RESEARCH OF THE VACUUM THERMOCYCLIC NITROGEN PROCESS IN A PLASMA PULSING GLOW DISCHARGE

Abstract

Analysis of literary sources and recent research, as well as patent information search showed that the use of vacuum thermocyclic nitriding technology in pulsating glow discharge plasma is limited by the lack of research on the relationship between the factors that determine the course of the process and general conclusions and recommendations for choosing the optimal parameters of this technology. These circumstances confirm the relevance of the research.

Most of the reasons for the destruction of structural elements of parts of machines and mechanisms are related to their cyclic strength, namely thermomechanical fatigue, which is expressed in the gradual accumulation of damage in the material under conditions of simultaneous exposure to variable loads, aggressive environment and temperature. This leads to the appearance of a fatigue crack, its development and the final destruction of the material. One of the important and promising directions in solving problems related to increasing the resistance to thermomechanical fatigue of structural elements is the use of vacuum thermocyclic nitriding in the plasma of a pulsating glow discharge. To analyze the mechanism of phenomena and control the process of vacuum thermocyclic nitriding in the plasma of a pulsating glow discharge, it is necessary to identify the interrelationship of factors that determine the course of the process.

The purpose of the article is to provide an analysis of the phenomena in the process of vacuum thermocyclic nitriding in the plasma of a pulsating glow discharge, to establish the interrelationship of factors that determine the course of the VTAPPTR process and to determine its optimal parameters.

As a result of the conducted research, the regularities of the influence of the parameters of the process of vacuum thermocyclic nitriding in the plasma of a pulsating glow discharge on the microhardness, the depth of diffusion saturation, the magnitude and distribution of residual stresses in the strengthened layers of steel surfaces were established. Based on the results of the experiments, the endurance limit and corrosion resistance of strengthened ion nitrided surface layers were determined. As a result of conducting research on the properties of the surface layers of samples strengthened by nitriding, it was established that thanks to the use of vacuum thermocyclic nitriding in the plasma of a pulsating glow discharge, the thickness of the diffusion layer is 40...300 μm; the microhardness of the surface layer reaches 7600 MPa; there are residual compressive stresses of the order of 445...950 MPa, corrosion resistance increases by 3.1 times, and. the endurance limit of steel structures at temperatures up to 640 °C increases by 15...20%.

The analysis of the conducted studies showed the absence of studies on the interrelationship of factors that determine the course of the process of vacuum thermocyclic nitriding in the plasma of a pulsating glow discharge and recommendations for the selection of technological parameters of vacuum thermocyclic nitriding in the plasma of a pulsating glow discharge, which would be used for the practical application of this technology. On the basis of the conducted experimental studies, it was established that the main mechanisms of increasing the endurance limit of materials due to the application of the process of diffusion saturation of the surface with nitrogen in a pulsating glow discharge in the thermocyclic mode are: creation of a favorable scheme of residual stresses; change in patterns of deformation of surface layers, their chemical and adhesive properties.