NiCr Coatings Research Articles

Comparison of Ni20Cr Coating on two Different Grades of Grey Cast Iron for Wear Resistance

Objectives: In this research work two substrate materials GIHC and GI250 are selected and are coated with Ni20Cr sing Detonation spray process. Methods/Statistical Analysis: Surface morphology of the coating has been studied by XRD and SEM/EDAX analysis. Wear tests were performed for the coated as well as uncoated samples on Pin-On-Disc apparatus using ASTM G99 standards. Findings: The aftereffects of wear information and SEM/EDAX investigation are utilized to consider the destroy conduct of the well used examples. From the outcomes it is discovered that covered examples demonstrate less wear misfortune when contrasted with uncovered examples and the total wear misfortune for explosion shower coatings increments with the expansion in load. Application/Improvements: Coatings are alluring in electrical protection and hostile to wear applications; viz. as defensive coatings for sleeve shafts, thermo-couples coats, siphon shafts and so on. Keywords: Detonation Spray, Grey Cast Iron, NiCr

Surface engineering-controlled tribological behavior and adhesion strength of Ni-Cr coating sprayed onto carburized AISI 4340 steel substrate

In this study, a nickel‑chromium (Ni-Cr) coating was sprayed onto carburized AISI 4340 (UNS G43400) steel substrate by high-velocity oxygen fuel (HVOF) method. As-sprayed Ni-Cr coating was subjected to ultrasonic nanocrystal surface modification (UNSM) technology to control the tribological performance and adhesion strength. The aim of the current study is to improve the durability of Ni-Cr coating by the application of UNSM technology. The UNSM technology reduced the surface roughness and increased the surface hardness of the as-sprayed coating by about 64 and 25% that were associated with the elimination of high peaks and valleys, filling up micro-pores, respectively, where the unfilled open-pores and micro-cracks may be found as a stress concentration cite to suppress a crack initiation and crack propagation and a less number of open-pores may hinder the initiation and propagation of micro-cracks. The evaluation of the tribological performance of Ni-Cr coatings was evaluated using a wear tester in dry conditions, while the adhesion strength was obtained using a progressive scratch tester. As a result, the friction coefficient of the as-sprayed coating was reduced from about 1.1 to 0.75, and the adhesion strength was increased from about 3.3 to 6.1 N by the application of UNSM technology. The reduction in surface roughness of the UNSM-treated coating can be considered as the main parameter that influences on the frictional behavior, while increase in surface hardness determines the wear resistance and adhesion strength. It was found that the UNSM technology improved the tribological performance and adhesion strength of the coating.

Effects of laser power on friction–wear performances of laser thermal sprayed Cr3C2–NiCr composite coatings at elevated temperatures

Cr3C2–NiCr composite coatings were fabricated on H13 hot work mould steel using a laser thermal spraying (LTS) at the laser power of 1200, 1400 and 1600 W. The surface and cross–section morphologies, chemical compositions, bonding strengths, phases and roughness of obtained coatings were analyzed using a scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), scratch, X–ray diffractometer (XRD), and atomic force microscopy (AFM), respectively. The friction–wear properties of Cr3C2–NiCr composite coatings at 600 °C were analyzed using a high temperature wear test, and the wear mechanism were also discussed. The results show that the Cr3C2–NiCr composite coatings are primarily composed of Cr7C3 and Cr3C2 hard phases, and NiCr binder phase, the average bonding strengths is 46.25 N, which forms the metallurgical bonding at the coating interface. The average coefficients of friction (COFs) of Cr3C2–NiCr coating fabricated at the power of 1200, 1400 and 1600 W is 0.65, 0.34, and 0.67, respectively; the corresponding wear volumes are 111.3, 101.1, and 143.2 mm3, respectively, the wear mechanism of Cr3C2–NiCr coatings is primary abrasive wear and oxidation wear.

Nickel-chromium (Ni–Cr) coatings deposited by magnetron sputtering for accident tolerant nuclear fuel claddings

Nickel-chromium coatings were deposited on Zr1Nb alloy using magnetron sputtering systems with «hot» Ni and cooled Cr targets. The effect of coating composition on high-temperature oxidation resistance and hydrogen uptake of Zr1Nb was studied. Hydrogen uptake of the alloy was measured in situ under gas-phase hydrogenation at 633 K. High-temperature oxidation was performed in air atmosphere at 1173–1373 K for 20 min. It was shown that the coating with high Ni content (83 at.%) drastically increases hydrogen uptake of the Zr1Nb alloy and demonstrates low oxidation resistance even at 1173 K. The coatings with Cr content ≥45 at.% have low hydrogen permeability which reduces the rate of hydrogen uptake of the alloy. The oxidation resistance of the NiCr coatings increases with Cr content in the as-deposited coatings. The pure Cr coating exhibits the best oxidation resistance: only 8 μm-thick oxide layer was observed. There is also found the intensive diffusion of nickel into the alloy during high-temperature oxidation of the samples coated by NiCr films with 55 and 17 at.% Ni. The as-deposited NiCr coatings are less brittle than the pure Cr coating, but their mechanical properties degrade stronger than for the Cr coating after the oxidation test.

A new approach to manufacture oxidation-resistant NiCrAl overlay coatings by electrodeposition

NiCrAl overlay coatings have been manufactured by means of conventional electrodeposition of Ni into a porous electrophoretic deposition layer of CrAl nanoparticles. The NiCrAl coatings are compact with a uniform distribution of Cr and Al elements in nano-length scale. They can thermally grow alumina scales in air at 1000 °C, with parabolic oxidation constants as low as that of the ternary coating counterparts prepared by means of physical vapor deposition technologies such as sputtering and arc ion plating.

The effect of the standoff distance on the microstructure and mechanical properties of cold sprayed Cr3C2-25(Ni20Cr) coatings

In this study, coatings were obtained by spraying two Cr3C2-25(Ni20Cr) powders, possessing different morphology and grain size distributions, on an Al 7075 alloy substrate at various standoff distances. The applied powders and process parameters allowed to produce deposits characterised by a compact microstructure and negligible porosity. Depending on the used powder, the obtained coatings showed variations in surface roughness and how the Cr3C2 particles were incorporated into the Ni20Cr matrix. The standoff distance significantly affected the coatings microstructure, mechanical properties, and deposition efficiency. The coatings obtained at a standoff distance of 50 mm were characterised by the highest hardness and amount of incorporated Cr3C2 particles. In turn, coatings sprayed at the distance of 30 mm possessed the highest microhardness and Young modulus, as well as lowest surface roughness.

Wear-resistant coating spraying technique for wear-proofing cover of coke dry quenching furnace

During the operation of a coke dry quenching system of coking plant, wear-proofing cover of the boiler was seriously eroded, and even the ceiling tube of the boiler was worn and torn. Thus, attentions were paid to the research, development and application of the wear-resistant coating spraying technique for wear-proofing cover of the coke dry quenching furnace. The Cr3C2–NiCr coatings for wear-proofing cover were fabricated via supersonic arc spraying process, and the residual coating of wear-proofing cover would be sampled for being analyzed after two years. The coating presents a dense microstructure with few pores and micro-cracks (the porosity is 4.65%). After thermal spraying of the wear-proofing cover, the hardness and the wear resistance of the surface are improved. The remaining coating is continuous and compact, with an average thickness of about 147 μm. Transverse micro-cracks parallel to the spreading direction of the coating surface are displayed on different areas of the coating, which demonstrates its serious erosion wear effect. The main chemical component of white zone is Fe–18Cr–Ni. The Cr level of light gray phase is about 77.57 wt.% and the O level is 22.43 wt.%. And the main chemical components of dark gray phase are C, O, Al, Si and Ca. X-ray diffraction patterns were adopted to implement phase analysis on the surface of coating sample, which indicated that the coating was composed of a large amount of Cr3O2 and a small amount of metal Cr.

Structural and Mechanical Properties of Arc-Sprayed Ni–Cr Coating Post-Treated by Surface Mechanical Attrition Treatment (SMAT)

This study focuses on the effects of a surface mechanical attrition treatment on the structural and mechanical behavior of arc-sprayed Ni–Cr coatings deposited on steel substrates. The surface of the as-sprayed and SMATed coatings was characterized by X-ray diffraction, Scanning Electron Microscopy, and non-contact profilometry. The coating porosity was evaluated by using image analysis software. The residual stresses were determined using X-ray diffraction with the sin2ψ. Indentation tests were carried out on the cross sections of the different coatings to evaluate their hardness. The wear properties of the coatings were assessed using a pin-on-disk tester at ambient temperature without lubrication. The results showed that surface mechanical attrition treatment (SMAT) induced a grain refinement on the coating surface due to severe plastic deformation, which was associated with a significant improvement of the mechanical properties.

Effect of Experimental Parameters on Wear Response of Thermally Sprayed Carbide Based Coatings

Friction and abrasive wear response of WC-12 Co and Cr3C2-25 NiCr coatings was studied. Abrasive wear experiments were conducted with SiC abrasive particles with varying load and sliding speeds. The results were analyzed using SEM, XRD and XPS observations of worn surfaces, wear debris and worn out abrasive paper. Friction coefficient diminished with rise in sliding speed and increased for increase in load while wear rates decreased for increasing sliding speed for both coatings. WC-12 Co coating had better wear resistance than Cr3C2-25 NiCr coating while Cr3C2-25 NiCr coating displayed lower friction coefficient. The variation in wear rate and friction response of coatings was due to combined effects of adhesion, abrasion and tribo oxidation effects. The composition of tribo films was strongly influenced by load and sliding velocity and altered friction and wear response of the coatings.

The effect of silicon as a reactive element for NiCrAl coating performance on hastelloy substrate

The isothermal oxidation behavior, microstructure, phase formation and microhardness of NiCrAl coatings with and without silicon addition were investigated. Characterization of heat treated and oxidized samples were carried out by X-ray diffractometer (XRD), scanning electron microscope (SEM) and vicker hardness tester. The NiCrAl and NiCrAlSi coatings were deposited with high velocity oxygen fuel (HVOF) on the surface of hastelloy substrate. Oxide scales consists of Al2O3 and NiCr2O4 phases were formed on the surface of coating sample after isothermal oxidation at temperature of 1000 °C for 100 hours. The addition of silicon increases the oxidation resistance of NiCrAl coating through the formation of Al2O3 phase, whereas on NiCrAl coating without silicon addition, mass loss was observed, which indicated scale spallation. The addition of silicon at 0.4wt% can prevent outward diffusion of refractory elements such as Mo from the hastelloy substrate. The measured hardness of NiCrAl and NiCrAlSi coatings were 317.53 and 330.9 Hv, respectively. The experimental results showed that NiCrAl with silicon addition improved the resistance of high temperature oxidation and hardness.

High-temperature corrosion behavior of selected thermally sprayed coatings in corrosive aggressive environment

The aim of this paper is to evaluate and compare the corrosion resistance of Hastelloy C-276 coating with Stellite 6 and Cr3C2%-25% NiCr coatings. The coatings were deposited using HP/HVOF (High Pressure/High Velocity Oxygen Fuel) thermal spraying technology. The corrosion test was conducted in the corrosive-aggressive environment of molten salts mixture in the composition of 40% Na2SO4–60% V2O5, simulating the corrosion environment of boilers for residual fuel oils. The corrosion test under cyclic conditions included 50 cycles at the temperature of 750 °C and subsequent cooling at the room temperature for 20 min. The corroded specimens were analyzed using scanning electron microscope (SEM) and elemental analysis (EDS). In comparison with Cr3C2-25% NiCr coating, both Stellite 6 and Hastelloy C-276 coatings provided the substrate material with sufficient protection against high-temperature corrosion. The corrosion mechanism of Hastelloy C-276 coating was based on the formation of protective oxide layer which prevented further penetration of corrosive media. Stellite 6 coating exhibited the corrosion attack along splat boundaries resulting in spat delaminating into the build-up. The corrosion mechanism of Cr3C2-25% NiCr coating included the attack on NiCr matrix resulting in gradual separation of carbide phases into the corrosive environment.

MORPHOLOGICAL, STRUCTURAL, MICROHARDNESS AND ELECTROCHEMICAL CHARACTERIZATIONS OF ELECTRODEPOSITED Cr AND Ni–W COATINGS

Currently, Ni-Cr coatings are widely used in a number of important applications due to their excellent properties. In this study, Ni-Cr alloys were electrodeposited from citrate bath onto Cu substrates by using different values of applied current densities. The effects of plating deposition current density on morphological and structural characterization of Ni-Cr electrodeposited coatings were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Microhardness of the coatings is also evaluated using Vickers’s microhardness. Potentio-dynamic polarization and electrochemical impedance spectroscopy (EIS) tests in 3.5 wt % NaCl solution were used to evaluate corrosion résistance of Ni-Cr coatings. The results showed that the surface morphology of the all coatings contained micro cracks and pores. XRD patterns indicate the formation of Ni-Cr and Cr3Ni2 phases. Microhardness measurements show that all Ni-Cr samples are harder than copper substrate. Electrochemical tests show that 3 A.dm-² is an optimal value of applied current density in the sense of the least value of Ecorr = -12.3 mV and the best charge transfer resistance Rp = 303.03 Ω.cm².

Microstructure and tribological performance of ZrB2–NiCr composite coating deposited by APS

Air plasma spraying technology was used to prepare ZrB2–NiCr coatings for the surface protection of gears and improving their service time. The morphology of the coating was investigated by means of scanning electron microscope. The generation of new phases and decomposition of old phases in the powders and coatings were explained by Gibbs free energy calculations. The hardness and wear resistance of the coatings were measured using a Vickers microhardness tester and a ball-on-disk tribometer, respectively. The results showed that ZrB2–NiCr composite coatings present typical thermal spraying morphologies, and mainly contain ZrB2, Ni4B3 and Ni phases. In addition, the coating with an added 20 wt%ZrB2 demonstrated the lowest wear loss and highest hardness (812 HV), which was about five times that of the substrate. The wear process generated some plate-like debris for the 20ZrB2–NiCr composite coating, which suggested the occurrence of adhesive and oxidative wear, while the other coatings also showed signs of adhesive and fatigue wear on observation of the worn surfaces.

Influence of Cr content on high-temperature oxidation behaviour of arc sprayed Ni–Cr coatings

ABSTRACTIn this study, the high-temperature oxidation behaviour of arc-sprayed Ni–Cr coatings with high Cr contents of 30, 45 and 50 at.% was investigated in comparison with reference AISI 1020 steel. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were utilised to characterise the oxide scales. The oxidation resistance of the steel substrates was found to be enhanced after the application of the Ni–Cr coatings since the oxidation kinetics followed the parabolic law. In addition, the oxidation rate of Ni–50Cr coating was 56.5% lower than that of Ni–30Cr coating, indicating that the oxidation performance of coatings was improved with increasing Cr content. The oxide layers of Ni–Cr coating were found to be a double layer structure protecting the substrate from severely oxidation, which composed of a top layer of NiO and a basal layer of Cr2O3 and NiCr2O4. The surface of Ni–30Cr coating contained lots of multi-angle NiO crystals, while the surface of Ni–50Cr coating contained a dense Cr2O3 structure, suggesting that the growth of NiO crystals was limited due to the large amount of Cr-rich oxides.

Oxidation resistance of uncoated & detonation -gun sprayed WC-12Co and Ni-20Cr coatings on T-22 boiler steel at 900°C

Oxidation is the major degradation problem in aircraft, marine, coal fired boilers, factories, and sand-bar gas turbines. It is due to the usage of variety of fuels coupled with elevated working temperatures, which dominances to the degradation in all the applications. In the present investigation oxidation behavior of uncoated and detonation Gun sprayed WC-12Co and Ni-20Cr coatings on T-22 boiler steel has been investigated at 900°C in Silicon wire tube furnace for total duration of 50 cycles under cyclic condition, each cycle consisted of keeping the samples for 60 minutes at 900°C temperature followed by 20 minutes cooling at room temperature. Oxidation kinetics of uncoated and coated sample has been established with the help of weight gain measurements. The exposed samples were characterized by scanning electron microscopy/energy dispersive spectroscopy (SEM&EDS).The Ni-20Cr coating, with morphological observations was found to be more protective than uncoated and WC-12Co coated on T-22 boiler steel.

Effect of Atomization Gases on the Elastic Modulus of Thermal-sprayed NiCr Coatings

Abstract Accurate evaluation of the elastic modulus of thermal-sprayed coatings is very important to ensure the safety and durability of industrial components, but it seems difficult via a conventional technique. Although the indentation technique is available to estimate the local modulus of coatings, it does not reflect the effects of porosity or cracks. Impulse excitation technology (IET) is a simple and accurate method to evaluate the elastic modulus of bulk materials. It was used to determine the modulus of thermal-sprayed coatings via relative method in this work. An analytical relationship among the moduli of the coating, the substrate and the coating/substrate system was derived. Thus, the modulus of coatings was obtained via the measured modulus of the samples before and after coating. Experiments on Q235 steels coated with NiCr coatings, were carried out to investigate the effect of atomization gases on the elastic modulus of NiCr coatings. The results indicate that the elastic modulus of NiCr coating prepared by air atomization (NiCr-Air) is higher than that of NiCr coating prepared by N2 gas atomization (NiCr-N2). The reasons for this are the formation of Ni(Cr2O4) reinforced NiCr alloy laminated composite, and the laminated composite structure has a positive influence on the elastic modulus.

Micro-Structures and High-Temperature Friction-Wear Performances of Laser Cladded Cr-Ni Coatings.

Cr–Ni coatings with the mass ratios of 17% Cr–83% Ni, 20% Cr–80% Ni and 24% Cr–76% Ni were fabricated on H13 hot work mould steel using a laser cladding (LC). The surface–interface morphologies, chemical elements, surface roughness and phase composition of the obtained Cr–Ni coatings were analysed using a scanning electron microscope (SEM), energy disperse spectroscopy (EDS), atomic force microscope (AFM) and X–ray diffractometer (XRD), respectively. The friction–wear properties and wear rates of Cr–Ni coatings with the different mass ratios of Cr and Ni at 600 °C were investigated, and the worn morphologies and wear mechanism of Cr–Ni coatings were analysed. The results show that the phases of Cr–Ni coatings with mass ratios of 17% Cr–83% Ni, 20% Cr–80% Ni and 24% Cr–76% Ni are composed of Cr + Ni single-phases and their compounds at the different stoichiometry, the porosities on the Cr–Ni coatings increase with the Cr content increasing. The average coefficient of friction (COF) of 17% Cr–83% Ni, 20% Cr–80% Ni and 24% Cr–76% coatings are 1.10, 0.33 and 0.87, respectively, in which the average COF of 20% Cr–80% Ni coating is the lowest, exhibiting the better anti-friction performance. The wear rate of 17% Cr–83% Ni, 20% Cr–80% Ni and 24% Cr–76% Ni coatings is 4.533 × 10−6, 5.433 × 10−6, and 1.761 × 10−6 N−1·s−1, respectively, showing the wear resistance of Cr–Ni coatings at a high temperature increases with the Cr content, in which the wear rate is 24% Cr–76% Ni coating with the better reducing wear. The wear mechanism of 17% Cr–83% Ni and 20% Cr–80% Ni and 24% Cr–76% coatings at 600 °C is primarily adhesive wear, and that of 24% Cr–76% coating is also accompanied by oxidative wear.

High temperature chlorine-induced corrosion of Ni50Cr coating: HVOLF, HVOGF, cold spray and laser cladding

To combat the high temperature chlorine-induced corrosion of materials in the biomass and waste fuel-fired thermal power plants NiCr coatings can be used. In this study, a commercially available Ni50Cr gas atomised powder was sprayed onto a power plant alloy using a liquid fuelled and a gas fuelled high velocity oxygen fuel thermal spray (HVOF), cold gas dynamic spray (CS) and laser cladding (LC). High temperature corrosion test was performed at 700 °C in a controlled environment corrosion test with 500 ppm HCl, 5 vol% O2 and bal. N2 for 250 h. KCl was deposited onto certain samples to understand the mechanism of high temperature chlorine-induced corrosion. The corrosion products were characterised in a SEM with EDX and XRD. A wide range of oxide morphology and distribution was found on the coating top surface which was primarily due to their processing techniques. Cross-section examination of the coatings showed various degrees of internal attack and scale growth. In the absence of any deposit on the surface, cold-sprayed coating showed the poorest performance since the corrosive ion penetrated ~600 μm after 250 h exposure, which is due to the inter-connected porosity. In presence of KCl deposit, laser cladded coating showed the best corrosion performance because the grooving pattern (traces of corrosive ion penetration) only penetrated 80 μm, which is predominantly due to its pore free microstructure.

Cyclic high temperature oxidation behaviour of bare and NiCr coated mild steel and low alloyed steel

Oxidation behaviour of low carbon and low alloyed steels at different Ni-Cr coatings thickness are studied, and also investigated the resistance offered by different coating thickness. Hardness of low alloy steel was increased from 202 to 342 VHN whereas that of mild steel was increased from 148 to 309 VHN after the application of coatings. Parabolic rate constant (Kp) for high temperature oxidation of bare, 200-250µm, and 250-300µm thick Ni-Cr coated low alloy steel were calculated to be 787.192, 0.235608, and 0.501787 (×10-10g2cm-4s-1) respectively, whereas that of mild steel were calculated to be 1104.49, 0.0309172, and 0.0978113 (×10-10 g2cm-4s-1) respectively.

Experimental investigations and effects studies on electrodeposited Ni-Cr composite coating using robust design approach

Electrocodeposition is acknowledged as superior technique for preparation metallic and alloy based composite coatings with enhanced properties. In this study an attempt has been made to deposit micron sized chromium particles in nickel matrix by electrocodeposition principles. The electrocodeposition setup is established and the composite coatings are prepared from watts type nickel bath. The experiments are framed by robust experimental design of Taguhci’s orthogonal array approach. The process parameters are considered for study and the L27 orthogonal array is chosen for experimental design. The Ni-Cr composite coatings are prepared over mild steel substrates. The outcomes, mass of deposit, area fractions of particles and microhardness of particles are evaluated methodically. The presence of Cr particles in nickel matrix is examined with SEM, XRD and EDS studies. The direct effects of electrodeposition process variables on microhardness of Ni-Cr thin film coatings are investigated with signal to noise ratio, mean effects and analysis of variances. Base on the significances the parameters are ranked by order. It has been revealed that current density has the predominant effects on microhardness of Ni-Cr and authenticated with scientific and statistical investigations. Regression model is developed for prediction of the microhadness of Ni-Cr coatings and the predicted values are well associated with experimentation outcomes.