Low cycle fatigue and high cycle fatigue of K4750 Ni-based superalloy at 600 °C: Analysis of fracture behavior and deformation mechanism
Low cycle fatigue and high cycle fatigue of K4750 Ni-based superalloy at 600 °C: Analysis of fracture behavior and deformation mechanism
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DOI：
10.1016/j.msea.2021.141588
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发表时间：
2021-07
期刊：
影响因子：
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通讯作者：
Kunlei Hou;Meiqiong Ou;Min Wang;Xianchao Hao;Yingche Ma;Kui Liu
中科院分区：
文献类型：
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作者：
Kunlei Hou;Meiqiong Ou;Min Wang;Xianchao Hao;Yingche Ma;Kui Liu
研究了新型铸造镍基高温合金K4750在600℃下应变控制低周疲劳（LCF）和应力控制高周疲劳（HCF）的断裂行为和变形机理。LCF中的裂纹从表面开始，沿垂直于加载方向的方向以条纹辅助的II阶段方式扩展。而在HCF中，裂纹主要起源于大尺寸夹杂物，其扩展遵循晶体学I阶段模式。两种试验中控制合金失效的组织也不同。MC碳化物加速了LCF中的裂纹扩展，在原始裂纹尖端前诱发了二次裂纹。而HCF中裂纹的形成主要受夹杂物、晶粒尺寸和晶粒取向的影响。它们以不利的形式存在导致合金过早失效和应力寿命数据的大量分散。此外，STEM观测表明，LCF中的变形发生在多个平行的{111}面上，并且具有高密度的缠结位错。产生的滑移带距离较近，平均间距小于0.1 μm。而在HCF中，滑移带的分布更为孤立，距离可达几微米。滑移带中的位错受γ′相反相边界的约束，经常成对地穿过γ/γ′结构。高度孤立的滑移带中的非均匀变形被认为是HCF中I阶段开裂的原因，这在本研究中进行了讨论。
The fracture behavior and deformation mechanism of a new casting Ni-based superalloy K4750 during strain-controlled low cycle fatigue (LCF) and stress-controlled high cycle fatigue (HCF) at 600 °C were investigated. The crack in LCF originated from surface and propagated perpendicular to the loading direction in a striations-assisted Stage II manner. Whereas, the crack in HCF mostly initiated at large-size inclusions and its propagation followed a crystallographic Stage I mode. The microstructures controlling the alloy failure in the two tests were also different. The crack propagation in LCF was accelerated by MC carbides which induced second cracks in front of the primary crack tip. By contrast, the formation of crack in HCF was more affected by the inclusion, grain size and grain orientation. Their presence in unfavorable forms led to premature failure of the alloy and a substantial scatter in the stress-life data. In addition, STEM observation showed that the deformation in LCF occurred on multiple parallel {111} planes with high density of entangled dislocations. The produced slip bands were in close proximity with average spacing below 0.1 μm. However, the distribution of slip bands in HCF was more isolated with separation up to a few microns. The dislocations in slip bands often traversed the γ/γ′ structure in pairs as constrained by the anti-phase boundary in γ′ phase. The heterogeneous deformation in highly isolated slip bands was deemed to account for the Stage I cracking in HCF, which was discussed in this study.