Introduction: Why Electron Microscopy Is Central to Failure Analysis
Metallurgical failure analysis requires characterisation of fracture surfaces, microstructures, corrosion products, and contamination at length scales from millimetres down to angstroms — information that optical microscopy cannot provide. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), combined with Energy-Dispersive X-ray Spectroscopy (EDS), are indispensable tools for the definitive identification of failure mechanisms in metals, alloys, and metallic coatings.
SEM in Metallurgical Failure Analysis
Fracture Surface Examination (SEM Fractography)
SEM fractography is the most powerful tool for identifying the fracture mechanism responsible for a metallurgical failure. The three-dimensional SEM images of fracture surfaces reveal:
- Fatigue striations: Parallel bands on the fracture surface recording the crack front position per load cycle — confirming fatigue failure and enabling crack growth rate estimation
- Ductile dimples (microvoid coalescence): Equiaxed dimples from tensile overload or elongated dimples from shear overload — indicating ductile fracture
- Cleavage facets: Flat, crystallographically oriented facets with river markings — indicating brittle cleavage fracture in ferrous materials
- Intergranular facets: Smooth, polyhedral grain boundary surfaces indicating grain boundary fracture from hydrogen embrittlement, temper embrittlement, SCC, or high-temperature creep
- Beach marks: Macroscopic concentric growth rings visible at lower SEM magnification — confirming fatigue and identifying the crack initiation site
SEM-EDS Corrosion Product Analysis
EDS analysis of corrosion deposits, oxide films, and surface contamination on failed metallic components identifies the elemental composition of corrosion products — distinguishing between oxides, chlorides, sulphides, and phosphates that indicate different corrosive environments. EDS elemental mapping reveals the spatial distribution of corrosion products across complex fracture surfaces.
Inclusion and Second Phase Characterisation
SEM-BSE (backscattered electron) imaging identifies inclusions and second phases as contrast variations across the polished metallographic section. EDS point analysis identifies inclusion compositions (aluminate, MnS, silicate) that correlate with crack initiation sites and confirm their role in the failure.
TEM in Metallurgical Failure Analysis
Transmission Electron Microscopy provides atomic-resolution imaging and diffraction patterns that reveal:
- Dislocation structures: Revealing the deformation history and stress state at the failure origin
- Grain boundary segregation: Identifying trace element segregation (sulphur, phosphorus, antimony) to grain boundaries — direct evidence for temper embrittlement or creep-induced boundary weakening
- Precipitate characterisation: Identifying precipitate phases at crack initiation sites — M23C6 carbides in sensitised stainless steel, gamma prime or gamma double prime phases in nickel superalloys, coherency stress precipitates in aluminium alloys
- Oxide film structure: Characterising passive film thickness, composition, and crystallinity at the corrosion front in SCC specimens
FIB (Focussed Ion Beam) systems prepare thin TEM specimens from specific locations on failure surfaces — enabling targeted atomic-resolution characterisation at the precise crack tip, grain boundary, or inclusion that initiated failure.
EBSD (Electron Backscatter Diffraction) in Failure Analysis
EBSD maps crystallographic orientation across polished sections, revealing:
- Grain misorientation: Identifying high-angle grain boundaries susceptible to intergranular attack
- Texture and anisotropy: Crystallographic texture from rolling or forging that creates directional strength and SCC susceptibility
- Plastic strain distribution: Kernel average misorientation (KAM) maps identify plastically deformed regions around crack tips and initiation sites.
Industrial Applications
In the aerospace industry, SEM fractography of turbine blade fatigue failures identifies fatigue crack initiation sites at inclusions or coating defects — driving material and coating process improvements. In the power generation industry, SEM-EDS corrosion analysis of boiler tube failures characterises ash deposit chemistry that drives corrosion mechanisms. In the automotive industry, SEM fractography of connecting rod fatigue fractures identifies manufacturing defects that initiated premature fatigue failures in engine components.
Conclusion
Electron microscopy techniques — including SEM, TEM, EDS, and EBSD — are indispensable for metallurgical failure analysis, providing the high-resolution imaging and compositional insights required to identify failure mechanisms with precision. From fracture surface interpretation and corrosion product analysis to atomic-scale microstructural characterisation, these tools enable definitive root cause determination. By integrating these advanced methods, engineers can not only diagnose failures accurately but also implement informed corrective actions, ultimately improving material performance, reliability, and safety in critical applications.
Why Choose Infinita Lab for Electron Microscopy Failure Analysis?
Infinita Lab provides SEM, SEM-EDS, EBSD, TEM, and FIB-TEM services for metallurgical failure analysis through our nationwide network of accredited electron microscopy and materials analysis laboratories, with expert fractographic and microstructural interpretation.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you.
Frequently Asked Questions (FAQs)
