Table of Contents

Materials and Structure





Alloy structures are formed at the atomic level by introducing more than one element into a material. The diagram illustrates two ways in which the solid solution can accommodate the added alloying element or elements. Crystals are characterized by a regular array of atoms (a) and a "repeat unit," the unit cell, contains information about the crystallography of the material. Alloying elements can be added to this structure in normally occupied sites to form a substitutional solid solution (b). Brass, the alloy between copper and zinc, is an example of this type of alloy. In other alloys the added alloying element is located at sites that are normally empty in the pure crystal structure. These "interstitial" sites are used in forming interstitial solid solutions (c). An important example of this type of alloy is a carbon steel.

More than one element may be added to a matrix material to achieve desired mechanical or corrosion properties. Stainless steels contain additions of nickel and chromium in addition to carbon. These larger alloying atoms use substitutional sites and the carbon the interstitial sites.

From: Newey and Weaver, "Materials Principles and Practice," Butterworths (1990)