Fig. 1 shows typical voltage values vary with the sliding distance of No. 6 coating. It is observed that the frictional curves are stable during the sliding process. Fig. 2 shows voltage values as a function of different constant loads. It can be seen that the voltage value is linearly proportional with the constant load, so the lateral force can be calculated through the proportional parameter between the load and voltage value, thus the friction coefficient is obtained as shown in Fig. 3. It can be observed that the coatings with RE have much lower friction coefficient values compared to the No. 1 coating without RE.
Fig. 1. V oltage values vary with the sliding distance of No. 6 coating.
Fig. 2. V oltages values as a function of different constant loads.
Fig. 3. Friction coefficient as a function of different coatings.
Furthermore, friction coefficient values of coatings doped with RE vary much less than that of undoped one. Therefore, it is educed that RE can decrease the friction coefficient value and fluctuation range effectively, and the lubrication function of CeO2 and La2O3 at high temperature during the friction process between the cermets and Al2O3 ceramic has also been reported, due to the nature of RE. For example, RE makes the microstructure more compact, denser and less porous, and the element distribution uniformly, leading to the reduction of lateral force at micro-scale. On the other hand, the addition of La2O3 and CeO2 can increase the crystal face distance of cermets, resulting in the action force between two crystal faces so as to decrease the friction coefficient. Furthermore, La2O3 and CeO2 with hexagonal layer structure have better lubrication function, and stable chemical properties at 973 K, which results in the decrease of friction coefficient further.
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