Amorphous Beilby layer

The amorphous Beilby layer (as it is often called) has properties markedly different from the rest of the solid. It is much harder, and is usually more soluble and electrolytically more anodic, a fact of considerable importance in the corrosion of metals, as it is often found that corrosion starts at those points (such as the neighbourhood of a punched hole) where some degree of surface flow, or damage to the crystalline structure, has taken place in the metal. It has, apparently, powers of dissolving other metals, not possessed by a crystalline surface. Thus Finch, Quarrell, and Roebuck1 found that if small amounts of metals were deposited by condensation from vapour on to a polished surface of another metal, patterns indicative of the crystalline structure of the deposited metal were obtained temporarily, but disappeared after a few minutes or even seconds. Permanent patterns of zinc on copper could only be obtained by very many successive depositions. If, however, metals were similarly deposited on crystalline surfaces of other metals, one deposition was always sufficient to give the pattern of the deposited metal. 

TWO SEPARATE ALTERED or damaged layers classically have been recognized on metal surfaces formed by cutting- or polishing-type processes namely, an amorphous-like "Beilby" layer and a plastically deformed layer. Modern work indicates that the Beiiby layer is not, in fact, formed by the common important methods of surface preparation but that a deformed layer always is. The detailed structure of this layer is reviewed. Some consideration is also given to residual elastic stresses, surface topography, and embedded abrasive. 

These parameters can be checked independently by their consistency with macro-scopically determined ones on mechanically polished samples. Mechanical polishing yields an amorphous and therefore isotropic Beilby layer resulting in an averaged isotropic complex refractive index niso. The correlation between niso and the anisotropic parameters is given by the equation ... 

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