Altering the Stability of Surface Plastic Flow via Mechanochemical Effects

Abstract

We demonstrate a link between surface plastic flow and ambient chemical environmenta mechanochemical effect-in large-strain deformation of metals, using high-speed in situ observations. This link, different from known mechanochemical effects, is studied using aluminum and an alcohol environment. Three distinct flow modes-sinuous, laminar and segmented-occur, depending on the alcohol action on the metal surface. Two transitions, one from sinuous to laminar and the other from sinuous to segmented flow are demonstrated. In both cases, the final flow modes are characterized by smaller deformation forces (order of magnitude) as well as much improved quality of the final surface. The action of the chemical medium itself is coupled to the flow mode, distinguishing it from other mechanochemical effects previously reported. The effect appears to be replicable to different degrees in other metal systems such as copper, iron, stainless steels and nickel. Based on the observations, a schematic stability phase diagram for plastic flow is proposed. Implications of the results for enhancing performance of cutting and surface deformation processes for soft and highly strain-hardening metals are discussed.

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