Forecasting and assessment of tribotechnical efficiency of the nitration case of machine parts

Abstract

Following the laws of tribology and tribotechnics, also the results of experimental studies of reality of structure and properties change in the zone of contact tribodeformation of structural steels and alloys of different structural classes subjected to nitriding, an approach to forecasting and comprehensive assessment of the tribotechnical efficiency of nitriding of structural materials and products made of them has been developed. Analysis of the patterns of changes in the structure of the diffusion zone of nitriding steels: abnormal, martensitic and austenic, and relative wear resistance tests, taking into account their composition and technological parameters of the treatment process, showed that maximum wear resistance was provided by a nitration coating containing hardening dispersed particles of incoherent nitrides, ensuring a lower liability to brittle behavior of the nitration case due to low level of matrix level microdeformation. At the same time, preliminary types of treatment (thermal treating and deformation processing) of nitriding steels contribute to structural and phase state of the surface layer, which has added tribological performance. For nitrided ferroalloys with different matrix lattices, the most significant characteristics of the structural state and properties of the surface layers affecting the level of surface fracture under friction have been found empirically: the particle size of nitrides of alloying elements, the distance between them, the density of their distribution, the matrix lattice microdeformation, the values of X-ray lines intrinsic broadening for structural components of the material in the friction deformation zone, the hardness of the nitration case and its changes under friction. These experimental results are taken as a principle of the proposed method for forecasting and assessment of metal tribotechnical efficiency. This principle of method is based on a tribological criterion containing micro- and macroscopic characteristics of the material in the zone of contact deformation under friction, the choice of fabricating methods for the product takes place to ensure an acceptable level of wear intensity. Then, by measurement, using surface large deformation method, the ability of the nitration case formed as a result of treatment according to the selected treatment schedule to perceive surface nondestructive plastic deformation is evaluated. It affords a basis for the selected nitriding treatment schedule. The completion of the assessment is the determination of the values of the maximum operability of the nitriding material under conditions of friction and wear (alarm pressure when a tribocouple operates steadily; critical pressure when it is inoperable, but its operation is possible with short-term overloads; the average total wear intensity of the couple combined). The totality of the identified parameters allows recommending the material, its working and predicting operating modes and durability of tribounit.