Cold spray, also known as Cold Gas Dynamic Spray(CGDS),introduces high pressure compressed gas (air pressure of 0.7 to 3.5 MPa,N2,He or mixed gas )into a shrink-expanded Laval nozzle ,and the air flow passed through the nozzle .Supersonic flow occurs after the throat ,and then the sprayed particles(particle size is generally 5 to 50 um)are fed axially from the upstream of the nozzle ,and the velocity is accelerated to about 300 to 120m/s after passing through the entire nozzle to form a high-speed particle jet.In the spraying distance(about 5 to 50 mm),the collision with the substrate undergoes severe plastic deformation to deposit a coating.

The structure of the cold spray coatings

    The upper part of Fig. shows the formation mechanism of the cold spray coating under microscopic conditions,The lower left side is a cold sprayed aluminum coating.It can be cleary seen that the cold spray coating is substantially free of pores and oxide inclusions.

Cold spray characteristics

    The beam temperature is low,generally between 0 and 600°C ，and the highest is only 1000°C;

    The particles are still in a solid state;

    High particle velocity,supersonic speed 500~1000m/s;

    The substrate has a small heat influence and a small residual stress(compressive stress),and a high-thickness coating can be prepared;

    High bonding strength,can reach more than 100MPa;

    The coating is dense,the pores are small ,the density is up to 98%,and the high thermal conductivity and high conductivity coating can be prepared;

    No adversr effects such as oxidation,phase change,segregation,grain growth;

    The spray deposition rate (DE) is high, between 80-90%.