采用真空非自耗电弧炉制备了不同含O量的Ti－46Al－8Nb－xO (原子分数)合金铸锭,研究间隙原子O对高Nb－TiAl 合金凝固组织及相转变的影响规律和作用机制.结果表明, 随着O含量的增加, Ti－46Al－8Nb－xO铸锭中α₂相含量逐渐增加.O的加入明显细化合金组织, 并且使得组织由双态组织向全片层组织转变.间隙原子O的添加使得Ti－46Al－8Nb合金由β相领先的凝固方式转化为以α相领先的凝固方式,同时使包晶反应α+L→γ向低Al区移动,共析反应α→α₂+β向高Al区移动, 扩大了α相区的范围.通过DSC分析表明, O原子可以明显提高合金的共析反应温度, 但随着含量的增加作用效果逐渐减弱.

Due to the low density, high specific strength, elastic modulus and oxidation resistance at high temperature, TiAl－based alloys have attracted much attention as a candidate of the next generation high temperature materials in aerospace and automobile application. Meanwhile, the excellent properties oxidation resistance, creep strength and tensile strength at the elevated temperature make the high Nb containing TiAl alloys be one of the promising development directions of future TiAl alloys. During the studies about alloying which is an efficient way to improve the performance of TiAl alloys, researchers have found that interstitial atoms B, C and N notably refine the grains and then improve mechanical properties including yield strength, micro－hardness, and tensile ductility of TiAl alloys. During the melting, casting, forging and the application environment, the TiAl alloys also are always inevitable to be contaminated by the O. In this work, the high Nb containing Ti－46Al－8Nb－xO alloys (atomic fraction) were prepared by non－consumable vacuum arc remelting under the protection of Ar atmosphere. The aim of the present work is to study the influence and the corresponding mechanism of oxygen atoms on the microstructure evolution and phase transformation of high Nb－TiAl alloys. The results indicate that oxygen atoms in Ti－46Al－8Nb－xO alloys remarkably increase the amount of α₂ phase. The increasing oxygen content leads to the grain refinement. Meanwhile, the duplex microstructures translate into fully lamellar. It indicates that the interstitial oxygen essentially reduces the kinetics of α→γ. Consequently, the fully lamellar is easier formation than the duplex microstructures. It is found that interstitial oxygen atoms preserve significantly influence on the microstructure of Ti－46Al－8Nb－xO alloys. With the increase of oxygen content, the β solidification translates into αsolidification and the peritectic reaction α+L→γ moves to a lower Al content. At the same time, the eutectoid reactionα→α₂+β shifts to a higher Al content which extends the area of α $ phase. The DSC results show the effect of oxygen on the phase transformation of Ti－46Al－8Nb. The DSC curves indicate that the addition of oxygen increases the eutectoid reaction temperature of Ti－46Al－8Nb－xO alloys, but this effect can be gradually reduced with the further increase of oxygen content.