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.

工程材料的氧化失效和应力腐蚀开裂（SCC）一直是材料科学和工程应用（如高温下的能量转换）中的一个长期存在的问题。该项目旨在了解NiFe二元合金（Ni-40 at.%）中热、机械和环境因素对晶界（GB）的相互作用为了实现这一目标，我计划通过微悬臂梁弯曲和断裂实验来变形双晶NiFe合金中的代表性晶界。不同的悬臂梁尺寸（尺寸效应），加载速率（扩散时间尺度），加载条件（应力效应），和环境（真空和氧化比较）将被认为是调查的应力-氧化相互作用和微观结构的演变：1）我研究的应力对氧化物生长速率的影响，通过量化氧化物侵入长度沿着GB在不同的环境中，在固定的温度和没有机械加载的情况下，通过生产微悬臂梁。比较了微悬臂梁内拉伸和压缩对扩散和氧化物形成的影响，进而对微悬臂梁失效的影响。2）在固定温度的原位微机械断裂实验中，采用多种加载速率和不同试样尺寸，研究了沿着晶界扩展裂纹尖端的扩散和氧化物形成。新的方法将进一步了解裂纹扩展与氧化物的形成。3)我量化的GB断裂韧性通过断裂试验的微观杠杆。这种断裂韧性的氧化物侵入长度，涉及到几何形状，加载速率，应力状态和GB类型的功能进行了研究。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断裂样品，我可以评估控制氧化物诱导断裂的机制：i）氧化物诱导的动态脆化; ii）应力辅助晶界氧化引起的断裂。将使用有限元模型来计算氧化物侵入长度、应力状态和几何效应。断裂韧性的实验结果进行了比较，以验证模拟和量化的氧化物的影响。所建立的模型可用于改进抗氧化金属的材料设计。