高温金属间化合物的定向凝固特性

THE SOLIDIFICATION BEHAVIOR OF HIGH TEMPERATURE INTERMETALLICS

高温金属间化合物是一类重要的高温结构材料,其中Ti-Al及Ni-Al等许多合金系在凝固时都存在连续的包晶反应.本文就包晶合金凝固的特性从多方面加以总结和分析.凝固过程中的包晶相变对组成相的生长与取向有不同的影响.除此之外,定向凝固包晶反应过程中,相的竞争与选择及界面形态的演化也将同时对金属间化合物的凝固组织产生重要的影响.在考虑了界面温度对生长速率的响应后,可以发现生长速度超过某一值后亚稳相将析出,而根据凝固条件不同可以以不同的凝固方式进行长大,形成如带状、浅胞状和枝/胞双相共生等形式的组织,其中共生组织更有利于提高材料的单向力学性能.虽然定性的分析已获得某些规律。但作为工程应用的具有包晶反应特点的高温金属间化合物的定向凝固研究还极不充分,需进行大量的基础的理论与实验研究.

Intermetallics are a new generation of high temperature structural materials. Many of the alloys solidified through peritectic reaction, for example in Ti-Al and Ni-Al systems. This paper summarized the solidification behaviors of peritectic alloys in several aspects. The peritectic reaction has an important influence on the phase growth and orientation of the solidifying materials. At the same time, the phase competing and the solid/liquid interface evolution will affect the solidification structures significantly. Taking account of growth velocity effect on interface temperature, when the growth velocity is higher than a critical value, metastable phase will grow and the microstructure will take different types, such as banding structure, cellular structure and cellular/dendrite two phases co-growth structure depending on the solidification conditions. Of the three structures, co-growth structure is beneficial to improve the axial mechanical properties. Although some qualitative laws have been achieved through theoretical analysis, the studies on directional solidification behaviors of the intermetallics with peritectic reaction are far from adequate, further detailed theoretical and experimental investigation need to be carried out.