Which statement best describes solid-solution strengthening?

Which statement best describes solid-solution strengthening?

• A. It uses dissolved solute atoms that distort the lattice to impede dislocations.
• B. It uses discrete precipitate particles to hinder dislocations.
• C. It relies on grain boundary diffusion for strengthening.
• D. It relies on phase transformation to create twins.

Answer: (A)

Solid-solution strengthening works because adding dissolved solute atoms into the metal lattice causes local distortions. These size-mismatch distortions create stress fields that interact with moving dislocations, making it harder for dislocations to glide and thus increasing the material’s strength. The statement that dissolved solute atoms distort the lattice to impede dislocations captures this mechanism directly. Other ideas describe different strengthening routes. Discrete precipitates lead to precipitation hardening, not solid-solution strengthening. Strengthening from grain boundary diffusion isn’t the mechanism used for improving strength, and phase transformations that produce twins refer to deformation modes like twinning rather than the lattice distortions from dissolved solutes.