Oxidation Resistance and Strength of TiAl Based Alloys in a Simulated

研究了γ - TiAl基合金Ti-48Al-2Cr-2Nb、Ti-48Al-2Cr-2Fe、Ti-48Al-2Cr-2W和Ti-48Al-2Cr-1W-1Ta （mol %）在1173 K模拟燃烧气体中25次循环（500 h）的循环氧化行为。利用x射线衍射仪、扫描电镜和电子能谱仪对氧化产物和亚表面进行了表征。除含铁合金外，所有合金均表现出优异的抗氧化性能，形成薄而粘附的氧化垢，至少可达25次循环。其中，含w合金的质量增益是Ti-48Al-2Cr-2Nb合金的1 / 3，表明w对合金质量的显著影响，Ta的行为与w相似。优异的抗氧化性是由于在氧化初期在鳞片中形成了明确而致密的Al_2O_3层。一个稳定的贫铝层（所谓的Z相）在刻度下方形成。除了掺杂效应外，Nb、Ta和W的影响似乎也稳定了贫铝层。然而，由于氧化，它们的质量增益比在实验室空气中测试的要小，尽管燃烧气体被认为比空气更具侵略性。另一方面，Ti-48Al-2Cr-2Fe氧化速度快，其氧化层由两层组成，外层是由非均匀分布的铁和铬氧化物组成的TiO_2层，内部是由Al_2O_3和TiO_2晶粒组成的多孔层。

The cyclic oxidation behavior of γ - TiAl based alloys, Ti-48Al-2Cr-2Nb, Ti-48Al-2Cr-2Fe, Ti-48Al-2Cr-2W and Ti-48Al-2Cr-1W-1Ta (mol %), was studied in a simulated combustion gas at 1173 K for up to 25 cycles (500 h). The oxidation products and subsurface areas were examined and characterized by using X-ray diffractometry, SEM and EPMA. All the alloys except Fe-containing one show excellent oxidation resistance for at least up to 25 cycles by forming thin and adherent oxide scals. In particular, the mass gains of W-containing alloys are a third of that of Ti-48Al-2Cr-2Nb, indicating significant effect of W. Ta seems to behave similarly as W. The excellent oxidation resistance is attributed to the formation of a definite and dense Al_2O_3 layer in the scale during the initial oxidation stage. A stable Al-depleted layer (so-called Z phase) is formed beneath the scale. The influence of Nb, Ta, and W seems to stabilize the Al-depleted layer in addition to the doping effect. However, their mass gains due to the oxidation are smaller than those tested in laboratory air, though the combustion gas was thought more aggressive than air. On the other hand, Ti-48Al-2Cr-2Fe oxidizes rapidly with scales consisting of two layers, an outer TiO_2 layer with heterogeneously distributed iron and chromium oxides and an inner porous layer which is a mixture of Al_2O_3 and TiO_2 grains.