Comparative Study on the Properties of Ti-6Al-4V Coatings Deposited by High Velocity Thermal Spray Methods

Thermal Spray Technology is emerging as an interesting alternative method to welding, metal deposition and laser cladding. Besides conventional spraying processes like Plasma Spray, Powder Flame Spray, Wire Flame Spray, and High-Velocity-Oxy-Fuel spray (HVOF), recent development of High-Velocity-Air-Fuel (HVAF) and Cold Gas Dynamic Spray (CGDS) processes have demonstrated excellent aptitudes to deposit coatings of oxidation sensitive materials, such as Titanium alloys, due to processing at lower particle temperature combined with high particle velocity . In the present study, HVAF and CGDS processes have been used to apply Ti-6Al-4V coatings onto substrates of similar material. The objective was to establish the state-of-the-art feasibility of handing out CGDS and HVAF processes for repair applications of Ti-based alloys in the aerospace industry. Coating properties were evaluated through microstructure analysis, Vickers and Rockwell hardness testing, tensile adhesion strength and Young’s modulus evaluation by four-point bending test. Whereas HVAF sprayed coatings still exhibited a large inhomogeneous microstructure with high amount of oxides, CGDS process provided an oxides-free state with a low porosity level, conferring to the Ti-6Al-4V coating high adhesion strength to the substrate and relatively good mechanical properties.