Case 1: Multi-layer and structured ceramics inspection
Ceramics are typically highly scattering and therefore it can be challenging to inspect ceramic components. The below figure 1 shows how MIR-OCT can be used to visualize lay thickness, uniformity, structures and defects in two types of ceramics: Zirconia and alumina. Figure 1(a) shows an illustration of the test sample, which is a ceramic stack composed of a zirconia plate (C1) and two alumina plates (C2+C3). The middle plate (C2) has various structures inscribed, which can be visualized when inspected using MIR-OCT. Figures 1(b) show a 3D view of the OCT data obtained when scanning the stack from the bottom through the alumina plate C3. The structure in the alumina plate C2 is very clearly seen in a top-down view, as shown in Figure 1(c). Scanning instead from the top of the stack through the zirconia plate C1, we can see that this ceramic plate is highly scattering and presents multiple defects. Even so, it is still possible to detect the backside of the structured alumina plate C2.
Figure. 1: MIR-OCT inspection of a ceramic stack with an embedded microstructure. (a) Schematic of the ceramic stack. (b) 3D scan of the stack when scanned through the alumina plate C3. (c) The microsctructure of alumina plate C2 visualized through alumina plates C2 and C3 (775 microns). (d) 3D scan of the stack when scanned through the zirconia plate C1.
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The Star to Guide the Way! The Polaris mid-IR supercontinuum laser is the light source of choice for applications requiring a near diffraction-limited output beam with a wide bandwidth and high output power. Applications include
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* at stable room temperature.
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Case 1: Underfilm corrosion detection in marine coatings
One of the big challenging in the NDE/NDT industry is detection of underfilm corrosion. The onset of corrosion at the substrate level means that it is not visible from the surface until the corrosion has progressed to a stage where the coating has completely failed and delaminated from the substrate. Therefore, early detection of underfilm corrosion is key to minimizing the damages and subsequent cost of repairs. Below is an example of how our OCT technology can be used to detect corrosion under a 369 µm thick layer of white high gloss alkyd enamel.
Figure 1: Detection and imaging of corrosion underneath 369 µm of high gloss coating. (a) Sample overview. (b) Surface image near the edge of the coating. (c) Sub-surface image at the same location as (b), clearly identifying corrosion underneath the coating. (d) Cross-sectional image of the edge of the coating.
Case 2: Monitoring wet film thickness
Another challenge with coating inspection is monitoring of wet film thickness. Often, wet film thickness is measured just after application of the paint using contact tools that leave marks, have low resolution, and require subsequent cleaning. Since our OCT system is non-contact, it can monitor the wet film thickness during during curing, providing information about the temporal dynamics. Below is an example of the measured wet film thickness of a blue anti-fouling hull paint during curing.
Figure 2: Measured film thickness during curing of a blue commercial anti-fouling hull coating.
Case 3: Coating defects in wind turbine blades
To ensure high efficiency of power generation, wind turbine blades are routinely maintained to counter the effects of erosion. The leading edge of the blades particularly susceptible to erosion, and therefore it is important to ensure that leading edge protective coatings are free from defects, such as bubbles and cracks. The presence of defects could lead to a reduced life time of the coating, as illustrated below:
The below figure shows an example of such defects detected using NORBLIS MIR-OCT, and the results were verified using X-ray CT scanning:
Figure 3: Detection of defects in wind turbine blade coating. Left column: MIR-OCT. Right column: X-ray CT (for validation). (a-d) Top down view. (e-j) cross-sectional view.
OCT can also be used to determine layer thickness and uniformity:
Figure 4: Using MIR-OCT for coating layer visualization.
Naturally, OCT is limited to scanning the outermost coating layers. However, unlike other techniques OCT is a field-deployable, non-contact and non-destructive method.
Case 4: Automotive paint inspection
We were approached by a company working in the automotive sector, that were interested in performing inspection on their paints using OCT. In this example the sample was an aluminium plate pre-treated for improved adhesion that was then applied a primer and top coating (see Figure below). The top coating contained ceramic flakes to give it a sparkling look.
Figure 4: Sketch of the automotive paint sample layer structure.
In this case, the company was interested in the following:
- Layer thicknesses
- Uniformity
- Defects
First, we look at the layer thicknesses. Figure 3 shows the maximum intensity signal in the cross-section of a random area on the sample over a 3x3 mm area. This correspond to 1.000 superimposed images. This was done to capture signals from the ceramic flakes in the top coating, since the contrast between top coating and primer in this case was not visible for this type of coating. This allowed us to give an estimate of the boundary between the top coating and the primer, based on the deepest observation of flakes. The line in the top is the boundary between air and top coating, and the bottom line is the boundary between the primer and the aluminium substrate. The thin metal adhesive layer is not observed, so it is assumed to be either less than 10 microns thick or very similar to the primer.
Figure 6: Cross-sectional view of a 3x3 mm scan of a random area on the sample showing the extend of the top coating and primer layers.
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(PRODUCT IN DEVELOPMENT) There is more to see! The Mirage ("to look at, to wonder at") Mid-IR OCT system is the first of its kind based on the NORBLIS supercontinuum laser technology, enabling fast and high-resolution sub-surface imaging in scattering media, such as:
Applications include
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