Which strengthening mechanism relies on finely dispersed particles that hinder dislocations?

• A. Solid-solution strengthening
• B. Grain-boundary strengthening
• C. Work hardening
• D. Precipitation hardening

Answer: (D)

Strengthening by finely dispersed particles that hinder dislocations is precipitation hardening. In this approach, small second-phase particles form within the metal matrix during aging. These precipitates act as obstacles to moving dislocations. The dislocations must either bow around the particles (the Orowan mechanism) or, if the particles are coherent enough, be cut through with extra energy, both of which raise the stress needed for plastic deformation.

This is different from solid-solution strengthening, which relies on lattice distortions from dissolved solute atoms rather than discrete particles; grain-boundary strengthening, which depends on barriers at grain boundaries and thus overall grain size; and work hardening, which builds up dislocation density through plastic deformation to impede further movement.