How to Test Coatings with Nano Indentation

Q: Our customer has asked us to test the mechanical properties of the coatings we use.
      How do we do this and why is it important?

A. Nanoindentation measures the mechanical properties of a coating with a very specific and controllable depth of penetration into the coating. A loose rule of thumb is to keep the indentation depth to about one-tenth of the coating thickness to eliminate the effect of the material beneath it. These shallow depth indentations cannot be controlled by conventional testing using Rockwell and Vickers indentation Testers.

The nanoindenter also:

• The information provided is not just "hardness". The true performance of a coating depends not only on the hardness value. Nanoindentation testing measures other properties such as modulus of elasticity, fracture toughness and creep, as well as other parameters whose importance to coating performance cannot be overstated. It cannot be overemphasized that a complete knowledge of all mechanical properties is important for understanding the performance of coatings.

• Can be used for quality control. The basic theory behind nanoindentation was established in the early 1990s and formed the basis for the nanoindentation standard ISO 14577. ISO 17025 standards are also available. Modern nanoindentation instruments can be calibrated to traceable standards. This traceability is important for quality assurance across multiple production sites and cannot be overemphasized if warranty and coating failure claims are subject to arbitration. 

• Not subjective. Traditional and legacy testing methods, such as pencil hardness and spring-loaded mechanical Testers, are inherently subjective and therefore can lead to product inconsistencies, potential coating failure and warranty issues. Rockwell and Vickers Hardness Testers rely on visual interpretation of indentation size and are therefore also prone to subjectivity. Nanoindentation is a non-subjective measure of agreement.

• Both hard and soft coatings can be measured. Nanoindentation instruments are capable of measuring the mechanical properties of materials as soft as rubber and as hard as ceramics. The technique relies on measured penetration depth rather than visual observation of dents, so measurements can be made on very thin coatings and highly elastic materials. Coatings that benefit from this type of testing include paints, powder coatings, electroplating, anodic coatings, and hard and ceramic coatings (such as titanium nitride, titanium aluminum nitride, and diamond-like carbon). 

The top five features to look for in a nanoindenter below:

1. Ease of use. The first commercial nanoindentation instrument was produced in 1985, but early instruments were cumbersome to use. The hardware and software of the current generation of nanoindentation instruments have been developed to address these issues. The easy-to-use instrumentation allows multiple groups to share the same unit and does not require a professional to operate, minimizing training needs. This means companies can save a lot of money. It also allows for more frequent testing.

2. Rugged and easy sample setup. A modern, powerful nanoindenter minimizes the chance of crashes due to user error. It also facilitates easy and fast sample preparation. Certain instruments have a special design feature that specifically protects the tip of the indenter but allows for quick measurements. Real-time feedback on coating performance characteristics allows for better quality control (QC), limiting costly rework, poor quality and potential warranty issues. Quality Assurance (QA) and incoming inspection departments also benefit from this technology, quickly determining whether incoming parts and materials meet required performance specifications.

3. Fast data measurement and processing times. In addition to fast and easy sample preparation, look for a nanoindenter with fast data acquisition and fully automated processing. Older instruments require longer setup and user intervention, and require manual calculation of thermal drift. The new nanoindentation instruments are fully automated using sophisticated operating software. Smart algorithms help the instrument detect surfaces accurately.

4. Stability in "normal" environments. Nanoindentation is an accurate measurement, and all such instruments require a somewhat stable vibration and temperature environment. Some instruments require a true laboratory setup, but others can be operated in less controlled environments. Choose the instrument type that fits your environment. ]

5. Ergonomic design. Three main criteria affect good instrument design for various applications and environments. The range of motion and electronics allow testing of different geometries in crowded labs as well as in near-line production due to space considerations. When space is at a premium, look for high-performance units with smaller physical dimensions that can work in "normal" environments. Some nanoindentation instruments have an open layout with a large range of motion in the X, Y and Z stages. Finally, integrated electronics minimizes the