12/07/2023
What is the diffusion process during friction?
In the process of friction, the friction surface is constantly and repeatedly subjected to stress and thermal action, which is bound to occur diffusion. Diffusion changes the surface structure and properties, and affects the friction and wear process. Therefore, the study of the diffusion process in friction has important practical significance and theoretical value.
It is difficult to study the diffusion process during friction experimentally. Qualitatively speaking, during the friction and ground diffusion process, the micro-volume of the friction surface is subjected to heat and force for many times, resulting in an unstable temperature field and pressure field, while having a large temperature gradient △T and pressure gradient △P, due to the existence of △P, △T, △G (concentration gradient), resulting in the directional flow of diffused atoms.
In the process of metal ground friction, the direction of diffused atom flow is determined by temperature field and pressure field. Due to the highest pressure and temperature at the metal surface, the atoms will migrate from some equilibrium positions at the lattice nodes to some other equilibrium positions. In the friction working volume of materials, the flow direction of diffused atoms is directed towards the contact area of the friction surface, while the vacancy migrates towards the inner surface layer. At this moment, the concentration of vacancy accumulation increases in the whole system, and the concentration of vacancy accumulation in the thermodynamic overhead causes the free energy of the system to decrease, resulting in the formation of diffusion gaps near the surface layer. Thus, surface macroscopic defects may occur.
The structural changes during friction will cause the diffusion of alloying elements and the redistribution of carbides. It has been reported that when the diffusion process is related to the formation of carbides, the alloy carbide forming elements in the collective are significantly depleted, and the wear resistance of the steel is also changed. In short, the frictional deformation ability is related to the agglomeration ability of alloying elements on the metal surface, the diffusion activity and the binding force with the matrix elements.
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