The paper describes the microstructure of the composite layers produced on chromium pre-coated AISI 1045 steel by oxynitriding under glow discharge conditions (duplex method). The layers were ...examined by the cross-section method using transmission electron microscopy. Their microstructure was composed of the 4 zones: a near-surface CrN–Cr2O3 mixture zone about 1 μm thick, a Cr2N zone about 4 μm thick, a chromium zone–the thickest–about 50 μm, and the thinnest (Cr,Fe)7C3 zone about 0.5 μm thick. Cr2O3 also occurred in the form of nano-crystalline aggregates, about 1 μm in size, situated in the upper part of the Cr2N zone. All the zones had a fine-grained structure, except the finest nano-crystalline zone situated at the surface. It was found that, during oxynitriding, the cracks present in the chromium coating are filled up by chromium nitrides and oxides. This may explain the observed improvement of the corrosion resistance.
The paper presents the results of investigations of the structure and corrosion resistance of chromium nitride, oxynitride and oxide layers produced on steels by electrochemical chromium deposition ...combined with glow discharge assisted nitriding, oxynitriding and oxydizing processes. The layers obtained were of the types: CrN+Cr
2N+Cr+(Cr,Fe); Cr
2N+Cr+(Cr,Fe); CrN+Cr
2N+Cr+(Cr,Fe)
7C
3; Cr
2N+Cr+(Cr,Fe)
7C
3; Cr(N,O)+Cr+(Cr,Fe)
7C
3 and Cr
2O
3. The corrosion resistance of the layers is high and can be modified by changing the process parameters, such as the temperature and chemical composition of the gas atmosphere.
The phase composition and hydrogen behavior in coatings produced on Armco iron by electrochemical deposition of chromium (Cr) and subsequent plasma-assisted nitriding were investigated. At cathodic ...Cr deposition, no hydrogen charging of the iron substrate occurs. The amount of hydrogen absorption within the Cr coating (50 μm thick) was measured as high as 450 ppm. Plasma-assisted nitriding of a galvanic Cr coating caused the formation of a surface layer consisting of compact nitrides (Cr
2N+CrN) and precipitates of nitride within the bulk of the Cr coating and a (Cr,Fe) alloy layer between the chromium coating and the steel substrate. The compact nitride layer prevented hydrogen escape from the Cr coating. The nitride precipitates served as hydrogen traps, and thus hampered hydrogen desorption. Hydrogen-assisted phase transformations in nitrided electroplated Cr coating were observed and are discussed.
New methods for improving the performance properties of surface layers on steels consists also the modification of the nitriding process. This paper presents the properties of multicomponent layers ...produced by glow discharge nitriding process followed by oxidizing, nitriding followed by PACVD technique carried out in the atmosphere composed of Ti(OC
3H
7)
4 vapours and by the electrochemical deposition of chromium on steel combined with the glow discharge assisted nitriding. The results of metallographical, X-ray examinations and the measurements of the corrosion and frictional wear resistance are presented. These treatments essentially improve the properties of nitrided layers and can be performed in a conventional apparatus designed for glow discharge assisted nitriding process during a sole technological operation.
Modifications of the plasma nitriding process, such as oxidizing or burnishing introduced at the final stage of the treatment, permit modifying the performance properties of nitrided layers. By ...combining the electrochemical chromium plating with plasma nitriding, we can produce composite layers of the CrN+Cr sub 2 N+(Cr,Fe) sub 2 C or CrN+Cr sub 2 N+(Cr,Fe) types, according to the thickness of the chromium coatings, types of steels and to the nitriding process parameters.
