Abstract
It has been reported that titanium materials suffer from fatigue fracture, so the working strain must be removed. However, when titanium is heated at elevated temperatures, the material will deteriorate due to absorbed gases such as atmospheric oxygen. Characteristic material changes of titanium were investigated when titanium was heated to 400, 600 and 800℃ for 40, 60 and 80 minutes, respectively. After these heat treatments, bend strength, strain amount, yield strength, hardness, color changes, diffusion of oxygen and nitrogen, and micro structural changes were investigated and compared. The main results were as follows.
1. The bend strength, yield strength and hardness decrease with increasing temperature. The influence of heating time was not recognized.
2. The strain amount was not influenced by temperature or heating time.
3. The weight gain due to air oxidation tended to increase with increasing temperature and heating time.
4. Inward diffusion of oxygen and nitrogen was observed during heating,
5. There were no changes in grain size before and of ter heating at 400℃ and 600℃. On the other hand, grain growth was observed when titanium was heated to 800℃.
6. Some of the working strain was removed with 600℃ heating which was not accompanied with grain growth.
