Enhancement of Ti-6Al-4V powder surface properties for cold spray deposition using fluidized Gas-Nitriding technique

Abstract

Modification of Ti-6Al-4V powder surface was achieved by treating fluidized powder in N2 gas at 700 °C and 800 °C for hold times between 10 and 30 min. The technique is expected to lower surface oxygen content, and improve material properties such as flowability, resistance to moisture adsorption, etc. A relative increase in surface nitrogen content was observed with increasing reaction temperature and soak time. Analysis by X-ray photoelectron spectroscopy (XPS) indicated the removal of oxides, hydroxyl groups, and other oxygen species with an increase in the atomic N/O and Ti/O ratios at the surface. Gas-nitriding of Ti-6Al-4V at 700 °C and 800 °C for 30 min resulted in an increase of the surface N/O atomic ratio from 0.02 to 0.56 and 0.76, respectively. The surface reaction with nitrogen did not affect the bulk structure or morphology of the powder. This was evidenced by XRD results indicating that there was no bulk phase TiN present or any significant change in the d-spacing values for characteristic Ti-6Al-4V peaks. Additionally, there was no significant increase in surface hardness of substrates following the deposition of nitrided powders. Nitriding of Ti-6Al-4V improved powder performance during cold spray deposition by eliminating nozzle fouling and reducing porosity in deposited layers.