We know about solid solutions (substitutional and interstitial types) and the requirements for forming one or the other. Now let us get into little more details about solid solution strengthening. This mode of strengthening is present in both single and polycrystalline materials. Here, dislocations encounter barriers on their path from the solutes present in the host lattice.

Solute atoms can interact with dislocations through the following mechanisms based upon various situations: (a) elastic interaction, (b) modulus interaction,

(c) long-range order interaction, (d) stacking fault interaction, (e) electrical interac­tion, and (f) short-range order interaction. The first three interactions are long — range barriers, and they are relatively insensitive to temperature and continue to act upto 0.6Tm. However, the last three are short-range barriers that contribute strongly to the flow stress only at low temperatures.