通过对6种不同Ru (0-5.1%, 质量分数, 下同)和Cr (0-5.7%)含量的镍基单晶高温合金1100 ℃的时效和热处理组织观察与γ/γ'两相的成分分析,研究了Ru和Cr的独立和交互作用对合金元素成分分配比及热处理组织演变的影响.经1100 ℃/8 h时效后, 在枝晶干处, 不含Ru和Cr的基础合金γ'相接近球形,Re在该合金γ/γ'两相中的成分分配比较低, 错配度接近于0.在基础合金中加入高Ru后, γ'相立方度和Re的成分分配比略有增大,错配度变负; 在不含Ru合金与含Ru合金中, 随着Cr含量的增大, γ'相的立方度和Re的成分分配比均显著增大, 错配度明显变负.1100 ℃非加载下的长期热处理研究表明: γ'相接近球形且错配度接近于0的合金γ'相形貌稳定, 在2000 h内只出现了粗化,没有发生筏排化现象; γ'相呈中间态并且错配度较小的合金γ'相粗化趋势较为明显; γ'相接近立方体形且错配度中等的合金在热处理800 h后形成近似筏排组织; 同时加入Ru和Cr, 随着Re的成分分配比和错配度的增大,γ'相为立方体形或长方体形的合金筏排化时间提前; 其中高Ru中Cr合金热处理200 h就出现筏排化趋势, 而错配度最高的高Ru高Cr合金热处理仅50 h就形成筏排组织.
The influences of Ru and Cr as well as their interaction on the elemental partitioning ratio and microstructural evolution have been investigated in six Ni–based single crystal experimental superalloys with various levels of Ru (0—5.1%) and Cr (0—5.7%) additions (mass fraction). The results indicate that γ′ precipitates are nearly spherical in the dendrite core of the base alloy (Ru and Cr–free), which has a low Re partitioning ratio and near zero lattice misfit, after aging treatment at 1100 ℃ for 8 h. The lattice misfit and Re partitioning ratio increase slightly and the γ′ precipitates change to be more cuboidal with the addition of 5.1%Ru in both Cr–free and Cr–containing alloys. Meanwhile, the Re partitioning ratio increases significantly with increasing the Cr content in both Ru–free and Ru–containing alloys, which in turn results in more negative lattice misfit and more cuboidal γ′ precipitates. After long–term thermal exposure at 1100 ℃, the nearly spherical γ′ precipitates with near zero lattice misfit in the alloy have no change in morphology, and are coarsened after a longer exposure time, while the alloy with intermediate γ′ precipitates and low lattice misfit is coarsened more severely. However, a nearly–rafted structure tend to form in the alloy with nearly cuboidal′ precipitates and intermediate misfit after heat treatment for 800 h. The time to form the rafted structure is significantly reduced in the alloys containing both Ru and Cr with high Re partitioning ratio and high lattice misfit as well as cuboidal or rectangular γ′ precipitates. The alloy containing high Ru and intermediate Cr exhibits a rafted trend after heat treatment for 200 h while the rectangular γ′ precipitates are rafted after heat treatment for only 50 h in the alloy containing high levels of Ru and Cr additions with the highest lattice misfit.
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