Ru对镍基单晶热暴露组织演变及持久性能的影响

Effects of Ru on Microstructural Evolution during Thermal Exposure and Stress-rupture Property of Ni-based Single Crystal Superalloys

摘要:

对比研究了不含Ru的USTB-F7及添加2.5 wt% Ru的USTB-F8两种镍基单晶高温合金的组织稳定性和持久性能。标准热处理与1100 ℃长期热暴露组织研究表明：合金USTB-F7中γ′相形貌介于球形和立方形之间，属中间态形貌；热暴露2000 h后，其形貌仍保持稳定，仅发生粗化而未发生筏排化。Ru的添加使Re元素在γ/γ′中的分配比增大，提高了合金USTB-F8的γ/γ′点阵错配度和γ′相的立方度，从而加速了长期热暴露过程中的筏排化进程，经2000 h热暴露发生了明显的筏排化现象。同时，合金USTB-F7热暴露700 h后在枝晶干处析出了富集Re、W和Cr元素的TCP相，Ru的加入有效地抑制了TCP相的析出，合金USTB-F8直至2000 h仍未析出TCP相。1100 ℃/140 MPa持久性能测试表明，Ru显著提高合金的持久寿命，这与Ru增加合金中的γ′相体积分数和γ/γ′点阵错配度，促进筏排组织的形成，并减小时效组织中的γ通道宽度有关。

Abstract:

The effects of Ru on the microstructural stability and stress-rupture property have been investigated for two experimental Ni-based single crystal superalloys with and without Ru (2.5 wt%) addition. The results of standard heat treatment and long-term thermal exposure at 1100 oC indicate that the intermediate γ′ precipitates in the dendrite cores of the Ru-free alloy do not change in morphology and only become coarsening after 2000 h thermal exposure. The Re partitioning ratio of γ/γ′ phases increases with the addition of Ru, thus resulting in more negative lattice misfit and more cuboidal γ′ precipitates. The Ru-containing alloy rafts after 2000 h thermal exposure. Meanwhile, TCP phases enriched in Re, W and Cr precipitate after 700 h thermal exposure in the dendrite cores of the Ru-free alloy while TCP phases are not observed even after 2000 h thermal exposure in the Ru-containing alloy. These results suggest that Ru addition suppresses the precipitation of TCP phases significantly. The investigation of stress-rupture properties at 1100 oC /140 MPa indicates that Ru addition increases the stress-rupture life of the baseline alloy (Ru-free) since Ru addition increases the γ′ volume fraction and decreases the width of γ channels after standard heat treatment, as well as increasing the γ/γ′ lattice misfit with a well rafting microstructure.