Interstital solid solution strengthening occurs when which of the following happens?

• A. Solute atoms replace host atoms with minimal lattice distortion.
• B. Relatively small solute atoms occupy interstitial positions between host atoms.
• C. The alloy forms a phase-separated mixture.
• D. The lattice experiences less distortion than in substitutional.

Answer: (B)

Interstitial solid solution strengthening happens when small solute atoms sit in the interstitial spaces between the host lattice atoms. These tiny atoms don’t replace host atoms; instead they fit into gaps and create local lattice distortions. Those distortions generate stress fields that interact with moving dislocations, making dislocation glide harder and thereby increasing the alloy’s strength and hardness. A is about substitution with minimal distortion, which is a different scenario. C describes phase separation, not a solid solution. D is incorrect because interstitials typically produce noticeable lattice distortion, not less distortion than substitutional cases.