Z. Zhao, B. A. Gillispie, T. Han, Delphi Research Labs, Shelby Township, MI
The kinetic spray process is a coating process that involves impingement of a substrate by metallic particles at high particle velocities. During the last several years, significant advancements in the fundamental understanding of the process have been made at Delphi Research Labs, which allowed us to greatly to enhance our capability in spraying difficult-to-deposit materials, especially with relatively large particles as feedstock and compressed nitrogen as the propellant gas (a challenging combination). In this work, we investigated coatings that were kinetically sprayed using large particles (53-150 mm). The emphasis is placed on understanding the effect of powder particles on the coating formation by the kinetic spray process. The examined particle characteristics in the present study include particle size, shape and morphology, and microstructure. The results indicated that the coating formation by the kinetic spray process is controlled primarily by two fundamental variables of sprayed particles: particle velocity and particle temperature. Very large sized particles, in spite of their relatively low particle velocities (as a result of acceleration by nitrogen rather than helium), can be rendered to exhibit enhanced sprayability, comparable to smaller size particles. This can be achieved by properly controlling the particle temperatures. It is found that kinetic spray using large size particles (~100 mm) can lead to relatively dense coatings with relatively high deposition efficiencies.
Summary: This work includes both experimental studies and computational simulations. The focus is primarily on the effects of various powder characteristics on the coating formation by the kinetic spray process.
