Assessment of Ductile, Brittle, and Fatigue Fractures of Metals Using Optical Coherence Tomography
Assessment of Ductile, Brittle, and Fatigue Fractures of Metals Using Optical Coherence Tomography
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DOI：
10.3390/met8020117
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发表时间：
2018-02-01
期刊：
影响因子：
2.9
通讯作者：
Podoleanu, Adrian Gh.
中科院分区：
文献类型：
--
作者：
Hutiu, Gheorghe;Duma, Virgil-Florin;Podoleanu, Adrian Gh.
一些法医现场调查，如运输中所需的调查（航空、海事、公路或铁路事故）或在恶劣条件下工作的部件（例如，管道或涡轮机）将受益于区分金属的韧性断裂和脆性断裂的方法/技术。因为材料缺陷是事故的潜在原因之一。如今，材料研究的黄金标准是扫描电子显微镜（SEM）。然而，SEM仪器体积大，价格昂贵，耗时，并且基于实验室;因此，原位测量是不可能的。为了解决这些问题，我们提出了一种替代的，低成本的，足够高的分辨率的技术，光学相干断层扫描（OCT）进行断裂分析，通过获得金属表面的形貌。本研究考虑了几种金属：低软碳钢、片状石墨铸铁、减摩合金、优质轧制钢、不锈钢和球墨铸铁。使用内部开发的扫频源（SS）OCT系统，主-从（MS）增强，并生成样品表面的高度轮廓。使用了两种配置：其中一个体素的尺寸为1000 μ m（3），第二个体素的尺寸为160 μ m（3），分别具有10 μ m和4 μ m的横向分辨率。这些高度分布允许得出这样的结论，即碳钢样品经受延性断裂，而铸铁和减摩合金样品经受脆性断裂。OCT图像的验证已使用以4 nm分辨率获得的SEM图像进行。虽然OCT图像的分辨率比SEM图像低得多，但我们证明它们足以获得金属材料晶粒的清晰图像，从而区分韧性和脆性晶粒，特别是使用分辨率更高的MS/SS-OCT系统。调查最后扩展到最有用的情况下，金属的疲劳断裂，我们证明，OCT是能够取代扫描电镜等调查。
Some forensic in situ investigations, such as those needed in transportation (for aviation, maritime, road, or rail accidents) or for parts working under harsh conditions (e.g., pipes or turbines) would benefit from a method/technique that distinguishes ductile from brittle fractures of metalsas material defects are one of the potential causes of incidents. Nowadays, the gold standard in material studies is represented by scanning electron microscopy (SEM). However, SEM instruments are large, expensive, time-consuming, and lab-based; hence, in situ measurements are impossible. To tackle these issues, we propose as an alternative, lower-cost, sufficiently high-resolution technique, Optical Coherence Tomography (OCT) to perform fracture analysis by obtaining the topography of metallic surfaces. Several metals have been considered in this study: low soft carbon steels, lamellar graphite cast iron, an antifriction alloy, high-quality rolled steel, stainless steel, and ductile cast iron. An in-house developed Swept Source (SS) OCT system, Master-Slave (MS) enhanced is used, and height profiles of the samples' surfaces were generated. Two configurations were used: one where the dimension of the voxel was 1000 mu m(3) and a second one of 160 mu m(3)with a 10 m and a 4 m transversal resolution, respectively. These height profiles allowed for concluding that the carbon steel samples were subject to ductile fracture, while the cast iron and antifriction alloy samples were subjected to brittle fracture. The validation of OCT images has been made with SEM images obtained with a 4 nm resolution. Although the OCT images are of a much lower resolution than the SEM ones, we demonstrate that they are sufficiently good to obtain clear images of the grains of the metallic materials and thus to distinguish between ductile and brittle fractures-especially with the higher resolution MS/SS-OCT system. The investigation is finally extended to the most useful case of fatigue fracture of metals, and we demonstrate that OCT is able to replace SEM for such investigations as well.