Cold Spray of Titanium

Cold Spray of Titanium

M. Jahedi, P. King, S. Zahiri, S. Gulizia, C. Tang

CSIRO Future Manufacturing Flagship

Gate 5, Normanby Road, Clayton, Vic 3168, Australia

CSIRO has invested generously in titanium research for more than a decade. The Cold Spray Team at Titanium Technologies Theme recognised the potential of cold spray technology for direct manufacturing and successfully adapted it for the direct manufacture of titanium components ranging from titanium billet, pipe and complex shape products. CSIRO has developed an innovative technology for direct manufacturing of continuous seamless titanium pipe using Cold Spray.

In Cold Spray, micron size particles are accelerated in the solid state by an inert, supersonic gas flow and impact against a substrate surface, resulting in the build up of a deposit.  Since in-flight temperatures do not approach melting point, many of the problems associated with high temperature thermal spray techniques such as melting, vaporisation, oxidation and thermal stresses, are avoided. In deposition the particles are deformed in solid state, bond together and the result is a cold rolled structure. In the absence of the melting and solidification the defects such as shrinkage porosity and gas entrapment can be avoided. Another advantage of the cold spray is no limit for size.

In this study the processes of bonding and microstructural evolution in cold sprayed titanium are investigated.  Two different commerical titanium powders were cold sprayed, and shown to have undergone plastic deformation at very high strain rates, resulting in extensive refinement in microstructure.  Large nanostructured areas were produced with high dislocation densities and subgrain sizes less than 100 nm.  Dense dislocation tangles, twins and elongated subgrains were observed in other places.  Adhesion of titanium particles occured due the formation of adiabatic shear bands at the particle interfaces.  The disruption of oxide films was observed there.