Nanoindentation is a method of measurement of the mechanical properties of small volumes of materials using an instrumented indentation technique. Elastic modulus, hardness, fracture toughness, creep and dynamic properties such as storage and loss moduli can be measured. In this and subsequent articles, we will look at some of the issues facing the user of a nanoindentation instrument. Our purpose is to educate and inform the prospective user of this type of equipment as to what can be measured and what factors influence the results obtained.
Figure 1. The IBIS Nanoindentation system from Fischer-Cripps Laboratories.
Application of Nanoindentation in Minerals Analysis
Nanoindentation can be used for a wide range of applications. Some applications require precise XY positioning of the indentation. An example is the measurement of mechanical properties of coke as used in the minerals processing industry:
Figure 2. Testing individual phases in coke to determine which particles contribute to strength of the coke as it is used in a blast furnace.
In this application, it is necessary to make indentations in the centre of the particles so that the readings are not influenced by the surrounding matrix. An optical microscope is used to position the indentation before testing, and to view the impression after testing. An XY positioning accuracy of about 0.5 microns or so is usually required.
Thin Film Testing
Another common application of nanoindentation is thin film testing. TiN films are often used as a hard coating on cutting tools. Manufacturers of such coatings are interested in changes in hardness of the film with different processing conditions
Figure 3. Titanium nitride film surface and residual impression with Berkovich indenter. This film is quite thick, about 5 µm.
These films are usually quite rough, with many irregularities and grain boundaries. It is usually necessary to undertake a series of tests at increasing maximum load to determine the hardness of the film. At low load, the values of H are influenced by the developing plastic zone. At high load, the results are influence by the presence of the substrate. The film hardness is usually taken to be that in a plateau region intermediate between the two.
Figure 4. Interpreting the hardness of a TiN film as a function of penetration depth.
A popular application of nanoindentation is the related test of scratch testing on a micron scale. Depending on the instrument capabilities, scratch testing can be done by moving the sample relative to the indenter tip while load is applied (either ramped or steady) to the indenter. At the same time, the lateral force needed to move the sample is typically measured. The ratio of the lateral force to the normal force is the coefficient of friction at the contact.
Figure 5. Scratch testing on a bond pad of an integrated circuit.
Other Applications of Nanoindentation Testing
Other applications are multi-phase steels, thermal barrier coatings, biological specimens such as teeth and bone, soft films (paint), heat treated surfaces and semiconductor wafers.
Much more valuable information about nanoindentation can be found in Fischer-Cripps' free downloadable IBIS Handbook of Nanoindentation
This information has been sourced, reviewed and adapted from materials provided by Fischer-Cripps Laboratories.
For more information on this source, please visit Fischer-Cripps Laboratories.