Cold spray (CS) is being use in both civil aviation and military aircraft fleets as a method for repairing obsolete or damaged parts mainly for dimensional repair. There is ongoing research by the United States Office of Naval Research examining the corrosion and mechanical property equivalency of CS repairs on aluminum alloys for structural applications on aircraft. Recent testing has shown that CS repairs of fatigue sample geometries with 15-30% blend outs are able to improve fatigue life to near that of an undamaged fatigue sample at two stress ratios. Tensile coupons with 15% CS repairs have also shown tensile properties within 90% of wrought material for two alloy systems. Other material property investigations, including corrosion, using this repair process are underway. Another key item requiring understanding for using cold spray on aircraft repair is the corrosion development and how it compared to conventional alloys. These combined results are critical to showing CS can be used to complete repairs of structural aircraft components.
Cold Spray (CS) is a solid-state deposition repair method that deposits 1-50um powder particles onto a substrate. A compressed gas acts as carrier to accelerate the particles through a converging-diverging nozzle to the substrate at supersonic speeds [1]. Critical impact velocity is the velocity that is required to achieve sufficient bonding. CS process parameters as well as powder properties can be adjusted to achieve such velocities [2]. The type of carrier gas will also change the spray velocity. Helium has the lowest molecular weight which allows for higher gas and particle velocity upon impact [3][4][5].
Historically, CS has been used as a surface coating, to aid in prevention of corrosion and surface wear. In recent years, CS has been used to make dimensional repairs to non-structural parts. With the improvement shown in mechanical properties, research to show the corrosivity of CS is required. Ngai et al showed the direct correlation between increasing porosity and increasing corrosivity. The presence of large intermetallic precipitates also increased corrosivity [6]. Industry research has shown the higher impact velocities of Helium sprays leads to lower porosity rates. [7]
