Typical failure modes of transparent conductive oxides deposited onto different substrates: PEN, glass and Si
Nano-indentation is a depth sensing indentation technique, which promises to become an important mechanical characterisation tool for electronics and sensors products. By using a nano-indentor, which can sample directly from the area of interest, engineers can begin to predict much more accurately how their products will behave.
A nano-indentor system is a sophisticated alignment assembly, a small load cell, a piezoelectric depth sensing device, a sample holder and an indenter at 90° to the sample holder. As the indenter is driven in and out of a sample at constant load, its penetration depth is continuously monitored. The resultant Load-Depth curve gives the information needed to determine hardness, elastic modulus and other material properties. Modern instruments allow the user to glean useful and accurate material property values with penetration depths as low as a few nanometres.
Typical applications include:
- Mapping of surface properties across small areas (measurements may taken as little as 1µm apart)
- Elastic and plastic properties of materials at the nano-scale
- Mechanical property measurement of individual phases or grains
- Creep analysis
- Nano-scratch and wear testing; primarily for cohesive and adhesive assessment of coatings
- Nano-indentation probes mechanical properties at high strain rate, investigating surface fatigue and fracture due to repetitive contact.
- Testing under heated and cooled conditions (-30 to 750°C)
- Testing in liquid environments (eg biomedical and corrosive environments)
Nano-indentation array across F65 / Alloy 625 dissimilar metal interface:
a) micrograph of cross section and indentation locations
b) nano-hardness. Location of interface is indicated; and
c) Elastic Modulus. Location of interface is indicated
These techniques provide more application specific material property data which is complementary to the basic ambient conditions test data and have allowed many users to accurately simulate the results of larger scale, expensive field testing in the laboratory environment.
Nano-indentation techniques can be applied to all material groups including metals, ceramics, composites, polymers and biological tissues.
Recently nano-indentation was used within two TWI projects on dissimilar metal interfaces for sub-sea applications and adhesion of transparent conductive oxides onto different substrates. This type of information in real scale may help to improve finite element simulations for reliability prediction of joined structures. These simulations are only useful industrially when they are given the correct gradient of mechanical properties across interfaces, and related activation energies if needed.
For further information on nano-indentation, or to request trials, please contact firstname.lastname@example.org