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Measurement is typically performed with a Berkovich indenter with force control/ Fast measurements are possible, for example with 10-s load, 5-s hold time, and 4-s load removal.
A total of more than 60 values can be determined.
Measurement is typically performed with a Berkovich indenter with force control/ Fast measurements are possible, for example with 10-s load, 5-s hold time, and 4-s load removal.
A total of more than 60 values can be determined.
The tests are typically performed with spherical tips with a radius between 5 and 10 μm. Stress maximum is most often in the coating and not in the substrate. Multiple scans of the surface are possible. The wear on the tip and impact of surface roughness is reduced by the small scratch length.
The tests are typically performed with spherical tips with a radius between 5 and 10 μm. Stress maximum is most often in the coating and not in the substrate. Multiple scans of the surface are possible. The wear on the tip and impact of surface roughness is reduced by the small scratch length.
Together with the Karlsruhe Research Center, a method has been developed that allows the entire stress-strain curve of metals to be determined from indentions made by spherical indenters. It is based on the use of neural networks to identify parameters and it also takes into consideration kinematic hardening.
Together with the Karlsruhe Research Center, a method has been developed that allows the entire stress-strain curve of metals to be determined from indentions made by spherical indenters. It is based on the use of neural networks to identify parameters and it also takes into consideration kinematic hardening.
Vickers hardness can be calculated from the indention hardness. A comprehensive study conducted by the Federal Institute for Materials Research and Testing (BAM) compared 20 materials using the conventional Vickers hardness method and the Vickers hardness method with values calculated with InspectorX algorithms and reevaluated using HIT. It showed a mean difference of < 10% vs. 25-30% with other software packages.
[T. Chudoba, M. Griepentrog, International Journal of Materials Research 96 (2005) 11 1242 – 1246]
Vickers hardness can be calculated from the indention hardness. A comprehensive study conducted by the Federal Institute for Materials Research and Testing (BAM) compared 20 materials using the conventional Vickers hardness method and the Vickers hardness method with values calculated with InspectorX algorithms and reevaluated using HIT. It showed a mean difference of < 10% vs. 25-30% with other software packages.
[T. Chudoba, M. Griepentrog, International Journal of Materials Research 96 (2005) 11 1242 – 1246]
Principle of the QCSM method
During depth sensing nanoindentation measurements for the determination if the indentation hardness HIT according to DIN EN ISO 14577, the load-displacement curve F(h) is measured with a certain maximum load. The hardness can only be given for the maximum depth which is reached in this measurement. A hardness profile along the depth can only be determined by many measurements with different loads on different places of the sample. This is a time-consuming procedure and requires much effort for the analysis of the data.
Amplitudes of all single oscillations during a dwell time of 1.4 s and for a frequency of 40 Hz. The first 12 of 56 oscillations are not used for averaging because creep effects are largest immediately after reaching the target force.
The Continuous Stiffness Measurement (CSM) method adds a continuous small oscillation to the force signal. The ratio of force and displacement amplitude delivers the contact stiffness between indenter and sample after some corrections which consider moving mass, frequency and damping coefficient. In the CSM method the static force during loading is for every oscillation slightly different. This complicates the averaging of several oscillations and the feedback control.
In contrast during the QCSM method the force is increased in small steps and the oscillation is only switched on during a short dwell time between about 0.5 s and 3 s (see principle of QCSM method). This allows an easy averaging of several oscillations and also the feedback control is more accurate. For example there are amplitudes from 56 oscillations measured at a frequency of 40 Hz and a dwell time of 1.4 s. In the QCSM method the first 20 % of the measured amplitudes are not considered for averaging to reduce the creep influence on the results. This is especially important for viscous materials.
For the micro wear tests the Universal Nanomechanical Tester ZHN with Lateral Force Unit LFU is used.
Parameter |
Film Material |
Film thickness µm |
Hardness GPa |
Young's modulus GPa |
Yield strength GPa |
Poisson's ratio |
|---|---|---|---|---|---|---|
Sample 1 |
a-C:H |
4 |
14.5 |
120 |
10.9 |
0.2 |
Sample 2 |
a-C (high sp3) |
5 |
50.0 |
542 |
30.1 |
0.2 |
Sample 3 |
a-C |
3 |
15.0 |
170 |
8.8 |
0.2 |
Sample 4 |
a-C:W (17%) |
3 |
14.5 |
140 |
9.5 |
0.2 |
Sample 5 |
a-C:H (structured) |
4 |
12.2 |
103 |
9.0 |
0.2 |
Experimental methodology
Challenge: Thermal stability of displacement measurement over 1 hour. Necessary drift rate < 0.001="">
The weakest element in a system is determining it‘s behaviour during loading. Therefore global test methods are advantageous. The mapping of mechanical properties with a nanoindenter is a step towards a global characterisation.
In the following an examples of measurement of a fused silica sample with indents:
Fig. 4: Contour plot of the force amplitude
Several indents have been done into a fused silica sample with a spherical indenter of about 10 µm radius. The same tip was also used for scanning the sample. Fig. 2 shows the glass surface with indents of 800 mN (upper left) and 2x 500 mN. Additional indents at lower forces have been fully elastic. One indent at 200 mN is hard to recognize optically, however, a small plastic deformation of some nanometer can be measured.
The mapping of the normal force signal allows a clear detection of the indent positions because the force becomes lower when the indenter slides into the impression and becomes bigger when it goes out. The force control is not fast enough to cancel out this effect.
Fig. 5: Young’s modulus mapping. The results at the indent positions are incorrect.
In fig. 3 a slight distortion is also visible at the position of the 200 mN indent. A similar result is available when only the force amplitude of the oscillation is presented (fig. 4).
For the determination of the Young’s modulus not only the contact stiffness is necessary – which can easily be obtained from the measured force and displacement amplitudes – but also the correct indentation depth. Therefore a zero point correction for the displacement measurement is necessary. It can be done in the same analysis window using the button „Zero point correction“. The result of the modulus mapping of fused silica is shown in fig. 5. The expected value of 72 GPa is well attained over the complete area with the exception of the indent positions. There the analysis model is incorrect which assumes a flat surface and therefore the results are too big.
The friction coefficient between diamond tip and glass is obtained from the ratio of lateral and normal force. It is shown in fig. 6 and 7. At the indent positions the friction is first going down in direction of movement according to fig. 3 and is increasing when the tip moves out of the impression.
In the flat area the friction coefficient is between 0.7 - 0.8. Only in the front part
of the sample it is a little lower. The reason for that is not clear.
The measurements of all the presented properties have been done during one scan which
was with about 2000s relatively long. A considerable reduction of the scan time is possible;
however, this may result in an increase of the scatter. The best parameters have to be checked
for every single sample.
