Coating of superplastic Ti-alloy substrates with Ti and Ti-O films by magnetron DC sputtering

In order to improve the biocompatibility of superplastic Ti-alloys such as Ti-6Al-4V or Ti-4.5Al-3V-2Fe-2Mo, coating of the alloy with pure titanium a nd Ti-O films by magnetron DC sputtering was examined. The sputter-depositi on of the pure titanium film and the Ti-O films were carried out in Ar gas and in Ar-O-2 gas mixtures, respectively. Both the pure titanium film depos ited in Ar and the Ti-O films deposited in Ar-O-2 appeared to be uniform an d adhesive. Under AES, the Ti/O ratio in depth direction was nearly constan t in each of the films and oxygen concentration increased with increasing o xygen content of the sputter gas. Based on XRD, it was concluded that oxyge n atoms dissolved into or-titanium crystals at lower oxygen contents, while suboxides such as Ti4O7 and Ti6O11 and oxides such as TiO2(anatase) were f ormed at higher oxygen contents. It was found that the orientation of the o r-titanium phase formed in the Ti-O films changed from (002) dominant to (0 11) dominant with increasing oxygen content. The Vickers hardness of the fi lms increased linearly with increasing oxygen content, and the maximum hard ness reached over Hv = 1600. Furthermore, it was found that the ductility o f the deposited pure titanium film was improved under such high temperature s as 800 degreesC and that its elongation reached over 160%, while the Ti-O films were still brittle under such a high temperature. (C) 2001 Elsevier Science B.V. All rights reserved.