Question 1
The surface and near surface regions of a material differ from the bulk of the same material for a
number of reasons. The surface layer (what we see) is a very thin layer of absorbed gases and water
vapor, and therefore non-representative of the bulk material. Directly below that is a layer of oxide which
occurs almost instantaneously as the material is exposed to atmosphere. Below that is the Beilby layer, a
distorted layer formed by the local melting, flow then solidification of metal due to polishing. The layer
below the Beilby layer is the worked layer, which is reminiscent of the forming process that produced the
material such as cutting, grinding, forging or shot peening. Below all of these layers lies the bulk material,
which is unaffected by the forming processes, polishing, chemical reactions (corrosion) and not
contaminated by the absorption of other elements.