Application Note | Steel Surface Analysis
Steel Surface Characterization Using 3D Profilometry
Camera Stitching to Select the Area, Then 3D Roughness and Pit Analysis
Research & Experimental Testing
Andrea Novitsky
Visual Design & Editorial
Andrew Shore
Introduction
The surface roughness and pitting of a steel surface are studied using first a video zoom camera and then the NANOVEA 3D Non-Contact Profilometer. Using both techniques allows the user to stitch a large image area and then visually select the precise area, or the entire stitched area, to be measured. The field of view and measurement range are only restricted by staging, which can be customized for nearly any application.
Importance of 3D Non-Contact Profilometry for Surface Characterization
Unlike other techniques such as touch probes or interferometry, the 3D Non-Contact Profilometer, using axial chromatism, can measure nearly any surface; sample sizes can vary widely due to open staging and there is no sample preparation needed. Nano through macro range is obtained during surface profile measurement with zero influence from sample reflectivity or absorption, with advanced ability to measure high surface angles and no software manipulation of results. It easily measures any material: transparent, opaque, specular, diffusive, polished, rough, etc. The technique of the non-contact profilometer provides an ideal, broad and user friendly capability to maximize surface studies, along with the benefits of combined 2D and 3D capability.
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Measurement Objective
The camera is used initially to stitch an image area of 6 mm², and then to visually select an area of interest of 2 mm² for measurement. The NANOVEA ST400 Profilometer is then used to create a height map of the surface, and the roughness and pitting were studied.
NANOVEA ST400 Standard
Optical 3D Profilometer
Results
Video Zoom Camera Image
3D Surface
The false color view and 3D view create a very different representation of the surface compared to the camera image. Combined, they provide the user a straightforward and comprehensive tool to observe the morphology of the surface.
Surface Analysis
Conclusion
In this application, we have shown how the NANOVEA 3D Non-Contact Profilometer combined with the video zoom camera can characterize a metal surface in a variety of ways. The camera allows visual imaging of the surface while also providing a tool to precisely select the area to be measured. The 3D scan of the surface shows the average roughness and total height to be 3.620 µm and 37.91 µm, respectively. The deepest pit on the surface was found to be 28 µm deep, and the total volume of the pits was 1.35 × 105 µm³. The data shown here represents only a portion of the calculations available in the analysis software.
Frequently Asked Questions About Steel Surface Characterization
Why combine a camera with a 3D profilometer?
The video zoom camera stitches a large image area so the user can visually select the precise area, or the entire stitched area, to measure; the profilometer then maps its heights.
What area was measured?
A 6 mm² area was stitched by the camera and a 2 mm² area of interest was selected for the 3D scan.
How rough was the steel?
The 3D scan gave an average roughness Sa of 3.620 µm and a total height Sz of 37.91 µm (ISO 25178).
How deep were the pits?
The deepest pit measured 28 µm deep in profile analysis.
Can the pits be counted and sized?
Yes. Treating the pits as islands below a threshold, the software counted 37 and reported their area, volume and maximum height.
Does surface reflectivity matter?
No. Axial chromatism measures with zero influence from sample reflectivity or absorption, on transparent, opaque, specular, diffusive, polished or rough surfaces, with no sample preparation.
