Influence of the composition of the cumulative lattice during thermal diffusion chromiing on the depth of the diffusion layer

Abstract

Presents the results of experiments on improving the technology of thermal diffusion chromium plating of structural steels through the use of an internal emission field created in the technological backfill during heating. To create a field in the separating part of the technological backfill, aluminum oxide was completely replaced by mixtures of two compositions: a mixture of scheelite (CaWO4) and serpentine (Mg3Si2O7); a mixture of scheelite (CaWO4), serpentine (Mg3Si2O7), MgO, dicalcium silicate (γ-2•CaO•SiO2). The choice of these materials was based on the results of preliminary experiments on measuring the thermionic current in them. Saturation of samples of steel 35CrNi2-3 with chromium was carried out at a temperature of 1000°C for 24 hours. For both variants of technological fillings, the ab-sence of sintering and good knockout of parts were noted. The chemical composition of the diffusion layer on metal samples was controlled using a JEOL JSM-6460LV universal scanning (scanning) electron microscope. The micro-hardness of the coatings was measured using an FM-800 microhardness tester. The results show that the additional use of cumulative lattices of nickel and nichrome for thermal diffusion chromium plating provides an increase in the depth of chromium diffusion by 1.5 times when saturated in the backfill of the same composition. In this case, the lattice material has little effect on the depth of chromium diffusion, but it influences the intensity of surface microalloying with nickel. The electron yield work of nichrome X20H80, equal to 4.5 eV, has been determined. It was found that the hardness of the diffusion layers formed on the surface correlates with the content of chromium and nickel in them. The hardness of the chrome layer is 790±10 HV and 820±10 HV, using nickel and nichrome cumulative lattices, respective-ly. In the case of saturation without grids, the hardness is 50 and 20 HV respectively lower.