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、(γ+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.

The effect of Hf on the as-cast, heat-treated microstructures and stress rupture properties under 1100 ℃ 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 γ 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.