镍基单晶高温合金疲劳行为的原位透射电镜研究
易 涛，赵治宇，韦 华，张跃飞，王江伟*，张 泽
(1.浙江大学 材料科学与工程学院，浙江 杭州 310027;2.浙江大学 建筑工程学院，浙江 杭州 310058)
摘 要 疲劳破坏是镍基单晶高温合金涡轮叶片常见的失效形式之一，研究循环变形过程中位错组态的演化行为对于理解和提升叶片服役寿命具有重要的意义。本文借助透射电子显微镜和原位力学样品台，研究了[110] 取向的René N5单晶高温合金亚微米柱在室温压-压循环载荷下的缺陷结构演变和疲劳损伤机理。结果表明，γ/γ′两相位错的循环不可逆滑移是亚微米柱变形损伤的主要来源，两相结构使其抵抗循环变形的能力存在差异，二者在循环载荷下的位错演化行为明显不同：强度较低的γ相通道中观察到“循环愈合”现象，预先存在的高密度位错在循环压应力和映像力的作用下逃逸至自由表面而湮灭，γ相强度提高；在基体“循环愈合”后，反相畴界剪切机制主导了γ′相的疲劳变形过程，超位错于表面形核并在γ′相内部运动以继续产生塑性。γ/γ′两相位错动态演化过程与单晶高温合金循环变形行为存在显著关联，在高温合金塑性变形机制研究中，原位透射电镜表征技术展现出潜在的应用前景。
关键词 单晶高温合金；低周疲劳；位错行为；原位电镜
中图分类号：TG132.3+2；TG113.25+5；TG111.8；TG115.5+7
文献标识码：A doi:10.3969/j.issn.1000-6281.2022.05.001
An electron microscopy study of the microstructures of modified Zn4Al alloys in relation with properties
PENG Chan-juan 1，LAI Yu-xiang 2，1*，XIANG Xue-Mei 1，SONG Wen-hao 1，
ZHOU Yu-lin 3，CHEN Jiang-hua 2，1*
(1. Center for High Resolution Electron Microscopy, College of Materials Science and Engineering, Hunan University, ChangshaHunan 410082; 2. Pico Electron Microscopy Center, College of Materials Science and Engineering, Hainan University, Haikou Hainan 570228; 3. Hunan Nonferrous Metals Holding Group CO. LTD., Changsha Hunan 410015, China)
Abstract The effects of three added modifiers (Al-5Ti-B, Sr, and RE) on the mechanical properties and microstructure of hypoeutectic Zn4Al alloy have been investigated based on Vickers hardness test, tensile test, scanning electron microscope, energy dispersive spectroscopy, and high-angle annular dark-field scanning transmission electron microscope. The three modifiers can significantly enhance the strength and ductility of Zn4Al alloy, and the RE modifier plays the best role in improving the strength and ductility of Zn4Al alloy. With the addition of modifiers, the morphology of the primary η-Zn phase transits from dendritic microstructure to nearly equiaxed graininess, and the (α+η) eutectoid microstructure transit from a predominantly lamellar microstructure to a predominantly ellipsoidal microstructure. Parts of the modifier elements added into Zn4Al alloys form intermetallic compounds that strengthen the resistance to grain boundary migration, and parts of them segregate at the solid-liquid interface that results in constitutional supercooling, which improves the grain microstructure.
Keywords Zn4Al alloy; modification; microstructure; mechanical property; electron microscopy
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