中文摘要：

通过对4种不同Hf含量（0~0.80%,质量分数,下同）的第二代镍基单晶高温合金DD11铸态及热处理态组织定量表征与1100℃,140 MPa持久性能测试,研究了Hf对相转变温度、（g＋γ＇）共晶组织、碳化物、微孔、凝固偏析、合金元素成分分配比及持久性能的影响.结果表明,添加Hf显著降低合金的固/液相线,降低微孔含量,提高铸态共晶组织体积分数、MC型碳化物含量以及凝固偏析程度.合金热处理后,随着Hf含量提高,固溶微孔含量显著降低、残余共晶和碳化物含量显著增加.添加Hf通过提高Re,Mo和Cr的成分分配比,增加γ/γ＇错配度,减小γ/γ＇界面位错间距,促进Re,Mo和Cr向γ相中偏聚,提高固溶强化效果,减小微孔含量等方式,显著提高DD11合金持久性能.但当Hf含量达到0.80%时,热处理后的残余共晶、碳化物含量较高,导致合金持久性能明显降低.

英文摘要：

The effect of Hf on the as-cast, heat-treated microstructures and stress rupture properties under1100 ℃ and 140 MPa was investigated in four second generation Ni-based single crystal superalloys DD11 with various levels of Hf（0~0.80%, mass fraction） additions. The results indicate that increasing Hf addition resulted in decreasing the solidus and liquidus temperatures, while it enhanced the volume fraction of（γ＋γ＇） eutectic and MC carbide as well as solidification segregation. The number of micropores reduced significantly and the volume fraction of residual（γ＋γ＇） eutectic and MC carbide increased after heat treatment as Hf content increased. Compared to the Hf-free alloy, the stress rupture life was observed to increase in the alloys with 0.40%Hf, but dropped in the alloy containing 0.80%Hf. Hf addition increased the elemental partitioning ratio of Re, Mo, Cr, resulting in increasing γ/γ＇ misfit and decreasing the spacing of γ/γ＇ interfacial dislocation networks. The solution strengthing effect was also improved with the enhanced concentration of Re, Mo and Cr in g phase in Hf-modified alloys. However,when the Hf content was 0.80% in DD11 alloy, the stress rupture properties was decreased obviously due to high volume fraction of residual（γ＋γ＇） eutectic and MC carbide in heat-treated microstructures.