Chromium Nitride Layers Research Articles

Surface chemical changes induced by low‐energy ion bombardment in chromium nitride layers

AbstractIn this work three types of CrNx layers—one close to Cr2N, the other to CrN and a third with high nitrogen content CrN1+x—were prepared by reactive magnetron sputtering. The samples were subjected to bombardment by Ar+ and N2+ ions applied in sequence. The relative atomic concentration and the chemical states of the elements in the surface layer were determined by x‐ray photoelectron spectroscopy. Alternate bombardment with Ar+ and N2+ ions (1–2 keV) resulted in significant compositional and chemical state changes. Although prolonged Ar+ bombardment did not decrease the nitrogen content of Cr2N below the nominal (CrN0.5) composition, it decreased the nitrogen content of the closely stoichiometric CrN appreciably, to about CrN0.8. At bombardment with N2+ ions nitrogen could be implanted into the Cr2N films, changing its composition up to about CrN0.8. It was shown that extra nitrogen could be incorporated also into the CrN samples, increasing the nitrogen content above the stoichiometric composition up to about CrN1.2. The CrN1+x‐type sample showed high stability towards Ar+ bombardment. Two significantly different chemical states of nitrogen were determined for the two types of nitrides: the N 1s peak at 397.5 ± 0.1 eV binding energy was characteristic of N in Cr2N and the peak at 396.5 ± 0.1 eV of N in the CrN state. The effect of Ar+ and N2+ bombardment on the surface composition discussed in this paper may provide information for elaboration of deposition conditions for CrNx coatings with predetermined chemical composition and structure. Copyright © 2002 John Wiley & Sons, Ltd.

Multi-layer structure for chemical vapor deposition diamond on electroplated diamond tools

In this work we established a process to overcome the deposition difficulty on electroplated diamond tools by a multi-layer structure. The process consists of the following steps: (1) diamond powder aggregation with nickel (this step is the conventional method for the production of electroplated tools); (2) electrochemical deposition of a chromium layer, but leaving the diamond grains partially uncovered; (3) nitridation of the chromium layer; and (4) deposition of the chemical vapor deposition (CVD) diamond layer. This method uses the advantages and overcome the disadvantages of each step. Electroplating with nickel is conventionally used due to its relatively good wettability to diamond. The direct aggregation of the diamond powder with a chromium layer results in looser grains and is not usable. The nickel layer is inadequate for diamond deposition; even after treatment in hydrogen atmosphere, diamond does not grow on it. The chromium nitride layer is well known to be very suitable for diamond growth, however, the thermal stress between these layers is very high limiting film thickness and its applicability. With the multi-layer structure obtained the CVD diamond film is deeply anchored by the diamond grains into the metal matrix and helps considerably to decrease the stress. The process has been developed on flat surfaces and tested on small conventional diamond burrs. The diamond films have been characterized by scanning electron microscopy (SEM), energy dispersive X-rays (EDS) and Raman spectroscopy (RS).

Corrosion resistance of chromium nitride and oxynitride layers produced under glow discharge conditions

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 multilayer effect in abrasion — optimising the combination of hard and tough phases

In the present investigation it is shown that the wear resistance of multilayer PVD coatings, combining relatively soft but tough chromium (Cr) and harder but more brittle chromium nitride (CrN), exceeds that of both its phases. This striking exception to the simple rules of mixtures — the multilayer effect in abrasion — is investigated with respect to physical mechanisms, layer thickness dependence and implications for multilayer design for abrasive applications.Multilayers of Cr and CrN were deposited on high speed steel using reactive magnetron sputtering. The coatings were characterised with respect to microhardness and abrasive wear resistance against a slurry of 2.5 μm diamond abrasives. The abraded surfaces were investigated by scanning electron microscopy and optical profilometry to reveal the microscopic wear mechanisms. A physical model for the layer thickness dependence for wear resistance of multilayer coatings was developed. Despite its simplifications, the model agrees very well with the experimental results.The advantage of Cr layers is their tendency to deform plastically rather than becoming removed by wear; the drawback is lack of penetration resistance. The penetration resistance, however, is the main advantage of the CrN layers. It was concluded, both theoretically and experimentally, that the multilayer effect is explained by the reduction of abrasive penetration depth in the Cr layers due to the underlying harder CrN layer.

Characterization of magnetron-sputtered chromium and iron nitride films

Chromium and iron nitride layers (with thicknesses of 100–1000 nm) were deposited onto silicon substrates via reactive rf magnetron sputtering. Stoichiometry, phase formation and surface morphology were analyzed by a combination of different methods: Rutherford Backscattering Spectrometry, Resonant Nuclear Reaction Analysis, Conversion Electron Mössbauer Spectroscopy, Scanning Tunneling Microscopy and X-Ray Diffraction.

A Comparative Study of Structure and Residual Stress in Chromium Nitride Films Deposited by Vacuum Arc Evaporation, Ion Plating, and DC Magnetron Sputtering

Chromium nitride layers have been deposited by three PVD techniques - vacuum arc evaporation, ion plating, and dc magnetron sputtering - for different substrate bias voltages, whereas the substrate temperature was always kept constant at 400 °C. X-ray diffraction (XRD) has been utilized to detect the phases, to determine the texture of the films, and to calculate lattice parameters and grain size. The samples have been subjected to stress detection by analysis of the stress induced sample bending. The subject of this study is the investigation of the dependence of structure and residual film stress on the substrate bias voltage for each method, and a comparison of the obtained results. The principal differences between the three deposition techniques are the composition, the percentage of ionization, and the average energies of the layer forming species. A clear correlation between these properties and the differences in the evolution of structure and residual stress in dependence on the substrate bias voltage for the different deposition techniques can be observed.

Complex characterisation of vacuum arc-deposited chromium nitride thin films

Chromium nitride layers were deposited on stainless steel substrates using the vacuum-arc technique. The nitrogen pressure was varied during film preparation. The chemical composition of the layers was determined by XPS and RBS. Special attention was paid to XRD including phase analysis, texture evaluation and stress determination. Different phase compositions were found depending on nitrogen incorporation. Only the film prepared under floating bias potential contained the nearly stoichiometric mononitride. The lattice constants of all detected phases show some deviation from tabulated values. The coatings are strongly textured. All films exhibit compressive residual stress. After subtracting the thermal stress the intrinsic stress was still found to be compressive and of low level. It was practically independent of the nitrogen concentration in the films. Excellent thermal stability of the coatings can be concluded from tempering experiments.

Deposition temperature dependent characteristics of magnetron sputtered chromium nitride films

Chromium nitride layers with CrN and Cr2N stoichiometry were deposited onto silicon substrates by means of reactive RF-magnetron sputtering at different substrate temperatures (300-830 K). The layer thicknesses were 100 to 1500 nm. Composition, surface roughness, grain size, microstructure and phase formation were analysed using RBS (Rutherford backscattering spectrometry), RNRA (resonant nuclear reaction analysis), PAC (perturbed angular correlation), STM (scanning tunnelling microscopy) and XRD (x-ray diffraction). RBS and RNRA depth profiling of the samples revealed for both nitrides homogeneous Cr and N concentrations over the whole layer depth. For Cr2N films, indications of a phase transformation due to the increased target temperature from a disordered Cr/N phase to the ordered Cr2N phase were obtained via XRD and PAC. The lateral grain size measured with STM and the vertical grain size measured with XRD are approximately the same for both nitrides at all deposition temperatures.

Corrosion and wear properties of multipurpose coatings deposited by ion-beam-assisted deposition

Electrochemical measurements and wear tests were performed on aluminium and aluminium alloy coatings containing magnesium for uniform and local pitting corrosion protection of low carbon steel substrates. Final hard chromium nitride and aluminium nitride layers were deposited at the surface of the protective films in order to lower friction and wear. The results show that wear and corrosion protection can be improved by use of bifunctional multilayers. The coatings for multipurpose application were generated by ion-beam-assisted deposition. The defined intrinsic film stress controlled by the ion-to-atom arrival ratio influences the corrosion properties. Increasing the ion-to-atom ratios usually improves the corrosion resistance.

D.c. magnetron sputtering of oxidation-resistant chromium and CrN films monitored by optical emission spectrometry

For applications at temperatures above 500 °C, Ti-6wt.%Al-4wt.%V was protected by sputtering chromium and chromium nitride layers from the embrittlement caused by oxidation. The coating processes were analysed in situ by means of optical emission spectrometry, whereby the deposition rate and the stability of the actual process conditions were monitored. Further, the nitridation of the chromium target (the source of the coating material) and the concentration ratio of the condensing binary compounds (Cr x N y ) can be assessed during the process. Compared with the uncoated material, the mass gain of Ti-6wt.%Al-4wt.%V due to oxidation could be decreased to about 3% by means of chromium and chromium nitride layers 3 μm thick. Also the brittle α case formation at the near-surface region of the titanium alloy is greatly reduced in the course of high temperature oxidation. As far as diffusion and reaction are concerned, an interpretation of the oxidation process on the titanium alloy is given by means of Auger depth profiles. The morphology of the layers is characterized by scanning electron microscopy pictures.

A comparison of the corrosion behaviour and hardness of steel samples (100Cr6) coated with titanium nitride and chromium nitride by different institutions using different deposition techniques

Deposition of hard coatings may influence the mechanical properties of the bulk material and its corrosion resistance. In this work we study the hardness of the coated and the back side of 100Cr6 steel plates. Electrochemical corrosion tests were performed in O 2-saturated acetate buffer of pH 5.6 at 25 °C. Chromium nitride and titanium nitride coatings prepared by different physical vapour deposition processes, such as arc, thermionic arc evaporation, magnetron sputtering and ion-beam-assisted deposition (IBAD) were compared. The results show that, for sufficient corrosion protection, chromium nitride layers have to be thicker than 500 nm. An increased nitrogen partial pressure in the evaporation chamber of the IBAD process improves the corrosion resistance significantly. The hardness of the substrates was reduced in the case of thermoionic arc evaporation only, indicating a deposition temperature of more than 250 °C. For this process, however, we obtained the best corrosion results.

Thick and homogeneous surface layers obtained by reactive ion-beam-enhanced deposition

A recently developed method, reactive ion-beam-enhanced deposition (RIBED), which consists of simultaneous or sequential deposition and implantation steps, has proved to be very effective in the production of surface compounds with interesting surface properties. This hybrid technique allows the depth of the treated region to be nearly independent of the projected range of the implanted ions and thereby thicker layers to be obtained than by conventional ion implantation. Moreover, with respect to unimplanted deposited layers, the ion beam increases the uniformity of the films and their adhesion to the substrate. In this work, we consider surface nitrides of chromium and boron, which are known to be hard and corrosion resistant. The surface compounds were characterized using various different techniques: Auger electron spectroscopy, secondary ion mass spectrometry, X-ray diffractometry and scanning electron microscopy. Electrochemical measurements were carried out on the chromium and boron nitride layers, obtained by RIBED, on iron.

LEED‐AES investigation on the influence of thermally segregated chromium on the oxidation of an iron‐chromium alloy

AbstractWhen heating a (111)‐oriented Fe1‐xCrx single‐crystal sample (0.05 ≦ x ≦ 0.10) for 15 minutes at 550 °C an unarranged surface layer rich in chromium and nitrogen, simultaneously, with x = 0.40 will ermerge. The low‐energy Auger signals of iron and chromium were involved for characterizing the chemical bond and the high‐energy ones used for quantitative analysis. The shape and the energy position of the transitions were exactly determined by integration, background subtraction and approximate deconvolution of the Auger electron spectra measured differentiatedly. Chromium nitride layers were detected which retard probably the formation of the FeO layer compared to Leygraf et al.While the adsorption isotherm at room temperature for the surface poor in chromium and crystallographically perfect shows two erratic changes of the sticking probability, the adsorption isotherm for the surface rich in chromium is a continuous curve with a higher increase in the lower dose‐region typical for random surfaces.

Nitriding of chromium and its alloys at 1000?1200�C

1. After nitriding, at the surface of chromium and its alloys there is formation of a nitride layer consisting of Cr2N nitride. Alloying elements in the test concentration range have almost no effect on kinetics of the growth of the outer nitride layer. 2. In alloys of the Cr-Ti system beneath the chromium nitride layer a zone of internal nitriding is observed, strengthened by dispersed particles of titanium nitride TiN. The growth kinetics for the diffusion layer obeys a parabolic rule and is controlled by nitrogen diffusion in the alloy. 3. Distribution and morphology of the titanium nitride precipitate are determined by titanium concentration in the alloy, temperature, and nitriding duration. With an increase in nitriding temperature there is coalescence of particles and a reduction in hardness in the internal nitriding zone. 4. Values of coefficients for penetration of nitrogen into chromium alloys calculated by experimental data correlate with the results of other works.