CrN Monolayer Research Articles

Exploring the effect of layer thickness on the elastoplastic properties of the constituent materials of CrN/CrAlN multilayer coatings: a nanoindentation and finite element-based investigation

This paper aims to assess the effect of layer thickness on the elastoplastic properties of the constituent materials of multilayer coating systems, as well as on the stress and strain fields in the vicinity of the coating/substrate interface. A methodology based on a trust-region reflective optimization algorithm, integrated with finite element analysis of the nanoindentation process, is employed to extract the elastoplastic properties of the distinct layers, constituting multilayer coating. This approach is validated on a CrN/CrAlN multilayer coating systems with varying layer thicknesses from 1 to 0.35 µm, by which Young's modulus (E), yield stress (σy), and work hardening exponent (n) of each individual coating material layer were obtained. The results revealed a reduction in the hardness and Young's modulus of either CrN, or CrAlN coating layer as the layer thickness decreased. Finite element analysis of the nanoindentation process demonstrated that decreasing the coating layer thickness leads to an increase in the plastic deformation within the coatings, which reduces the stress concentration in this area. The simulation results suggest that an optimum thickness of 0.5 μm of CrAlN and CrN monolayer materials would improve the adhesion properties of CrN/CrAlN multilayer coatings.

Numerical Analysis of Cavitation Erosion in 316L Steel with CrN PVD Coating.

The erosion process of a 4 μm monolayer CrN coating deposited on 316L stainless steel due to cavitation was investigated using finite element analysis (FEA). To estimate load parameters from cavitation pit geometry resulting from high impact velocity and high strain rate, the explicit dynamic solver was employed. Water microjet impacts at velocities of 100, 200 and 500 m/s were simulated to recreate different cavitation erosion intensities observed in the experiment. The resulting damage characteristics were compared to previous studies on uncoated 316L steel. The relationship between impact velocity and postimpact geometry was examined. Simulations revealed that only impact at 500 m/s can exceed the maximum yield stress of the substrate without penetrating the coating. Subsequent impacts on the same zone deepen the impact pit and penetrate the coating, leading to direct substrate degradation. The influence of impact velocity on the coating degradation process is discussed.

Corrosion resistance of CrN film deposited by high-power impulse magnetron sputtering on SS304 in a simulated environment for proton exchange membrane fuel cells

Insufficient corrosion resistance and conductivity are two major problems hindering the wide application of stainless steel (SS) bipolar plates in proton exchange membrane fuel cells. This study explores the use of CrN monolayer and multilayer films to improve the performance of SS304 bipolar plates, which are realized by high-power impulse magnetron sputtering with single pulse width or alternating pulse width. The effect of pulse width on the film structure and composition was characterized by various characterization techniques. Furthermore, corrosion and interfacial contact resistance (ICR) test results show that monolayer CrN film using a single long pulse of 40 μs has the lowest corrosion current density of 0.08 μA/cm2 (0.6 V vs. Ag/AgCl) and ICR of 3.15 mΩ cm2 in all coated samples. As the pulse width increases, vacancy-like defects in film decrease and the density increases, which is attribute to high bombardment flux and high average power of long pulse during deposition.

On the Wear Behaviour of Bush Drive Chains: Part II—Performance Screening of Pin Materials and Lubricant Effects

In this second part of the paper series, parameter investigations of the tribological system chain pin/bush contact, carried out on a specifically developed pin on bush plate model test technique, are presented. Both the pin material and the lubricant varied widely. In case of the pin materials, a Cr-N monolayer coating and a Cr-N-Fe-based multilayer coating were investigated. As for the lubricants used, two different performing engine oils from the field were tested as well as fresh oils, some of which were diluted with a soot surrogate (carbon black) and diesel fuel in different amounts. The results show, among other things, that friction and wear performance strongly depend on the combination of pin material and lubricant used. In this context, especially the Cr-N-Fe in combination with the used engine oils showed a high wear resistance and low friction losses compared to the Cr-N reference. In the case of fresh oils with soot, the friction losses were higher but comparable between the pin materials, and a slightly better wear performance of the Cr-N was observed due to an agglomeration effect of the soot surrogate. In general, it was found that especially soot-free oils show clear wear advantages independent of the pin material used. Thus, soot clearly has a wear-promoting component. The investigations of this study suggest that a leading mechanism that is based on a corrosive–abrasive effect in the tested system, but this is more related to the soot surrogate carbon black than engine soot.

Magnetic phase transition in a machine trained spin model: A study of hexagonal CrN monolayer

By employing the combination of non-collinear density functional theory, artificial neural network, and classical Monte Carlo simulation we study the ferromagnetic phase transition in CrN monolayers. The artificial neural network is successfully trained from different spin alignments to reproduce interaction energy at the DFT level in two dimensions. The training is performed solely based on spin spatial angles and second-order interactions energy without any speculation for the shape of spin Hamiltonian. The neural network model predicts the angle-dependent spin energy and mimics the magnetic anisotropy energy. The neural network is then validated for a larger supercell size against density functional theory results. Finally, the trained neural network spin model is used to study the finite temperature magnetization and phase transition in the two-dimensional CrN monolayer. The Curie temperature of the CrN monolayer is estimated equal to 600 K from the temperature-dependent magnetization and specific heat.

Microstructure and Surface Topography Study of Nanolayered TiAlN/CrN Hard Coating

The microstructure and surface topography of PVD hard coatings are among the most important properties, as they significantly determine their mechanical, tribological and other properties. In this study, we systematically analyzed the microstructure and topography of a TiAlN/CrN nanolayer coating (NL-TiAlN/CrN), not only because such coatings possess better mechanical and tribological properties than TiAlN and CrN monolayer coatings, mainly because the contours of the individual layers, in the cross-sectional STEM or SEM images of such coatings, make it easier to follow topographic and microstructural changes that occurred during its growth. We investigated the effects of the substrate rotation modes on the microstructure and surface topography of the NL-TiAlN/CrN coating, as well as on the periodicity of the nanolayer structure. The influence of the substrate material and the ion etching methods were also studied, while special attention was given to the interlayer roughness and influence of non-metallic inclusions in the steel substrates on the growth of the coating. The topographical features of the NL-TiAlN/CrN coating surface are correlated with the observations from the cross-sectional TEM and FIB analysis. Selected non-metallic inclusions, covered by the NL-TiAlN/CrN coating, were prepared for SEM and STEM analyses by the focused ion beam. The same inclusions were analyzed prior to and after deposition. We found that substrate rotation modes substantially influence the microstructure, surface topography and periodicity of the NL-TiAlN/CrN layer. Non-metallic inclusions in the substrates cause the formation of shallow craters or protrusions, depending on their net removal rates during the substrate pretreatment (polishing and ion etching), as compared to the matrix.

CrN Coating on 316L Stainless Steel via Inductively Coupled Plasma‐Enhanced Magnetron Sputtering as Bipolar Plates for Proton‐Exchange Membrane Fuel Cells

Herein, CrN monolayer films are deposited on 316L stainless steel (316LSS) via inductively coupled plasma (ICP)‐enhanced magnetron sputtering technology to compensate the defects of bare 316LSS in an acidic, hot, and humid proton‐exchange membrane fuel cell (PEMFC) environment. To assess the anticorrosive performance and conductivity of CrN‐coated 316LSS, the electrochemical behavior and interfacial contact resistances (ICRs) of samples are measured before and after the modification. The results of the potentiodynamic polarization test show that CrN‐coated 316LSS possesses high anticorrosion performance according to the ultralow corrosion current density of 0.094 and 0.078 μA cm−2 under the imitated PEMFC anode and cathode environments, respectively. These values are far below the USA Department of Energy's requirements of <l μA cm−2. In addition, the ICR of CrN‐coated 316LSS also satisfies the DOE's target (<10 mΩ cm2), which is obtained to be 7.8 mΩ cm2 under 140 N cm−2. Through analysis of potentiostatic polarization and electrochemical impedance spectroscopy, it suggests that CrN‐coated 316LSS combines better long‐term stability under the working voltages of two electrodes in PEMFCs with better electrochemical impedance than bare 316LSS. Consequently, CrN coating on 316LSS via ICP‐enhanced magnetron sputtering technology can be potentially suitable for bipolar plate applications in PEMFCs.

Anti-corrosion performance of the conductive bilayer CrC/CrN coated 304SS bipolar plate in acidic environment

A bilayer CrC/CrN coating prepared on 304 stainless steels (304SS) using reactive radio frequency magnetron sputtering technique (RF-MS) is investigated in acidic fuel cell environment. Compared to the CrN monolayer, the synergistic function of bilayer structure effectively hinder penetration of corrosive substance through defects, significantly increases anti-corrosion of substrate. This is attributed to the increased compactness of coating and the good matching between layers to effectively enhance interfacial adhesion. Interfacial contact resistance (ICR) of the CrC/CrN covered 304SS is lower than that of substrate. These effects are closely associated with inherent characteristic and combined preparation method of the coating.

Magnetic Phase Transition in a Machine Trained Spin Model: A Study of Hexagonal Crn Monolayer

Magnetic Phase Transition in a Machine Trained Spin Model: A Study of Hexagonal Crn Monolayer

Easy-axis rotation in ferromagnetic monolayer CrN induced by fluorine and chlorine functionalization.

On the basis of first-principles calculations, we investigate the absorption of fluorine and chlorine on ferromagnetic monolayer CrN focusing on the mechanism of spin reorientation. We use density functional theory in combination with the spin Hamiltonian approach to study the electronic and magnetic properties of monolayer CrN upon single-side adsorption of F and Cl atoms. While the electronic structure of ferromagnetic CrN remains half-metallic after functionalization, its preferred axis of magnetization is rotated toward the in-plane direction due to the orbital moment suppression. The half-coverage of CrN is found to be thermodynamically stable and ferromagnetically ordered at room temperature. Our findings demonstrate the possibility of altering the magnetic properties of a two-dimensional magnet after the adsorption of F and Cl, which opens a route to the detection of these gases using magnetic or optical measurements.

First-principles studies of the elastic and magnetic properties of monolayer CrN

Two-dimensional (2D) materials with robust ferromagnetism properties have high potentials for application in the field of spintronics. However, extensively pursued 2D sheets, including pure graphene, monolayer BN, and layered transition metal dichalcogenides, are either nonmagnetic or weakly magnetic. The elastic, electronic and magnetic properties of monolayer CrN are calculated using the plane wave pseudo potential method based on first-principles density function theory. Upon determining through calculation that the structure of the monolayer CrN nanosheet is stable, its layer modulus [Formula: see text] shows that its strain resistance is stronger than that of graphene. Through strain analysis, materials with a monolayer CrN type of structure can be obtained. It is determined that 10% of the change in equilibrium area is still applicable to the 2D EOS, showing that this structure is quite stable. The spin-polarized electronic band structure is also calculated under different plane symmetry strains. The plane strain can be used to effectively adjust the metallic and magnetic properties of the material. Analyses of the band structure and density of states reveal that this material is half-metallic, where the origin of the ferromagnetism is related to [Formula: see text]–[Formula: see text] exchange interactions between the Cr and N atoms. Monolayer CrN has semimetallic properties and strong ferromagnetic (FM) properties. The FM effect can enhance the stability of the material. The results show that monolayer CrN is a semimetallic material with good elastic properties and a strong FM property. This material is therefore expected to have good application rospects in the field of spin electronics.

Controllable enormous valley splitting in Janus WSSe on CrN monolayer

Manipulation of valley polarization in low-dimensional systems is desirable for future applications in information process and storage. Here, we design two-dimensional WSSe/CrN van der Waals heterostructures and control the valley degree of freedom based on the first-principles calculations. Combining the internal electric field and magnetic proximity effect, the interfacial interaction and the valley splitting are efficiently modulated in the system. Intrinsic enormous valley splitting of 103 meV and 144 meV are generated in S- and Se-terminated WSSe/CrN heterostructures, which corresponds to the effective Zeeman magnetic field of 1280 and 1574 T, respectively. A prominent anomalous Hall conductivity at K valley is induced by time-reversal symmetry breaking and sizable Berry curvature. Furthermore, valley splitting can be manipulated continually by the in-plane strain and interlayer distance. The largest valley splitting of 272 (240) meV and the effective Zeeman magnetic field of 2560 (2275) T are achieved for S (Se)-terminated WSSe/CrN heterostructures, respectively, under the compressive interlayer distance. It is found that the changes of induced spin charges around S and W atom are responsible for the modulated valley splitting. This work opens new vistas for the design of valleytronic devices.

Modeling the half-metallicity of the CrN/GaN (1 1 1) heterostructure

Spin-polarized total-energy calculations are employed to investigate the structural, electronic and magnetic properties of the CrN epitaxial growth on the GaN (1 1 1) surface. Cr adsorption and incorporation were considered as initial stages. The adsorption takes place at high symmetry sites, and in the incorporation, Cr replaces Ga. The structures stability is studied with the surface formation energy (SFE) formalism. Results show that in the range from Ga-rich to Ga-poor conditions, and from Cr-rich to Cr-intermediate conditions, the ferromagnetic CrN monolayer is the most stable structure. The interface shows half-metal characteristics, where the minority spins displays a large band-gap. When depositing extra CrN layers, the structure displays the CrN rock-salt phase as the most stable configuration. The epitaxial growth of 2 and 3 CrN layers depicts antiferromagnetic (AFM) characteristics; moreover the interface remains with half-metal properties and Dirac-cone-like features. However, the band-gap of the minority spins is reduced, therefore, it is expected that a large number of CrN bilayers could drive the system to a half-metal to metallic transition. Calculations establish a strategy to generate 100% polarized carriers injection to GaN, which poses this CrN/GaN (1 1 1)||(1 1 1) heterostructure as a component to construct spintronic devices.

The Effect of Bilayer Periods and Their Thickness in Magnetron Sputtering Protective Multilayer Coatings for Tribological Applications

CrN/CrAlN thin films were deposited by DC reactive magnetron sputtering. The influence of CrN/CrAlN bilayer thickness on the microstructure, mechanical, and tribological properties was studied. Crystallinity of the layers was characterized by x-ray diffraction. The microstructure of all coatings was observed by scanning electron microscopy. Results exhibit that bilayer thickness was a dominant factor. The analyses showed a columnar microstructure for the CrN/CrAlN coatings. Owing to their denser structure and interfacial strengthening, CrN/CrAlN multilayer coatings exhibited higher mechanical properties than that of monolayers. Indeed, CrN/CrAlN multilayer coating with four bilayers and thickness gradient reaches a maximum of hardness around 43 GPa. Also, its resistance to spallation reaches 97 N which is a very excellent value. After ball-on-disk wear tests, it is found that all multilayer films exhibited a good wear resistance, especially the one with four bilayers and different CrN and CrAlN monolayers thickness. The lowest coefficient of friction is obtained for the coatings with 4 bilayers.

The effect of nickel on the high-temperature properties of multilayer ceramic coatings

The structure and composition of multicomponent TiCrMoN-Ni arc-PVD coatings with high nickel concentration (more than 8 at.%) are studied at bias potentials of 80-140 V. All coatings are characterized by a layered structure, the modulation period tends to decrease as increasing the bias potential. After annealing at 850 °C in vacuum, the coatings retain their layered structure without signs of dissolution of layers in each other. Nickel sublayers retain their polycrystalline structure, at the same time, the monolayer CrN are formed due to recrystallization.

Ultra-low Young’s modulus and high super-exchange interactions in monolayer CrN: A promising candidate for flexible spintronic applications* *Project supported by the National Natural Science Foundation of China (Grant No. 61888102), the National Key Research and Development Program of China (Grant No. 2016YFA0202300), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB30000000).

Monolayer CrN has been predicted to be half-metallic ferromagnet with high Curie temperature. Due to bulk CrN’s biocompatibility, the monolayer is a promising candidate for bio-related devices. Here, using first-principles calculations based on density functional theory, we find that the formation energy of the bulk CrN stacking from layers with square lattice is only 68 meV/atom above the convex hull, suggesting a great potential to fabricate the monolayer CrN in a square lattice by using molecular beam epitaxy method. The monolayer CrN is then proved to be a soft material with an ultra-low Young’s modulus and can sustain very large strains. Moreover, the analysis of the projected density of states demonstrates that the ferromagnetic half-metallicity originates from the splitting of Cr-d orbitals in the CrN square crystal field, the bonding interaction between Cr–N, and that between Cr–Cr atoms. It is worth noting that the super-exchange interaction is much larger than the direct-exchange interaction and contributes to the ultra-high Curie temperature, which is obtained from Monte Carlo simulations based on Heisenberg model. Our findings suggest that the monolayer CrN can be an indispensable candidate for nanoscale flexible spintronic applications with good biocompatibility and is considerable appealing to be realized in experiment.

Electrically switchable Rashba-type Dzyaloshinskii-Moriya interaction and skyrmion in two-dimensional magnetoelectric multiferroics

Realizing topological magnetism and its electric control are intensive topics in spintronics due to their promising applications in information storage and logic technologies. Here, we unveil that both can be achieved in two-dimensional (2D) magnetoelectric multiferroics. Using first-principles calculations, we show that a strong Dzyaloshinskii-Moriya interaction (DMI), which is the key ingredient for the formation of exotic chiral magnetism, could be induced in 2D multiferroics with vertical electric polarization via the Rashba effect. We verify that such a significant DMI can promote the stabilization of sub-10-nm skyrmions in 2D multiferroics with perpendicular magnetic anisotropy such as a CrN monolayer. In addition, the presence of both magnetization and electric polarization in 2D multiferroics provides us with the unique opportunity for the effective electric control of both the strength and chirality of the DMI and thereby the topological magnetism. As an example, we introduce four multiferroic skyrmions with different chiralities and polarities that can be manipulated by an external field.

Ferromagnetic hybrid nodal loop and switchable type-I and type-II Weyl fermions in two dimensions

As a novel type of fermionic state, hybrid nodal loop with the coexistence of both type-I and type- II band crossings has attracted intense research interest. However, it remains a challenge to realize hybrid nodal loop in both two-dimensional (2D) materials and in ferromagnetic (FM) materials. Here, we propose the first FM hybrid nodal loop in 2D CrN monolayer. We show that the material has a high Curie temperature (> 600 K) FM ground state, with the out-of-plane [001] magnetization. It shows a half-metallic band structure with two bands in the spin-up channel crossing each other near the Fermi level. These bands produce both type-I and type-II band crossings, which form a fully spin-polarized hybrid nodal loop. We find the nodal loop is protected by the mirror symmetry and robust against spin-orbit coupling (SOC). An effective Hamiltonian characterizing the hybrid nodal loop is established. We further find the configuration of nodal loop can be shifted under external perturbations such as strain. Most remarkably, we demonstrate that both type-I and type-II Weyl nodes can be realized from such FM hybrid nodal loop by simply shifting the magnetization from out-of-plane to in-plane. Our work provides an excellent candidate to realize FM hybrid nodal loop and Weyl fermions in 2D material, and is also promising for related topological applications with their intriguing properties.

Effect of modulation ratio on structure and mechanical properties of WB2/CrN films deposited by direct-current magnetron sputtering

WB2/CrN multilayer films with thick modulation period about 500 nm but different modulation ratios (tWB2:tCrN = 1.2, 2, 3 and 4) were deposited on steel substrates by magnetron sputtering, and the effect of modulation ratio on the structure, residual stress and tribo-mechanical properties of the WB2/CrN multilayer films was systematically studied. Additionally, WB2 and CrN monolayer films with various thicknesses were also prepared to discuss the growth behavior and the related properties of the WB2/CrN multilayer films. All the sample films present the columnar growth, and the particle size in the WB2 monolayers is smaller than that in the corresponding WB2 sublayers. The preferred orientation of WB2 (260–400nm) and CrN monolayers (132–220 nm) is (101) and (111), respectively. However, the multilayered structure changes the orientation of CrN sublayers to (002), and crystalline Cr2N phase is detected in WB2/CrN multilayers caused by the element diffusion at interface. Moreover, the multilayered structure reduces the compressive stress of the WB2 films greatly by diffusion of point defects to interfaces and an indirect effect of interfaces on stress via film structure with soft CrN, and the residual stress of the WB2, CrN and WB2/CrN films is −2.64∼-4.16, −0.85–0.57 and −1.49∼-2.61 GPa, respectively. Furthermore, film hardness ranging from 27.9 to 33.0 GPa mainly obeys the rule of mixture. The adhesive strength drops greatly from 26 to 17 N with the increasing tWB2:tCrN, and the tensile CrN bottom-layer deteriorates the adhesive strength of the WB2/CrN multilayers with tWB2:tCrN = 2. Overall, WB2/CrN films with tWB2:tCrN = 3 show better wear resistance with lower friction coefficient ∼0.35 and wear rate about 3.6 × 10−7 mm3/mN benefiting from their higher hardness, lower roughness, proper toughness and compressive stress.

Electrochemical behavior of TiN, CrN and TiN/CrN nanostructured coatings on the nickel-chromium alloy used in dental fixed prosthesis

ABSTRACT The aim of this research is the evaluation of the influence of TiN, CrN and TiN/CrN nanostructured coatings on corrosion resistance of nickel-chromium dental alloy in artificial saliva environment with two pH levels (3.0 and 6.5). Nickel-chromium alloy tested in this study were more resistant to corrosion in artificial saliva conditioning media when coated with different types of coating materials, as compared to uncoated alloy. The electrochemical measurements propose that the alloy with CrN coating has shown a high corrosion resistance in different pH levels. The superior passivation of CrN monolayer coating in modified Fusayama artificial saliva solution may be concluded from two essential factors, passive range, and corrosion current density. The passive range is well-developed, while the corrosion current density is much lower if compared to the other groups. Also, the Nyquist and polarization plots reveal that TiN, CrN and TiN/CrN nanostructured coatings have an excellent corrosion resistance which is considered much higher if compared to the substrate. The values of corrosion current density for CrN nanostructured coating in artificial saliva environment with two pH levels of 3.0 and 6.5 were 1.373 × 10−8 and 5.416 × 10−8 A.cm−2, respectively that were the lowest corrosion current density values among the other samples.