Oxidation Behavior of Intermetallic Compound TiAl under Low Oxygen Partial Pressure

金属间化合物TiAl在低氧分压下的氧化行为

• 批准号: 09650782
• 负责人: YOSHIHARA Michiko
• 金额: $ 1.79万
• 依托单位: Yokohama National University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1997
• 资助国家: 日本
• 起止时间: 1997 至 1998
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09650782/
• 关键词: intermetallics; TiAl; oxidation in a low pressure; formation of alumina layer; oxygen solubility; Z-phase; stability of surface layer

Oxidation behavior of intermetallic compound TiAl has been studied under low oxygen partial pressure of about 10^<-3> Pa using a After oxidation, the phases formed during oxidation were detected by X-ray diffraction. TiAl shows deteriorated oxidation behavior in air, because it dose not form a continuous and dense A1208 layer on the surface. However, when TiAl is oxidized under low oxygen partial pressure, a protective and continuous Al_2O_3 layer is formed on the surface resulting in superior improvement in oxidation resistance. The mechanism to form a continuous Al_2O_3 layer is resulted from the formation of Z-phase as an Al depletion layer which can dissolve a large amount of oxygen. This may retard the formation of TiO_2 and aid to form a continuous Al_2O_3 layer. In the case of the intermetallic compounds with higher Al content, TiAl_2 and TiAl_3, they do not form a phase with higher solubility of oxygen as an Al depletion layer during oxidation. As a resu1t, these compounds do not show any improvement by the heat treatment under low oxygen air pressure. This suggests strongly that Z-phase plays an important role to form a continuous and protective Al_2O_3 layer during the heat treatment in a low air pressure. To confirm a stability of the protective surface layer formed during the oxidation under low partial pressure of oxygen, indentation tests using Vicker's hardness tester and SEM observation were done. As a result, when the protective surface layer is suffered damages, some cracks are induced in the surface layer, however, the effect of the heat treatment under low partial pressure of oxygen is maintained. This is probably due to self-healing of the protective scale yielded from enhanced Al diffusion through dislocations induced by the strains in the vicinity of the damages.

用X射线衍射仪研究了金属间化合物TiAl在10 ~（-1）Pa低氧分压下的氧化行为<-3>。TiAl在空气中的氧化性能较差，这是因为其表面没有形成连续致密的Al_（120）_8层。而当TiAl在低氧分压下氧化时，在其表面形成一层连续的Al_2O_3保护层，从而使其抗氧化性能得到上级改善。形成连续Al_2O_3层的机理是由于形成了能溶解大量氧的Z相作为Al耗尽层。这可能会阻碍TiO_2的形成，并有助于形成连续的Al_2O_3层。Al含量较高的金属间化合物TiAl_2和TiAl_3在氧化过程中不形成氧溶解度较高的相作为Al耗尽层。结果表明，这些化合物在低氧空气压力下热处理没有任何改善。这表明在低气压热处理过程中，Z相对形成连续的Al_2O_3保护层起着重要作用。为了确认在低氧分压下氧化期间形成的保护表面层的稳定性，进行了使用维氏硬度计的压痕试验和SEM观察。结果，当保护表面层受到损伤时，在表面层中引起一些裂纹，然而，保持了在低氧分压下的热处理的效果。这可能是由于在损伤附近的应变引起的位错增强Al扩散产生的保护膜的自愈。