Additively manufactured hierarchical stainless steels with high strength and ductility

Abstract

Many traditional approaches for strengthening steels typically come at the expense of useful ductility, a dilemma known as strength–ductility trade-off. New metallurgical processing might offer the possibility of overcoming this. Here we report that austenitic 316L stainless steels additively manufactured via a laser powder-bed-fusion technique exhibit a combination of yield strength and tensile ductility that surpasses that of conventional 316L steels. High strength is attributed to solidification-enabled cellular structures, low-angle grain boundaries, and dislocations formed during manufacturing, while high uniform elongation correlates to a steady and progressive work-hardening mechanism regulated by a hierarchically heterogeneous microstructure, with length scales spanning nearly six orders of magnitude. In addition, solute segregation along cellular walls and low-angle grain boundaries can enhance dislocation pinning and promote twinning. This work demonstrates the potential of additive manufacturing to create alloys with unique microstructures and high performance for structural applications.

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Figure 1: Typical microstructure of a laser powder-bed-fusion (L-PBF) produced 316L stainless steel (SS).
Figure 2: Tensile properties of L-PBF 316L stainless steels (SS).
Figure 3: Synchrotron X-ray diffraction (SXRD) measurements during tensile deformation of an L-PBF 316L SS.
Figure 4: Deformation structures of an L-PBF 316L SS after different levels of strain.

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Acknowledgements

The authors thank S. Khairallah, T. Haxhimali, G. Guss, S. Burke, P. Alexander, B. El-dasher, W. King and C. Kamash for their experimental assistance and/or inspiring discussion. J. Li is acknowledged for his initial contribution to the model set-up. R.T.O. acknowledges support from the US Department of Energy, Basic Energy Sciences, Materials Science and Engineering Division, under Contract No. DEAC02-07CH11358. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract No. DE-AC52-07NA27344. ChemiSTEM was performed at the OSU Electron Microscope Facility which is supported by NSF MRI grant number 1040588 and by the Murdock Charitable Trust and the Oregon Nanoscience and Micro-Technologies Institute. This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

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Y.M.W., T.V., J.T.M., T.T.R. and M.K.S. characterized microstructures. T.V., J.Y., W.C. and Z.L. performed mechanical testing. Y.M.W., J.Y., N.P.C. and R.T.O. conducted in situ SXRD experiments and analysed the resultant data. P.J.D. and M.J.M. were involved with processing parameter development and sample print. Z.Z., Y.Z. and T.Z. constructed the models and conducted simulations. Y.M.W., T.V. and T.Z. drafted the initial manuscript. Y.M.W. conceived, designed, and led the project. All co-authors contributed to the data analysis and discussion.

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Correspondence to Y. Morris Wang.

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Wang, Y., Voisin, T., McKeown, J. et al. Additively manufactured hierarchical stainless steels with high strength and ductility. Nature Mater 17, 63–71 (2018). https://doi.org/10.1038/nmat5021

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