Polish on metals

Abstract

In the first year of this century, Beilby (1901) made microscopic and visual observations on the polished surfaces of metals. He stated that such surfaces were covered with a glass-like layer and finally reached the conclusion (Beilby 1921) that this polished layer was similar to a supercooled liquid, the metallic atoms being in the positions which they would occupy, at a given instant, in the liquid state. His ideas did not gain general acceptance, however, amongst metallographers and other workers— thus, while Desch (1922) supports the Beilby theory, yet Tammann (1925) is definitely opposed to it. This question as to the structure of the polish layer on metals can only be decided definitely by X-rays or electron diffraction, although an experiment described by Finch, Quarrell and Roebuck (1934) is of interest. They found that zinc atoms, evaporated on to a polished copper surface, dissolved or sank into the polish layer, showing that the latter possesses one of the properties of a liquid. There will be considerable difficulty in directing a beam of X-rays so as to be incident only on the polish layer of a specimen since this layer is so thin and since the X-rays have such a great penetrating power; one would expect that the pattern of the underlying metal would always be obtained. Cathode rays, on the other hand, will not penetrate more than a distance of about 500 A into a solid before being inelastically scattered and may therefore be used for the study of polish, when incident so as to make a small angle with the surface.