CrAlN Coatings Research Articles

Room and high temperature tribological performance of CrAlN(Ag) coatings: The influence of Ag additions

The present study aims to investigate the effect of the addition of Ag on the tribological performance of a CrAlN coating system, at room and high temperatures (600 °C). The addition of Ag, in general, has been seen beneficial in lowering the coefficient of friction (COF) at room and high temperatures. Independent of the decrease of COF with Ag additions, the specific wear rate was degraded. The only exception was the CrAlNAg9 coating with 8.6 at.% of Ag which exhibited the lowest specific rate at room temperature while maintaining its comparable wear resistance properties with that of reference CrAlN coating at 600 °C. The CrAlNAg9 coating also demonstrated coefficient of friction (COF) of 0.16 and 0.26 at room temperature and 600 °C, respectively. Formation of Ag and AgCrO2-rich tribolayer during sliding at high temperature was responsible for lubricious properties of CrAlN(Ag) coatings. However, doping the coatings with small content of Ag (around 2.4 at.%) was not effective in decreasing the COF, nor the specific wear rate under high temperatures. On the other hand, high concentration of Ag (11.8 at.% and above) had a detrimental influence on mechanical properties and poor resistance to oxidation at elevated temperature compromising both friction and wear properties of the CrAlNAg12 and CrAlNAg16 coatings.

Performance evaluation of CrAlN and TiAlN coatings deposited by HiPIMS in micro drilling of a Ni-based superalloy

The current study aimed at investigating the effects of CrAlN and TiAlN coatings deposited using high power impulse magnetron sputtering (HiPIMS) on the performance in micro drilling of Incoloy 825. Influence of feed which played a major role on size effect was studied for the uncoated and coated micro drills in terms of thrust force along with its bandwidth and average flank wear. Particular emphasis was placed on the exploration of the mechanism of wear of the coated micro drills in comparison with their uncoated counterpart. Rate of rise in thrust force gradually decreased and was accompanied by a fall in bandwidth with the number of holes. HiPIMS coated micro drills were successful in mitigating thrust force, bandwidth and rate of progression of wear. However, TiAlN consistently outperformed the CrAlN coating owing to the superior hardness, coating adhesion and tribological properties. TiAlN also exhibited remarkable capabilities to resist elastic and plastic deformation under the regime of ploughing (lower feed) and the condition of higher chip load (higher feed).

Effect of pulsed electromagnetic frequency on the microstructure, wear and solid erosion resistance of CrAlN coatings deposited by arc ion plating

Effect of pulsed electromagnetic frequency on the microstructure, wear and solid erosion resistance of CrAlN coatings deposited by arc ion plating

Effect of nitrogen pressure on the microstructure, mechanical and electrochemical properties of CrAlN coatings deposited by filter cathode vacuum arc

CrAlN coatings were prepared on Al–Si alloys using filter cathode vacuum arc deposition technique with nitrogen as the reactive gas and Cr25Al75 alloy target as the arc source. The effect of nitrogen pressure on the microstructure, mechanical properties and electrochemical properties of the coatings had been systematically studied. The results showed that the composition, structure and performance of the CrAlN coating depended on the nitrogen pressure. As the nitrogen pressure increased, the Al and Cr content decreased while the N content increased slowly in the coating. Meanwhile, the phase structure gradually changed from AlN phase to CrN phase. The hardness of the CrAlN coating increased significantly with the increase of nitrogen pressure from 0.04 to 0.06 Pa due to the formation of CrN phase and grain refinement. However, further increasing the nitrogen pressure to 0.07 Pa, the hardness was reduced owing to the deterioration of the surface quality caused by target poisoning. Moreover, the adhesion strength of the coating gradually decreases, and the corrosion resistance of the CrAlN coating first increased and then decreased with increasing the nitrogen pressure. The CrAlN coating deposited at a nitrogen pressure of 0.05 Pa had the best corrosion resistance, with the highest polarization resistance, charge transfer resistance and pore resistance, which was related to the combined effect of great compactness and AlN-dominant phase structure in the coating.

Influence of Interlayer Materials on the Mechanical Properties and Thermal Stability of a CrAlN Coating on a Tungsten Carbide Substrate

CrAlN coatings have earned significant attention for use in cutting tool coating applications due to their excellent properties such as high hardness and superb oxidation resistance. It is well known that the interlayer between the coating and the substrate can influence the mechanical properties of the coatings. In this work, three interlayers—CrN, CrZrN, and CrN/CrZrSiN—were synthesized between a CrAlN coating and a tungsten carbide substrate to improve the mechanical properties and thermal stability of the CrAlN coating. All the CrAlN coatings with their respective interlayers showed high hardness values in the range of 34.5 to 35.1 GPa, and they were not significantly affected by the interlayer type. However, wear and scratch tests showed that the CrAlN coatings with CrN and CrN/CrZrSiN interlayers exhibited an improved friction coefficient of 0.33 and adhesion strength (Lc2) of 69 N compared to the CrAlN coating with the CrZrN interlayer. These improved wear properties were attributed to the H/E ratio of the interlayer between the coating and the substrate, in that the CrN and CrZrSiN interlayers effectively induced a smooth transition of the coating stress under a loading condition. During the thermal stability tests, the hardness of the CrAlN coating with the CrN/CrZrSiN interlayer was maintained up to 1000 °C due to the excellent oxidation resistance of the CrZrSiN layer, which contained an amorphous SixNy phase.

Effects of TiN/CrN, CrAlN, and TiN Coatings on the Performance of AISI M2 Tool Steel

The aim of this study is to investigate the effects of various ceramic-based coatings on the performance of AISI M2 high-speed steel punch used in the nut piercing process. AISI M2 punches were coated with TiN, TiN/CrN, and CrAlN utilizing a physical vapour deposition method. The total stroke number of the punches was used to evaluate the tool life of TiN, CrAlN, and TiN/CrN coated AISI M2 punches. AISI M2 punch coated with TiN/CrN was able to work up to greater stroke numbers than punches coated with TiN and CrAlN. Hardness and wear tests were performed to study the wear resistance of TiN/CrN and CrAlN coatings under relatively normal load conditions compared to actual working conditions (impact loading conditions) in the piercing process. The hardness and wear resistance of the CrAlN coating were greater than those of the TiN/CrN coating. The wear performance of the CrAlN coating was higher at normal loads and sliding speeds while the tool life of the TiN/CrN-coated punch was better under impact loading conditions.

Failure mechanisms of CrN and CrAlN coatings for solid particle erosion resistance

In this study, CrN and CrAlN coatings were deposited on the surface of aerospace titanium alloys using the arc ion plating technology to investigate the effect of the microstructure of the coatings on the mechanical and erosion resistance properties. The cross-sections of the coatings were observed by Scanning Electron Microscope(SEM), the microstructures were characterized by Transmission Electron Microscope(TEM), and the crystalline structures were tested by X-ray diffraction (XRD); furthermore, the hardness of the coatings was determined by a micro-Vickers hardness tester, the film-base bond strength was measured by a scratch tester, the change in curvature was measured by laser scanning and the residual stress was calculated. The fracture mechanism of the coating was elucidated by simulating the fracture pattern of the cross-section of the erosion crater. The results indicated that the thicknesses of the CrN and CrAlN coatings were almost the same, but the number of large particles on the surface of the CrAlN coating was higher. Both sets of coatings exhibited a nanocrystalline structure with a grain size of around 10 nm. Due to the doping of the Al element, the CrAlN coatings exhibited a hardness of 2846 HV and a higher residual stress of −1.831 GPa. Both the CrN and CrAlN coatings showed lower erosion rates than the titanium substrate at 30° and 90° angles of attack. The results of finite element simulations indicated that the more ductile CrN coating exhibited a better stress absorption capacity, and a typical brittle fracture failure mechanism was observed for both sets of coatings.

Tribomechanical and microstructural properties of cathodic arc-deposited ternary nitride coatings

Sintered carbides are promising materials for surfaces that are exposed to extreme wear. Owing to their high service load, ceramic-based thin films are coated on carbides using different techniques. In this study, non-toxic and cobalt-free powder metallurgy-sintered carbide samples were coated with TiN, TiAlN, CrAlN, and TiSiN ceramic-based thin film coatings by cathodic arc physical vapor deposition. The microstructure (phase formation, coating thickness, surface roughness, and topography), mechanical properties (hardness, modulus of elasticity, and plasticity indices), and tribological properties (nanoscratch and wear behavior) of the thin film coatings were investigated. No cracks or defects were detected in these layers. The ceramic-based ternary nitride thin film coatings exhibited better mechanical performance than the TiN coating. The TiN thin film coating had the highest average surface roughness, which deteriorated its tribological performance. The ternary nitride thin film coatings exhibited high toughness, while the TiN thin film coating exhibited brittle behavior under applied loads when subjected to nanoscratch tests. The wear resistance of the ternary nitride coatings increased by nearly 9–17 times as compared to that of the TiN coating and substrate. Among all the samples investigated, the substrate showed the highest coefficient of friction (COF), while the TiSiN coating exhibited the lowest COF. The TiSiN thin film coating showed improved mechanical and tribological properties as compared to other binary and ternary nitride thin film coatings.

Impact Abrasive Wear Resistance of CrN and CrAlN Coatings

The impact wear resistance of the hard coating is very important in the high-temperature environment of the nuclear power plant. CrN and CrAlN coatings were prepared using multi-arc ion plating. The impact abrasive wear resistance of the coatings was investigated at varied temperatures through a controlled kinetic energy impact wear rig, and their impact mechanism was elucidated. No extensive spalling was found on the surface of the CrN and CrAlN coatings after 104 impacts under the no-sand condition. The excellent antioxidant properties of the CrN and CrAlN coatings can protect the substrate from oxidation under the no-sand condition at 500 °C. The impact mechanism of the two coatings was plastic deformation under the no-sand condition, and it was mainly material removal under the sand condition. The depth and width of wear scar were larger under the sand condition than under the no-sand condition. The impact wear region was divided into a mixed impact zone and a sand impact zone. Compared with the CrN coating, the CrAlN coating had lower impact force and shallower impact wear scar, proving that it has better anti-impact wear properties.

Effect of structure, phase, and elemental composition of AlN, CrAlN, and ZrAlN coatings on their electrochemical behavior in 3% NaCl solution

AbstractThin coatings AlN, AlZrN, and AlCrN were deposited by pulsed magnetron sputtering. The high‐speed steel Т1, structural alloy steel 5140, and structural carbon steel 1017 were used as substrates. The magnetron current, nitrogen content in the gas mixture, and bias voltage on the substrate were changed to obtain nanostructured and amorphous layers of coatings with different elemental compositions. The voltammetry and impedance spectroscopy were performed on the coated samples in 3% NaCl solution. The corrosion behavior of the coatings was characterized by the corrosion current density icorr, the polarization resistance Rp (at the corrosion potential), the ratios icorr,s/icorr, and Rp/Rp,s, where subscript s refers to the substrate. It was shown that the coatings under study (except AlN) are electrochemically active, and the corrosion processes occur not only on the substrate in the coating discontinuity but on the coating surface as well. The coatings AlN/T1, AlZrN/5140, AlCrN/T1, and AlCrN/5140 with icorr ~ 10−7 A cm−2 are found to be the most corrosion‐resistant in 3% NaCl. The paper discusses factors affecting the corrosion behavior of the investigated coatings.

Effect of plasma nitriding ion current density on tribological properties of composite CrAlN coatings

CrAlN coatings were synthesized on pre-plasma nitrided M2 high speed steels using different ion current densities. The effect of plasma nitriding pretreatment on the microstructures and tribological properties of composite CrAlN coatings had been studied. The results showed that the nitriding efficiency could be significantly enhanced by higher ion current density. The thickness of nitrided layer increased from 43 μm to 63 μm with the increase of ion current density. The nitrided layers without either compound layer or grain boundary precipitation were produced with all experimental ion current densities. Radial cracks also appeared at the Rockwell-C indentation edge of the composite CrAlN coating due to the conformal effect. Moreover, radial cracks of the composite coatings originated from the hard and brittle nitrided layer. The highest interfacial adhesion of the composite CrAlN coating reached 105 N. Furthermore, the wear resistance of CrAlN coating was improved by combining nitriding pretreatment with coating deposition, and the composite coating (PN4/CrAlN) possessed the superior wear resistant.

Effect of multilayer CrN/CrAlN coating on the corrosion and contact resistance behavior of 316L SS bipolar plate for high temperature proton exchange membrane fuel cell

• The CrN/CrAlN coating greatly improved the contact angle and corrosion resistance of 316L SS. • The CrN/CrAlN coating reduced the ICR and increased the surface conductivity of 316LSS. • Single fuel cell test assembled with CrN/CrAlN coating enhanced the performance of HT-PEMFC. Stainless steels have received wide attention as a substitute material for bipolar plates in high temperature proton exchange membrane fuel cell (HT-PEMFC). In the present work, the CrN, CrAlN and multilayer CrN/CrAlN coatings were deposited on 316L SS to increase the corrosion resistance and decrease the interfacial contact resistance. The deposited coatings exhibited face centered cubic phase structure and it was verified from the X-ray diffraction pattern. X-ray photo electron spectroscopy results showed the formation of both CrN and CrAlN layers on 316L SS. CrN/CrAlN coating is more helpful in water management due to low surface roughness and high contact angle in the HT-PEMFC environment. The corrosion resistance behavior of all the samples were studied in 85% H 3 PO 4 solution at 140 °C purged with H 2 (HT-PEMFC anode) and O 2 (HT-PEMFC cathode) gases. The results showed that all the coatings considerably improved the performance of 316L SS and superior corrosion resistance was observed for CrN/CrAlN multilayer coating, whose protective efficiency was 98.12% and 96.14% in the two simulated HT-PEMFC environments. The results of electrochemical impedance spectroscopic studies demonstrated higher impedance for CrN/CrAlN coating. Surface morphological studies performed after corrosion studies revealed that protection ability of CrN/CrAlN coating still remained acceptable. A very low interfacial contact resistance value of 6 mΩ cm 2 at 140 N/cm 2 was observed for CrN/CrAlN coating. Moreover, after corrosion studies, the interfacial contact resistance value of CrN/CrAlN coated 316L was much lower than that of CrN and CrAlN coatings due to the increased oxidation resistance. The maximum power density of about 0.93 W/cm 2 at 2 A/cm 2 and output voltage of 0.96 V was observed for CrN/CrAlN coating.

Hybrid reactive sputtering of transition metal aluminum oxynitrides

Transition metal aluminum nitrides like CrAlN and TiAlN coatings are widely used to improve performances of cutting tools. Incorporation of oxygen leads to the transition metal aluminum oxynitrides CrAlON and TiAlON, resulting in reduced friction against steel compared to nitride coating and further improved cutting performance. In previous studies, over stoichiometric chemical compositions with increased non-metal to metal ratios of z > 1 were observed in oxynitride CrAlON and TiAlON coatings. Nevertheless, the reason for the non-metal to metal ratios of z > 1 is not clarified yet. The current study aims to contribute to this issue. For this purpose, CrAlON and TiAlON coatings were deposited with four different oxygen to reactive gas flow ratios jO2/(jO2+jN2) using a direct current magnetron sputtering (dcMS) / high power pulsed magnetron sputtering (HPPMS) hybrid process. The plasma composition was investigated at the substrate side in front of both, the dcMS and HPPMS cathode. Subsequently, the chemical and phase composition of the deposited coatings was examined. It can be concluded that a higher oxygen content of reactive gas mixture jO2/(jO2+jN2) increases non-metal to metal ratios z in the plasma. This results in higher non-metal to metal ratios z in the coating. The findings reported in this study expand the understanding of the reason for over stoichiometric chemical composition of transition metal aluminum oxynitrides.

Lapping and polishing of additively manufactured 316L substrates and their effects on the microstructural evolution and adhesion of PVD CrAlN coatings

Laser powder bed fusion (LPBF) enables the manufacturing of three-dimensional parts from metallic powder with a high degree of design-freedom. Due to the low hardness in order to protect tribologically stressed surfaces against severe wear, the surface of LPBF parts made of 316L stainless steel needs to be modified by coating processes such as physical vapor deposition (PVD) using hard coatings. Although 316L is among the most investigated material for LPBF, the deposition of PVD hard coatings such as ternary nitride coatings on additively manufactured 316L substrates has not been studied yet.This study aims at evaluating the effects of lapping and polishing of 316L stainless steel substrates processed by LPBF on the resulting surface integrity and its influence on the microstructural evolution and adhesion of PVD CrAlN coatings. A 316L substrate bulk material served as reference throughout the investigations. The 316L substrate CrAlN coating composites were examined with respect to the microstructural characteristics and residual stresses using nanoindentation and two-dimensional X-ray diffraction. To assess the adhesion of the CrAlN coating on the differently pre-treated 316L substrates, scratch and Rockwell C adhesion tests were conducted. The resulting scratch tracks and Rockwell C indents were metallographically examined in order to determine the failure modes. The results demonstrate that the deposited PVD CrAlN coatings differ in their texture and mechanical properties, such as hardness and residual stresses, depending on the 316L substrate surface conditions. The CrAlN coatings generally exhibit good adhesion to both the 316L LPBF substrate and 316L bulk material. However, the findings indicate improved adhesion of CrAlN coatings on lapped 316L substrates. The residual stress gradient at coating-substrate interface and imperfections at the surface of the 316L LPBF substrate are found to primarily influence the performance and failure mode of the CrAlN coating.

The Effect of Al and Ti Transition Metals on the Wear Resistance of Ceramic Based CrN Coatings; Investigation under Ambient Air and Vacuum Conditions

In the present study, CrN, CrAlN and CrAlTiN coatings were deposited using the cathodic arc evaporation technique. The structural investigations of these CrN based coatings were performed by scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, X-ray diffractometer. The hardness and adhesion strength values of coatings were determined via Vickers type microhardness tester and progressive load scratch tester, respectively. The wear performance of samples was established at ambient air and vacuum condition. All coatings grew in the “T zone” growth model and had a dense and columnar structure. The XRD patterns presented predominantly (220), (110), and (111) reflections. It was demonstrated that the quaternary coating had a higher texture parameter as 0.68, which was related to the highest thickness and hardness. Also, CrAlTiN coatings with the smallest mean crystallite size of ∼87 nm showed the best hardness, and this ensured relatively high scratch resistance. CrN and CrAlTiN coatings improved wear performance under ambient air condition but were not striking as under vacuum condition. The quaternary coating had a superior performance in the vacuum condition, but due to the high sensitivity of Ti to oxygen, it fell behind the CrN coating under ambient air condition.

Influence of Ag additions on the structure, mechanical properties and oxidation behaviour of CrAlNAg coatings deposited by sputtering

In this work, the influence of Ag additions into CrAlN coatings on the surface morphology, chemical composition, structure, hardness and oxidation behaviour was studied. Increasing the Ag content decreased the size of the morphological features and produced a more compact coatings. All coatings displayed a fcc structure typical of transition metal nitrides; the silver phase was indexed for the coatings with Ag concentration ≥8.6 at.%. XPS results confirmed that Ag existed as nanoclusters within the coating structure. A maximum hardness of around 23 GPa was observed for the 8.6 at.% of Ag. The decrease of the hardness with further increase in the Ag content was ascribed to the much softer character of this phase. The reference CrAlN coating displayed the best oxidation resistance and the lowest onset point of oxidation. The good oxidation resistance of this coating was attributed to the formation of a continuous and protective thin Cr2O3 layer on the top of the oxide layer. Ag additions degraded the oxidation resistance of the coatings, since the diffusion of Ag to the top surface of the oxide scale created extra paths for ions diffusion in the protective Cr-O layer. The formation of AgCrO2 phase in CrAlNAg9 coating, for the particular temperature of at 800 °C, was responsible for the low oxidation resistance of the coating as compared to the same coating oxidized at 900 °C.

Structure, mechanical and thermal properties of Y-doped CrAlN coatings

CrAlYN coatings with different Y contents (0, 5 and 12 at.%) were deposited by cathodic arc evaporation to investigate the influence of Y-addition on the structure, mechanical and thermal properties of CrAlN coatings by using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermal gravimetric analysis and nanoindentation. The structural transformation of single phase cubic Cr0.42Al0.58N and Cr0.39Al0.56Y0.05N coatings to cubic–wurtzite mixed Cr0.32Al0.56Y0.12N coating leads to a drop in hardness from (30.2±0.7) GPa of Cr0.42Al0.58N and (32.0±1.0) GPa of Cr0.39Al0.56Y0.05N to (25.2±0.7) GPa of Cr0.32Al0.56Y0.12N. The incorporation of 5 at.% Y retards the thermal decomposition of CrAlN, verified by the postponed precipitation of w-AlN and N-loss upon annealing. Correspondingly, Cr0.39Al0.56Y0.05N coating consistently exhibits the highest hardness value during thermal annealing. Nevertheless, alloying with Y exerts an adverse effect on the oxidation resistance of CrAlN.

Influence of Aluminum Content on the Impact Fatigue of HPPMS CrAlN Coatings on Tool Steel

Influence of Aluminum Content on the Impact Fatigue of HPPMS CrAlN Coatings on Tool Steel

Multilayer architecture design to enhance load-bearing capacity and tribological behavior of CrAlN coatings in seawater

Steel materials employed in severe conditions including strong corrosion, high load and multi-factor coupling damages can easily cause incredible degradation until failure, and the protective CrN-based coatings should be one of promising candidates to relieve those damages for the steel equipment or components. In present paper, the monolayer CrAlN and multilayer Cr/CrAlN coatings were successfully deposited on steel substrates by multi-arc ion technology, and their microstructure, mechanical, tribological and corrosion performances were systematically investigated. The results show that the special multilayer Cr/CrAlN coating could possess much better load-bearing capacity and wear resistance than that of monolayer CrAlN coating, which was due to the facts that the multilayer architecture can effectively release the internal stress and inhibit the expansion of defects. Particularly, the multilayer interfaces could effectively prevent the aggressive medium in seawater infiltrating into the inside of coating, and thus the multilayer Cr/CrAlN coating could have higher corrosion resistance compared to monolayer CrAlN coating. As a result, this multilayer Cr/CrAlN coating could achieve excellent combined performances, indicating that it has greatly potential application as protective coating in seawater.

REACH regulation challenge: Development of alternative coatings to hexavalent chromium for minting applications

Aiming to improve the protection of human health and the environment, REACH regulation was enforced across European Union, accelerating the need to find alternative solutions to the electrodeposition processes of hexavalent chromium employed in several industrial applications. Electroplated chromium coatings are widely used due to their physical and mechanical properties that allow a longer service life of products that usually fail due to wear. Minting is one of those applications where good mechanical and tribological properties are required and where hard chromium has an important usage without being outmatched by other coatings. This study presents the development of an alternative coating to hard chromium with outstanding mechanical properties, in particular high resistance to cyclic loads . Cr( Al , Si )N coatings have been produced by reactive DC magnetron sputtering . Focusing on mechanical properties, an increase in the hardness was observed with the consecutive addition of elements to the base matrix (CrN), ranging from ≈10 GPa in CrN coatings up to ≈17 GPa for the CrAlSiN coatings. In nano-impact tests, CrAlN coatings had the best performance and no crack events by fatigue were observed by SEM after 50 impacts, with load maximum 20mN, with an estimated maximum contact pressure of 1.5 GPa much higher than the one requested for coinage. The fatigue wear was governed by the H/E ratio and plasticity index showing that Cr( Al , Si )N coatings deposited by reactive magnetron sputtering can be considered excellent candidates for cyclic loading, as in minting applications. • In nano-impact tests, CrAlN coatings withstood 1.5 GPa without failure. • Depth of initial indentation after 50 impacts was lower in CrAlN than in steel. • Cr( Al , Si )N coatings are viable alternatives to hard chromium under cyclic loads.