Journal of Friction and Wear最新文献

Abstract

The structure and properties of powder steel–copper alloy antifriction pseudo-alloys infiltrated with materials of various compositions are studied, it is shown that mechanical and tribological properties are determined both by the composition and structure of the steel skeleton and, to a large extent, by the composition and structure of the infiltrate. It has been established that the limiting content of lead in the infiltrate, which ensures the absence of lead deposits on the sample surface and a large (10–15%) residual porosity, should not exceed 3%. The use of a mixture of copper powders and alloying additives for infiltration is more technologically advanced than atomized bronze powders. It is shown that the wear resistance of pseudo-alloys with a chromium steel skeleton depends to a lesser extent on the composition of the infiltrate, since the main contribution to wear resistance is made by a hard steel skeleton. The introduction of 3–5% ultrafine aluminum oxide powders into the infiltrate leads to an increase in the seizure pressure by 1.2 MPa and wear resistance by 20–30% due to the refinement of the copper alloy structure and the deceleration of dislocations that arise during deformation due to friction. It is shown that during the wear of pseudo-alloys in the surface layer the structure is refined, martensite is formed in the skeleton, and, accordingly, the microhardness increases by 720–760 MPa.

The following carbon nanostructures (CNSs) are used: shungite nanocarbon (Sh), multilayered graphene oxide (GO), multiwalled carbon nanotubes (Taunit-M), and fullerene C60. Medical Vaseline (MV) free from any additives or thickeners is used as a lubricant base. Tribological tests are carried out using a 2070 SMT-1 friction machine at a load of 2000 N. The roughness parameters of steel rollers before and after the tests are studied by profilometry. Detailed characteristics of contacting surfaces before and after friction are obtained by scanning and transmission electron microscopy. The experimental data are analyzed using the Hertz and Johnson–Kendall–Roberts models. According to the data on efficiency coefficients k_ef, the studied dispersions are ranked as follows in the order of deterioration of antiwear properties: MV/GO (0.5 wt %), k_ef of 50% > MV/Taunit-M (1.5 wt %), k_ef of 40% > MV/C60 (0.5 wt %), k_ef of 15% > MV/Sh (0.5 wt %), k_ef of 5%, which is in agreement with the above-mentioned sequence of CNSs at low loads. The reason for the best and worst wear factors upon using CNSs in the dispersions under study and factors affecting the values of wear in the hard friction mode are considered. The results of the study can be a basis for the development of new plastic lubricating compositions with carbon nanostructure additives for use in heavily loaded friction units.

Analytical and numerical modeling approaches for the contact-working system of turbo- and electric machines have been developed. The simulation allows determining some dynamic characteristics and loads in the rotor–stator system when there is a loss in clearance between them and there occurs subsequent motions with impacts or without separation from each other. In the system, the rotor and stator are deformable, the stiffness of rubbing surfaces is variable, and the working clearance between them is extremely small (50–500 times less than the rotor radius at the contact point). It is shown that the effect of the absolute elasticity for stator generates a significant change in natural oscillations of the coupled rotor–stator system, that is, a significant change in its eigenfrequencies and eigenmodes. It is noted that the elastic deformation of rubbing surfaces leads to a nonlinear increase in their contact stiffness, which consists of quasi-static and dynamic components. The consequences of an extremely small clearance are an elastic deformation of the contact surfaces commensurate with it (up to half the clearance size at the point of contact) during whirling with slipping of rotor over stator, as well as the disappearance of pure rolling, which is accompanied by the actual absence of rotary speeds even at low frequencies of contact whirling. The resulting diagrams of changes in the contact stiffness and whirling frequencies and the XY trajectories can serve as sources of initial information for identifying the operation of a real rotary machine on the threshold of a dangerous whirling with slipping and whipping and for further studies of contact oscillations of rotors.