Nanoindentation and sclerometry for coated cutting tools studying

Surface topography and roughness measurement

The surface relief was measured using a NIOS Nanoscan scanning nanohardness tester in the mode of semi-contact scanning probe microscopy (see Appendix 1).

Hardness and elasticity modulus measurement

Measuring dynamic nanoindentation

The hardness and elasticity modulus was measured using a NIOS Nanoscan scanning nanohardness tester by the measuring indentation method in accordance with the recommendations of the international standard ISO 14577 (see Appendix 2).

Table 3. Sample #1. Measurement of hardness and elasticity modulus of a sample areas with film

Elasticity modulus: 675 ± 105 GPa (15.8%)

Table 4. Sample #1. Measurement of hardness and elasticity modulus of a sample areas without film

Elasticity modulus: 420 ± 65 GPa (15.5%)
Hardness: 8.2 ± 2.0 GPa (24.8 %)

Table 5. Sample #2. Measurement of hardness and elasticity modulus of a sample areas with film

Elasticity modulus: 196 ± 20.3 GPa (15.8%)
Hardness: 18.9 ± 3.5 GPa (21.0 %)

Table 6. Sample #2. Measurement of hardness and elasticity modulus of a sample areas without film

Elasticity modulus: 700 ± 125 GPa (17.5%)
Hardness: 21.5 ± 2.2 GPa (10.2 %)

Sclerometry

In addition, the hardness was measured using NIOS Nanoscan scanning nanohardness tester by sclerometry — by scratching and analyzing the profile of the scratches from the image of the residual trace (see Appendix 3).

Table 7. Sample #1. Measurement of hardness of a sample areas with film

Adhesion and wear resistance

During scratching with a variable load of 200 μN to 60 mN, the film lifted off at a load of 30 mN.

Appendix 1. Stiffness measurement

The stiffness was measured using NIOS Nanoscan scanning nanohardness tester in the mode of measuring the dependence of loading - displacement (see Appendix 4).

Surface mapping

Scanning nanoscale hardness testers NIOS Nanoscan allow you to obtain images of three-dimensional surface topography by scanning probe microscopy. Scanning is performed in tapping mode with a diamond tip mounted on a piezoceramic probe. The resonant oscillations of the probe occur with a frequency f ~ 10 kHz and with an amplitude A <50 nm. During the scanning process, the frequency For the amplitude A of the oscillations is kept constant.

In the frequency scanning mode, a constant stiffness of the indenter contact area with the surface is ensured. In this mode, it is recommended to study materials with relatively high values of hardness and elastic modulus (metals and alloys, crystalline materials, ceramics). In this case, the influence of the presence of contamination on the surface of the sample is eliminated or significantly reduced.

In the amplitude scanning mode, viscous contact of the probe with the surface is maintained constant, which allows one to study soft materials (polymers, plastics).
The size of the maximum scanning window is 100×100×10 μm.

The actual resolution achieved during scanning is limited by the radius of the contact spot of the tip with the surface and is of the order of 10 nm in the XY plane and not worse than 1 nm along the Z axis, which is typical for scanning force microscopes operating in air.

Fig.9. 3D image of the surface relief of polycrystalline SiC

Roughness measurement

Appendix 2. Measuring indentation

On the basis of the NIOS Nanoscan, a method for measuring hardness is implemented, based on measuring and analyzing the dependence of the load when an indenter is pressed into the surface of the material on the indenter penetration depth. This method is the basis of the standard for measuring hardness ISO 14577.
For mechanical tests, an indenter of the Berkovich type is used, which is a trihedral diamond pyramid with an angle at the apex of about 142º.

The method of measuring dynamic indentation is as follows: the indenter is pressed into the surface of the sample at a constant speed, when the specified load is reached, the indenter is retracted in the opposite direction. During this test, the values of the load and the corresponding indenter displacement are recorded.

A typical experimental graph of the dependence of the load (P) on the indentation depth (h) is shown in Fig.10. It consists of two parts corresponding to the loading and unloading process. In the framework of this method, the hardness H of the sample is determined by the equation:

Here, A_c is the area of the fingerprint at the maximum value of the applied load P_max.

Fig.10. The loading curve, and the contact diagram with values used in the methodology for calculating elasticity modulus and hardness

The value of the reduced modulus of elasticity is calculated as follows:

Here, the constant b depends on the shape of the indenter, and the stiffness of the contact S is determined by the angle of inclination of the tangent to the unloading curve at the point P_max:

The contact area at maximum load A_c is determined by the indenter geometry and contact depth h_c and is described by the so-called needle shape function:

Appendix 3. Sclerometry hardness measurement (scratching and analysis)

The hardness measurement using the NIOS Nanoscan sclerometry method consists in applying scratches to the surface of the material and scanning the resulting indents. Previously, the shape of the tip is calibrated on the reference material by applying a series of scratches at different loads. The value of the hardness of the material is calculated relative to the hardness of the standard by the ratio of the loads and the widths of the resulting scratches on the studied and reference materials (Fig.11).

Fig.11. Sclerometry hardness measurement

Scanning and surface modification is carried out with the same tip in one measurement cycle. This avoids the difficulty of finding scratches and indentations and significantly reduces the time spent on measurements.

Appendix 4. Measurement of stiffness of beams and membranes

Fig.12. Membrane measurement scheme	Fig.13. Loading / unloading curve: segment of the free deflection of the membrane (a), abutment of the membrane in the substrate (b)