging-diverging de Laval nozzle above the critical velocity for deposition onto a substrate. The process produces only mild heating of the substrate compared to most conventional metal deposition or welding technologies, hence the nomenclature of "cold" in cold spray, even though there is heating of the gas in almost all cases. There are also no toxic fumes or other harmful emissions from cold spray because the accelerant gases are: 1) inert (helium, nitrogen, or air), and 2) the heating source is electric and is controlled at temperatures below the melting temperature of the material being sprayed. Furthermore, because parts are being repaired and refurbished rather than replaced, there is tremendous cost, energy, and overall environmental benefit, making cold spray a very "green" technology and an excellent technology for enhancing the long-term sustainability of high value assets.