Understanding stress-oxidation interaction on grain boundary failure: in situ microscale crack propagation experiments

了解应力-氧化相互作用对晶界失效的影响：原位微尺度裂纹扩展实验

• 批准号: 418649505
• 负责人: Dr.-Ing. Xufei Fang
• 金额: --
• 依托单位: Werkstoff- und Grenzflächenmechanik (IAM-MMI)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/418649505?language=en
• 关键词: Understanding; stress; oxidation; interaction; grain

Oxidation-induced failure and stress corrosion cracking (SCC) of engineering materials has been a long-standing issue in material science and engineering application, for instance, energy conversion at elevated temperatures. This project aims to understand the interplay of thermal, mechanical, and environmental factors on the grain boundaries (GBs) in a NiFe binary alloy (Ni-40at.%Fe alloy, fcc, gamma-phase).To achieve this goal, I plan to deform representative GBs in bi-crystal NiFe alloy via micro-cantilever bending and fracture experiments. Various cantilever sizes (size effect), loading rates (diffusion time scale), loading conditions (stress effect), and environments (vacuum and oxidation for comparison) will be considered to investigate the stress-oxidation interaction and the microstructure evolution:1) I study the stress effect on the oxide growth rate by producing micro-cantilevers by quantifying the oxide intrusion length along the GBs with and without mechanical loading in different environments at fixed temperature. I compare the effects of tension and compression within the micro-cantilevers on diffusion and oxide formation, and thus on the micro-cantilever failure.2) I study the diffusion and oxide formation at the evolving crack tip along the GBs by using multiple loading rates and different sample sizes during in situ micromechanical fracture experiments at fixed temperature. New method will further the understanding of crack propagation with oxide formation. 3) I quantify the GB fracture toughness via fracture tests of micro-cantilevers. This fracture toughness is studied in function of the oxide intrusion length that relates to geometry, loading rates, stress states and GB type. Then I determine the most robust GB type with the highest resistance to oxidation and fracture.4) By examining the fractured sample using high resolution scanning electron microscopy and transmission electron microscopy, I can evaluate the mechanisms which govern the oxide-induced fracture: i) oxide induced dynamic embrittlement; ii) fracture induced by stress-aided grain boundary oxidation.Finite element modelling will be used to calculate the oxide intrusion length, stress states, and geometry effect. Experimental results of the fracture toughness are compared to the modeling to validate the simulations and quantify the influence of the oxide. The developed models can be used to improve the material design of oxidation resistant metals.

工程材料的氧化引起的衰竭和应力腐蚀破裂（SCC）一直是材料科学和工程应用中的长期问题，例如，在升高温度下的能量转换。该项目旨在了解Nife二进制合金（Ni-40AT。％FE合金，FCC，Gamma-phase）中晶界（GB）的热，机械和环境因素的相互作用。通过微抗逆转录弯曲和断裂实验变形了双晶纳夫合金中的代表性GB。将考虑各种悬臂尺寸（尺寸效应），加载速率（扩散时间尺度），负载条件（压力效应）和环境（比较真空和氧化）来研究应力氧化相互作用和微结构的演化：1）I研究应力对氧化物生长速率的影响，通过在固定温度下在不同环境中进行机械载荷沿GBS沿GB的氧化物侵入长度量化氧化物生长速率。我比较微型委托人内部的张力和压缩对扩散和氧化物形成的影响，因此对微型委托人的失败进行了比较。2）我研究了沿GBS沿GBS不断发展的裂纹尖端的扩散和氧化物形成在原位微机械断裂实验中，在固定温度下进行了不同的样本量。新方法将进一步了解氧化物形成的裂纹传播。 3）我通过微型委托人的断裂测试量化了GB断裂韧性。研究了这种断裂韧性在与几何形状，加载速率，应力状态和GB类型有关的氧化物侵入长度的功能中进行了研究。然后，我确定了对氧化和断裂抗性最高的最强大的GB类型。4）通过使用高分辨率扫描电子显微镜和透射电子显微镜检查破裂的样品，我可以评估控制氧化物诱导的骨折的机制：I）氧化物诱导的动态互惠； ii）由应力辅助晶界氧化引起的断裂。将使用Finite元素建模来计算氧化物侵入长度，应力状态和几何效应。将断裂韧性的实验结果与验证模拟并量化氧化物的影响进行比较。开发的模型可用于改善抗氧化金属的材料设计。