microprecipitates

Microprecipitates are very small solid particles that form within a solid solution when an alloy is heat treated. They are typically nanometer-scale and dispersed through the host matrix. These precipitates arise from a supersaturated solid solution after quenching and subsequent aging, and their crystal relation with the matrix can change as they grow—from coherent to semi-coherent to incoherent.

Nucleation generally occurs at defects such as dislocations, grain boundaries, or vacancies. Early-stage precipitates in some alloys are Guinier-Preston zones, which may evolve into more stable, detectable precipitates with aging. Growth is diffusion-controlled, so the size, distribution, and volume fraction of microprecipitates depend on temperature, time, and alloy composition.

The presence and properties of microprecipitates strongly influence mechanical behavior. They impede dislocation motion, producing precipitation hardening that raises yield strength and hardness. The strength contribution depends on particle size, spacing, coherency, and volume fraction. Overaging, where precipitates coarsen and lose coherency, can reduce strength but may improve other properties such as ductility or high-temperature stability.

Common contexts include aluminum alloys (for example, systems forming Guinier-Preston zones and subsequent theta''/theta' and theta phases), nickel-based superalloys, and various steels where carbide or intermetallic precipitates form. Characterization typically relies on transmission electron microscopy, atom probe tomography, and diffraction techniques to assess size, distribution, and crystal structure.

Microprecipitates thus play a central role in tailoring strength, hardness, creep resistance, and overall performance of metallic materials through controlled aging and alloy design.