Metal fracture surfaces are a key basis for determining failure modes. Metal specimens with good electrical conductivity can be directly observed by secondary electron (SE) imaging without coating, clearly revealing the shape and distribution of crystal grains, precipitates, and fracture surface features. By identifying microscopic characteristics such as dimples, fatigue striations, and intergranular fracture, the fracture type can be determined as ductile, brittle, fatigue, or stress corrosion cracking. The magnification of a desktop SEM is sufficient to resolve these fine features indicative of specific failure mechanisms. EDS can further analyze the composition of inclusions or corrosion products at the fracture initiation site, helping trace the root cause of fracture. A typical procedure includes cleaning the fracture surface, polishing if necessary, selecting an appropriate accelerating voltage and imaging mode, and progressively observing and recording features from low to high magnification.
Metal corrosion significantly affects material performance and service life. SEM can observe the micromorphology of corrosion areas, including general corrosion, pitting, crevice corrosion, intergranular corrosion, exfoliation corrosion, and stress corrosion cracking. SE imaging reveals pit morphology, depth, density, corrosion product coverage, and crack initiation/propagation. BSE imaging helps distinguish compositional differences between corrosion products and the metal matrix. Corrosion products often appear loose, porous, cracked, layered, or granular; high depth-of-field imaging displays their three-dimensional structure. EDS determines elemental composition and distribution, indicating enrichment of oxides, chlorides, sulfides, and carbonates and the presence of corrosive elements. Cross-sectional analysis can reveal corrosion layer thickness, layered structure, and the interface between the corrosion front and matrix, helping evaluate corrosion severity, corrosion resistance, and the effectiveness of protective measures.
During the production, processing, transportation, and use of metallic materials and components, various foreign substances may adhere to their surfaces, such as particulate contamination, dust, oil stains, salts, polishing residues, equipment wear debris, plating solution impurities, or embedded inclusions. These foreign substances can affect the quality of subsequent welding, painting, electroplating, bonding, sealing, and assembly. Desktop scanning electron microscopy (SEM) can observe the shape, size, quantity, distribution, adhesion state, and bonding relationship of foreign substances with the substrate. Combined with energy-dispersive X-ray spectroscopy (EDS), their elemental composition can be identified, thereby helping to determine the source of the foreign matter. For contaminants of different natures, such as metal chips, oxides, silicates, salts, and organic residues, morphological and elemental information can corroborate each other, providing a basis for incoming inspection, process control, cleanliness evaluation, and failure analysis.
The internal structure of metallic materials usually requires sample preparation steps such as cutting, mounting, grinding, polishing, and etching before observation. Desktop scanning electron microscopy (SEM) can be used to analyze grain size, phase composition, inclusions, precipitates, voids, microcracks, segregation, coating structure, weld heat-affected zone, and additive manufacturing melt pool microstructure. Secondary electron (SE) imaging can be used to observe microstructural morphology, while backscattered electron (BSE) imaging can differentiate different phases based on atomic number contrast. Combined with energy-dispersive X-ray spectroscopy (EDS), the chemical composition of each phase can be further determined. This capability can be applied to heat treatment process evaluation, casting microstructure analysis, welding quality assessment, powder metallurgy microstructure observation, additive manufacturing material research, and microstructural tracing in failure analysis.
