Material-Independent Mechanochemical Effect in the Deformation of Highly-Strain-Hardening Metals
A Udupa and K Viswanathan and M Saei and JB Mann and S Chandrasekar, PHYSICAL REVIEW APPLIED, 10, 014009 (2018).
Soft and highly-strain-hardening metals such as iron, aluminum, and tantalum, often called "gummy," are notoriously difficult to cut. This is due to their tendency to exhibit redundant, unsteady plastic flow with large-amplitude folding, which results also in macroscale defects on the cut surface and large energy dissipation. In this work, we demonstrate that this difficulty can be overcome by merely coating the initial metal surface with common adhesive chemical media such as glues and inks. Using high-speed in situ imaging, we show that the media act by coupling unsteady surface-plastic-flow modes with interface energetics-a mechanochemical action-thereby effecting a ductile-to- brittle transition, locally. Consequently, the unsteady plastic flow with folding transitions to a periodic segmentation-type flow in the presence of the surface media, with near absence of defects on the cut surface and significantly lower energy dissipation (a reduction of up to 80%). This mechanochemical effect is controllable and not material specific, with the chemical media demonstrating comparable efficacy across different metal systems. This makes it quite distinct from other well-known mechanochemical effects, such as liquid-metal embrittlement and stress-corrosion cracking, that are both highly material specific and catastrophic. An analytic model incorporating local flow dynamics, stability of dislocation emission, and surface-media energetics is found to correctly predict the onset of the plastic-flow transition. The benign nature and simplicity of the media suggest wide-ranging opportunities for improving the performance of cutting and deformation processes for metals and alloys in practical settings.
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