Influence of Alloying Elements on the oxidation Characteristics of Ti-Al Intermetallic Compounds

含Hf高达5.2%的TiAl试样进行等温氧化，在1100至1400 K的温度范围内，在大气压下的纯氧流。在1200和1300 K下，添加0.2%Hf对降低氧化速率非常有效。用常规方法进行金相检验，发现添加Hf后，最初形成的Al_2O_3氧化膜保持得很好。然而，Hf的进一步添加导致在1200 K下的氧化的轻微增强和在1300 K下的效果的逐渐减小。在1300 K下添加5.2%Hf几乎没有效果。添加0.2%Zr与添加0.2%Hf类似地有效。这些添加剂还改善了在室温和1300 K之间变化的温度下至少100个循环（360 ks）的循环氧化的抗性。然而，这两种添加剂的效果变得很小，在1350 K和1400 K时，它是相反的。Ti_3Al和Ti_3Al-21%Nb试样在1100 ~ 1300 K的温度范围内，于常压下，在纯O_2、Ar-21%O_2或N_2-21%O_2气流中进行等温氧化。氧化气氛中的N_2使Ti_3Al的氧化速率略有降低。这是由于TiN的形成导致铝在试样表面附近富集。在氧化膜/Ti_3Al-21 Nb基体附近形成了一层薄的TiN层，导致TiN层下Al_2O_3的富集，从而大大降低了氧化速率。

TiAl coupon specimens containing Hf of up to 5.2% were isothermally oxidised in a temperature range 1100 to 1400 K in a flow of purified oxygen under atmospheric pressure. The addition of 0.2% Hf is very effective to decrease the oxidation rate at 1200 and 1300 K.Metallographic examinations using the conventional methods revealed that the initially formed Al_2O_3 scale is maintained very sound by the addition. However, further additions of Hf result in a slight enhancement of oxidation at 1200 K and a gradual decrease of the effect at 1300 K.There is almost no effect by the addition of 5.2% Hf at 1300 K.The addition of 0.2% Zr is similarly effective as the addition of 0.2% Hf. These additives also improve the resistance to cyclic oxidation with temperature varying between room temperature and 1300 K for at least 100 cycle (360 ks). However, the effect of the both additives becomes small at 1350 K and at 1400 K it is inverted. Ti_3Al and Ti_3Al-21%Nb coupon specimens were isothermally oxidised in a temperature range 1100 to 1300 K in a flow of purified O_2, Ar-21%O_2 or N_2-21%O_2 under atmospheric pressure. The N_2 in the oxidation atmosphere decreases the oxidation rate of Ti_3Al a little. This is attributable to the formation of TiN resulting in the enrichment of Al near the specimen surface. A thin TiN layr is formed near the scale/Ti_3Al-21Nb substrate, leading to the enrichment of Al_2O_3 beneath the TiN layr and thus to a considerable decrease in the oxidation rate.