J. Mater. Sci. Technol. ›› 2022, Vol. 123: 168-176.DOI: 10.1016/j.jmst.2022.01.024

• Research Article • Previous Articles     Next Articles

4D imaging of void nucleation, growth, and coalescence from large and small inclusions in steel under tensile deformation

Yi Guoa,b,*(), Timothy L. Burnettb, Samuel A. McDonaldb,c, Michael Dalyb, Andrew H. Sherryd, Withers Philip J.b   

  1. aShenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
    bHenry Royce Institute, Department of Materials, University of Manchester, M13 9PL, UK
    cEuropean Synchrotron Radiation Facility (ESRF), 6 rue J Horowitz, 38000 Grenoble, France
    dNational Nuclear Laboratory, Chadwick House, Birchwood Park, Warrington, WA3 6AE, UK
  • Received:2021-11-01 Revised:2021-12-22 Accepted:2022-01-10 Published:2022-10-01 Online:2022-09-30
  • Contact: Yi Guo
  • About author:*E-mail address: yguo@imr.ac.cn (Y. Guo).

Abstract:

Samples of SA508 grade 3 nuclear pressure vessel ferritic steel were subjected to tensile straining whilst being simultaneously imaged in 3D in real time using high resolution, high frame rate time-lapse synchrotron computed tomography (CT). This enabled direct observation of void development from nucleation, through growth to coalescence and final failure validating many inferences made post-mortem or by theoretical models, as well as raising new points. The sparse, large inclusions were found to nucleate voids at essentially zero plastic strain (consistent with zero interfacial strength); these became increasingly elongated with straining. In contrast, a high density of small spherical voids were found to nucleate from the sub-micron cementite particles at larger strains (> 200%) only in the centre of the necked (high triaxiality) region. An interfacial strength approaching 2100 MPa was inferred and soon after their nucleation, these small voids coalesce to form internal microcracks that lead to the final failure of the specimen. Perhaps surprisingly, under these conditions of generally low triaxial constraint the large voids are simply cut across and appear to play no significant role in determining the final failure. The implications of these results are discussed in terms of ductile fracture behaviour and the Gurson model for ductile fracture.

Key words: Void growth, Ductile fracture, Synchrotron X-ray tomography, 4D imaging, Bainitic steel