[SY-O4] Formation Mechanism of Tribofilm of Silicon Carbide under Water Lubrication: Molecular Dynamics Simulations
Water lubrication has the characteristic of low environmental burden. It is known that silicon carbide (SiC) shows quite low friction coefficient by the formation of a tribofilm on the surface of SiC during water lubrication. Understanding of its mechanism is essential to improve friction characteristic for practical use and application. However, it is difficult to observe directly such a complicated phenomenon including friction and chemical reaction by experiments. Therefore, in this study, molecular dynamics method which can simulate chemical reaction was conducted to analyze the structure and formation mechanism of tribofilm in the friction process of amorphous SiC under water environment.
In the simulation, we prepared the model consisting of two amorphous SiC substrates sandwiching water molecules. The substrates have rough surfaces and the two of substrate surfaces can be in contact during the friction. The substrates were given a constant pressure (3 GPa) and slid for 1000 ps at 100 m/s.
We performed the sliding simulation of SiC under water lubrication. In the initial structure, the surface of the substrates was corrugated. However, the rough surface of the substrates was smoothed while Si atoms from the a-SiC substrate reacted with water molecules and formed bonds with O atoms of H2O during friction. Firstly, we investigated the change in number of water molecules and Si-O-Si bonds during friction. It was found that the number of water molecules decreased constantly while the number of Si-O-Si bonds increase correspondingly. This result shows that Si reacts with H2O to form a SiO2 layer. Next, we investigated the change in the distribution ratio of C and Si before and after friction. The ratio of C was increased around the substrate surfaces and that of Si was increased on the substrates indicating that the bilayer tribofilm of the SiO2 and C rich SiC was generated on the substrate by the tribo-chemical reaction.
In the simulation, we prepared the model consisting of two amorphous SiC substrates sandwiching water molecules. The substrates have rough surfaces and the two of substrate surfaces can be in contact during the friction. The substrates were given a constant pressure (3 GPa) and slid for 1000 ps at 100 m/s.
We performed the sliding simulation of SiC under water lubrication. In the initial structure, the surface of the substrates was corrugated. However, the rough surface of the substrates was smoothed while Si atoms from the a-SiC substrate reacted with water molecules and formed bonds with O atoms of H2O during friction. Firstly, we investigated the change in number of water molecules and Si-O-Si bonds during friction. It was found that the number of water molecules decreased constantly while the number of Si-O-Si bonds increase correspondingly. This result shows that Si reacts with H2O to form a SiO2 layer. Next, we investigated the change in the distribution ratio of C and Si before and after friction. The ratio of C was increased around the substrate surfaces and that of Si was increased on the substrates indicating that the bilayer tribofilm of the SiO2 and C rich SiC was generated on the substrate by the tribo-chemical reaction.