Abstract A quantitative investigation of the porosity and its effects on mechanical properties was conducted on brazed materials presenting macroscopically brittle behavior with various defect levels. Three different techniques for evaluating the porosity and the fracture mechanisms were compared: (i) pre-mortem X-ray computed tomography (XCT), (ii) post-mortem laser scanning confocal microscopy (LSCM), and (iii) post-mortem scanning electron microscopy (SEM). The apparent surface area of the pores was evaluated by segmenting the height maps produced by LSCM and the electron backscattered images produced by SEM. The results show good agreement for different porosity levels. The LSCM height maps for opposite fracture faces were virtually stitched together in order to reconstruct three-dimensional (3D) images of the whole brazed joints. These proved to be similar to the XCT 3D segmented images, yet with some discrepancies due to local plastic deformation. Quantitative volume fraction and spatial distribution of pores were assessed as well as the identification of fracture mechanisms. Interestingly, it was noted that two specimens with different ultimate tensile strengths presented the same porosity amount, but different distributions. Two distinctive features were identified in the broken specimens: plastically teared pillars and walls that were separating the pores before fracture, and plateaus of approximately constant height with micro-sized dimples showing interfacial fracture. Although the specimens exhibited a macroscopic brittle behavior, these features are characteristic of ductile fracture. The most probable scenario for fracture was conjectured as follows: (i) Final fracture occurs in the near-surface region of the samples and conversely early damage develops in the volume, (ii) Interfacial fracture within plateaus is responsible of the rupture/strength of the brazed specimen but detrimental effect is induced by the tearing if highly voided regions are present in the joint.

中文翻译：

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孔隙率对钎焊马氏体钢拉伸性能的影响：2D 和 3D 检验前与检验后表征

摘要 对呈现宏观脆性和各种缺陷水平的钎焊材料进行了孔隙率及其对机械性能影响的定量研究。比较了评估孔隙率和断裂机制的三种不同技术：(i) 验尸前 X 射线计算机断层扫描 (XCT)，(ii) 验尸激光扫描共聚焦显微镜 (LSCM)，和 (iii) 验尸扫描电子显微镜（SEM）。通过分割由 LSCM 产生的高度图和由 SEM 产生的电子背散射图像来评估孔的表观表面积。结果显示了不同孔隙度水平的良好一致性。相对断裂面的 LSCM 高度图被虚拟缝合在一起，以重建整个钎焊接头的三维 (3D) 图像。这些被证明与 XCT 3D 分割图像相似，但由于局部塑性变形而存在一些差异。评估了孔隙的定量体积分数和空间分布以及断裂机制的识别。有趣的是，注意到具有不同极限拉伸强度的两个试样呈现相同的孔隙率，但分布不同。在破碎的样品中发现了两个显着特征：在断裂前分隔孔隙的塑性撕裂柱和壁，以及具有显示界面断裂的微型凹坑的高度近似恒定的平台。虽然试样表现出宏观脆性行为，但这些特征是韧性断裂的特征。推测最可能发生断裂的情况如下：