Mg-Zn-Y三元合金中二十面体准晶相生长形貌及其演化

Growth Morphology and Evolution of Icosahedral Quasicrystal in Mg-Zn-Y Ternary Alloys

采用常规凝固方法在Mg-Zn-Y三元合金系中获得了大体积分数的二十面体准晶。二十面体准晶相有2种典型形貌特征:一种为花瓣状,另一种为多边形形状。这是准晶在生长过程中形貌演化的结果。合金的成分和冷却速率是影响准晶形貌的主要因素。准晶合金中生成的低温相越多,冷却速率越慢,准晶相生长的时间和空间条件越好,准晶相越容易由花瓣状演化成多边形状。准晶的形成有包晶反应参与,包晶反应是一种由初生固态相扩散控制的反应,因此,准晶在生长初期和最终形态其元素含量有明显差别,分析表明,准晶生长初期Mg元素含量偏低,Zn和Y元素含量偏高。

A large volumetric fraction of icosahedral quasicrystal was gained through ordinary solidification technology in Mg-Zn-Y ternary alloys. The icosahedral quasicrystal in Mg-Zn-Y ternary alloys have two typical morphology features： petal-like, polygon-like. The different features of icosahedral quasicrystal are attributed to their morphology evolution. Alloying composition and cooling rate are major factors affecting the morphology of icosahedral quasicrystal. In the solidification process ofquasicrystal alloys, the more the low-temperature phases and the less the cooling rate, the much more easily the changing into the polygon-like morphology from petal-like one takes place. Peritectic reaction occurs during the icosahedral quasicrystal formation which leads to element content difference in primary stage and in final stage of icosahedral quasicrystal evolution. The composition analyses show that Mg content is lower but Zn and Y contents are higher in the primary stage of quasicrystal growth.