Non-destructive detection of coating delamination using reflected time-domain terahertz waveforms.

Area of Science:

• Materials Science
• Non-destructive Testing
• Coatings Technology

Background:

• Adhesive failure in anti-corrosion coatings causes delamination, leading to structural compromise.
• Corrosive agents ingress through thin gaps created by delamination.
• Early detection of delamination is crucial for maintaining structural integrity.

Purpose of the Study:

• To investigate terahertz pulsed imaging (TPI) for detecting sub-resolution air gaps in anti-corrosion coatings.
• To assess TPI's capability to identify delamination by measuring apparent thickness changes.
• To demonstrate TPI as a non-destructive method for early delamination detection.

Main Methods:

• Terahertz pulsed imaging measurements were performed on a quartz window over an air gap and multi-layered paint systems.
• Apparent thickness changes in overlaying layers were measured to infer the presence of sub-resolution gaps.
• Scanning electron microscopy (SEM) was used to estimate delamination thickness in paint systems.

Main Results:

• An increased apparent thickness of the quartz window was observed over a 19 µm air gap, consistent with theoretical predictions.
• TPI detected a 9.9-13.1 µm increase in apparent base coating thickness in aged paint systems with delamination.
• Delamination layer thickness was estimated to be 10 µm using SEM.

Conclusions:

• Terahertz pulsed imaging can detect air gaps below its minimum resolvable thickness by analyzing apparent thickness variations.
• This technique provides a non-destructive means for early-stage delamination detection in protective coatings.
• TPI enhances the assessment of coating integrity and structural health monitoring.