Wickmann Carsten, Benz Christopher, Heyer Horst, Witte-Bodnar Kerstin, Schäfer Jan, Sander Manuela
Institute of Structural Mechanics, University of Rostock, Albert-Einstein-Str. 2, 18059 Rostock, Germany.
Institute of Physics, University of Rostock, Albert Einstein-Str. 23-24, 18059 Rostock, Germany.
Materials (Basel). 2021 Sep 15;14(18):5315. doi: 10.3390/ma14185315.
The aim of the present work was to investigate the 'fine granular area' (FGA) formation based on artificially generated internal defects in additively manufactured Ti6Al4V specimens in the early stage of fatigue crack growth in the 'very high cycle fatigue' (VHCF) regime. Fatigue tests were performed with constant amplitude at pure tension-compression loading ( = -1) using an ultrasonic fatigue testing setup. Failed specimens were investigated using optical microscopy, high-resolution 'scanning electron microscopy' (SEM), and 'focused ion beam' (FIB) techniques. Further, the paper introduces alternative proposals to identify the FGA layer beneath the fracture surfaces in terms of the 'cross section polishing' (CSP) technique and metallic grindings with special attention paid to the crack origin, the surrounding microstructure, and the expansion of the nanograin layer beneath the fracture surface. Different existing fracture mechanical approaches were applied to evaluate if an FGA formation is possible. Moreover, the results were discussed in comparison to the experimental findings.
本研究的目的是在“超高周疲劳”（VHCF） regime下，研究增材制造Ti6Al4V试样在疲劳裂纹扩展早期基于人工制造的内部缺陷形成的“细颗粒区”（FGA）。使用超声疲劳试验装置在纯拉压载荷（R = -1）下进行恒幅疲劳试验。使用光学显微镜、高分辨率“扫描电子显微镜”（SEM）和“聚焦离子束”（FIB）技术对失效试样进行研究。此外，本文介绍了基于“横截面抛光”（CSP）技术和金属研磨来识别断口表面下方FGA层的替代方案，特别关注裂纹起源、周围微观结构以及断口表面下方纳米晶粒层的扩展。应用不同的现有断裂力学方法来评估FGA形成的可能性。此外，将结果与实验结果进行了比较讨论。
