Quality Control of DLC Layers

Significance of the Topic

Diamond-like carbon (DLC) coatings are indispensable across multiple industries due to their exceptional hardness, wear resistance and low friction. Reliable quality control of DLC layer thickness and uniformity is critical for performance and longevity of components in tooling, automotive parts, medical implants and precision devices.

Objectives and Study Overview

This application note aims to demonstrate a non-destructive, contact-free infrared microscopy approach for rapid and accurate determination of DLC coating thickness. It contrasts traditional destructive methods with FT-IR interferometric measurements and highlights benefits for routine QC and failure analysis.

Methodology

The measurement protocol involves placing a coated sample under the FT-IR microscope in reflection mode without any surface preparation. Multiple reflections of the IR beam within the DLC layer produce a sinusoidal interference pattern in the spectrum. The spacing between interference maxima correlates directly with coating thickness once the refractive index (n=2.41 for DLC) is entered into the evaluation routine.

Used Instrumentation

• LUMOS II FT-IR microscope featuring a long working distance and motorized stage for point-by-point or area mapping
• OPUS spectroscopic software including a dedicated layer thickness evaluation function and chemical imaging module

Main Results and Discussion

Interferometric IR-microscopy delivers coating thickness values from local measurements and mapping data visualizes homogeneity across complex geometries. Thickness values in the example blade ranged from 1.70 µm to 1.76 µm. The approach is significantly faster, non-destructive and less error-prone compared to ball-grinding methods and suitable for uneven or curved surfaces.

Benefits and Practical Applications

• Rapid, contactless thickness measurement without sample preparation
• Applicable to complex shapes such as gear wheels and injector nozzles
• Automated mapping for assessing layer uniformity
• Suitable for both R&D and routine industrial QC or failure analysis

Future Trends and Potential Applications

Integration of IR-microscopy into automated production lines and in-situ monitoring systems is expected. Advances in software, including AI-driven spectral evaluation and higher-resolution imaging, will expand applicability to other thin films and coatings. Coupling with process analytics could enable real-time control of deposition parameters.

Conclusion

FT-IR microscopy using the LUMOS II instrument and OPUS software offers a reliable, fast and non-destructive method for DLC layer thickness determination and homogeneity mapping. This method enhances quality control workflows and supports both research and industrial applications.