Four-dimensional observation of ductile fracture in sintered iron using synchrotron X-ray laminography

ABSTRACT

Synchrotron X-ray laminography was used to examine the time-dependent evolution of the three-dimensional (3D) morphology of micropores in sintered iron during the tensile test. 3D snapshots showed that the networked open pores grow wider than 20 µm along the tensile direction, resulting in the internal necking of the specimen. Subsequently, these pores initiated the cracks perpendicular to the tensile direction by coalescing with the surrounding pre-existing microvoids or with the secondary-generated voids immediately before fracture. Topological analysis of the barycentric positions of these microvoids showed that they form the two-dimensional networks within the ∼20 µm of radius area. These observations strongly indicate that the microvoid coalescence could occur on shear planes formed close to the enlarged open pores or between closed pores by strain accumulation and play an important role in the crack initiation.

KEYWORDS:

• Sintered steel
• ductile fracture
• X-ray laminography
• microvoid topology
• persistence diagram

Acknowledgements

Synchrotron radiation experiments were performed at the BL20XU beamline of SPring-8 with the approval of Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2016B 1416). We are grateful to Drs. Masato Niibe, Hiroki Adachi and Hiroyuki Toda for their assistance with our work at SPring-8. We are also grateful to Professors Tomoyuki Shirai for the helpful discussions on PH analysis. We also thank Dr. Vidit Nanda at Oxford University for providing the useful free software Perseus and for the advice. We would like to thank Drs. Toshinori Ozaki and Tamara Farache for English language editing.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Y. Ozaki received the D.Sc. degrees from Hokkaido University, Sapporo, Japan, in 1987. She joined Kawasaki Steel Corporation (JFE Steel Corporation), Tokyo, Japan, in 1988. Since 2016, she has been with the Department of Material Science and Engineering, Kyushu University, where she is currently a Professor. Her main areas of research interest are consolidation mechanisms of metallic powder including metallic glasses, and microstructural control of sintered alloy steels. Dr. Ozaki is a member of several societies such as the Japanese Institute of Metals and Materials (JIM), the Iron and Steel Institute of Japan (ISIJ), and European Powder Metallurgy Association. She is also a member of the Science Council of Japan. She was awarded Japan Institute of Metals and Materials Industrial Achievement Award from JIM in 2011, Scientific Achievement Contribution Prize (Mishima Medal) from ISIJ in 2013, and so on.

Y. Mugita is a student of the Department of Materials Physics and Chemistry, the Graduate School of Engineering, Kyushu University. He joined the group of Professor Furukimi, who has investigated the mechanism of ductile fracture of Wrought steels using high energy X-ray CT. Mr. Mugita won the best presentation prize at the annual meeting of the Japanese Society of Powder and Powder Metallurgy (2017).

M. Aramaki is an Assistant Professor in the Department of Materials Science and Engineering at Kyushu University Japan. He received his Ph.D. degree from the Faculty of Engineering at Kyushu University focusing attention on aspects of superplastic phenomenon in steels. He studies a variety of areas pertinent to the strength and ductility of metallic materials.

O. Furukimi received the M.Eng. degrees from Tokyo University in 1977. He joined Kawasaki Steel Corporation (JFE Steel Corporation) in 1977. He received his Ph.D. from the Faculty of Engineering at Tohoku University, focusing attention on improvement toughness of steel plates for storage tanks of low temperature use in 1989. Since 2005, he has been with the Materials Science and Engineering at Kyushu University, where he was a Professor until he retired in 2018. His main area of research interests is mainly a void nucleation, growth and coalescence mechanism of metals during plastic deformation. He also conducts researches in the field of heat treatment. He was a vice chairman for the Japan society for heat treatment from 2017 to 2018.

S. Oue received the B.E. and the M.E. degrees from Kyushu respectively in 1992 and 1994, respectively. In 1994, he joined the Department of Materials science, faculty of Engineering, Kyushu University, as an Assistant Professor. His current research interests include electrochemistry, electroplating, electrowinning of metals, microscopic observations of electroplating. He is a member of the Mining and Materials Processing Institute of Japan (MMIJ), the Surface Finishing Society of Japan (SFJ), Japan Society of Corrosion Engineering, and the Iron and Steel Institute of Japan. He was also awarded the Best paper award of the MMIJ in 2004, 2010, 2019, and the Incentive award of MMIJ in 2009.

F. Jiang received the Ph.D. degree in 2013 from Kyushu University, Japan. He is currently an assistant professor of the Department of Mechanical Engineering, Yamaguchi University. His research focuses on the study of multiscale flow, transport processes and mechanical behavior of spatially heterogeneous systems consisting of complex geometries.

T. Tsuji is a Professor at Department of Earth Resources Engineering, Kyushu University, and a Lead Principal Investigator in International Institute for Carbon-Neutral Energy Research (I2CNER). He also works as a Department Head of Cooperative Program for Resources Engineering, Kyushu University. He obtained his Ph.D. from the Department of Earth and Planetary Science, the University of Tokyo in 2007.

Dr. A. Takeuchi was received Ph.D. degrees in engineering from Tsukuba Univ., in 1999. He is now in the Japan Synchrotron Radiation Research Institute (JASRI). His research includes x-ray imaging, especially x-ray microscope using synchrotron radiation.

M. Uesugi received Ph.D. degrees in physics from Osaka Univ. He joined Japan aerospace exploration agency (JAXA) as a senior researcher from 2011 to 2016. He is currently a senior researcher in Japan Synchrotron Radiation Research Institute (JASRI). His main areas of research interests are evolution of solid material in early solar nebula, using synchrotron radiation tomography, and development of new techniques for the 3D analysis of material structures by SR-CT and XRD, and software for the analysis.

K. Ashizuka obtained the D. Eng. degree in 2013 from the Department of Material Science and Engineering, Kyushu University, Japan. He is currently a senior researcher for Steel Research Laboratory, JFE Steel Corporation. His research focuses on the study of development of alloyed steel powders for high strength sintered machine parts.

ORCID

S. Oue http://orcid.org/0000-0003-2713-3463

F. Jiang http://orcid.org/0000-0002-8111-4979