渗硅TiAl基合金的氧化动力学

Oxidation Kinetics of Siliconized TiAl-based Alloy

改善TiAl基合金的高温抗氧化性能可更大限度地发挥其性能优势,固体渗硅是一种工艺简便且行之有效的方法,深入了解渗硅TiAl基合金的氧化动力学对保证其安全应用以及进一步的理论和实验研究具有重要意义。对经不同温度、时间固体渗硅处理的TiAl基合金在90 0℃下长期循环氧化过程中的动力学研究表明,其氧化过程通常包含三个阶段,即抛物线、线性和二次氧化阶段。提高渗硅温度有利于提高抗氧化性能。其中,经1 2 5 0℃渗硅2h的试样表现出优异抗高温氧化性能,在所测试的1 0 0 0h以内的整个循环氧化过程中仅出现抛物线氧化阶段,经90 0℃氧化1 0 0 0h后,增重小于0 . 3mg·cm- 2 ,相应的抛物线型氧化速率常数,Kp≈6 . 0 3×1 0 - 5mg2 (cm4 ·h) ,优异的抗氧化性能与其表层形成致密的Al2 O3层和相对稳定的Ti5Si3层有关。

The potential excellent properties of TiAl-based alloys could be brought into play to more extent in the application as high-temperature structure materials if their high-temperature oxidation resistance can be further improved. Pack siliconizing is one of convenient and effective methods in improving their oxidation resistances. In this paper, the long-term cyclic oxidation test was performed on siliconized TiAl-based alloy specimens and the oxidation kinetics was analyzed. The results show that the oxidation process usually consists of three stages before crack and spallation of the surface layer, which are the parabolic, the linear and the quadratic stages. The higher the siliconization temperature or the longer the siliconization time is, the longer the parabolic stage is, and the better the oxidation resistance becomes. For the specimen that was siliconized at 1250°C for 2 h, however, only the parabolic region appeared during the whole cyclic oxidation test at 900°C up to 1000 h. The weight gain is less than 0.3 mg&middotcm-2 after cyclic oxidation at 900°C for 1000 h, and the corresponding parabolic oxidation rate constant, Kp is about 6.03×10-5 mg2/(cm4h). The excellent oxidation resistance is attributed to the formation of a composite coating with a stable Ti5Si3-based layer and a dense Al2O3-based layer.