Influence of the technology of thermal diffusion chroming on the depth of the diffusion layer

Abstract

Previously, the author’s works were shown that the introduction of powders of electron emitters or oxygen anions into the composition of the technological filling creates an electric field between the particles of the filling and the part to be saturated. The cumulative effect of this field and the diffusion flow leads to the intensification of diffusion processes and an increase in the diffusion depth of the main saturating element, chromium. This paper presents new results on improving the technology of thermal diffusion chromium plating of structural steels through the use of an internal emission field. In the experiments, the saturation of 35X2H3 steel samples was carried out in sealed containers at a temperature 1000°C for 24 hours. The elemental composition of the diffusion layer was monitored on transverse sections in the direction from the saturated surface to the base metal of the sample using a JEOL JSM-6460LV universal scanning electron microscope. The microhardness of the coatings was measured on an FM-800 microhardness tester. It is shown that partial or complete replacement of aluminum oxide in the technological filling with powders of natural and artificial oxide materials (serpentine and scheelite) has a positive effect not only on the knock-out of parts from containers, but also significantly increases the depth of the chromium diffusion layer. Moreover, the most effective is the use of scheelite powder in the saturating mixture. The use of additional equipment for thermal diffusion chromium plating in the form of cumulative gratings, both for chromium plating in mixtures of traditional composition and in mixtures with minerals, provides an increase in the depth of chromium diffusion by at least 2 times and an increase in the hardness of coatings from 10 to 70 HV. It also enriches the surface layers of the saturated part with the lattice metal element.