Exciting Upgrades to Our Scanning Electron Microscope by Lloyd M. Meissner, P.E.

Crane Engineering has been at the forefront of forensic investigations for decades. Our first Scanning Electron Microscope (SEM) was purchased in 1995. The SEM allows for high magnification imaging of fracture surfaces of metals, ceramics and plastic samples.  It is a key tool used in forensic investigations, complementing photographs and optical microscopy. 

This SEM is also equipped with an X-ray detector, called an EDS (Energy Dispersive X-ray Spectroscopy). The X-ray detector is used to identify the elemental chemistry of samples examined by SEM.  This analysis is key in determining why a sample fractured. It shows elemental residues (of chlorine (Cl) for example) which can be quite detrimental to the structural integrity of some metals, especially stainless steels.

In September of 2016, Crane Engineering upgraded our SEM with a new X-ray detector.  This new detector is called a Silicon Drift Detector (SDD) which is far superior to the previous Lithium Drifted Silicon (SiLi) detector.  The SDD has significantly faster count rates, which then equate to better resolution and the ability to map the surface of the sample chemically. These maps then point to areas of interest where there is chemical variation.  Previously, variations in chemistry were determined by a point by point (or subset area by area) technique.  With the new SDD, a full chemical map of the area of interest can be attained in a matter of minutes, instead of hours.

In the example shown below, the scanning of a sample of 4140-steel revealed contamination locations (purple on the left SEM image) caused by manganese concentrations (blue) and sulfur concentrations (red) which were the initiation points of a fracture. This provided a clear and conclusive picture of how to correct the problem—a cleaner grade of steel was recommended.  The upgraded SEM/EDS technology pointed to the fracture origin more quickly providing conclusive failure analysis.

Please contact me to discuss how we can use our SEM/EDS as a failure analysis tool for your project or with any materials related problems you may have.