Cold spray, also referred to as supersonic particle deposition, is a high-energy solid-state coating and powder consolidation process. It is an efficient method for the application of metals, metal alloys, and metal blends for numerous applications.
Cold spray uses an electrically heated high-pressure carrier gas, like nitrogen or helium, to accelerate metal powders through a supersonic de Laval nozzle above a critical velocity for particle adhesion. The bonding mechanism is a combination of mechanical interlocking and metallurgical bonding from re-crystallization at highly strained particle interfaces.
Cold spray can create mixtures of metallic and nonmetallic particulates to form a coating or freestanding structure by means of ballistic impingement upon a substrate. The cold spray process is applicable to corrosion-resistant coatings (zinc and aluminum), dimensional restoration and repair (nickel, stainless steel, titanium, and aluminum), wear-resistant coatings (chromium carbide – nickel chromium, tungsten carbide – cobalt, and tungsten copper), electromagnetic interference (EMI) shielding of components and structures, high strength dissimilar material coatings for unique manufacturing solutions, and field repair of components and systems.
There are many benefits to using cold spray in lieu of thermal sprays, including:
Cold spray presents some fascinating microstructural characteristics:
Adhesion strength > 10 ksi [68 MPa]
High strengths > 100 ksi [689 MPa]
Hardness: 407 HV
Cold spray is in the family of thermal spray processes; however, it has the lowest overall temperatures and highest velocities of the thermal spray family. As a result, cold spray coatings are deposited in the solid state and possess the highest strengths of any thermal spray process.
Cold spray coatings can generally retain bulk powder microstructure except in regions of extreme plastic deformation at particle boundaries, where dynamic recrystallization can occur resulting in a submicron grain structure and high levels of particle-particle bonding, and it does not increase the oxide content in the coating over the base oxygen level present in the starting powder. Because it is a solid-state process, the coatings are in a generally compressive, rather than tensile, residual stress state. This can have a positive impact on fatigue and mechanical strength of the coating.
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