Evidence of twinning-induced plasticity (TWIP) and ultrahigh hardness in additively-manufactured near-eutectic Ni–Nb

Morgan R. Jones, N. Scott Bobbitt, Frank W. DelRio, Mark A. Wilson, Hannah C. Howard, Melina A. Endsley, Jonathan W. Pegues, Ping Lu, Andrew B. Kustas, Irene J. Beyerlein, Michael Chandross, Nicolas Argibay

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Abstract

The temperature-dependent hardness of additively-manufactured near-eutectic Ni–Nb was investigated. This alloy was found to have solidified into a two-phase nanoscale microstructure with peak hardness of H ≅ 14–17 GPa at temperatures up to 400 °C, above which irreversible softening was observed despite retention of significant strength compared to traditionally-synthesized Ni-based superalloys. Experiments and molecular-dynamics simulations show that deformation for single-phase nanocrystalline volumes was confined to intragranular slip-band formation in δ-Ni3Nb and to intergranular grain-boundary sliding in μ-Ni6Nb7. However, microscopy in the nanostructured two-phase regions after severe plastic deformation indicated that phase boundaries acted as nucleation sites for dislocations, promoting twinning-induced plasticity (TWIP) in the μ-Ni6Nb7 grains. This work highlights (1) that additive manufacturing techniques enable formation of unique microstructures that exhibit superior mechanical properties, and (2) that multi-phase intermetallic compounds provide a route to mitigate brittle fracture though the promotion of twinning-induced plasticity. High strength and the absence of interface decohesion (cracking) suggests that multi-phase intermetallic systems may be a viable route for design of new printable superalloys. These results suggest that additive manufacturing methods and rapid solidification via non-equilibrium pathways may enable a pathway for achieving high combined strength and ductility.
Original languageEnglish
Pages (from-to)9723-9736
Number of pages14
JournalJournal of Materials Science
Volume58
Issue number23
DOIs
StatePublished - Jun 1 2023
Externally publishedYes

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