What is the Difference Between Intermetallic Compounds and Solid Solution Alloys

The key difference between intermetallic compounds and solid solution alloys is that intermetallic compounds have a uniform structure, whereas solid solution alloys have a non-uniform structure.

Intermetallic compounds are substances consisting of solid phases which include two or more metallic or semi-metallic elements arranged in an ordered structure. Solid solution alloys are a type of alloy material that is made to improve the strength of pure metal.

CONTENTS

1. Overview and Key Difference
2. What are Intermetallic Compounds 
3. What are Solid Solution Alloys 
4. Intermetallic Compounds vs Solid Solution Alloys  in Tabular Form
5. Summary

What are Intermetallic Compounds?

Intermetallic compounds are substances consisting of solid phases and include two or more metallic or semi-metallic elements arranged in an ordered structure. We can name these materials as intermetallic or intermetallic alloys. Often, these compounds have a well-defined and fixed stoichiometry. Generally, intermetallic compounds are hard and brittle, having high-temperature mechanical properties. We can classify these compounds are stoichiometric and non-stoichiometric intermetallic compounds.

When considering the properties and applications of these compounds, they generally have high melting points and are brittle at room temperature. There can be cleavage or intergranular fracture modes of intermetallic compounds because of the limited independent slip systems that are needed for plastic deformation. However, there can be ductile fracture modes of intermetallic compounds as well. This ductility can be improved in these compounds through alloying other materials such as boron, which can improve grain boundary cohesion.

Some common examples of intermetallic compounds include magnetic materials such as alnico, sendust, and Permendur, superconductors such as A 15 phases and niobium-tin, shape memory alloys, etc. The intermetallic compounds we can find from history include Roman yellow brass, Chinese high tin bronze and type metal, SbSn.

What are Solid Solution Alloys?

Solid solution alloys are a type of alloy material that is made to improve the strength of a pure metal. The process of the production of a solid solution alloy is known as solid solution strengthening. This process is performed by the addition of atoms of one element to the crystalline structure of another element, where the former element is named as the alloying element and the latter is named as the base metal. This addition forms a solid solution.

Generally, the addition of an alloying element causes a local non-uniformity in the pure metal. This makes the plastic deformation difficult through impending dislocation movement via stress fields. On the other hand, alloying beyond the solubility limit can cause the formation of a second phase which leads to the strengthening through other mechanisms, e.g. formation of intermetallic compounds.

There are different types of solid solution alloys, such as substitutional solid solutions and interstitial solid solutions. These two types differ from each other according to the size of the alloying element. If the alloying element atom is larger than the solvent atom of the solution, it can replace the solvent atoms in the crystal lattice and cause substitutional solid solution formation. If the atoms of the alloying element are smaller than the solute atoms, they tend to fit in the interstitial sites between the solvent atoms and form interstitial solid solutions.

Difference Between Intermetallic Compounds and Solid Solution Alloys

Intermetallic compounds and solid solution alloys are alloy substances having mixtures of metals and/or nonmetals. The key difference between intermetallic compounds and solid solution alloys is that intermetallic compounds have a uniform structure, whereas solid solution alloys have a non-uniform structure.

The following table summarizes the difference between intermetallic compounds and solid solution alloys.

Summary – Intermetallic Compounds vs Solid Solution Alloys

Intermetallic compounds and solid solution alloys are alloy substances having mixtures of metals and/or nonmetals. The key difference between intermetallic compounds and solid solution alloys is that intermetallic compounds have a uniform structure, whereas solid solution alloys have a non-uniform structure.

Reference:

1. “6.6.1: Solutions of Solids IN SOLIDS: Alloys.” Chemistry LibreTexts, Libretexts, 14 July 2020.

Image Courtesy:

1. “Substitutional solute” By Substitutional_solute.png: The original uploader was Siamrut at English Wikipedia.derivative work: Zerodamage – This file was derived from: Substitutional solute.png: (CC BY-SA 3.0) via Commons Wikimedia
2. “Interstitial solute” By Interstitial_solute.png: Siamrut at English Wikipedia / *derivative work: Zerodamage – This file was derived from: Interstitial solute.png: (CC BY-SA 3.0) via Commons Wikimedia