SEM – EDS Application Examples
Metallurgical Associates employs over 30 years of experience in utilizing Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) to improve our clients products, processes and profitability. These powerful techniques provide essential information for successful failure analysis, contaminant identification, and a wide range of metallurgical and materials evaluations.
SEM is capable of imaging at high magnification (up to 200,000X) with a deep field of focus. Images of fractures, contaminants and other materials samples often do not give a reference point of how powerful this capability is. As a result of our long experience in SEM, Metallurgical Associates is occasionally called on by clients outside the manufacturing, legal and insurance industries. These include medical research, the source of the sample imaged at left. Feature “A” is a red blood cell, feature “B” is a white blood cell and feature “C” is a bacteria. The sample is a vascular graft, basically a spliced in artificial vein. The magnification is 10,000X, approximately five percent of the SEM’s ultimate magnification capability.
SEM image of fatigue fracture through a failed bearing at 2000X magnification. Fatigue is the most common type of fracture affecting engineered components. Fatigue fractures occur when a component is subjected to alternating stresses. Each stress alteration, or cycle, produces a microscopic linear crack which appears as repeated parallel lines. These microscopic cracks progress until the remaining un-cracked area of the component can no longer sustain the next load cycle, resulting in complete failure. An in-depth discussion of fatigue is presented in the Spring 2009 Metallurgical Associates Newsletter.
When combined with SEM, Energy Dispersive Spectroscopy (EDS) provides powerful analytical capabilities. The SEM image at left shows an embedded particle (lower center) at the end of a wear track in a hydraulic cylinder. Magnification 200X.
EDS analysis of the particle revealed that it is composed of silicon and aluminum, indicating silicon sand contamination as its source. Sodium, sulfur, chlorine, potassium and calcium are also present from the hydraulic fluid and dirt which has entered the hydraulic system along with the sand particles. Iron has adhered to the sand particle during the scoring of the cylinder wall, as indicated by the iron peak. Additional information on EDS analysis of contaminants is available in the Winter 2007 Metallurgical Associates Newsletter.
Metallurgical Associates analysis of cracks in a welded structure identified areas of lack of fusion in several of the welds. This SEM image shows the characteristic smooth, soft edged features of lack of weld fusion. Our recommended changes to the welding procedure prevented future cracking. Magnification 500X.
SEM image of fracture resulting from hydrogen embrittlement. This failure mode results from the absorption of hydrogen atoms into a component which then accumulate at the grain boundaries, exerting an internal tensile stress. The hydrogen may originate from a variety of sources including acids from plating or pickling, moisture from corrosion, or improperly stored welding rods. Magnification 2000X.
Near surface casting defects are potential fracture initiation sites, acting as stress raisers. This shrinkage porosity in a continuous cast wire resulted in fracture during subsequent drawing to the final wire diameter. Magnification 500X.