Nanoindentation

Find out more with our Nanoindentation Tech Note

Figure 1 shows specifically targeted indents in gray cast iron

Figure 1 shows specifically targeted indents in gray cast iron

The NanoTest Vantage offers a combination of industry-leading instrumental stability with excellent performance over a wide load range.

Compliance to industry standards – The NanoTest Vantage is fully compliant to all relevant international nanoindentation standards including ISO14577 and ASTM E2546–07

How it works

The NanoTest Vantage uses electromagnetic force application and capacitive depth measurement to measure the elastic and plastic properties of materials on the nano-scale.

  • Indentation testing
  • Hardness and modulus mapping
  • Depth profiling
  • Creep properties
  • Two load heads – low load (up to 500 mN) and high load (up to 30 N)

Hardness and modulus mapping

Figure 2 shows a 15 x 25 indent array (1 µm pitch) mapping the distribution of hardness and stiffness of intermetallic phases in a solder bond.

Figure 2 shows a 15 x 25 indent array (1 µm pitch) mapping the distribution of hardness and stiffness of intermetallic phases in a solder bond.

Rather than targeting specific unique sites, it is often useful to look at the distribution of hardness and modulus across a large area of interest. This can highlight areas of non-uniformity due to structural anomalies, variation in surface treatments or simply changes in properties at joints and boundaries. The stability of the NanoTest Vantage ensures excellent reproducibility of results over the duration of the test period.

Depth profiling load/partial-unload technique

Traditionally indentation was performed at one depth in the material. However, it is often of interest to investigate how hardness and modulus vary from the surface into depth in the sample. The ‘load/partial-unload’ technique included in the NanoTest software allows load cycling which allows hardness and modulus measurements to be made at different depths in the sample in just one indent cycle.

Figure 3 (above) shows the rapid profiling of hardness and elastic modulus as it varies with depth on a hard amorphous carbon film on a softer substrate.

Figure 3 shows the rapid profiling of elastic modulus as it varies with depth on a hard amorphous carbon film on a softer substrate.

Figure 4 (left): The inflexion point (a) in the multi-cycle indentation marks the transition to substrate-dominated load support. A significant elbow is seen on the unloading curve (b) which relates to a phase transformation.

Figure 4 : The inflexion point (a) in the multi-cycle indentation marks the transition to substrate-dominated load support. A significant elbow is seen on the unloading curve (b) which relates to a phase transformation.

Indentation Creep

In addition to providing reliable measurements of hardness and modulus, excellent system stability enables tests of longer duration, such as indentation creep experiments. These can be used to reliably extract properties such as the stress exponent or creep compliance and, in conjunction with the high temperature module, the activation energy for creep processes.

Figure 5 shows excellent agreement between fitted and experimental data for the creep of PMMA during a 700s hold at 100mN in the determination of the viscoelastic properties of polymers.

Figure 5 shows excellent agreement between fitted and experimental data for the creep of PMMA during a 700 s hold at 100 mN in the determination of the viscoelastic properties of polymers.

To find out more, take a look at our creep testing page.

 

Wide load and depth range

The NanoTest Vantage offers excellent load & depth ranges, with a dynamic resolution system which optimises the load and depth resolutions according to the peak load/depth set. This ensures excellent resolution throughout the ranges.

The low noise floor and high sensitivity enables accurate measurements of thin films for MEMS applications.

Figure 6: 1mN peak load indentations in sapphire show contact to be completely elastic. Raising the peak load to 2mN shows elasto-plastic contact.

Figure 6: 1 mN peak load indentations in sapphire show contact to be completely elastic. Raising the peak load to 2 mN shows elasto-plastic contact.

Figure 7 shows 10 indentations to peak loads of 100-500 mN on fused silica (blue) and sapphire (red).

Figure 7 shows 10 indentations to peak loads of 100-500 mN on fused silica (blue) and sapphire (red).

Theory of Nanoindentation

Depth Sensing nanoindentation systems allow the application of a specified force or displacement history, such that force, P, and the displacement, h, are controlled and/or measured simultaneously and continuously over a complete loading cycle.

1) Setting experiment parameters

The user defines a load cycle, consisting of load, hold and unload periods.

Loading and unloading rates can be programmed, and experiments can be controlled either by setting a peak load or a peak depth.

The shape of this loading curve is extremely important and will vary depending on the sample being tested. For example, polymers and soft materials will need a significantly longer creep period in order to ensure the creep exponent has been removed during unloading. Peak loads (and hence depths) chosen will also affect results, due to ‘indentation size effects’.

2) How are hardness and modulus calculated?

Shown is a typical nanoindentation curve, acquired on fused silica, a widely used reference sample in this field.

The instrument starts with the probe in contact with the sample surface, using a tiny contact load.

The load is then increased at a given rate, as determined by the user. As the load increases, the depth of the probe in the material will increase.

Once the probe has reached the pre-set experiment target (this can be either a maximum load or a maximum depth), it is good practice to then hold at peak load in order to look at creep properties. The probe is then removed from the sample, leaving a residual indent.

Hardness and modulus are calculated using data taken from the slope of the tangent to the unloading curve.

The extremely small force and displacement resolutions possible with the MML NanoTest, which are as low as 3 nN and 0.001 nm, respectively, are combined with very large ranges of applied forces (0 – 500 mN) and displacements (0-50 µm or more). This allows the NanoTest to be used to characterize nearly all types of material systems.

The following properties may be measured:

  • Hardness
  • Modulus
  • Creep
  • Plastic Depth/Contact Depth
  • Elastic recovery parameter
  • Plasticity Indices
In this example, load will be applied at a constant rate until peak load is reached after 50s. Force is then held constant for 25s in order to look at creep, and then load is removed at a constant rate over 50s.

Figure 8: In this example, load will be applied at a constant rate until peak load is reached after 50 s. Force is then held constant for 25 s in order to look at creep, and then load is removed at a constant rate over 50 s.

Shown is a typical nanoindentation curve, acquired on fused silica, a widely used reference sample in this field.

Figure 9 is a typical nanoindentation curve, acquired on fused silica, a widely used reference sample in this field.

Benefits over traditional hardness testing

During traditional macro or micro scale indentation, a hard tip, typically a diamond, is pressed into a sample with a known load. After a set period of time the load is removed. The area of the residual indentation in the sample is measured and the hardness, H, is defined as:

H = P/Arwhere P = Maximum Load
Ar = Residual Indentation Area

In order to determine the indent area, a powerful microscope is needed, and valuable time-dependent information will be lost. However, an alternative method may be used – depth sensing indentation.

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