CSAT - Cold Spray Factoid #4

The power of cold spray is clear. The underlying science of its bonding? Not so clear... Here is our final cold-spray fact leading up to CSAT and LSAAT.

Some believe that the strong bonding in cold spray coatings is a result of 'adiabatic shear instability' at the particle-substrate interface. Upon high-velocity impact, intense plastic deformation generates localized heat, leading to a temporary decrease in material strength and further deformation. This facilitates a jetting phenomenon, creating a mechanical interlock and a metallurgical bond without melting.

Alternatively, there is hydrodynamic plasticity (jetting/spallation), which is primarily a pressure-driven phenomenon. Here, the strong pressure waves interact with the expanding edge of the particle and the material in the jetting region is prone to localized fragmentation

Experimentally, everyone agrees that it works! Which theory do you find most compelling?

Particle Splat vs. Critical Velocity (Photo creds (Micrographs) by Kiran Judd, Ph.D. at Worcester Polytechnic Institute)