CrN Layers Research Articles

Mapping the mechanical properties in nitride coatings at the nanometer scale

We report on a multilayered structure comprising of rock-salt (rs) structured CrN layers of constant thickness and AlN layers of varying thicknesses, which surprisingly enables the growth of metastable zinc-blende (zb) AlN layers for certain layer-thickness combinations. The multilayer exhibits an atomic and electronic structure gradient as revealed using advanced electron microscopy and electron spectroscopy. Gradient structures are also accompanied by a modulation of the chemical compositions. A combined experimental analysis based on valence electrons and inner shell electrons allowed mapping the mechanical properties of the multilayer at the nanometer scale and further unveiled the effect of oxygen impurities on the bulk modulus. We found that the presence of oxygen impurities causes a remarkable reduction of the bulk modulus of rs-CrN while having no significant effect on the bulk modulus of the stable wurtzite structure wz-AlN layers. The findings are unambiguously validated by theoretical calculations using density functional theory.

Structure and corrosion behavior of ZrN/CrN nano-multilayer coating deposited on AISI 304 stainless steel by CAE-PVD technique

ABSTRACT In this study, a zirconium nitride/chromium nitride nano-multilayer coating was deposited on AISI 304 specimen using cathodic arc evaporation-physical vapor deposition (CAE-PVD). The characterization of the samples were evaluated by scanning electron microscopy (SEM), field emission-SEM (FE-SEM), and X-ray diffraction (XRD). To evaluate effect of immersion time on the electrochemical behavior of ZrN/CrN nano-multilayer coating using electrochemical impedance spectroscopy (EIS) measurements were carried out in 3.5 wt. % NaCl media. Using the CAE-PVD method, nano-multilayer ZrN/CrN coating with high adhesion and density was successfully produced. A unique high polarization resistance of ZrN/CrN nano-multilayer coatings in comparison to AISI 304 stainless steel without coating was made. As well as the desirable behavior corrosion results showed that in the ZrN/CrN nano-multilayer coating to the AISI 304 substrate within the 3.5 wt. % NaCl, there is a barrier against corrosive agents that is preventing corrosion occurrence. The SEM images disclosed that there were not any pits or severe damages on the surface of the ZrN/CrN nano-multilayer coating. The FE-SEM micrographs show that the coating structure contains alternate layers of ZrN and CrN. The energy dispersive spectroscopy (EDS) analysis and x-ray map were disclosed elements distribution in the cross-section of the nano-multilayer coating.

Magnetization of Fe4N thin films: Suppression of interfacial intermixing using buffer layers

We studied the magnetization (Ms) of 60 nm thick polycrystalline Fe4N thin films deposited using reactive dc magnetron sputtering. The optimum substrate temperature (Ts) to grow an stoichiometric Fe4N phase is about 673 K, in agreement with earlier works. However, at this Ts, we found that significant intermixing is taking place at the substrate-film interface, affecting the Ms of Fe4N film, adversely. We performed secondary ion mass spectroscopy (SIMS) measurements to extract the extent of such intermixing. It was found that Si from the SiO2 substrate get interdiffused into Fe4N film forming an undesired interface extending up to almost half of the film. As a result, the average Ms of Fe4N film get reduced by about 25% as compared to its theoretical value. To prohibit such intermixing, we placed thin layers of Ag, Cu, or CrN as a buffer layer between the substrate and Fe4N film. Such buffer layer suppress the extent of interdiffusion remarkably. From SIMS measurements, we found that among all buffer layers, CrN is most suitable as it reduces the extent of intermixing to a minimum level. Magnetization measurements performed using bulk magnetization and polarized neutron reflectivity (PNR) methods also clearly revealed that the Ms was the highest when CrN buffer layer was used. From these results, it becomes apparent that the intermixing taking place at the substrate-film interface plays a vital role in affecting the Ms of Fe4N thin films. To further suppress such intermixing an attempt was also made to bring down the Ts from 673 to 523 K. Obtained results are presented and discussed in this work.

Corrosion mechanism investigation of TiAlN/CrN superlattice coating by multi-arc ion plating in 3.5 wt% NaCl solution

This study focuses on effects of layered design method on the corrosion resistance of the coatings. The different corrosion behaviors could be extracted from the microstructure and electrochemical properties for nanoscale multilayer coating (TiAlN/CrN) and single layer coatings (TiAlN and CrN). Based on the analysis of microstructure characterization, electrochemical response and corrosion morphology, it may provide a reference for the development of new anti-corrosive films. The three different coatings were prepared by the process of multi-arc ion plating on 316 stainless steel. In the deposition of TiAlN/CrN multilayer coating, the almost 150 nm Cr film was first deposited as a transition layer, and then CrN and TiAlN individual layers were alternately deposited with a single layer thickness of 10 nm. The influences of the layered construction on the electrochemical performance of the multilayer and single layer coatings were investigated in a neutral saline solution (3.5 wt% NaCl), for which potentiodynamic polarization and electrochemical impedance spectroscopy were employed. The 316 stainless steel was regarded as comparative group. The surface and cross-sectional morphology of the as-deposited coatings were investigated by scanning electron microscope (SEM). The crystal structure and preferred orientation were analyzed by X-ray diffraction (XRD). The interface characteristic of the multilayer TiAlN/CrN coating was detected by transmission electron microscope (TEM). After the 15 days immersion corrosion test, the surface morphology of the samples were observed by the means of SEM and laser scanning confocal microscope (LSCM). The results showed that all the coatings exhibited a face centered cubic structure (fcc) and the multilayer coating presented (200) preferred orientation and coherent interface. In comparison with polarization curves of the substrate and the TiAlN and CrN single layer coatings, the corrosion potential of the TiAlN/CrN multilayer coating shifted positively to −0.36 V, the corrosion current density decreased to 0.047 μAcm−2 and the polarization resistance is 124.69 kΩ cm2. In terms of EIS, the TiAlN/CrN multilayer coating possessed the low value of CPE (10.9 × 10−6 Ω−1 cm−2 sn) and high value of n (0.9) in all samples. Furthermore, the corrosion morphology of the TiAlN/CrN multilayer coating was more close to the morphology of as-deposited coating. Therefore, the TiAlN/CrN multilayer coating exhibited superior corrosion resistance compared with 316 stainless steel and the single coatings. The roles of the layered design in enhancing the corrosion resistance can be summarized as: multilayer design can change the original growing mode of the coating, block the pinholes, reduce the inherent defects and form passive coating with compactness.

Nanoscale architecture of (CrN/ZrN)/(Cr/Zr) nanocomposite coatings: Microstructure, composition, mechanical properties and first-principles calculations

The main principles of formation of microstructure and properties of the nanostructured films consisting of periodically alternating multilayers of CrN/ZrN transition metal nitride films and Cr/Zr pure metals were investigated. First-principles calculations were carried out to give more insight in the physics of the strength enhancement of the deposited coatings. A special coating architecture, which consisted of 7 metallic and 40 nitride bilayers in each modulation period, was developed and then used. The thickness of single metallic bilayer was 16 nm, while the thickness of nitride bilayer was 25 nm. Microstructure studies showed mainly the presence of cubic CrN and ZrN with (200) and (111)/(200) preferential orientations, respectively. The analysis of the defect structure near the CrN and ZrN layer interfaces revealed the presence of dislocations, despite the small size of nanolayers and nanocrystallites, and the disorientation of the planes of nanocrystallites. The maximal hardness, reduced elastic modulus, elastic strain prior to plastic deformation and resistance to plastic deformation of the nanocomposite (CrN/ZrN)/(Cr/Zr) coatings were reached 34 GPa, 330 GPa, 0.1 GPa and 0.36 GPa, respectively, due to the multilayer-in-multilayer design and structural peculiarities of experimental coatings.

Ion-plasma strengthening through the use of piston rings

ABSTRACT The multilayer ion-plasma coating TiN/CrN, 6 layers of CrN and 5 lauers of TiN, for hardening of piston rings is proposed. It is established that as a result of hardening, the wear rate of rings decreases 15.7 times. A new method for estimating the residual thickness of the coating, which gives recommendations for improving the quality of coatings, is proposed.

Characteristics and properties of Cr[sbnd]N compound layer produced by plasma nitriding of Cr-electroplated of AISI 304 stainless steel

In this work, plasma nitriding of the Cr-electroplated coating on a 304 stainless steel (304 SS) was carried out at 700 °C in pure ammonia for different times (2 h, 3 h and 4 h). After plasma nitriding, a thin (1–2 μm) and compact chromium nitride layer mainly composed of Cr2N phase was formed on the surface region of Cr-electroplated coating. The corrosion resistance of CrN layers was examined in the proton exchange membrane fuel cell working environment to evaluate the possible application of the duplex-treated 304 stainless steel for bipolar plates. Before and after corrosion test the interfacial contact resistance was measured to determine the effect of nitriding on the electrical conductivity of all samples. The results show that the CrN compound layer has a very low passive current density 0.13 μA cm−2 and interfacial contact resistance 4.5 mΩ cm2.

Improved Mechanical Properties, Wear and Corrosion Resistance of 316L Steel by Homogeneous Chromium Nitride Layer Synthesis Using Plasma Nitriding

Here, pulsed plasma nitriding of AISI-316L austenite stainless steel is conducted in a narrow range of temperature 510-550 °C and simultaneous combination of expanded austenite phase, and homogenous, dense chromium nitride phase is attained in a single processing unit, with relative low-cost equipment and single-step processing. The results show a noteworthy enhancement in nanohardness at 530 °C, whereas best wear resistance is achieved by processing at 550 °C. A dual-layer structure is obtained constituted of expanded austenite phase covered by quite homogenous chromium nitride phase, which is probably responsible for the dramatic surface improvement. The wear mechanism is changed after plasma processing (abrasive to adhesive wear), and the friction coefficient is reduced and smoother, particularly for the sample treated at 530 °C. Interestingly, the corrosion resistance is also found to be enhanced, even in the presence of chromium nitride (which usually deteriorate the corrosion resistance), which is probably credited to the formation of fine-grained and homogeneous CrN layer over the expanded austenite phase. This study suggests that the development of homogenous CrN layer over the expanded austenite structure is highly valuable for mechanical and tribological features, and it enhances the corrosion resistance.

Nanoscale evolution of stress concentrations and crack morphology in multilayered CrN coating during indentation: Experiment and simulation

The layered architecture approach allows designing mechanical and fracture properties of hard coatings. The current study investigates the performance of a multilayered CrN coating, consisted of 5 μm CrN sublayers of very similar mechanical properties and microstructure but different residual stress states, during in-situ wedge indentation. A finite element model of the indentation was developed and validated against measurements of the local multiaxial stress fields during indentation, characterized by means of X-ray nanodiffraction analysis with a spatial resolution of 500 nm. By means of numerical fracture mechanics the effect of the multilayered structure on the formation and morphology of mode II cracks is analyzed. The configurational force concept was applied to investigate the crack driving forces and crack extension angles of static cracks in different geometrical arrangements. The simulation results agree well with the experimental findings and reveal a shielding effect preventing an interface-near crack from entering the CrN layer with the higher compressive residual stresses. Furthermore, the possibility to match the numerical results with the locally resolved experiments allowed determining validated material parameters for the deformation and fracture behavior. The work revealed e.g. that a KIIC of around 1 MPa∙m1/2 is an appropriate choice for the investigated CrN coating.

Exchange bias and exchange spring effects in Fe/CrN bilayers

We studied exchange bias and exchange spring effects in magnetic bilayer thin films of Fe and CrN grown by molecular beam epitaxy. First, the relationships between exchange bias, coercivity, and blocking temperature and the Fe and CrN layers thicknesses are studied. Second, the exchange spring effect is observed and studied in all samples. The exchange spring breaks free at critical applied field strengths while creating planar domain walls at lower applied fields. First-principles calculations are performed to understand the magnetic interactions between the Fe and CrN layers at their interfaces. The calculations are key to understanding the experimental observations.

Tribocorrosion response of duplex layered CoCrMoC/CrN and CrN/CoCrMoC coatings on implant grade 316LVM stainless steel

The objective of this work was to improve the tribocorrosion performance of biomedical grade 316LVM stainless steel via the application of duplex layered coatings. Two different PVD coatings were deposited via magnetron sputtering: (1) an underlying CoCrMo carbon S-phase layer followed by an outermost CrN layer designated as CrN/S and; (2) an underlying CrN layer followed by an outermost CoCrMo carbon S-phase designated as S/CrN. Tribocorrosion of the coated and uncoated 316LVM was studied against an alumina ball which was made to slide in a reciprocation motion in Ringer's solution. The contributions of wear, corrosion and their synergy were elucidated by performing tests under open circuit, cathodic and anodic potential conditions. The resultant wear scars were analysed via SEM, EDS, optical microscopy and contact profilometry. Both coatings displayed superior tribocorrosion response to AISI 316LVM with CrN/S exhibiting the best performance. CrN/S displayed lowest coefficient of friction under all electrochemical conditions (~0.10–0.15) and a material loss under anodic condition with a 93% decrease when compared to 316LVM. The CrN/S scars exhibited a smooth morphology under all test conditions in contrast with the other two test materials which displayed shearing marks oriented along the sliding direction under OCP and anodic conditions. By considering the resultant scar morphologies, a hypothesis is being proposed to explain the tribocorrosion degradation mechanisms encountered.

Influence of CrN, TiAlN monolayers and TiAlN/CrN multilayer ceramic films on structural, mechanical and tribological behavior of β-type Ti45Nb alloys

CrN, TiAlN single layers, and CrN/TiAlN multilayer ceramic films were deposited on Ti45Nb substrates by an industrial cathodic arc PVD process. The phase structures, the cross-sectional morphology, adhesion strength, surface hardness, and tribological behavior of the resulting uncoated and coated samples were evaluated in detail. The results showed that the preferred orientation was changed from (200) in CrN and TiAlN single layer films to (111) plane in the TiAlN/CrN multilayer films. The multilayered TiAlN/CrN films had smaller crystallite size than the single CrN and TiAlN films. The multilayer film coated samples exhibited the maximum surface hardness and the best adhesion strength among all samples. In addition, the results of wear tests present that all ceramic coatings showed better tribological properties than uncoated TiNb45 substrate materials and the best performance was observed from multilayer film-coated samples.

Phase transformations in nickel- and titanium-based alloys during chemical heat treatment

The structure of surface areas and cores of Ni-40Cr-4Al and Ti-6Al-5V alloys in the process of thermal and chemical heat treatment - nitriding, oxidation and carburizing was studied by X-ray diffractometry, optical microscopy and hardness measurement. Ni-40Cr-4Al alloy after quenching contains two supersaturated solid solutions based on fcc-Ni and bcc-Cr and a small amount of compound Ni3Al; subsequent aging leads to decrease in the degree of supersaturation of fcc-Ni and increase in the amount of bcc-Cr and Ni3Al. Nitriding leads to the formation of continuous CrN layer 3-4 µm thick on the surface, decomposition of Ni3Al and formation of AlN in underlying layer 100-140 µm thick. After nitriding high microhardness value of CrN (up to 1060 HV) and a slight decrease from 740 to 650 HV in the subsurface layers due to the transformation of Ni3Al to AlN were found. The surface layer of Ti-6Al-5V alloy is oxidized by erosion cutting in water, but the oxides formed during this process do not influence on subsequent diffusion saturation. During nitriding, oxidation, carburizing of Ti-6Al-5V alloy, diffusion layers are formed. They are characterized by the increased amount of α-solid Ti solution and formation of the surface intermediate phases. The thickness of the hardened layers is 8-20 μm. The hardness of these layers is 1000 HV for oxidation, 1000 HV for nitriding, 570 HV for carburizing.

Effects of constituent layers and interfaces on the mechanical and tribological properties of metal (Cr, Zr)/ceramic (CrN, ZrN) multilayer systems

The influences of constituent layers and interfaces on the mechanical and tribological behaviors of metal (Cr, Zr)/ceramic (CrN, ZrN) multilayer coatings were systematically investigated in the present study. Four sets of multilayer coatings (Cr/CrN, Cr/ZrN, Zr/CrN and Zr/ZrN) with the same number of interfaces were synthesized by multi-arc ion plating technique. The crystalline structures of the multilayer coatings were determined by X-ray diffraction and morphologies were observed by scanning electron microscope and transmission electron microscope. Furthermore, the nanoindenter, Vicker indenter, scratch tester and ball-on-disk tribometer were employed to evaluate the hardness, indentation toughness, adhesion strength and tribological properties of as-prepared coatings, respectively. Results revealed that the multilayer coatings with different constitute layers and interfaces presented different microstructures and properties. Based on the analysis of the cross-sectional indentation topographies, Zr interlayers exhibited higher crack resistances compared to Cr interlayers. Zr/CrN multilayer coating showed the highest hardness of 28 GPa, the strongest strength adhesion (>100 N) and the lowest wear rate. The excellent tribological performance of Zr/CrN multilayer coating was mainly ascribed to the high crack resistance of Zr layer, high wear-resistant layer of CrN as well as the local coherent interface between Zr and CrN sublayers.

Effect of plasma nitriding and modulation structure on the adhesion and corrosion resistance of CrN/Cr2O3 coatings

This paper examines the corrosion resistance of high-speed steel (HSS) substrates subjected to plasma-nitriding (PN) before being coated with CrN (in a single layer) or CrN/Cr2O3 (in multiple layers). Low-temperature (∼300 °C) nitriding treatment was applied for various durations (1 h, 3 h, and 5 h) with the aim of maximizing the adhesion strength and corrosion resistance of the HSS substrate. The multilayer coatings were applied in various thickness ratios of CrN vs Cr2O3 using high-power impulse magnetron sputtering (HiPIMS). The purpose of this study was to investigate the influence of plasma nitriding and Cr-based coating layers on the microstructural characteristics as well as the adhesion and corrosion characteristics. Specimens that underwent PN treatment for 5 h presented Lc1 and Lc2 values of 40.2 N and 78.9 N, respectively. The adhesion strength of the CrN/Cr2O3 multilayer coated PN-HSS substrate (PN-5h) (Lc 1 = 93.8 N) greatly exceeded that of the CrN-coated specimens. These results demonstrate that plasma nitriding and the modulation period strongly affect the adhesion strength between Cr-based coatings and the underlying HSS substrate. Corrosion resistance was characterized in terms of corrosion current, as follows: CrN/Cr2O3 multilayer > CrN layer > base-HSS. These findings also demonstrate that the application of a CrN/Cr2O3 multilayer coating can greatly enhance the corrosion resistance of HSS.

Triple sandwich design of multilayered (CrN/ZrN)/(Cr/Zr) hard coating with nanoscale architecture: microstructure and composition

A novel multilayered (CrN/ZrN)/(Cr/Zr) coating of a ‘triple sandwich’ design was fabricated by the cathodic arc physical vapour deposition technique. The thickness of (CrN/ZrN)/(Cr/Zr) coating was 56 microns, and the thicknesses of constituent (CrN/ZrN) and (Cr/Zr) films were 1070 and 115 nm, respectively. Preferential crystallographic orientation for nitride layers was (200). This evidenced the formation of coherent interfaces between CrN and ZrN layers through the epitaxial stabilization of one material in the structure of another lattice. It was found that the diffraction peaks of CrN and ZrN shifted slightly to lower diffraction angle, which pointed to the presence of intrinsic stress in the experimental sample. The average grain size values for ZrN and CrN were 12.5 and 9.5 nm, respectively. The TEM results showed the formation of the face-centered cubic (fcc) phase in nitride layers. The substrate-coating region had a polycrystalline structure. The sample demonstrated relatively high micro- and nanohardness of 28.5 and 34 GPa, respectively.

The change in the elastic modulus values for the thickness of a multilayer coating based on TiN and CrN layers

The results of investigations the cross section microstructure of a multilayer coating with a thickness of about 6 μm obtained by cathode arc evaporation, are presented. The top layer of the coating is TiN with a thickness of 200 nm, and the base consists of alternating layers of CrN and CrCN with a thickness of 200 nm per layer. Microhardness (H) and elasticity modulus of (E) were measured on the coating surface, on the CrN / CrCN layer surface, and over the cross section of the coating by nanoindentation (NI). It is established that the E values gradient from the surface with E = 313 GPa to the substrate with E = 176 GPa is smooth. The critical load of adhesive strength of the coating determined in the scratch test was 120 N.

Lateral Spin Valve Based on the Two-Dimensional CrN / P / CrN Heterostructure

Two-dimensional magnetic materials are being proposed as building blocks for future spin valves. The authors consider an insulating spacer of blue phosphorus, sandwiched between two hexagonal CrN monolayers, and calculate the lateral spin-dependent transport in the heterostructure using density functional theory plus Boltzmann transport theory. Spin transport in CrN/P/CrN is strongly dependent on doping, as well as the mutual orientation of magnetization in the individual CrN layers, with a resulting magnetoresistance of up to 12%.

Effects of multi-layer structure on microstructure, wear and erosion performance of the Cr/CrN films on Ti alloy substrate

Titanium alloy usually exhibited poor wear and erosion wear resistance. In this work, Cr/CrN films with different alternating structures of metal Cr layer with ceramics CrN layer were deposited on Ti-6Al-4V (TC4) by multi-arc planting to improve their properties. The result showed the main phases of the Cr/CrN films were Cr, Cr2N and CrN. Addition of the softer Cr layers and multi-layer structures disturbed the columnar growth of CrN layers, suppressed the CrN (111) orientation while promoted the growth of CrN (200) orientation. Also, the grain size decreased and micro-strain increased with increasing the alternating layer numbers. Compared with Ti substrate, the wear resistance of Cr/CrN coated samples significantly improved by decreasing the abrasive wear, and the Cr/CrN-10 film with alternating layer numbers of 10 showed the lower friction coefficient and higher wear resistance. The erosion experiments showed the Cr/CrN-5 film with alternating layer numbers of 5 showed the lower erosion rate, which might be due to the addition of ductile Cr layer conditioning the erosion deformation.

Conductive surface oxide on CrN(001) layers

Epitaxial CrN(001) layers that are exposed to an O2-containing atmosphere exhibit a conductive 2D surface oxide with a sheet conductance Gs,oxide = 5.9 × 10−5 [Ω/◻]−1. This is demonstrated using in situ transport measurements in a 90% Ar–10% O2 mixture with continuously increasing pressure from <10−6 to 240 Pa, showing a conductance increase that is independent of the CrN thickness d = 10 and 300 nm but is absent for control samples that are capped with insulating AlN prior to oxygen exposure. This suggests n-type doping of semiconducting CrN through substitutional replacement of N surface atoms with O. Cooling to 77 K leads to a decrease in Gs,oxide to 3.9 × 10−5 [Ω/◻]−1, indicating that the conduction electrons are not fully delocalized. The overall results indicate a path towards 2D electron transport devices in refractory transition metal nitrides and may explain the large variation in previously reported transport properties of CrN.