Effect of Particle Morphology and Size Distribution on Cold-Sprayed Pure Titanium Coatings

The effects of commercially pure titanium particle morphology (spherical, sponge, and irregular) and size distributions (mean particle sizes of 20-49 mu m) on the cold spray process and resulting coating properties were investigated. Numerous powder and coating characterizations were performed including: powder oxygen and nitrogen contents, powder flowability, powder compressibility, coating microhardness, coating porosity, LOM/SEM analyses, and XRD. Compared to spherical powders, the sponge and irregular CP-Ti powders had higher oxygen content, poorer powder flowability, higher compression ratio, lower powder packing factor, and higher average particle impact velocities. XRD results showed no new phases present when comparing the various feedstock powders to corresponding coatings. A higher particle temperature was also obtained with larger particle size for all feedstock powder morphologies processed with the same set of spray parameters. A spherical powder with 29 mu m mean particle size was found to have the lowest porosity coating and best cold sprayability. The relationships of several as-cold sprayed coating characteristics to the ratio of particle impact and critical velocities were also discussed.