University of Oulu

Misra, R., Injeti, V., Somani, M. (2018) The significance of deformation mechanisms on the fracture behavior of phase reversion-induced nanostructured austenitic stainless steel. Scientific Reports, 8 (1), 7908. doi:10.1038/s41598-018-26352-1

The significance of deformation mechanisms on the fracture behavior of phase reversion-induced nanostructured austenitic stainless steel

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Author: Misra, R. D. K.1; Injeti, V. S. Y.1; Somani, M. C.2
Organizations: 1Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical, Materials and Biomedical Engineering, University of Texas at El Paso
2Center for Advanced Steel Research, The University of Oulu
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 3 MB)
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Language: English
Published: Springer Nature, 2018
Publish Date: 2018-08-16


We describe here the relationship between grain structure, deformation mechanism and fracture characteristics in an austenitic stainless steel. This was accomplished using the novel concept of phase reversion that enabled a wide range of grain size from nanograined/ultrafine grained (NG/UFG) to coarse-grained (CG) regime to be obtained in a single material through change in temperature-time annealing sequence. In the NG/UFG structure, a marked increase in abundance of stacking faults (SFs) and twin density with strain was observed that led to a decrease in the average spacing between adjacent SFs, thus converting stacking faults into twins. Twinning in NG/UFG structure involved partial dislocations and their interaction with the grain boundaries, including SF overlapping and the coordinated nucleation of partial dislocations from the grain boundaries. The plastic zone in the NG/UFG structure resembled a network knitted by the intersecting twins and SFs. With SFE ~30 mJ/m², the minimum stress for twin nucleation was ~250 MPa for the experiment steel and the corresponding optimal grain size (dop) wa ~120 nm. In contrast, in the CG structure, strain induced martensite formation was the deformation mechanism. The difference in the deformation mechanism led to a clear distinction in the fracture behavior from striated fracture in high strength-high ductility NG/UFG alloy to microvoid coalescence in the low strength-high ductility CG counterpart. The underlying reason for the change in fracture behavior was consistent with change in deformation mechanism from nanoscale twinning in NG/UFG alloy to strain-induced martensite in the CG alloy, which is related to change in the stability of austenite with grain size. An analysis of critical shear stress required to initiate twinning partial dislocations in comparison to that required to nucleate shear bands is presented. The appearance of striated fracture in the NG/UFG alloy suggests a quasi-static step wise crack growth process.

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Series: Scientific reports
ISSN: 2045-2322
ISSN-E: 2045-2322
ISSN-L: 2045-2322
ISBN Print: 2018
Volume: 8
Issue: 1
Article number: 7908
DOI: 10.1038/s41598-018-26352-1
Type of Publication: A1 Journal article – refereed
Field of Science: 216 Materials engineering
Funding: V.S.Y. Injeti and R.D.K. Misra gratefully acknowledge support from the National Science Foundation, USA through grant #DMR1602080.
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