Al-Ni-Y三元共晶合金定向凝固组织定量分析

摘要

In order to research the microstructure variation of the Al-Ni-Y ternary alloy with puling-down rates and observe the structure by the optical microscopy (OM) and scanning electronic microscopy (SEM), the upward directional solidification of the alloy with chemical composition of Al-1.0%Ni-3.0%Y (mole fraction) was carried out at the constant temperature gradient of 5 K/mm and different pulling-down rates (1−50 mm/min). The characteristic parameters of the alloy structure, such as the volume fractions and size of each phase and eutectic structure, and the eutectic lamellar spacing were analyzed quantitatively by quantitative metallography and MIAPS software. The results show that the microstructure of the alloy behaves obvious characteristics of directional growth after it is directionally solidified. With the increase of pulling-down rates, the gradual transformation of the microstructure of Al-Ni-Y ternary eutectic alloy transforms fromα(Al)+Al 3Y+Al23Ni6Y4 ternary eutectic at the pulling-down rate of 1 mm/min to two eutectics consisted of theα(Al)+Al3Y phase irregular chrysanthemum-like eutectic andα(Al)+Al23Ni6Y4 regular lamellar eutectic at the pulling down rate of more than 5 mm/min. When the pulling-down rate increases to 50 mm/min, the complete chrysanthemum- like eutectic structure gradually crushes and transforms intoα(Al) and Al3Y phase dendritic eutectic. The mathematical relationships among the characteristic parameters and pulling down rates are unambiguous.%在5 K/mm温度梯度下，在不同的下拉速率(1~50 mm/min)下对成分为Al-1.0%Ni-3.0%Y(摩尔分数)三元共晶合金进行下拉定向凝固。通过光学显微镜(OM)、扫描电子显微镜(SEM)观察横纵截面的组织，研究定向凝固后合金组织的变化规律；应用MIAPS软件和定量金相法定量分析合金组织中各组成相及共晶团的尺寸、体积分数以及共晶层片间距等形貌特征参数随凝固条件(v)的变化。结果表明：定向凝固后，合金组织定向生长特征明显；随着下拉速率的增加，Al-Ni-Y三元共晶合金组织由1 mm/min时的α(Al)+Al3Y+Al23Ni6Y4三相共晶组织逐渐转变为下拉速率5 mm/min以上时的α(Al)+Al3Y相组成的菊花状共晶和α(Al)+Al23Ni6Y4相组成规则层片状共晶所组成的两个两相共晶组织；当下拉速率增加到50 mm/min时，完整的菊花状共晶组织特征消失，组织破碎细化，转变为α(Al)+Al 3