中文摘要：

硼（B）是强化镍基单晶合金小角度晶界的重要微量元素,但目前关于B对镍基单晶合金显微组织影响的系统报道非常有限。通过对3种不同B含量（质量分数分别为0、0.01%、0.02%）的第二代镍基单晶合金DD11铸态及热处理态组织定量表征,研究了B对相转变温度、（γ＋γ′）共晶组织、硼化物的影响。结果表明：B显著降低合金的固液相线,提高铸态共晶组织体积分数;0.01%B的加入,合金中未出现M3B2型硼化物相;而0.02%B的加入,显著促进了骨架状硼化物的形成,降低合金初熔点,引起残余共晶含量的大幅度提高;骨架状硼化物吸收较多的Cr、Mo和W等元素,降低合金的固溶强化效果,可导致单晶合金基体的蠕变性能大幅度降低。研究结果对认识单晶合金中微量元素B的作用机理及优化B成分范围具有理论指导意义。

英文摘要：

Boron（B）is added into single crystal superalloys as a micro-alloying element to strengthen low angle grain boundaries.However,there are limited systematic investigations about the effect of B on the microstructures of single crystal superalloy.We studied the influences of B on phase transition temperature,（γ＋γ′）eutectic and borides by analyzing the quantitative characterization of the as-cast and heat-treated microstructures of 3kinds of second generation Ni-based single crystal superalloys DD11 with various additions of B（mass fraction of 0,0.01%and 0.02%）.The results indicate that increasing B addition can significantly decrease the solidus and liquidus temperature and enhance the volume fraction of（γ＋γ′）eutectic.The borides of M3B2 are not observed in the alloy with 0.01% B addition.However,when the B addition is 0.02%,the script-like borides are precipitated in the interdendritic region and the incipient melting point is decreased,and thus the volume fraction of residual eutectic issignificantly improved.The script-like borides are rich in Cr,Mo and W,which decreases the solid solution strengthening effect,and thus creep properties of the alloy may be significantly decreased.This study would be helpful for the understanding of B＇s role in Ni-base single crystal superalloys and the optimization of B content.