RESEARCH OF RESIDUAL STRESSES ON COATINGS OBTAINED USING COMPOSITE POWDER MATERIALS

Abstract

The purpose of the work is to conduct research on the nature of the distribution of residual stresses of coatings on structural materials obtained using composite saturating media. Residual stresses appear after chemical-thermal treatment during cooling as a result of the elastic interaction of the diffusion layer and the core having different volumes and coefficients of thermal expansion. The ratio of the volumetric characteristics of the layer and the core also affects the magnitude of the residual stresses in the surface layer. Residual stresses significantly determine the possibility of practical use of diffusion coatings. Moreover, the magnitude, sign and nature of their distribution affect the adhesion strength of the coating to the hardened material. Residual stresses arising in the diffusion layer are often the cause of microcracks and peeling of the coating. As a rule, the level of residual stresses is higher, the greater is the difference in the temperature conditions of production, the thermophysical and physico-mechanical properties of the base materials and the protective coating. One way to influence the nature of the distribution of internal stresses in protective coatings is to dope them. The nature of the distribution of residual stresses over the thickness of multicomponent coatings indicates that their alloying with boron, chromium, and aluminum makes it possible to obtain FeB and Fe 2 B phases, which are alloyed with silicon, chromium, and aluminum. Residual compressive stresses from 360 to 410 MPa appear on the surface of the layers. The boride phase Fe 2 B is in a state of volumetric stress with a significant gradient of stresses in depth. It was found that in the process of producing multicomponent coatings doped with chromium, aluminum, boron, titanium and tungsten, the value of the residual compressive stresses increases with increasing carbon content in the substrate. So when the carbon content in the substrate changes from 0.02% C to 0.8% C when alloyed with chromium and aluminum, they are 110 and 260 MPa; when alloying with chromium, aluminum, boron – 200 and 410 MPa; when alloying with chromium, aluminum and titanium – 20 and 330 MPa; chromium, aluminum and tungsten – 45 and 210 MPa, which is associated with a large difference in the physicomechanical properties of the base material and the protective coating.