Influence of the method of inputing a cobalt-containing emitter on the depth of the diffusion layer of chrome

Abstract

The results of thermal diffusion chromium plating of samples of steel 35CrNi2-3 in technological back filling containing oxide-emitters of oxygen anions in the separating part, which create a thermionic field during heating, are presented. In one variant of saturation, powder of metallic cobalt was added to the metal part, in the second case, to accelerate diffusion processes, a cumulative lattice made of cobalt sheet was installed near the saturating surface. The saturation was carried out at a temperature of 1000 °C for 24 hours. The elemental composition of the diffusion layer was monitored using a JEOL JSM-6460LV universal scanning (scanning) electron microscope. The microhardness of the coatings was measured using an FM-800 microhardness tester. Microstructural analysis was carried out on an opti-cal microscope Axio Observer D1.m. It has been established that the presence of cobalt both in the form of a powder and in the form of a cumulative lattice contributes to the acceleration of the diffusion of chromium by 1.2–1.5 times compared with saturation without the addition of cobalt. The results obtained are experimental confirmation of the hypothesis about the mechanism of acceleration of chromium diffusion during thermal diffusion chromium plating by a thermionic flux of charged particles. The phase composition of the saturated surfaces consists of a solid solution of Cr–Fe, carbide ((Cr,Fe)7C3) and nitride ((Cr,Fe)2N and CrN) phases. Cobalt, being a non-carbide-forming element, is present in insignificant amounts in the Cr–Fe solution and does not form separate phases. It has been established that the oxide and metal components of the mixture upon heating have a complex nature of interaction, which determines the gas formation of the saturated surface and requires investigation by thermodynamic modeling methods.