A. la Monaca; D. Axinte; Z. Liao; N. Neate; M. Hardy
Acta Materialia 297 (2025) 121377
High-strain-rate shear deformation of advanced alloys is the bases of a wide range of processing methods (e.g.
cutting, forming, shot peening) for highly engineered components used in a wide range of industries (e.g.
aerospace, nuclear, automotive). When such shear deformations occur, layers of very fine equiaxed grains have
been widely reported which are commonly explained via a continuous dynamic recrystallization (CDRX)
mechanism. However, employing a cutting operation to induce shear deformations at high strain rates (10^4–10^5
s-1) in a Ni-based superalloy we found features that cannot be explained by this classical approach. Here we
quickly stopped the shear deformation process so that the phenomena leading to grain refinement can be inferred
by examining the deformation zones in a time successive manner. Our analysis using Transmission Kikuchi
Diffraction (TKD) and Transmission Electron Microscopy (TEM), we prove that the grain refinement is much
more complex than previously reported as this is the result of a bi-modal mechanism where Geometric Dynamic
Recrystallization (GDRX) combines with CDRX leading to unique microstructural features. We further supported
the proposed bi-modal grain refinement mechanism by showing differences in mechanical properties by per
forming micro-pillar compression tests within targeted deformation zones (i.e. dominated by CDRX and
GDRX+CDRX). These findings highlight new mechanisms of dynamic recrystallization caused by high-strain-rate
shear deformations which have pivotal importance on how to conduct key manufacturing processes so that the
properties of resultant recrystallized layers can be controlled.