Nanostructure formation and its effects on the mechanical properties of kinetic sprayed titanium coating

The nanostructure formation during kinetic spraying of commercially pure titanium (CP-Ti) were studied using transmission electron microscopy (TEM) and finite element modeling (FEM) considering conductive heat transfer. The high-velocity impacted particles, subjected to severe plastic deformation (SPD), were found to be tightly bonded, and also considerably homogeneous and randomly orientated equiaxed nanograins, including some recovered grains having a low dislocation density, were found to be formed over wide areas inside the coating due to strain accumulation and the resultant thermal history enhanced by subsequent impacts of the particles. The bimodal grain structure consisting of both larger grains having high-density dislocations (>250 nm) and smaller dislocation-free grains with non-equilibrium grain boundaries (<100 nm) was determined to be associated with both the strain hardening and the ductile dimple fracture of the coating.