Micro- and nanostructure of a titanium surface electric-spark-doped with tantalum and modified by high-frequency currents

We have studied the characteristics of the porous microstructure of tantalum coatings obtained by means of electric spark spraying on the surface of commercial grade titanium. It is established that, at an electric spark current within 0.8–2.2 A, a mechanically strong tantalum coating microstructure is formed with an average protrusion size of 5.1–5.4 $\mu$m and pore sizes from 3.5 to 9.2 $\mu$m. On the nanoscale, a structurally heterogeneous state of coatings has been achieved by subsequent thermal modification at 800–830$^\circ$C with the aid of high-frequency currents. A metal oxide nanostructure with grain sizes from 40 to 120 nm is formed by short-time ($\sim$30 s) thermal modification. The coating hardness reaches 9.5–10.5 GPa at an elastic modulus of 400–550 GPa.