Cr2N Layer Research Articles

Optimization of wear-resistant coating architectures using finite element analysis

The goal of this work was to develop an approach for the design of multilayer coatings with enhanced toughness to fracture and improved adhesion for wear-resistant applications. Finite element analysis (FEA) was utilized to investigate the distribution of stress in single layer, bilayer and multilayer films under combined normal and tangential loads. Two-dimensional models were created for single layer CrN and Cr2N films and for a number of multilayer combinations of Cr, CrN and Cr2N layers. The FEA results were validated for uncoated solids through comparison with analytical solutions for Hertzian contacts, with and without frictional effects. A good fit was observed in all cases. Then the influence of film architecture and substrate material on the mechanical stress within the films was studied. It was determined that metallic layers had significantly lower σxx stress than ceramic layers, while both σyy and τxy stress within the layers was largely independent of the layer material. Simulation data was then compared to actual data obtained from several chromium nitride based thin films with architectures corresponding to those of the FEA models. Coatings were deposited by unbalanced reactive magnetron sputtering on A2 steel and 2024 aluminum substrates. Residual stress in the films was determined from sin2 Ψ x-ray measurements. When used in multilayer architectures CrN films had high compressive stress on both steel and aluminum substrates, while Cr films had lower compressive stress on steel substrates and tensile stress on aluminum substrates. The residual stress in Cr2N layers could not be determined due to overlap of the x-ray peak. Coating adhesion was measured by a scratch test and wear rates were measured using a pin-on-disk testing apparatus under normal loads of 4 and 10 N for the aluminum and A2 steel substrates, respectively. The strongest correlations were found between the σxx stress at the film–substrate interface and coating adhesion and wear resistance. The stress at the interface between ceramic layers and metallic substrates was very high, resulting in an overall reduction in performance of single layer Cr2N and multilayer CrN/Cr2N films. The highest adhesion and the lowest wear rates were observed in the films that consisted of alternating CrN layers separated by thin Cr layers. Increasing the thickness of the Cr layers degrades the performance of the films due to a decrease in the overall stiffness of the coating.

Influence of Cr xN y coatings deposited by magnetron sputtering on tool service life in wood processing

Cubic CrN(200) and a mixture of 25% CrN+75% Cr 2N(111) coatings were deposited by magnetron sputtering onto carbide tools and tested in wood machining. The composition of the layers was determined by X-ray photoelectron spectroscopy (XPS) analyses. Scanning electron microscopy (SEM) observations showed that Cr 2N layers have a columnar structure while CrN layers seem to be featureless. Secondary ion mass spectroscopy (SIMS) profiles have shown a good homogeneity of the layers and no interdiffusion of the different species into the substrate. The mechanical properties of the chromium nitride coatings were characterized by residual stress measurement, hardness measurements and scratch adhesion tests. The layers have some compressive stresses in the range −1.7/−2.1 GPa and −0.4/−1 GPa for CrN and Cr 2N, respectively. The more adherent layers are CrN ones which exhibit hardness up to 1900–2100 HV. Cr 2N layers are harder (up to 1900–2100 HV) but less adherent. Machining tests were performed up to 5 and 10 km of cutting distance with industrial routers on Oriented Strand Board. Tool wear and service life were compared between the uncoated and coated tools. First, it has been observed that the edge wear is very high, just at the beginning of the routing process. The best result was shown by a carbide tool CrN coated on both faces; the service life of this tool is four times higher than the one of an uncoated tool.

Evaluation of PVD nitride coatings, using impact, scratch and Rockwell-C adhesion tests

In this work the scratch test, the impact test and the Rockwell-C adhesion test were compared by investigating the adhesion properties of three types of sputtered physical vapour deposition coatings: TiN, CrN and Cr 2N. Each coating type was deposited on polished SAE 52100 steel, with different thicknesses in the nominal range of 2–20 μm, to evaluate the thickness influence on the test results. All the tests showed a ductile behaviour for the TiN coating with small delaminations and a brittle behaviour for the CrN and Cr 2N coatings with relatively large delaminations. An increase of the dimensions of the delaminations with increased coating thickness was detected for all layer types. With the scratch test a significant increase in upper critical load with layer thickness was observed for all of the coatings. However, there was considerable variability especially for the Cr 2N coatings. The impact tests showed no coating failure for the TiN layer, and a decreasing impact crater volume with increasing layer thickness, whereas the CrN and Cr 2N layers failed after 10 3 impacts and showed an increasing impact crater volume with increasing layer thickness. The studies demonstrate the usefulness of using these test methods for differentiating between the behaviour of different coatings under various contact conditions.

Xenon-beam-induced atomic transport through Cr/Al and Cr2N/Al interfaces

Cr layers (60–75 nm) on Al substrates and Cr2N layers (40–120 nm) on Al+3 wt.% Mg substrates were irradiated at 80 K and 300 K with 150–900 keV Xe-ions. The ion-beam-induced interface mixing was analyzed by means of Rutherford Backscattering Spectrometry (RBS). Both systems exhibit fairly small mixing rates, with those of Cr/Al being enhanced at 300 K target temperature, due to radiation-enhanced diffusion. The observed interface broadening is compared with predictions of ballistic and thermal spike mixing models. The low-temperature mixing rates in the system Cr/Al are underestimated by the ballistic model, but are rather well reproduced by local spike models. Mixing in the Cr2N/Al system at both temperatures, on the other hand, seems to be rather well described by the ballistic model.

窒化チタン／窒化クロム多層膜の形成とその耐孔食性

Monolayer TiN films often display poor corrosion resistance due to localized weak spots, and multilayer film composed of several TiN and thin Cr2N layers was therefore studied in an effort to improve pitting corrosion resistance. A thin Cr2N layer with a mixing layer formed with the underlying materials was produced by N++N2+ ion implantation into the Cr layer. The multilayer film showed a dense, homogeneous rupture face, unlike the columnar structure observed in the monolayer TiN film. In an anodic polarization test in 3.5wt.% NaCl solution, austenitic SUS 304 stainless steel coated with the multilayer film showed better pitting corrosion resistance than specimens coated with the monolayer TiN film. After this corrosion test, many shallow corrosion marks were observed in the surface of the multilayer film in contrast to the deep pits observed in the surface of the monolayer TiN film. It is thought that the improved pitting corrosion resistance of the multilayer film was due to its stronger inter-column characteristics obtained by the interposing of the multiple thin Cr2N layers.

クロム板へのＭｅＶ窒素イオン多重注入 ＩＩ． 窒素濃度プロファイルに対する熱処理効果

Polycrystalline chromium metal plates (purity>99.99%) were implanted with nitrogen ions (N2+) at energies of 500keV, 1MeV, 1.5MeV and 2MeV and the doses of from 3×1017 to 1×1018N atoms/cm2. The implanted chromium plates were annealed repeatedly at varying temperatures from 250°C to 800°C. The depth profiles of nitrogen concentration was investigated by Rutherford Backscattering Spectrometry (RBS) and the crystallinity of the nitride layer was studied by XRD. At temperatures up to 400-500°C, CrN converted to Cr2N and phase transition were observed. However, the amorphous nature of the nitride layer formed was kept after annealing. The maximum Cr2N layer thickness of obtained by multiple implantation (2MeV-1.5MeV-1MeV, total=2.1·1018) and subsequent annealing was 650nm (from 200nm to 850nm in depth scale).