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Fig.6. Graph for determining the values of k _1' ν(ν-1) and k ₁ ν(ν-1) depending on the parameter ν.
For run-in surfaces, friction occurs under conditions of elastic contact; the coefficient of friction does not depend on the load:
(5.16)
Factors affecting sliding friction.
1. Influence on the coefficient of friction of such factors as frictional constants τ ₀ and β; physical and mechanical properties of the surfaces of contacting bodies - HB, E, µ, α _g ; parameters characterizing the microtopography of surfaces - ν, r, t _m , R _p , k ₁ loading parameter p _r can be estimated based on equations (1)-(5).
2. The structure and physical and mechanical properties of the contacting bodies have a significant effect on the coefficient of friction. So, for metals with the same name with a crystal cubic lattice (Al-Al; Cu-Cu; Fe-Fe), the friction coefficient is higher than for metals with hexagonal packing (Cd-Cd; Mn-Mn; Zn-Zn) (Fig. 5.7) .

Fig.5.7. The dependence of the friction coefficient f on the shear yield strength τ _t for various metals.
3. For friction pairs made of different metals, the coefficient of friction is lower than for identical ones.
4. The friction coefficient of materials is significantly affected by the nature of the “secondary structures” formed on the surface (for example, oxide films, etc.) or pre-deposited thin coatings. The ratio of the physico-mechanical properties of the coating and the substrate is important. If the metal is soft and elastic, while the oxide is hard and brittle, then the films are easily destroyed, and juvenile contact occurs at low loads. If the metal has the same deformation properties as its oxide, then this film is deformed together with the metal without being destroyed (for example, Cu), provides a decrease in the adhesive effect and prevents external friction from being overcome. To ensure a low friction coefficient, it is necessary that the surface film ensures complete separation of the contacting surfaces (ensuring the rule of a positive strength gradient in depth), but should not be too thick in order to avoid an increase in the deformation component of the friction coefficient, since in a thick film the deformation component of the friction coefficient becomes noticeable. Figure 8 shows this in relation to the dependence of the coefficient of friction of hardened steel on steel coated with an indium film on the thickness of this coating.