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Understanding raft formation and precipitate shearing during double minimum creep in a γ′-strengthened single crystalline Co-base superalloy
Philosophical Magazine ( IF 1.6 ) Pub Date : 2020-10-28 , DOI: 10.1080/14786435.2020.1836415
F. Xue 1 , C. H. Zenk 1 , L. P. Freund 1 , S. Neumeier 1 , M. Göken 1
Affiliation  

ABSTRACT The compressive creep deformation behavior of a Co-base single-crystalline superalloy is studied in the high temperature / low stress regime at 950°C/150 MPa. Emphasis is placed on the mechanisms causing the double minimum creep behavior consisting of a local and a global creep rate minimum. The local minimum occurs at ∼0.2% strain with dislocation accumulation at γ/γ′ interfaces after bowing out of dislocations in horizontal matrix channels. Plate-like rafting occurring normal to the applied stress axis in the early creep stages is regarded as the primary reason for the decreasing creep rate until the global minimum takes place at ∼0.8% strain. In the final creep stage following the global minimum the creep rate accelerates due to coarsening and extensive precipitate shearing. The shearing by partial dislocations leads to the formation of numerous stacking faults, nano/microtwins, and occasionally to the formation of small amounts of ordered D019-Co3W precipitates. The reasons for twinning and second phase formation as well as differences of the deformation mechanisms between Co- and Ni-base superalloys during double minimum creep are discussed in detail in this work.

中文翻译:

了解γ'强化单晶钴基高温合金双极小蠕变过程中筏的形成和沉淀剪切

摘要 研究了钴基单晶高温合金在 950°C/150 MPa 的高温/低应力状态下的压缩蠕变变形行为。重点放在引起由局部和全局蠕变速率最小值组成的双重最小蠕变行为的机制上。局部最小值出现在~0.2% 应变处,在水平矩阵通道中的位错弯曲后,位错积累在 γ/γ' 界面。在早期蠕变阶段垂直于施加应力轴发生的板状漂流被认为是蠕变速率下降的主要原因,直到全局最小值出现在 0.8% 应变处。在全局最小值之后的最后蠕变阶段,由于粗化和广泛的沉淀剪切,蠕变速率加快。部分位错的剪切导致大量堆垛层错、纳米/微孪晶的形成,偶尔还会形成少量有序的 D019-Co3W 沉淀。在这项工作中详细讨论了孪晶和第二相形成的原因以及钴基和镍基高温合金在双最小蠕变过程中变形机制的差异。
更新日期:2020-10-28
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