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Solid Solution Strengthening

High purity metals, while useful, are often softer and weaker than their alloys. The mechanical properties such as yield strength and tensile strength can be determined by the type and amount of impurity added.

One of the most common techniques to harden metals is Solid Solution Strengthening.

The process involves dissolving one metal into another (in a liquid state), this is known as casting.

The casting process involves pouring the liquid metal or metals into a mould and then leaving it to cool, the mould can be various shapes depending on the application. The base metal is known as the solvent and the impurity added is the solute.

There is a limit to the amount of solute that can be dissolved into the solvent, known as the solubility limit.

We are going to analyse the addition of Nickel to Copper

Figure 1 - effect of alloying Nickel with Copper

Figure 1 shows how the yield and tensile strength change with increasing amounts of Nickel added to copper. These charts can be used to determine the percentage necessary for the required characteristics. This is also important as the Nickel is more expensive than copper, so not adding excess is important.

Why do the Tensile strength and Yield change?

To explain these changes, we need to examine the structures at the atomic level.

  • The impurity is surrounded by the host atoms imposing strains on the atoms within the material crystalline lattice.