Study on the surface modification of nanostructured Ti alloys and coarse-grained Ti alloys

Commercial purity titanium (CP-Ti) and a Ti-6Al-4V alloy (Ti64) were processed by high-pressure torsion (HPT) to 10 and 20 turns. The HPT processing produced a nanostructured microstructure and a significant strength enhancement in the CP-Ti and Ti64 samples. After 20 turns the samples of HPT-processed CP-Ti and Ti64 were subjected to laser surface treatments in an air atmosphere using different scanning speeds and laser powers. The surface roughness of the laser-modified samples increased with increasing laser power and this produced a hydrophilicity due to a lower contact angle. After a holding time of 27 days, these samples underwent a hydro-philic-to-hydrophobic transformation as the contact angle increased from 13 to as much as 120 for the CP-Ti sample and for the Ti64 sample the contact angle increased from 10 to 126. In addition, the laser surface modification process was carried out with different atmospheres (air, vacuum and O2) on heat-treated but unstrained CP-Ti and Ti64 samples and the contact angle changed due to the surface element content. Thus, as the carbon content increased from 28% to 47% in CP-Ti in vacuum environment, the surface contact angle increased from 22 to 140. When a laser surface modifi-cation process is conducted under oxygen-less conditions, it is concluded that the contact angle increases rapidly in order to control the hydrophobic properties of Ti and the Ti alloy