Mechanisms of corrosive freeze-thaw damage in AA7075 using time-resolved x-ray microtomography and correlative electron microscopy

IF 6.6 2区材料科学 Q1 MATERIALS SCIENCE, MULTIDISCIPLINARY

npj Materials Degradation Pub Date : 2024-12-27 DOI:10.1038/s41529-024-00547-6

Ankit Kumar, Eshan Ganju, Daniel Sinclair, Nikhilesh Chawla

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Abstract

Aluminum aircraft structures experience severe corrosion from exposure to aggressive chloride environments, including cyclic freezing and thawing of residual water during ascent and descent, introducing a cyclic freeze-thaw component to the corrosion process. While corrosion mechanisms in aircraft structures are well studied at constant temperatures, the microstructural and mechanistic behavior under freeze-and-thaw conditions remains unclear. To understand transformations induced by cyclic temperature, we used three-dimensional (3D) x-ray computed tomography (XCT) with scanning electron microscopy (SEM) to study the behavior of AA7075-T651 in a simulated seawater environment undergoing freezing and thawing cycles. Rods immersed in saltwater were thermally cycled above and below freezing, and structural changes were intermittently characterized in 3D. Under freeze-thaw conditions, cracks initiated within corrosion pits through ice expansion, causing progressive crevice growth and spalling along inclusions and grain boundaries with intermediate misorientation angles. Damage mechanisms in freeze-thaw and conventional corrosion environments are compared, with correlations to microstructural evolution.

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利用时间分辨x射线显微断层扫描和相关电子显微镜研究AA7075腐蚀冻融损伤机制

铝制飞机结构暴露在腐蚀性的氯化物环境中会遭受严重的腐蚀，包括在上升和下降过程中残余水的循环冻结和融化，在腐蚀过程中引入了循环冻融成分。虽然飞机结构在恒温条件下的腐蚀机制已经得到了很好的研究，但在冻融条件下的微观结构和力学行为仍然不清楚。为了了解循环温度引起的转变，我们利用三维（3D） x射线计算机断层扫描（XCT）和扫描电子显微镜（SEM）研究了AA7075-T651在模拟海水环境中经历冻融循环的行为。浸泡在盐水中的棒在冰点以上和冰点以下进行热循环，并在三维上间歇性地表征结构变化。冻融条件下，由于冰的膨胀，腐蚀坑内部产生裂纹，导致裂缝沿夹杂物和晶界逐渐扩大和剥落，并伴有中等取向角偏差。比较了冻融和常规腐蚀环境下的损伤机制，以及与微观结构演变的关系。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

npj Materials Degradation MATERIALS SCIENCE, MULTIDISCIPLINARY-

CiteScore

7.80

自引率

7.80%

发文量

审稿时长

6 weeks

期刊介绍： npj Materials Degradation considers basic and applied research that explores all aspects of the degradation of metallic and non-metallic materials. The journal broadly defines ‘materials degradation’ as a reduction in the ability of a material to perform its task in-service as a result of environmental exposure. The journal covers a broad range of topics including but not limited to: -Degradation of metals, glasses, minerals, polymers, ceramics, cements and composites in natural and engineered environments, as a result of various stimuli -Computational and experimental studies of degradation mechanisms and kinetics -Characterization of degradation by traditional and emerging techniques -New approaches and technologies for enhancing resistance to degradation -Inspection and monitoring techniques for materials in-service, such as sensing technologies