discussionFriction vs. distance curves obtained from the pin-on-disk anal-ysis are characterized by a running-in period and a steady stateregime that in this case should have rapidly increased if the coatingwas totally removed by the pin. In the running-in period the surfaceof the pin and the surface of the disk accommodate their reciprocalcontact geometry by increasing the real contact area: this causesan increase in the friction coefficient as the contact area rises. Toestimate the steady-state coefficient of friction, approximately thefirst 40 results (out of 2300 for each run) attributed to running-inwere discarded. The average coefficient of friction reported in Fig. 4was calculated for each distance tested up to 3000 m. In Table 3, is the standard deviation and * is the coefficient of variation, i.e.the ratio between the standard deviation and the average value inpercentage. The metallic coating has the lowest friction coefficientwhile the two ceramic ones are very similar, due to their similarnature and composition. From wear scar measurements the wearrate was calculated by