Allvac 718Plus alloy is a promising Ni-based superalloy with excellent thermal stability and mechanical properties up to 704 °C. The γ′ coarsening, σ precipitation and the resulting degraded tensile properties at room and elevated (704 °C) temperatures during long-term thermal exposure at 704 and 760 °C are systematically investigated in this work. The results showed that a higher exposure temperature and a longer exposure time significantly accelerate the γ′ coarsening and σ precipitation. The σ particles were detrimental to the alloy by acting as the preferential nucleation sites for cracks, and the reduction in tensile strengths was mainly caused by the increasing size of γ′ precipitates during thermal exposure. Furthermore, there were significant differences between the deformation mechanisms of room-temperature and elevated-temperature (760 °C) tensile tests. Concerning the deformation mechanism of γ-matrix, planar slipping dominates during tensile testing at room temperature, while the formation of stacking faults and microtwinning are primary during tensile testing at elevated temperature (760 °C). The dominant precipitation strengthening mechanism depended on the γ′ characteristics of different thermal exposure conditions and the tensile temperature. The 704 °C/100 h exposure sample shows a dislocation shearing mechanism when tested at room or elevated (760 °C) temperature. Notably, the 760 °C/1000 h exposure sample exhibits a mixed precipitation strengthening mechanism of Orowan bypassing and superlattice stacking faults shearing when tensile tested at room temperature while showing a dislocation and superlattice stacking faults shearing mechanism when tensile tested at elevated (760 °C) temperature.

中文翻译：

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Allvac 718Plus 高温合金在长期热暴露过程中的析出和拉伸行为

Allvac 718Plus 合金是一种很有前途的镍基高温合金，具有优异的热稳定性和高达 704 °C 的机械性能。这项工作系统地研究了在 704 和 760 °C 的长期热暴露期间，在室温和高温 (704 °C) 下的 γ′ 粗化、σ 沉淀以及由此产生的拉伸性能下降。结果表明，较高的暴露温度和较长的暴露时间显着加速γ′粗化和σ析出。σ颗粒作为裂纹的优先成核位点对合金有害，抗拉强度的降低主要是由于热暴露过程中γ'析出物尺寸的增加造成的。此外，室温和高温（760℃）拉伸试验的变形机制存在显着差异。就γ基体的变形机制而言，室温拉伸试验中平面滑移占主导地位，而高温（760℃）拉伸试验中主要是堆垛层错和微孪晶的形成。主要的沉淀强化机制取决于不同热暴露条件和拉伸温度的γ'特性。在室温或高温 (760 °C) 下测试时，704 °C/100 小时暴露样品显示出位错剪切机制。值得注意的是，760 °C/1000 h 暴露样品在室温拉伸测试时表现出 Orowan 旁路和超晶格堆垛层错剪切的混合沉淀强化机制，而在高温 (760 °C) 拉伸测试时则表现出位错和超晶格堆垛层错剪切机制。 ） 温度。