CrN Coatings Research Articles

Oxidation resistance of Cr2N and (Cr,W)2N coatings deposited on ferritic stainless steel

In this study, Cr2N and (Cr,W)2N coatings were deposited on Crofer 22 APU ferritic stainless steel as protective coatings by using cathodic arc evaporation. Oxidation kinetics of the Cr2N- and (Cr,W)2N-coated samples were evaluated through isothermal tests in an atmospheric furnace at 800°C for 1000h. The results showed that (Cr,W)2N comprised Cr2N and W2N and possessed a fine-grained columnar structure. The average grain sizes of Cr2N and W2N were 7.2 and 5.0nm, respectively, and that of the deposited Cr2N coating was 12.7nm.After oxidation at 800°C for 1000h, both the Cr2N and (Cr,W)2N coatings had bilayer scales comprising Cr2O3 and (Mn,Cr)3O4. The Cr2N and (Cr,W)2N coatings exhibited similar oxidation curves and a two stages of oxidation mechanism. The main reason for the occurrence of the dominant oxidation mechanism transfer is the growth of Cr2O3 and (Mn,Cr) 3O4 spinel. Moreover, the doping of W benefited the formation of a χ phase to precipitate at the oxide/coating interface, which acted as a diffusion barrier retarding the reaction rate between Cr and O.

Comparative study on the load carrying capacities of DLC, GLC and CrN coatings under sliding-friction condition in different environments

DLC, GLC and CrN coatings of different thicknesses were prepared by PVD technology using their respective mature process parameters. Field emission scanning electron microscope (FESEM), laser confocal microscopy, and Raman spectrometer were used to analyze the morphologies and microstructures of the coatings. Nanoindentation measurements and scratch tests were executed to characterize mechanical properties. The load carrying capacities of these coatings in ambient air, distilled water and oil environments were investigated by a reciprocating tribometer with gradually increasing applied load. Results show that the CrN(2h) coating has the best load carrying capacity in ambient air and base oil, the GLC coating possesses the best load carrying capacity in distilled water. The DLC coating exhibits lower friction when it survives under low load. The different load carrying capacities of these coatings under sliding-friction condition are closely related to their surface roughness, coating thickness and mechanical properties.

Hydrogen permeability of diamondlike amorphous carbons

The hydrogen barrier properties of the coatings of nitride and diamondlike amorphous carbon (DLC) were evaluated. Using plasma chemical vapor deposition and sputtering, ZrN, TiAlN, AlCrN, CrN, and DLC coatings were deposited with a thickness of about 3 μm. It was confirmed that all coatings have an impact on decreasing the hydrogen permeation rate. Specifically, by coating stainless steel with a DLC coating, the hydrogen permeation rate was reduced to 1/1000 or lower compared to that without a coating. By providing a buffer layer of Cr-N, the hydrogen barrier function was improved. DLC coatings with high hydrogen content had an especially high hydrogen barrier function. For hydrogen diffusion in coatings, the movement of atoms through hydrogen trap sites is important. There are both sp3 and sp2 bonds in DLC coatings, and excess hydrogen can be found in the interstitial space and the above-mentioned hydrogen trap sites. It is suggested that the hydrogen trap sites in a DLC coating with high hydrogen content are likely already filled with hydrogen atoms, and the movement of new hydrogen atoms could be limited.

Corrosion protection of steel with multilayer coatings: Improving the sealing properties of physical vapor deposition CrN coatings with Al2O3/TiO2 atomic layer deposition nanolaminates

Atomic Layer Deposition (ALD) of Al2O3/TiO2 nanolaminate was applied to improve the sealing properties of CrN coating deposited with Physical Vapor Deposition (PVD) on high speed steel (HSS). The corrosion protection properties were explored with Linear Sweep Voltammetry and visual estimation. Nearly two orders of magnitude decrease in corrosion current density was obtained by applying plasma pre-treatment prior to ALD coating. Sealing of CrN pinholes was shown with Focused Ion Beam/Scanning Electron Microscope technique. The effect of the ALD deposition parameters to adhesion of the ALD coatings was investigated with Rockwell indentation and microscope analysis. Thickness and refractive index of the ALD coatings were measured with ellipsometry, and density and roughness of the ALD coatings were investigated with X-Ray Reflectivity measurements. Neutral Salt Spray testing was used to investigate the corrosion resistance of PVD/ALD nanolaminates on HSS dental curettes.

Corrosion Resistance Behavior of Single-Layer Cathodic Arc PVD Nitride-Base Coatings in 1M HCl and 3.5 pct NaCl Solutions

The electrochemical behavior of single-layer TiN, CrN, CrAlN, and TiAlN coatings on 304 stainless steel substrate, deposited using state-of-the-art and industrial size cathodic arc PVD machine, were evaluated in 1M HCl and 3.5 pct NaCl solutions. The corrosion behavior of the blank and coated substrates was analyzed by electrochemical impedance spectroscopy (EIS), linear polarization resistance, and potentiodynamic polarization. Bond-coat layers of pure-Ti, pure-Cr, alloyed-CrAl, and alloyed-TiAl for TiN, CrN, CrAlN, and TiAlN coatings were, respectively, first deposited for improved coating adhesion before the actual coating. The average coating thickness was about 1.80 µm. Results showed that the corrosion potentials (Ecorr) of the coated substrates were shifted to more noble values which indicated improvement of the coated substrate resistance to corrosion susceptibility. The corrosion current densities were lower for all coated substrates as compared to the blank substrate. Similarly, EIS parameters showed that these coatings possessed improved resistance to defects and pores in similar solution compared to the same nitride coatings developed by magnetron sputtering. The charge transfer resistance (Rct) can be ranked in the following order: TiAlN > CrN > TiN > CrAlN in both media except in NaCl solution where Rct of TiN is lowest. While the pore resistance (Rpo) followed the order: CrAlN > CrN > TiAlN > TiN in HCl solution and TiAlN > CrN > CrAlN > TiN in NaCl solution. It is found that TiAlN coating has the highest protective efficiencies of 79 and 99 pct in 1M HCl and 3.5 pct NaCl, respectively. SEM analysis of the corroded substrates in both media was also presented.

Synergistic Effect of Additives on Friction and Wear Properties in Combination of Boron Cast Iron and CrN Coating

Synergistic Effect of Additives on Friction and Wear Properties in Combination of Boron Cast Iron and CrN Coating

Tribological Behavior of PVD Hard Coated Cutting Tools under Cryogenic Cooling Conditions

Cryogenic assistance is used to improve machining performance and to enhance tool life under extreme contact conditions (pressure and temperature). This paper focuses on the influence of cryogenic cooling conditions using liquid nitrogen within the context of machining Ti6Al4V with CrN-coated carbide cutting tools. Friction behavior of both CrN-coated and uncoated pins with and without cryogenic cooling were evaluated using a home-made laboratory tribometer. The adhesive and plastic friction coefficients were evaluated using a finite element model of the pin-Ti6Al4V system through an inverse methodology. Finally, the contribution of the CrN coatings was evaluated under both cryogenic cooling and dry conditions.

PHYSICAL AND MECHANICAL PROPERTIES AND WEAR RESISTANCE OF CRN/ALN SYSTEM COATINGS DEPOSITED BY MAGNETRON SPUTTERING

The paper presents the results of investigation of CrN/AlN system coatings obtained by magnetron-ion reactive sputtering. Coating versions with a periodic nanocomposite structure with a layer period L = 1,5÷3,2 nm and a relative Cr content in the Cr/(Al + Cr) coating range of 68–85 % are studied. It is found that the coatings have a dense morphology and a columnar grain structure, which is typical for them. For all the samples, diffraction maxima corresponding to the cubic lattice are observed, being a superposition of the two compositions of CrN and AlN coatings. No peaks corresponding to AlN with a hexagonal structure type are recorded. Neither CrAlN peaks are found, that means that no homogeneous coating is formed. Experimental studies of the microhardness, modulus of elasticity, plasticity index and wear resistance of coatings obtained under different spraying conditions are conducted. Measurements showed that the microhardness and modulus of elasticity of the coatings obtained vary between H = 32÷42 GPa and E = 350÷420 GPa, respectively. The maximum plasticity index value H/E = 0,115 is reached at L = 3,2 nm, which corresponds to the coating versions with the greatest hardness. However, the H/E = 0,1 values are also fairly high with a minimum layer period (L = 1,5 nm) and a high Cr content. Abrasive wear coefficients of the coatings obtained vary in the range kс = (2,0÷2,8)·10–13 m3/(N·m). The minimum values of wear are reached at the maximum period of coating layers, i.e. with the greatest hardness, which agrees well with the classical theory of wear. At the same time, high wear resistance is observed at a low L, which indicates a correlation of the values of H/E and kс. Based on the experimental data, a group of neural network models is built that establish the relationship between the deposition process mode parameters (current on magnetrons) with the elemental composition of coatings, as well as the period of coating layers and relative chromium content with the physical and mechanical properties and abrasion resistance of CrN/AlN coatings.

Tribocorrosion behaviors of CrN coating in 3.5 wt% NaCl solution

Chromium nitride coatings are synthesized on the stainless steels by plasma immersion ion implantation and deposition. The microstructure and tribocorrosion behaviors of the as-deposited coatings are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, reciprocating-sliding tribometer and electrochemical testing. The results show that the CrN coatings have a typical columnar growth structure consisting of face-centered cubic crystals. The CrN coatings greatly enhance the corrosion resistance and wear resistance of the stainless steel. However, frictional forces induce numerous micro-cracks which act as the diffusion channels for NaCl solution. Multi-scale Cl ion corrosion occurs simultaneously during the tribocorrosion and a force-corrosion synergy interaction induces the multi-degradation (e.g., intersecting cracks and layer delamination) of the CrN coating. The synergistic damage mechanisms of wear and corrosion are systematically discussed.

The influence of plasma nitriding on microstructure and properties of CrN and CrNiN coatings on Ti6Al4V by magnetron sputtering

In this paper, the CrN and CrNiN coatings were deposited on the non-nitrided and nitrided Ti6Al4V alloys with the method of closed-field unbalanced magnetron sputter ion plating (CFUBMSIP). The influence of plasma nitriding treatment on microstructure, mechanical and tribological properties of Physical Vapor Deposition (PVD) films was evacuated by means of SEM (EDS), XRD, Rockwell-C indentation testing, nanoindentation testing, and ball-on disc tribotesting. With the addition of Ni, the preferred orientation changes to CrN (200) and the grain is refined. The indentation tests indicated that the duplex treated samples exhibited the best combined properties. The nanoindentation testing results showed that the hardness of the coatings increased, the plastic deformation reduced and they had higher H3/E2 values than PVD coatings with the plasma nitriding before PVD treatment due to the increase of substrate's load bear capacity after plasma nitriding process. The friction and wear tests demonstrated that the tribological performance of the PVD coatings improved after plasma nitriding which is attributed to the enhanced the mechanical compatibility between the hard PVD coating and soft substrate and the resistance of CrN coating is better than that of CrNiN coating because of the transfer layer (constituted of TiN and Ti2N) deposited by nitriding.

Effect of Ni content on the electrical and corrosion properties of CrNiN coating in simulated proton exchange membrane fuel cell

In this paper, CrNiN coatings with various Ni content are deposited on 304ss bipolar plates by closed field unbalanced magnetron sputter ion plating from CrNi alloy targets. Simulative working environment of proton exchange membrane fuel cell (PEMFC) is applied to test the electrical and corrosion properties of uncoated 304ss and CrNiN-coated samples. The influence of Ni content on microstructure, phase structure, contact angle with water and electrochemical performance is investigated. Results show that all the coated samples significantly enhanced the corrosion resistance of the 304ss, and the CrN-coated 304ss sample without Ni has the best corrosion resistance of 153.8 and −141.9 mV in the simulated anodic and cathodic environments, respectively. Electrochemical impedance spectroscopy (EIS) studies reveal that the resistance of CrN coating is higher than that of other coated samples and 304ss in the cathodic environment. Furthermore, Interfacial contact resistance (ICR) studies revealed that CrN coating has a superior ICR of 11 mΩ cm2 at a compaction force of 160 N cm−2. In addition, the contact angle of the CrNiN coatings with water is approximately 114°, which is beneficial for water management in PEMFC. Analysis result indicates that the enhanced performance of the coated 304ss bipolar plates is related to the high film density determined by closed field unbalanced magnetron sputter ion plating, and the synergistic function of the CrNiN layered structure.

XPS investigations of tribofilms formed on CrN coatings

Action of lubrication additives in the case of uncoated steel surfaces, including the type and mechanism of tribofilm formation is well known and understood. However, contact type of tribofilms which might form under the tribological contact between CrN coated surfaces, remains more or less unexplored. The aim of this investigation was to study the type of tribofilms formed on the CrN coated steel samples subjected to lubricated reciprocating sliding contact under different contact conditions Contact surface and tribofilms formed were studied by X-ray Photoelectron Spectroscopy (XPS). Sample surfaces were first imaged by Scanning Electron Microscopy (SEM) to determine areas of tribofilm formation as well as areas not affected by tribological contact. In these areas survey and high resolution (HR) XPS measurements were performed to obtain information about surface chemistry and oxidation states of the constituent elements. It was found that differences between different samples, observed by the XPS measurements, may reflect differences in chemistry of tribofilms formed under different contact conditions.

Influence of titanium or aluminum doping on the electrochemical properties of CrN coatings in artificial seawater

Abstract CrN, CrTiN and CrAlN coatings were deposited on Si (100) via co-sputtering chromium, titanium and aluminum targets by using unbalanced magnetron sputtering, respectively. And the relevant microstructure and composition were characterized. The influences of the doping elements on the microstructural and electrochemical properties of CrN coatings in the artificial seawater were analyzed via the open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. As a result, the CrN coating exhibits the favorable corrosion resistance. On the contrary, the easy occurrence of hydration reaction for AlN would lower the compactness of CrAlN, subsequently deteriorate its corrosion resistance. Thus, the CrAlN coating presents the worst electrochemical properties in spite of its highest electrical resistivity. In particular, the CrTiN coating exhibits the outstanding corrosion resistance with relatively higher charge transfer resistance (R ct ), polarization resistance (R P ) due to its great compactness.

On the plastic deformation of chromium-based nitride hard coatings deposited by hybrid dcMS/HPPMS: A fundamental study using nanoscratch test

Tribological behavior and elastic-plastic deformation of hard coatings deposited by physical vapor deposition (PVD) under normal and lateral loads can be investigated using innovative nanoscratch tests. However, a comprehensive study of thin PVD coatings requires a precise insight into mechanisms of the observed plastic deformation. Nanoscratch analyses on nanostructured PVD hard coatings and investigations of the mechanisms of resulted plastic deformation are the subjects of current research. In the presented work, two coatings CrN and (Cr,Al)N deposited on quenched and tempered AISI 420 steel substrate were investigated. The coatings were synthesized using a hybrid technology, consisting of direct current and high power pulse magnetron sputtering dcMS/HPPMS. Nanoscratch tests were performed with constant normal loads applying Berkovich and conical indenters. Despite significant hardness, these coatings deformed plastically under applied forces. Plastic deformation of the coatings was investigated by means of confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) were applied to explore the mechanism of plastic deformation of the investigated coatings. Based on the results of CLSM and SEM, (Cr,Al)N exhibited a higher resistance against plastic deformation compared to CrN. The TEM investigations furthermore revealed that neither micro-crack formation nor dislocation motion inside the individual grains led to the observed plastic deformation. The dominating mechanism of the plastic deformation of investigated coatings is explained by sliding of grain boundaries (GBS) as the main reason.

Effect of Bias Voltage on Microstructure and Mechanical Properties of CrN Coatings Prepared by Single Target Magnetron Sputtering

CrN coatings were deposited by reactive magnetron sputtering at different substrate bias voltages. The effects of bias voltage on micro-structure and mechanical properties of CrN coatings were studied by scanning electron microscopy, X-ray diffraction, micro-hardness tester and a multi-functional tester for material surface properties, respectively. The results showed that bias voltage had a great influence on morphologies of CrN coatings and CrN coatings presented obvious preferred orientation with the increase of bias voltage. In addition, bias voltages in a certain range can also improve hardness and adhesion of CrN coatings, but higher voltages were not good. In this paper, the adhesion and hardness of CrN coatings presented the trend that a rise first followed by a decline with the ever-increasing bias voltages at the same time, but CrN coating had the superior mechanical properties when the bias voltage was-100 V.

Tribological Dependence of the High-Performance Ferrous-Based Coating on Different Coating Counterparts in Engine Oil

ABSTRACTA ferrous-based coating with significant chromium was fabricated on aluminum alloy substrate using a plasma spray technique. The tribological performance of the as-fabricated ferrous-based coating sliding against different coatings including Cr, CrN, TiN, and diamond-like carbon (DLC) in an engine oil environment were comparatively studied. Results showed that the high hardness of the sprayed ferrous-based coating was achieved due to the dispersion strengthening effect of Cr7C3 phase embedded in the austenite matrix. The ferrous-based coating exhibited low friction coefficients when coupled with these four coating counterparts, which could be attributed to the boundary lubricating effect of engine oil. However, both friction and wear of the ferrous-based coating were different when sliding against these different coating counterparts, which might be closely related to the surface roughness, self-lubricating effect, and mechanical properties of the coupled coatings. Ferrous-based coating sliding against CrN and DLC coatings exhibited good tribological performance in engine oil. The best coating counterpart for the ferrous-based coating in an engine was DLC coating.

3D FEM modelling for stress simulation and experimental investigation of dual-gradient coating using PVD

Abstract In this work, AlZrCrN composite dual-gradient coating was deposited on cemented carbide substrate using physical vapor deposition. Using the composite dual-gradient structure design, the thermal residual stress between layers was decreased and the bonding strength between coating and substrate was increased. Finite element simulation indicates that thermal residual stress in composite dual-gradient coatings is significantly smaller than that in CrN and ZrN single coatings. The bonding strength between composite double-gradient coating and substrate is found to be greater than that of the single-layer coating. The factors and conditions influencing the performance of composite dual-gradient coating can be obtained through numerical calculation. Based on the simulation, coating structure that has a gradual transition from the internal high-plastic long-comb Cr/CrN layer to the outer AlZrCrN wear-resistant layer with stubby morphology was prepared.

Microstructure and mechanical properties of Cr–Ni–N coatings deposited by HiPIMS

Cr–Ni–N coatings, the Ni content of which was altered from 0 to 6·3 at-%, were deposited by a hybrid coating system consisting of high power impulse magnetron sputtering and radio frequency magnetron sputtering. The effects of Ni addition to Cr-N coatings on the microstructure and mechanical properties of the coatings were investigated in this study. The instrumental analysis revealed that the Ni element was incorporated into Cr-N crystals as solid solutions, while excess Ni was precipitated as nanocrystalline phases at the Cr-N grain boundaries. The toughness of the Cr–Ni–N coatings was significantly improved with Ni content increased. In addition, the hardness of the coatings slightly increased from 30·4 to 32·6 GPa due to the grain refinement effect and solid solution hardening. From the tribological tests, the highest wear resistance was obtained from the sample having a Ni content of 2·7 at-%.

Effects of die core treatments and surface finishes on the sticking and galling tendency of Al–Si alloy casting during ejection

In the process of high pressure die casting of aluminium alloys tool surfaces are severely damaged by cast alloy sticking and soldering which promote galling during casting ejection. As a consequence, casting quality is lowered and production efficiency is reduced. Although die casting tools are greatly improved by application of diffusion layers and surface coatings, effects of surface topography on performance of such treated tools are scarcely recognized. This investigation gives an insight in the effects of surface topography on the sticking tendency and galling of Al–Si alloy toward the H11 steel, plasma nitrided steel, and duplex treated steel with CrN and TiAlN PVD top coatings. The sticking tendency was evaluated by ejection test during which the force required to eject the sample from the casting was measured. It was found that the ejection force does not depend on chemical composition of the investigated materials. However, the ejection force of coated samples strongly depends on their surface topography. The coated samples which were polished after the deposition exhibited the highest ejection force. Wear conditions inherent in this specific tribo-system are recognised and interpreted for surfaces with different topography.

Tribological Behaviour of PVD Coatings Lubricated with a FAP− Anion-Based Ionic Liquid Used as an Additive

This paper studies 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ionic liquid ([BMP][FAP]) as a 1 wt% additive to a polyalphaolefin (PAO 6) in the lubrication of CrN and TiN PVD coatings. Friction and wear behaviour were determined by using a ball-on-plate reciprocating tribometer at two loads (20 and 40 N) and a reciprocating frequency of 10 Hz. The tribological behaviour of this mixture has also been compared to a traditional oil additive, like zinc dialkyldithiophosphate (ZDDP). As an additive, ionic liquid exhibited an important friction and wear reduction compared to the base oil. However, tests conducted with ZDDP show slightly better results. XPS was used to analyse wear surfaces. The interactions of each additive with the surface contributed to improving the tribological behaviour of the lubricants.