3.2.2. Dry Test Tungsten Carbide on 100Cr6

The results of the tribological linear reciprocating ball-on-disc evaluation using a 100Cr6 disc and a tungsten carbide triboball for 50 mN and 200 mN load force are shown in Figure 5. The general comparison to the pairing 100Cr6/100Cr6 shows that the coefficient of friction is lower for all tested surfaces. On the polished reference surface, the coefficient of friction is 0.18 in the beginning and rises slightly up to 0.25 for a load force of 50 mN. With increasing load (Figure 5b), the COF increases to values of 0.55 at the end of the evaluation time of 500 s. The LSFL-structured surfaces lead to a COF increase over the entire evaluation time. For parallel and perpendicular movements, the COF starts at 0.45 and stays nearly constant for parallel sliding direction. The COF for the perpendicular movement on LSFL is higher (c.f. dry test 100Cr6/100Cr6) and rises to a steady state at 0.5. This behaviour also appears for the higher load force of 200 mN. The COF for LSFL-0 and LSFL-90 is initially 0.57 and increases to 0.6 for a parallel movement and to 0.68 for a perpendicular sliding direction. The LBIA surface introduce a small COF increase at the beginning of the test for both test loads. Using a perpendicular movement, the COF shows a time-based increase and runs from 0.24 to 0.3 for 50 mN and from 0.27 to 0.41 for 200 mN. Contrary to this behaviour, the parallel movement on the LBIA surface reveals a slight COF decrease with ongoing evaluation time. For 50 mN the COF decreases from 0.21 to 0.19. Using a load force of 200 mN, the COF reduces from 0.19 to 0.16.

**Figure 5.** Temporal evolvement of the coefficient of friction using tungsten carbide triboball without lubrication for a load force of 50 mN (**a**) and 200 mN (**b**).
