To use titanium alloys with excellent properties as prosthetic materials, the amount of the oxide film produced after firing and its physical properties, which have major effects on their binding with porcelain, were studied in pure titanium and Ti-6Al-4V alloy.
The following results were obtained:
1. The amount of the oxide film was related to conditions of firing. It was greater as the rate of the increase in the temperature was slower, the duration of firing was longer, and the final firing temperature was higher.
2. The color of the oxide film was also related to conditions of firing. Pure titanium became whiter, and Ti-6Al-4V alloy became browner, as the amount of film produced was greater.
3. The hardness was similarly related to the amount of film produced. The materials were harder as the film was thicker.
4. At 1, 000°C the expansion rate of Ti-6Al-4V alloy was about twice that of pure titanium. The coefficient of expansion of the alloy was also slightly greater at 200-700°C. Pure titanium has a transition point near 885°C at which the crystalline structure changes from α-phase to β-phase, but this transition point was not observed in Ti-6Al-4V alloy.