Microscopy is the bedrock of many materials investigations. To offer quick turnaround microscopy services, REXP2 Research LLC maintains in-house optical microscopy capabilities and, working with outside laboratories, can specify, manage, and analyze Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), micro-Raman, and surface topography investigations. The table at the end of this page lists all in-house imaging capabilities. All in-house instruments have cameras for capturing color images and video. We use ImageJ and Adobe Photoshop as well as custom Python code for image analysis. Below is an example of how using multiple optical imaging modes can quickly reveal the condition of a surface and causes of damage or lack of performance.
In many cases, optical microscopy can reveal surface details of significance on a part without having to resort to more costly SEM. We use multiple imaging modes to extract the most information from your specimen. Our in-house Differential Image Contrast (DIC) or Nomarski microscopy capability provides three dimensional contrast to flat specimens, capturing height and depth information. When coupled with bright field and dark field imaging, this provides a more complete analysis of the surface. The example shown in the micrographs above is an electrical contact The bright field image shows wear and corrosion, but does not really provide much information on the extent of wear resulting from repeated sliding insertion and removals. Bright field, the most common optical imaging mode, provides little out of focus-plane information. The dark field image combined with critical focusing on the Nomarski image establishes that the corrosion is in-fact on top of the contact substrate. The Nomarski contrast image then reveals the surface topography of the wear grooves, showing much more extensive damage than anticipated by the simple bright field image. Thus, corrosion appears to be a continuous process and sliding wear is an intermittent process. This specimen was not birefringent. However, if this specimen or its corrosion products showed birefringence, e.g., an alpha-titanium or graphitic substrate, polarized light microscopy (PLM), a capability of our company, would have provided a fourth imaging dimension for analyzing this problem.
In some alloys, microstructures are revealed with Nomarski contrast or polarized light on polished sections without etching. This is particularly the case when both hard and soft phases are present.
Relevant blog postings
In-house microscopy capability matrix
|Technique||Transmission (Diascopic)||Reflection (Episcopic)||Applications|
|Bright field||✓||✓||Metallography, thin sections|
|Dark field||✓||✓||Metallography, thin sections|
|Differential image contrast (DIC, Nomarski)||✓||Surface relief, wear scars, corrosion, failure analysis|
|Polarized Light||✓||✓||Metallography, graphite, crystal orientation, texture|
|Phase contrast||✓||Liquids with particles or microorganisms|
|Stereo||✓||✓||Failure analysis, wear, corrosion|