快速凝固Ni-Al合金中的组成相

PHASES PRECIPITATED IN RAPIDLY SOLIDIFIED Ni-Al ALLOYS

选取了 Ｎｉ－Ａｌ系六种合金成分（Ｎｉ２５Ａｌ７５，Ｎｉ３１．５Ａｌ６８．５，Ｎｉ３９Ａｌ６１，Ｎｉ７０Ａｌ３０，Ｎｉ７２．２Ａｌ２７．８，Ｎｉ７４Ａｌ２６），采用熔体旋铸法分别制备出不同厚度（３０－１２０μｍ）的条带试样．用ＸＲＤ的Ｋ值法对其组成相作了定量测定 结果表明．快速凝固组成相与常规凝固组成相有较大差异．快速凝固析出的相中，具有较低液相线温度的化合物相有较大幅度的增加；冷速不同，组成相中各相的含量也不相同．用当前快速凝固的形核理论和枝晶生长模型对实验结果作了理论分析与计算．结果表明，具有较高液相线温度的化合物相是先析出相，而具有较低液相线温度的化合物相具有生长速度上的优势．分析认为，快速凝固的冷却速率和竞争相之间的生长速度的差异是最终相组成变化的主要原因．

Rapidly solidified ribbons(30-120 mum in thickness) of Ni-Al alloys with 25%-74%Ni(atomic fraction) were obtained by melt spinning. The phases in as-quenched samples are quantitatively analyzed by X-ray diffraction (XRD) K-value method. The results indicate that the phases in the rapidly solidified samples differ significantly from those in the conventional cast ingots. In rapidly solidified alloys the amount of phases with lower liquidus temperature is larger than that in conventional solidified alloys. The amount of constitutive phases varies also with cooling rate for the same alloy. By using nucleation theory and dendrite growth model of rapid solidification alloy, the experimental results were analysed and it is shown that the phase with higher liquidus temperature is the primary phase, while the growth velocity of phase with lower liquidus temperature is larger than that with higher liquidus temperature. The deferences of cooling rate and of the growth velocity between the competing phases are the main factors resulting in the change in the constitutive phases.