Cold Spray Characteristics of Commercially Pure Ti and Ti-6Al-4V

Abstract

Ti and Ti-6Al-4V coatings were deposited by cold gas dynamic spray process using nitrogen as propellant gas. For Ti, the inlet gas temperature and pressure were varied for two different powder morphologies in such a way that the average particle velocity ranged from ~600 to 850 m/s. In addition, the nozzle traverse speed was varied. For all conditions, the deposition efficiency, the porosity, and the microhardness were measured. It is shown that the porosity level decreased as the gas temperature and pressure increased, whereas the velocity, deposition efficiency, and microhardness increased. Furthermore, it is observed that a lower nozzle traverse speed engendered a softer coating. The coating adhesion on a grit 24 Al2O3 blasted mild steel surface was established to be greater than 78.8 MPa. In addition, a Ti-6Al-4V coating was produced and was determined to be slightly more porous compared to a CP Ti coating.

Mechanical behavior of Ti cold spray coatings determined by a multi-scale indentation method

“…Average deposition velocities ranging from 608 to 805 m/s were obtained for spherical coatings and from 652 to 859 m/s for non-spherical coatings. The higher average velocity obtained for non-spherical powder compared to spherical powder is typically explained by the higher drag forces experienced by the irregular powder [31,36]. For one coating sprayed with He and spherical powder, the deposition velocity reached 1173 m/s.…”

“…The size and morphology of the powders were reported previously [31]. The average particle diameters of the powders were 29 m for the spherical powder and 63 m for the non-spherical.…”

“…The difference in the true hardness between coatings prepared with the different powders may be due to differences in the starting powders and the way they deform upon impact. A higher oxygen content in the non-spherical powder [31] compared to the spherical powder may explain some of the increase in hardness.…”

“…For each coating, a total of ten micrographs were collected at 500× magnification, from which an average porosity was calculated. It should be noted that the porosity and microstructural characterization carried out was for the same coatings, but for cross-sections a few millimeters away from the cross-sections in previous reports [31]. Porosity was measured across the coating thickness (approximately 50 m away from the coating -substrate interface and the coating surface regions) using a commercially available image analysis software (Clemex Vision Fig.…”

“…Many of the general aspects of deposition and starting materials, including measurements of velocity, the size, morphology, composition and microstructure of the powders were previously published [31,32]. Briefly summarizing sample preparation, coatings prepared with nitrogen had gas pressures from 2 MPa to 4 MPa and gas preheat temperatures ranging from 300 • C to 800 • C. The Ti powders were fed at a rate of 20 g/min at a gun standoff distance of 4 cm.…”