Localized recrystallization during creep in nickel-based superalloys GTD444 and René N5
Localized recrystallization during creep in nickel-based superalloys GTD444 and René N5
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DOI：
10.1016/j.actamat.2014.03.052
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发表时间：
2014-07
期刊：
影响因子：
9.4
通讯作者：
H. RettbergLuke;T. Pollock
中科院分区：
文献类型：
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作者：
H. RettbergLuke;T. Pollock
研究了两种镍基高温合金定向凝固（DS）GTD 444和单晶（SX）René N5在高温（982° C）和低应力（179-206 MPa）条件下的蠕变损伤机制。电子背散射衍射分析表明，局部动态再结晶试样蠕变到高应变水平和最终断裂。在碳化物簇和蠕变空洞周围观察到再结晶，并且在远离断裂表面的区域中不太常见。平均再结晶晶粒直径为0.71 μ m，在982° C下50 h后，平均再结晶晶粒直径已增长至1.221 μ m。再结晶晶粒的长大是通过γ′相在界面处的溶解和随后的不连续析出来缓解过饱和而实现的。为了考虑局部再结晶对宏观蠕变速率的影响，建立了再结晶加速的三次蠕变模型。该模型预测，轴向应变速率增加约一个数量级的再结晶断裂的发病，有利的实验测量的应变速率在第三蠕变制度从180小时到破裂的加速度相比。局部化动态再结晶的观察提供了新的见解发生在第三蠕变制度的损伤过程。
Creep damage mechanisms in two nickel-based superalloys, directionally solidified (DS) GTD444 and single crystal (SX) René N5, crept at high temperature (982° C) and low stress (179–206 MPa), have been studied. Electron backscatter diffraction analyses showed localized dynamic recrystallization in specimens crept to high strain levels and to final fracture. Recrystallization was observed around clusters of carbides and creep cavities, and was less common in areas away from the fracture surface. The average recrystallized grain diameter was 0.71 μ m, which, after 50 h at 982° C, had grown to an average of∼ 2.31 μ m. Growth of the recrystallized grains occurred by the dissolution of the γ′ precipitates at the interface followed by discontinuous precipitation to relieve supersaturation. To consider the influence of localized recrystallization on macroscopic creep rates, a model for recrystallization-accelerated tertiary creep was developed. The model predicts that the axial strain rate increases by approximately one order of magnitude from the onset of recrystallization to rupture, comparing favorably to the experimentally measured accelerations in strain rate in the tertiary creep regime from 180 h to rupture. The observation of localized dynamic recrystallization provides new insight into the damage processes that occur in the tertiary creep regime.