Anthony Beeman
HW 4
Problem 1
1) Do some research about the structure of real solid surfaces. Focus on microstructural, chemical and material property variations commonly encountered. Identify an illustrative example and write a short essay (≈ 200 words) summarizing your findings.
Structure of Real Solid Surfaces
Metals only exist in one bulk structural form. Most commonly being body centered cubic
(BCC), face centered cubic (FCC), and HCP (hexagonal closed pack)
1
. An ordered surface may be obtained by cutting the bulk structure along a particular plane to expose an array of atoms.
Miller index surfaces are used to see what surface atomic structures are formed. Various surfaces will exhibit different physical properties and surface chemical reactivity.
The outer surface of a material will contain several layers that exhibit chemical, physical, and structural properties that are significantly different than the bulk material properties. The subject layers consist of deformed, modified, or chemically reacted planes. Manufacturing processes typically physically deform and modify the subject planes while oxidation will chemically alter the surface of the material.
However, it should be noted that chemically altering the surface is not always negative.
Chemically altering the surface of the materials by way of surfacing hardening significantly improves the wear resistance of parts without affecting the bulk material properties
2
. Surface hardening is commonly seen in industry with components such as cam, bearings, turbine applications, and automotive components. Most surface treatments result in compressive residual stresses at the surface that reduce the probability of crack initiation and propagation.
References
1.
Structure of solid surfaces. www.chemwiki.ucdavis.edu. The Dynamic Chemistry
Ebook. UC Davis 2015.
2.
Schneider, Michael, Chatterjee, Madhu. Introduction to surface hardening of steels*.
2013 ASM International. www.asminternational.org