Microstructure, Mechanical Properties and Oxidation Behavior of a Hot-Extruded TiAl Containing Ta

摘要:

对热挤压后新型TiAl合金Ti-46.5Al-3Ta-2Cr-0.2W的微观结构，力学性能及氧化行为进行了研究。结果表明，该合金挤压后微观组织主要由γ和α2相组成近片层组织，其片层晶粒尺寸为50~70 μm。通过不同冷却速率获得了等轴，近片层及全片层的结构，尤其是在油淬后的组织中发现了大量的块状相。拉伸试验结果表明，挤压后的合金室温屈服强度和抗拉伸强度分别从807和846 MPa，降至800 ℃的620和760 MPa，而其伸长率从2.16%提高至3%左右，说明该合金在高温条件下依然具有较高的强度。断口观察表明，与其他合金相比，该合金的裂纹长度较小，而且Ta的添加有利于合金塑性的提高。最后对新型TiAl基合金在800 ℃氧化行为进行了讨论，发现Ta的加入可以降低氧在TiAl合金的溶解度，同时因其本身具有低的扩散率，在升高温度时能抑制TiO2的生长

Abstract:

The microstructure, the mechanical properties and the oxidation behavior of a novel Ti-46.5Al-3Ta-2Cr-0.2W (at%) alloy after hot extrusion were investigated. The results show that the alloy is mainly composed of γ and α2 phases, which has fine near lamellar microstructure with colony sizes of 50~70 μm after hot extrusion. The different microstructures after hot extrusion were obtained by different cooling rates, and a great amount of massive phase were found at grain boundaries by oil quenching. Tensile test results exhibit that the yield strength (YS) and ultimate tensile strength (UTS) of the alloy after hot extrusion decrease from 807 and 846 MPa at room temperature to 620 and 760 MPa at 800 °C, respectively, and the elongation (EI) of the alloy increases from 2.16% at room temperature to 3% at 800 °C which means that the alloy still keeps higher strength at elevated temperature. The observation of fracture surfaces shows that the crack length of the present alloy is smaller, and the additive of Ta increases the ductility of Ti-46.5Al-3Ta-2Cr-0.2W alloy at room temperature. The oxidation behavior of the novel TiAl based alloy in the experimental range was discussed. It is found that the addition of Ta can reduce the oxygen solubility into the TiAl alloy and suppress TiO2 growth at elevated temperature due to the low diffusivity