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Bulk nanostructured metals introduced by severe plastic deformation contain an excess of lattice defects. A nanostructured copper (Cu) processed by a high-pressure torsion technique was examined during in situ heating to investigate microstructural relaxation and quantify the evolution of microstructural parameters using high-energy synchrotron microbeam X-ray diffraction. While general microstructural relaxations, such as recovery, recrystallization, and subsequent grain growth, were observed, the key microstructural parameters, including grain size, microstrain, dislocation density, and thermal expansion coefficient, and their changes at critical temperatures were uniquely described and quantified through diffraction data. Based on this analysis, the stored energies driving thermally activated microstructural changes were estimated for individual defect types — grain boundaries, dislocations, and vacancies — that are expected to significantly influence the relaxation behavior of nanostructured Cu. This study demonstrates the effectiveness of diffraction characterization techniques for gaining a comprehensive understanding of the thermal stability of bulk nanostructured materials.
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In Situ Heating Neutron and X‐Ray Diffraction Analyses for Revealing Structural Evolution during Postprinting Treatments of Additive‐Manufactured 316L Stainless Steel
Herein, lab‐scale X‐ray diffraction and in situ heating neutron diffraction analyses for evaluating the structural changes at postprinting nanostructuring and structural relaxation upon heating, respectively, in an additive‐manufactured (AM) 316L stainless steel are conducted. The nanostructured AM steel after nanostructuring by high‐pressure torsion reached crystallite sizes of 23–26 nm, a dislocation density of ≈45 × 1014 m−2and a microstrain of >0.008. A limited amount of deformation‐inducedε‐martensite was observed at a local region in the nanostructured AM steel. The time‐resolved neutron diffraction experiment upon heating successfully visualizes the sequential structural relaxation and linear thermal lattice expansion in the nanostructured AM steel. In practice, by calculating the changes in crystallite sizes, microstrains, and dislocation densities, the relaxation behaviors of the nanocrystalline AM steel is observed: 1) recovery with slow stress relaxation with increasing hardness up to 873 K, 2) recrystallization with accelerated stress relaxation at 873–973 K; and 3) grain growth above 973 K with (iii′) total stress relaxation in lattices up to 1023 K. In addition, this manuscript makes connections between the critical subjects in materials science of advanced manufacturing, metal processing and properties, and novel time‐resolved characterization techniques.
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- Award ID(s):
- 1810343
- PAR ID:
- 10308361
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Engineering Materials
- Volume:
- 24
- Issue:
- 4
- ISSN:
- 1438-1656
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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