Vickers Hardness: How can we improve with nanoindentation?

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The most important parameter for the quality control in many manufacturing industries is hardness. From steel to soft polymers, hardness is the easiest way to determine the efficacy of the processes used to develop these materials. Two popular methods of measurements are Vickers hardness in hard materials and Shore hardness in soft materials. Both of these techniques are super easy to use but lack the accuracy needed to measure the small differences in properties which in most cases is needed to continually improve the quality of production. They are often inappropriate techniques for cases such as thin films providing inaccurate measurements. The key question we are faced with is “How can we accurately measure small hardness differences across materials to improve the consistency in our production processes?

This article is focused on the Vickers hardness measurements. In order to highlight the inadequacies in this measurement method, we need to understand its working principle. The most basic Vickers hardness measurement setup needs a Vickers indenter to indent into the material and a microscope to measure the size of the indent. During the measurements, the sample under investigation is indented in the first step at a prescribed load and then the area of the indent is measured. The load is divided by the area of the indent which gives the Vickers hardness of the material.

There are multiple limitations to this approach. The very basic one is that the measurements are user dependent. 10 different operators will measure 10 different diagonal sizes and corresponding area of the indents giving 10 different Vickers hardness for the same material. The second most important factor to consider is that the size of the indent should be large enough to be measured by an optical microscope with considerable accuracy. These limitations make the Vickers hardness measurements applicable to applications when larger error margins are allowed. In the industries looking to grow and remain competitive in the current environment, these errors are too large to ignore.

A very classic example is the thin film hardness measurements. If we have to measure the hardness of a 200 nm thin film and we make a Vickers indent 1 micron deep, this is plain wrong. Even if we manage to make a Vickers indent 100 nm deep, the measurements will still be wrong because of the ‘substrate effect’ and good luck with the indent size measurements using an optical microscope. With the technological advancements in nano-micro mechanical testing, the correct way to measure hardness is by using nanoindentation thin film measurements. The two biggest advantages of nanoindentation measurements are: 1) they are automated without the need to measure the indent size and thus user independent, 2) the mathematical correction applied to the measurements subtracts the effect of substrate giving true thin film modulus and hardness. The nanoindentation measurements do not need a dedicated operator. Hundreds of measurements on multiple samples can be set up to run during the night and even over weekends providing industries maximum returns on their instrument investment.

The fast pace of development and the current industry trends demand companies to be at the forefront of technology. For the development of thin films in materials, nanoindentation hardness measurements can provide invaluable insights needed to advance their properties. The technique is applicable for measurement in materials across polymers, consumer electronics, semiconductors, biomedical, aerospace, automotive, Pharmaceuticals, protective coatings and many more industries.

Hopefully, this article shed some light on the advantages of nanoindentation hardness measurements. I will be publishing more articles on the understanding of advancements in mechanical testing at nano-micro scales in the near future. Please feel free to contact me with any questions.