Cold Spray Deposition of a Powder Produced from a Beta Titanium Alloy
TWI Industrial Member Report 1163-2023 [pdf / 4101 KB]
By Henry Begg, Feifei Zhang and Heidi Lovelock
Cold spray is a promising technology for the repair of titanium alloys as material can be deposited without significant oxidation and with no thermal input into the substrate, which could affect the underlying metallurgical condition of the part.
However, achieving sufficiently dense, well-bonded coatings using a cost effective process gas (i.e. nitrogen) has proved challenging to date. Attempts at repair often aim to use a deposit with the same composition to that of the substrate. This ensures that properties such as coefficient of thermal expansion and Young’s modulus match as well as possible. Similar composition also ensures that any galvanic couples formed between substrate and deposit are minimised in corrosive environments. However, for high density material to be deposited, impacting powder particles must adequately deform to ensure pores are not formed.
In titanium alloys such as Ti-6Al-4V, it is thought that the powders produced from conventional gas atomisation have limited ductility due to their microstructure of primarily of hexagonal close packed alpha (or alpha’). As such, depositing alternative titanium alloys with greater ductility may provide a route to higher performance deposits, despite issues surrounding depositing a dissimilar metal combination.
- Powders produced from both Ti-6Al-4V and Ti-10V-2Fe-3Al by gas atomisation exhibit non-equilibrium microstructures comprising various martensitic phases.
- Cold spray deposits using both powders exhibited high deposition efficiencies, but produced coatings with minimal difference in porosity (~3% in both cases).
- Coatings produced from Ti-10V-2Fe-3Al exhibited higher adhesion strength, but lower cohesive strength than similar coatings produced from Ti-6Al-4V.
Backscattered SEM micrograph of cold spray deposited Ti-6Al-4V
Backscattered SEM micrograph of cold spray deposited Ti-10V-2Fe-3Al