熱処理によるチタンインプラント材の機械的性質の変化

抄録

Removal of residual strain in titanium materials caused by machining leads to decreases in their tensile strength and hardness. However, such a decrease is not considered to be problematic provided their strength is sufficient to bear occlusal pressure. Furthermore, the elongation percentage of titanium materials of certain diameters deviates from the standard value established by JIS, leading to decreases in their fatigue destruction strength. It is considered that if the fatigue destruction strength can be improved, stable mastication can be obtained for a long time after implantation. Therefore, heat treatment of titanium materials with different diameters was performed at 350, 400, and 450°C, and its influence on their mechanical properties was evaluated in this study.
The tensile strength and hardness of titanium materials before treatment were higher in the order of 4mm＞5 mm＞3 mm in diameter. The tensile strength and hardness decreased by heat treatment. On the other hand, the elongation percentage of titanium materials before treatment was higher in the order of 3 mm＞5 mm＞4 mm in diameter. The elongation percentage of the 4-mm material deviated from the standard value established by JIS. The elongation percentage of each diameter titanium material increased by heat treatment. The increase was highest in the 4-mm titanium material heated at 450°C, and its elongation percentage was within the standard value established by JIS. Furthermore, the increase in the elongation percentage was lowest in the 3-mm titanium material. After heating titanium materials, oxygen, nitrogen, and carbon were slightly diffused on the surface layer. Metallographic observation revealed that the morphology of crystal grains differed among titanium bars with different diameters.