放射光ナノトモグラフィによるAl-Zn-Mg合金中の3D亀裂進展挙動解析

抄録

Hydrogen embrittlement behavior in Al-Zn-Mg alloys was investigated to establish development guidelines for the next-generation high-strength Al-Zn-Mg alloys. In this study, the crack growth behavior of the hydrogen-charged Al-Zn-Mg alloys with Zn content increased to 10 mass% were examined by synchrotron X-ray tomography. The morphologies of intergranular and quasi-cleavage crack-tip were visualized with the resolution of about 150 nm by imaging-type X-ray tomography developed in recent years. In order to evaluate their crack driving force, crack-tip opening-displacement (CTOD) were directly measured from tomographic images. The average CTODs of intergranular and quasi-cleavage crack were 0.14 μm and 0.23 μm, respectively. It has been revealed that the hydrogen embrittlement crack-tip was sharp and its driving force was quite low. Analysis of the stress fields in the vicinity of crack-tip was carried out based on the crack-opening profiles. Both intergranular and quasi-cleavage cracks were found to follow the RDS singularity in the immediate vicinity of the crack-tips. It has been clarified that although cracks caused by hydrogen embrittlement are low fracture resistance, unlike so-called brittle fracture, limited plastic-deformed regions were present at the crack-tip.