Diffusion Chromising of Steel by Chemical Vapour Deposition Using Chloride Compounds: 2 Coating Structure

Abstract

The surface structure and composition of coatings obtained by diffusion chromising has been investigated. The coatings were prepared by gas phase diffusion chromising using metallic chromium and iron(III)chloride as reagents. The average chromium content of the coating was determined by direct current plasma atomic emission spectrometry. The structure and composition of the coatings were investigated by electron microscopy, energy dispersive X-ray microanalysis, X-ray diffraction, glow discharge optical emission spectrometry, and X-ray photoelectron spectrometry. A diffusion coating with 50-55 wt-%Cr on the surface was obtained. The average chromium content of the coating was 20-30 wt-%. The coating layer was uniform with no boundary layer between base metal and coating. An oxide or hydroxide layer (20-50 nm thick) was found on the surface. Formation of a carbide (Cr₂₃C₆)layer was detected in some cases.