**2.4 Fretting tests**

Fretting wear, which is considered a nuisance in several branches of industry such as aeronautics, nuclear industry, etc., refers to the degradation of the contact surface resulting from wear, which requires an overhaul or replacement of the machine components. It is defined as the wear that takes place during a low amplitude oscillatory movement between two apparently immobile solids under a load normal to the contact surface. Such a phenomenon is observed especially in assemblies subjected to vibrations. To simulate the industrial process, a test bench was developed within the laboratory and subsequently installed on a fatigue machine (MTS).

The fretting tests were carried out on an MTS tension compression hydraulic machine. A sphere-on plane configuration was employed as shown in **Figure 6(a)**. The counter-body was a polycrystalline alumina ball with 24 mm diameter, a Young's modulus of 310 GPa, and a hardness of 2300 Hv0.05. The flat coating alloy (10 mm × 10 mm × 12 mm) specimens were manufactured from a cast bar of

#### **Figure 4.**

*Scanning electron micrograph of a cross section of multilayered TiAlZrN/TiAlN/TiAl coating as made by fractography.*

#### **Figure 5.** *Energy dispersive spectroscopy (EDS) of multilayered TiAlZrN/TiAlN/TiAl coatings.*

AISI4140 steel. During the test, the instantaneous displacement, the normal force, and the tangential force were monitored and recorded for every cycle.

The fretting tests were conducted with displacement control, using an extensometer as a displacement transducer. When it is possible to plot the hysteresis loops of the fretting-wear stresses from the instantaneous measurement of the tangential force as a

**323**

*Fretting Wear Performance of PVD Thin Films DOI: http://dx.doi.org/10.5772/intechopen.93460*

function of the sliding distance for normal force values between 50 and 750 N and the sliding ranges from ± 20 μm to ± 100 μm [3, 5, 15–17]. The area of the fretting loop corresponds to the dissipated energy during the fretting cycle (Ed), whereas the residual opening of the cycle (i.e., the residual displacement when Q = 0) is related to the full

*Illustration of the experimental fretting wear approach: (a) fretting log of one fretting cycle and test bench,* 

The fretting tests were conducted in dry conditions at an ambient temperature of 25°C and a relative humidity of 60%. Prior to the fretting test, the specimen and counter-body were cleaned with acetone and alcohol. Hundred to 2000 fretting cycles were performed. The tests were stopped in two different ways: once the displacement was stopped abruptly after the last fretting cycle, and once the displacement amplitude was reduced to zero during several cycles. However, to quantify the wear volume, a specific 3D surface profilometry methodology, fully developed in reference, [15] is applied. It consists of determining

plane fretting scars. A system wear volume is then deduced from the following

However, other conditions have been tested to investigate the effect of certain parameters suspected of having a dominant role in the wear mechanism. These conditions will be given in due course. Furthermore, optical observations are coupled

with scanning electron microscopy to examine posttest fretting scars.

cycles and

) and the transfer volume

). This analysis is performed both on sphere and

( ) ( ) − + − + V V V plane V V orb system =− +− (1)

sliding amplitude (δg) (**Figure 6(b)**). All tests were performed at 20 × 103

*(b) full slip fretting loop, and (c) 3D wear trace, obtained by optical profilometer.*

the frequency was set at 5 Hz [3, 5, 15, 18].

the wear volume below the reference surface (V<sup>−</sup>

above the reference surface (V<sup>+</sup>

relationship:

**Figure 6.**

*Fretting Wear Performance of PVD Thin Films DOI: http://dx.doi.org/10.5772/intechopen.93460*

**Figure 6.**

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

*Scanning electron micrograph of a cross section of multilayered TiAlZrN/TiAlN/TiAl coating as made by* 

AISI4140 steel. During the test, the instantaneous displacement, the normal force,

as a displacement transducer. When it is possible to plot the hysteresis loops of the fretting-wear stresses from the instantaneous measurement of the tangential force as a

The fretting tests were conducted with displacement control, using an extensometer

and the tangential force were monitored and recorded for every cycle.

*Energy dispersive spectroscopy (EDS) of multilayered TiAlZrN/TiAlN/TiAl coatings.*

**322**

**Figure 5.**

**Figure 4.**

*fractography.*

*Illustration of the experimental fretting wear approach: (a) fretting log of one fretting cycle and test bench, (b) full slip fretting loop, and (c) 3D wear trace, obtained by optical profilometer.*

function of the sliding distance for normal force values between 50 and 750 N and the sliding ranges from ± 20 μm to ± 100 μm [3, 5, 15–17]. The area of the fretting loop corresponds to the dissipated energy during the fretting cycle (Ed), whereas the residual opening of the cycle (i.e., the residual displacement when Q = 0) is related to the full sliding amplitude (δg) (**Figure 6(b)**). All tests were performed at 20 × 103 cycles and the frequency was set at 5 Hz [3, 5, 15, 18].

The fretting tests were conducted in dry conditions at an ambient temperature of 25°C and a relative humidity of 60%. Prior to the fretting test, the specimen and counter-body were cleaned with acetone and alcohol. Hundred to 2000 fretting cycles were performed. The tests were stopped in two different ways: once the displacement was stopped abruptly after the last fretting cycle, and once the displacement amplitude was reduced to zero during several cycles. However, to quantify the wear volume, a specific 3D surface profilometry methodology, fully developed in reference, [15] is applied. It consists of determining the wear volume below the reference surface (V<sup>−</sup> ) and the transfer volume above the reference surface (V<sup>+</sup> ). This analysis is performed both on sphere and plane fretting scars. A system wear volume is then deduced from the following relationship:

$$\mathbf{V}\_{\text{system}} = \left(\mathbf{V}^- - \mathbf{V}^\*\right) \mathbf{plane} + \left(\mathbf{V}^- - \mathbf{V}^\*\right) \mathbf{orb} \tag{1}$$

However, other conditions have been tested to investigate the effect of certain parameters suspected of having a dominant role in the wear mechanism. These conditions will be given in due course. Furthermore, optical observations are coupled with scanning electron microscopy to examine posttest fretting scars.
