Effect of Ta on microstructural evolution and mechanical properties of a solid-solution strengthening cast Ni-based superalloy, IN617B alloy, considered as a potential candidate for castings in 700 degrees C advanced ultra-supercritical (A-USC) coal-fired power plants, has been studied in this paper. Detailed observation reveals the alloys with different contents of Ta have similar solution treated microstructure. During long-term thermal exposure at 700 degrees C, Ta addition refines gamma' particles and enhances the thermal stability of gamma' phase by decreasing the gamma-gamma' lattice misfit. With increasing Ta content the solubility of Mo in matrix decreases, which promotes the transformation of film-like M23C6 at grain boundaries (GBs) into blocky M6C carbide with the reaction of M23C6 -> Mo--Cr(+Mo,Ta) M6C. Consequently, the morphology of GB carbide changes from continuous film structure to dispersed block structure. In addition, local concentration of metal elements leads to the precipitation of trace amount of s phase which is not affected by Ta concentration. Nearly all the tensile properties at 700 degrees C of the alloy after long-term thermal exposure are improved noticeably with the increase of Ta content. But, the plasticity of the alloy with 2.0 wt. % Ta addition decreases remarkably due to the excessive Ta content leading to severe M6C coarsening at GBs. The alloy achieves optimal mechanical properties with about 1.0 wt. % Ta content. (C) 2017 Elsevier B.V. All rights reserved.

中文翻译：

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Ta对固溶强化铸造镍基合金在700°C长期热暴露过程中显微组织演变和力学性能的影响

Ta 对固溶强化铸造镍基高温合金 IN617B 合金显微组织演变和机械性能的影响，IN617B 合金被认为是 700 摄氏度先进超超临界 (A-USC) 燃煤电厂铸件的潜在候选者，已在本文中进行了研究。详细观察表明，不同Ta含量的合金具有相似的固溶处理显微组织。在 700 摄氏度的长期热暴露期间，Ta 的添加细化了 gamma' 粒子并通过减少 gamma-gamma' 晶格失配来增强 gamma' 相的热稳定性。随着Ta含量的增加，Mo在基体中的溶解度降低，这促进了晶界（GBs）处的膜状M23C6转变为块状M6C碳化物，反应为M23C6 -> Mo--Cr(+Mo,Ta) M6C。最后，GB碳化物的形貌由连续的薄膜结构转变为分散的块状结构。此外，金属元素的局部浓度导致微量s相的析出，不受Ta浓度的影响。随着Ta含量的增加，合金在长期热暴露后的700℃拉伸性能几乎全部显着改善。但是，合金的塑性为 2.0 wt。由于过多的Ta含量导致GBs处严重的M6C粗化，％Ta添加量显着降低。该合金以约 1.0 重量％达到最佳机械性能。% 钽含量。(C) 2017 Elsevier BV 版权所有。金属元素的局部浓度导致微量s相的析出，不受Ta浓度的影响。随着Ta含量的增加，合金在长期热暴露后的700℃拉伸性能几乎全部显着改善。但是，合金的塑性为 2.0 wt。由于过多的Ta含量导致GBs处严重的M6C粗化，％Ta添加量显着降低。该合金以约 1.0 重量％达到最佳机械性能。% 钽含量。(C) 2017 Elsevier BV 版权所有。金属元素的局部浓度导致微量s相的析出，不受Ta浓度的影响。随着Ta含量的增加，合金在长期热暴露后的700℃拉伸性能几乎全部显着改善。但是，合金的塑性为 2.0 wt。由于过多的Ta含量导致GBs处严重的M6C粗化，％Ta添加量显着降低。该合金以约 1.0 重量％达到最佳机械性能。% 钽含量。(C) 2017 Elsevier BV 版权所有。由于过多的Ta含量导致GBs处严重的M6C粗化，％Ta添加量显着降低。该合金以约 1.0 重量％达到最佳机械性能。% 钽含量。(C) 2017 Elsevier BV 版权所有。由于过多的Ta含量导致GBs处严重的M6C粗化，％Ta添加量显着降低。该合金以约 1.0 重量％达到最佳机械性能。% 钽含量。(C) 2017 Elsevier BV 版权所有。