microvoids

Microvoids are tiny cavities within a solid material. They are smaller than visible pores and can occur in metals, polymers, ceramics, and composites. Their sizes range from sub-micron to a few micrometers, depending on material and processing history.

Common formation mechanisms include gas entrapment during casting or foaming, shrinkage porosity during solidification, phase separation in polymers, and sintering defects in ceramics. In ductile metals, microvoids often nucleate at weak inclusions or second-phase particles during plastic deformation and can grow and coalesce under stress, leading to fracture.

Effects: Microvoids reduce density and stiffness and may decrease strength and fracture resistance by acting as stress concentrators. However, in some engineered materials, a controlled population of microvoids or void-based microarchitectures can enhance toughness by distributing strain and absorbing energy.

Detection and characterization: Microscopy (optical and electron) allows direct imaging of microvoids, while X-ray computed tomography enables three-dimensional porosity mapping. Porosimetry and density measurements provide estimates of volume fraction, and statistical analysis yields size distributions.

Applications and relevance: microvoids are a consideration in quality control for casting, powder metallurgy, and additive manufacturing; in metal foams and polyurethane foams they contribute to energy absorption and insulation properties.