Formation of Fine Holes and Protrusions on Ti-6Al-4V Alloy by Argon-Ion Sputter-Etching

Fabrication of fine surface textures is one of the most effective technologies to provide new functions for materials. In this research, argon-ion sputter-etching was applied to an α+β type Ti-6Al-4V alloy placed on a SUS304 steel disk at a radio frequency power of 200 W, 250 W and 300 W for 0.9 ks to 21.6 ks. For the 1013 K annealed specimens, fine holes smaller than 500 nm diameters were densely formed on the surfaces when the sputter power was 250 W and sputter time was 0.9 ks. However, when the sputter time increased to more than 1.8 ks, the holes disappeared and the groups of grain-shaped protrusions were formed in flat areas. For the 1323 K solution-treated specimens, the fine holes were also formed at the sputter power of 250 W and at a sputter time shorter than 1.8 ks. The holes connected to ridge-shaped protrusions with increasing sputter time and finally changed to independent and uniformly distributed protrusions. Energy dispersive X-ray analyses revealed an increase in the V and Fe contents on the sputtered surface. This corresponds that the Fe particles arrived from the SUS304 disk dissolved into the alloy and strongly combined with V atoms, which resulted in the selective sputtering of Al and Ti. It is considered that the argon ion radiation has induced the decomposition of surface region to fine areas with different V and Fe contents, and the fine holes are formed by preferential sputtering of the lower V and Fe contents areas.