Electro-chemo-mechanical treatment: Facilitating steel grinding under electrochemical reduction of active cations
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E. D. Shchukin Institute for Physical Chemistry, Russian Academy of Science, Moscow, Russia and Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, Maryland 21218 (Received 20 July 1992; accepted 30 April 1993)
Earlier it was shown that some liquid metals may facilitate the cutting of hard materials, being strongly surface-active media with respect to these solids (decreasing their surface energy), e.g., Zn for steels, Cd for titanium alloys, etc. Recently, a similar physico-chemical principle has been proposed and realized in the course of active metals (Zn, Cd) depositing on the surface of a treated sample (ground tempered steel, 50 HRC) by means of reduction of their cations on a sample used as a cathode in a corresponding electrochemical cell, at room temperature, with a very small amount of active substance, and at very low current densities (—50 mA/cm 2 ); under such conditions, grinding is 1.5-2 times more effective than in the same aqueous solutions without current.
I. INTRODUCTION The mechanical behavior of solids is substantially dependent on surface physico-chemical phenomena caused by surrounding media. These surface phenomena include both reversible adsorption (and chemisorption) interactions resulting in surface energy decreases, i.e., the Rehbinder effect,1 and the accompanying phenomena of dissolution, corrosion, catalytic processes, and other chemical reactions associated with the solid/environment interface.2 Apart from these specific mechanisms, various effects of environment-sensitive mechanical behavior are characterized by the joint action of mechanical stresses and molecules (atoms, ions) in the active media which facilitate fracture and reconstruction of interatomic bonds in the course of new surface cell formation.3 Depending on experimental conditions, effects of environmental-sensitive mechanical behavior may be manifested in the form of strength decreases, embrittlement (ductility reduction), fragmentation, and/or a lower resistance to plastic deformation in metal. Combinations of the above effects may be observed as well. These effects may play a particularly important role in the thin regions of material adjacent to the surface. They are related to the impact of active components in lubricants and lubricant-cooling media in processes of friction and wear, treatment by a press, cutting, and other techniques. These active components include organic surfactants and additions of elemento-organic compounds, as well as
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J. Mater. Res., Vol. 8, No. 9, Sep 1993
highly surface-active media such as melts of metals and salts.4 Electrical polarization plays an important role in surface physico-chemical phenomena and greatly affects the mechanical properties of metals. For example, the electrocapillary effect leads to a drop in hardness owing to a free surface energy decrease while shifting from the potential of zero charge. This effect has been observed5 using the method of decaying pendulum oscillations, as well as by the indentation technique.6'7 It
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