不同条件下Ti/Al固相反应中界面相的生长规律

Growth Law of Interfacial Layer in Ti/Al Solid-State Reaction Under Different Conditions

摘要:

采用爆炸焊-冷轧工艺制备了Ti/Al复合板，然后将不同压下率（0%、27%和55%）的爆炸焊-冷轧Ti/Al复合板在600、625和650 ℃的真空和大气环境下退火，退火时间最长为576 h，并研究了温度、轧制压下率和真空环境等工艺条件对界面相生长规律的影响。研究结果表明，在Ti/Al界面生成了TiAl₃(h)和TiAl₃(l)两种相，温度越高，界面层中TiAl₃(h)所占比例越高。另外，TiAl₃相的平均晶粒尺寸也随着温度升高而增大。不同条件下TiAl₃相的生长均可分为氧化膜控制、化学反应控制和扩散控制生长3个阶段。在氧化膜控制生长阶段，TiAl₃相的动力学常数很小，界面层厚度相对比较均匀。在化学反应控制生长阶段，界面层有较大凸起，界面层厚度均匀性较差。在氧化膜和化学反应控制生长阶段，温度越高，TiAl₃相的动力学常数越大。由于晶粒尺寸与温度对TiAl₃相互扩散系数的作用相互抵消，在扩散控制生长初期阶段，退火温度越高，动力学常数越大，在扩散控制生长后期阶段，温度越高，动力学常数越小。TiAl₃相的厚度均匀性随着退火时间的延长而增大，温度越高，相同退火时间下的界面层厚度均匀性越好。在600 ℃较低温度，冷轧在化学反应控制生长阶段和扩散控制生长阶段的初期能够提高TiAl₃相的生长速度和厚度均匀性，其中压下率越大，TiAl₃相的生长速度和厚度均匀性越大。而在650 ℃较高温度，冷轧在化学反应和扩散控制生长阶段对TiAl₃相的生长速度和厚度均匀性影响较小。在氧化膜控制生长阶段，TiAl₃相在真空环境下的动力学常数比大气环境下的动力学常数大，在化学反应和扩散控制生长阶段，TiAl₃相在真空环境下的动力学常数与空气环境下的动力学常数很接近，但是真空环境下TiAl₃相的厚度均匀性比空气环境下的TiAl₃相厚度均匀性好。

Abstract:

The Ti/Al composite sheets were fabricated by explosive welding (EXW) and cold rolling (CR) with a reduction of 0%, 27% and 55%. Then, the EXW-cold rolled Ti/Al composite sheets were annealed at 600, 625 and 650 ℃ under air and vacuum environment for different durations, and the annealing time was up to 576 h. The effects of temperature, rolling reduction and vacuum environment on the growth of interfacial layer of Ti/Al composite sheets were investigated. The results show that two modifications of titanium trialuminide (TiAl₃(h) and TiAl₃(l)) are formed at Ti/Al interface, and the higher the temperature, the larger the volume fraction of TiAl₃(h) phase. Furthermore, the average grain size of TiAl₃ phase is also increased with the increase in annealing temperature. The growth of interfacial layer at Ti/Al interface under different conditions can be divided into three stages: the first stage is controlled by oxide films, the second stage is controlled by chemical reaction, and the last stage is controlled by diffusion. At the stage controlled by oxide films, the kinetics constant is very little, and the interfacial layer thickness is relatively uniform. At the stage controlled by chemical reaction, there are some large humps at the interfacial layer, and the thickness uniformity is very poor. At the early stages controlled by oxide films and chemical reaction, the higher the annealing temperature, the larger the kinetics constant of TiAl₃ phase. Due to the opposite effect of grain size and temperature on the interdiffusion coefficient of TiAl₃ phase,at the early stage of diffusion-controlled growth, the higher the annealing temperature, the greater the kinetics constant. At the later stage of diffusion-controlled growth, the higher the temperature, the smaller the kinetics constant. The thickness uniformity of interfacial layer becomes better with the prolongation of annealing time at different temperatures, and the higher the temperature, the better the thickness uniformity at the same annealing time. At 600 ℃, cold rolling can improve the growth rate and thickness uniformity of TiAl₃ phase at chemical reaction-controlled stage and early diffusion-controlled stage, and the greater the reduction, the faster the growth rate and the better the thickness uniformity. However, at 650 ℃, cold rolling has little effect on the growth rate and thickness uniformity of TiAl₃ phase at chemical reaction-controlled and diffusion-controlled stages. At the stage controlled by oxide films, the kinetics constant under vacuum environment is larger than that under air environment. At the chemical reaction-controlled and diffusion-controlled stages, the kinetics constant under vacuum environment is almost the same as that under air environment, but the thickness uniformity of TiAl₃ phase under vacuum environment is better than that under air environment.