Solid solution strengthening

The solid-solution strengthening changes the mechanical properties of solids through the incorporation of interstitial or substitution atoms .

Solids with a long-range order have a regular crystal structure . If foreign atoms are incorporated into the crystal structure, this (the crystal lattice ) is distorted. If the distortion originates from individual atoms or molecules, one speaks of a point defect . Atoms with a similar atomic radius occupy a substitution place in the crystal lattice, significantly smaller atoms (in the case of metals in practice H, O, B, C, N) an interstitial place. The distortion of the crystal lattice prevents sliding movements in the crystal. Sliding movements can then no longer run in one plane, but have to move around the distortions, which requires more energy. So the material has become stronger .

Solid solution strengthening in metals

Solid solution strengthening is used specifically in metals to harden them . Pure metals (e.g. Fe, Al, Cu, Ni, Mg) are very soft with a few exceptions. Only through solidification do metals become as hard as we know it from everyday life. Solid solution strengthening is one of four elementary strength-increasing methods and requires that other elements dissolve in the parent metal. There are metals with complete solubility , which means that the two metals form only one phase for each concentration , and metals with limited solubility, in which a second phase forms when the solubility limit is exceeded . A mixed crystal has only one phase; two phases are called a crystal mixture . However, a mixture of crystals can also have solid solution strengthening. The higher the concentration of dissolved foreign atoms, the higher the solid solution strengthening. In the same way, a greater deviation in the atomic radii causes greater solidification. In general, smaller substitution atoms cause a higher degree of solidification than larger substitution atoms due to the lattice distortion. However, the more the atomic radii differ, the lower the solubility for the substitution atoms. The solubility is also temperature dependent. In most cases, the solubility of foreign atoms increases with temperature. Solid solution strengthening is therefore a strength-increasing method that is resistant to heating. In addition to the hardness, the solid solution strengthening also increases the tensile strength . Elongation at break , electrical conductivity and melting temperature generally decrease.