NiCr Coatings Research Articles

Optimization of Electrodeposited Ni-Cr Composite Coatings by using Taguchi Design and Grey Relational Method

In this investigation, the Nickel (Ni) – Chromium (Cr) composite deposits was developed from conductive type nickel plating bath through electrodeposition technique. The Cr particles concentration in bath were taken in three different proportions such as 10 g/l,20 g/l and 30 g/l and got deposited on the Ni plate. The design of experiment technique, L27 orthogonal array of Taguchi method was employed for conducting experiments with different combination of parameters and its level. The parameters taken into consideration were current density level, pH range, bath temperature, Cr concentration in bath and stirrer speed. The experiment includes the measurement of micro hardness, area fraction of Cr, mass of deposit and coating thickness of coated samples with variable input parameters. The main effects of process parameters and their influences on the responses were analyzed. The outcomes shows that Cr concentration in bath and pH range are the most significant parameters for better enhanced responses measured. Microstructure examinations were conducted to analyze Cr deposition in prepared Ni plates using optical metallurgical microscope, scanning electron microscope (SEM) micro images and Energy Dispersive X-Ray (EDX) spectroscopy studies. Furthermore, the decision-making procedure was carried out for maximization of multi-performance measured responses using grey relational analysis (GRA). The optimized plating parameters levels are found to be 4 A/dm2 for Current density, 2.5 for pH, 45˚C for bath temperature, 30 g/l for bath concentration and 300 rpm for agitation speed to have the maximum micro hardness of 1037 HV, 370 mg of mass of deposit, 42% of Cr particle area fractions and 112 µm of coating thickness. Subsequently the obtained optimal combination of process parameters was validated through confirmation experiment. The results shows that the confirmation test responses are well associated with predicted response values on the Ni-Cr coatings.

Comparative Study of HVOF Cr3C2–NiCr Coating with Different Bonding Layer on the Interactive Behavior of Fatigue and Corrosion

In order to improve material service life under a fatigue and corrosion coupling environment, a high-velocity oxygen fuel (HVOF) Cr3C2–NiCr coating with a bonding layer was prepared. The objective was to obtain the optimum bonding layer for the HVOF Cr3C2–NiCr coating, which included a laser cladding (LC) Ni625 layer, extreme high-speed laser material deposition (EHLA) Ni625 layer and HVOF NiCr layer. Fatigue properties of the samples with various bonding layers were investigated by means of a four-point bending fatigue test. Electrochemical impedance spectroscopy (EIS) and the salt spray test were executed after the bending fatigue test to simulate the interactive effect of fatigue and corrosion atmosphere. Failure surfaces were characterized by scanning electron microscopy (SEM) and an energy-dispersive spectrometer (EDS) to indicate the details of corrosion products. Corrosive behaviors of samples were adequately demonstrated according to the results, which included the curves of potentiostatic polarization, impedance magnitude and phase degree, and corrosion products. The result showed that the cycles of perforative cracking for the sample with the EHLA Ni625 bonding layer was almost three times than that of the sample with the HVOF NiCr layer. The magnitude of EIS reduced from ~105 to ~103 for the sample after BFT. Eventually, the main improvement mechanism of the HVOF Cr3C2–NiCr coating with the EHLA Ni625 bonding layer was attributed to the grain refinement of the bonding layer and performed a good level of metallurgical bonding with the substrate.

Effect of Y2O3 addition on microstructure and friction-wear performances of laser cladded CrNi coatings on AISI H13 steel

PurposeThis paper aims to analyze the effect of Y2O3 mass fraction on the tribological performance of CrNi coating, which solved the problem of wear resistance on AISI H13 steel.Design/methodology/approachY2O3 reinforced CrNi coatings were fabricated on AISI H13 steel. The microstructure and phases of obtained coatings were analyzed using a super-depth of field microscope and X-ray diffraction, respectively, and the effects of Y2O3 mass fraction on the microstructure and wear resistance were methodically investigated using a wear tester.FindingsThe average coefficients of friction and wear rates of Y2O3 reinforced CrNi coatings decrease with the increase of Y2O3 mass fraction, in which the Y2O3 plays a role of friction reduction and wear resistance. The wear mechanism of Y2O3 reinforced CrNi coating is primary abrasive wear, accompanied by adhesive wear, which is contributed to the grain refinement and dense structure by the Y2O3 addition.Originality/valueThe Y2O3 was added to the CrNi coating by laser cladding, and the effect mechanism of Y2O3 mass fraction on the tribological performance of CrNi coating was established by the wear model.

Effect of Y2O3 mass fraction on electrochemical corrosion performances of laser cladded CrNi coatings in 3.5% NaCl solution

PurposeThe purpose of this study is to investigate the effect of Y2O3 mass fraction on the electrochemical corrosion performance of CrNi coating, which provided a foundation for the performance optimization of CrNi coatings.Design/methodology/approachCrNi coatings with the different Y2O3 mass fractions were fabricated on AISI H13 steel by laser cladding, and the effect of Y2O3 mass fraction on the electrochemical performance of CrNi coating in 3.5% NaCl solution was investigated using an electrochemical workstation.FindingsThe electrochemical corrosion performance of CrNi coating enhances with the increase of Y2O3 mass fraction, and the CrNi–15%Y2O3 coating has the largest polarization resistance and the lowest corrosion current density, which displays the best electrochemical performance among the CrNi–5%Y2O3, –10%Y2O3 and –15%Y2O3 coatings. The protective films are formed with the increase of Y2O3 mass fraction, which inhibits the occurrence of electrochemical corrosion.Originality/valueThe Y2O3 was first added to the CrNi coating to improve its electrochemical corrosion performance, and the influence of Y2O3 on the corrosion resistance of the CrNi coating was discussed by the corrosion model.

Nd:YVO4 Laser Irradiation on Cr3C2-25(Ni20Cr) Coating Realized with High Velocity Oxy-Fuel Technology—Analysis of Surface Modification

The high-velocity oxy-fuel (HVOF) technique has been extensively used for the deposition of hard metal coatings. The main advantage of HVOF, compared to other thermal spray techniques, is its ability to accelerate the melted powder particles of the feedstock material to a relatively high velocity, leading to good adhesion and low porosity. To further improve the surface properties, a mechanical machining process is often needed; however, a key problem is that the high hardness of the coating makes the polishing process expensive (in terms of time and tool wear). Another approach to achieving surface modification is through interaction with a thermal source, such as a laser beam. In this research, the effects of laser scanning rate, scanning strategy, and number of loop cycles were investigated on an HVOF-coated surface. Cr3C2-25(Ni20Cr) was selected as the coating and Nd:YVO4 as the laser source. The results demonstrate the significance of the starting coating morphology and how the laser process parameters can be tuned to generate different types of modifications, ranging from polishing to texturing.

Investigating load-dependent wear behavior and degradation mechanisms in Cr3C2–NiCr coatings deposited by HVAF and HVOF

Wear resistant coatings that comply with non-toxic environment goals are highly desirable. Cr3C2–NiCr is a promising alternative to the toxic, ‘Co’- containing WC–Co coatings to mitigate wear. The purpose of this study was to examine the suitability of Cr3C2–NiCr coatings for automotive brake disc application by systematically investigating their dry sliding wear behavior at different test conditions. Therefore, High Velocity Air Fuel (HVAF) and High Velocity Oxy Fuel (HVOF) were employed to deposit Cr3C2–NiCr coatings. The powder feedstock and as-deposited Cr3C2–NiCr coatings were characterized for their microstructure and phase composition using SEM and XRD. Mechanical properties (hardness, fracture toughness), porosity and surface topography of the as-deposited coatings were evaluated. The coatings were subjected to sliding wear tests at different normal loads (5 N, 10 N and 15 N) using alumina ball as the counter surface. Coefficient of friction (CoF) evolution of HVAF and HVOF deposited coatings, along with their wear performance, was obtained for different normal load conditions. The wear performance ranking of HVAF and HVOF processed coatings was influenced by the test conditions, with HVAF coatings demonstrating better wear resistance than HVOF coatings at harsh test conditions and the HVOF coatings performing better under mild wear test conditions. Detailed post-wear analysis of worn coatings, the alumina ball counter-body and the resulting debris was performed to reveal the degradation mechanisms at different test conditions. Findings from this work provide new insights into the desirable microstructural features to mitigate wear, which can be further exploited to deposit wear-resistant coatings.

Long-term corrosion behavior of HVOF sprayed Cr3C2–NiCr coatings in sulfide-containing 3.5 wt.% NaCl solution

In this work, Cr3C2–NiCr coatings were fabricated by high-velocity oxygen-fuel (HVOF) spraying. Under the help of scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and optical microscope (OM), the phase compositions and microstructure of the coatings were characterized. The long-term corrosion behavior of HVOF sprayed Cr3C2–NiCr coating (HC) and Q345 steel was probed in 3.5 wt.% NaCl solution (S1) and 3.5 wt.% NaCl solution containing 20 ppm Na2S (S2). With the extension of immersion time, the corrosion rate of HC in different solutions showed an overall trend of increasing first and then decreasing. The corrosion rate of Q345 steel in both of the solutions showed a growing trend, while the trend in the sulfide-containing solution was even sharper. The corrosion rates of HC in S1 and S2 were both lower than those of Q345 steels, especially in S2. Owing to the generation of the dense protective film on the HC surface as well as the accumulation of corrosion products, after 70 d of immersion, HC exhibited better corrosion resistance in S2 than that in S1.

A comparative study of the wear performance of hard coatings for nuclear applications

Hard chromium plate (HCP) has been the wear resistant coating of choice in the nuclear industry for decades, but new protective coatings are required as a result of the hazardous nature of Cr(VI) compounds used in electroplating. This study compares the wear performance of candidate replacements materials, Cr2O3 and Cr3C2–NiCr. These two coatings are also compared with HCP and a WC-(W,Cr)2C–Ni coating assessed in an earlier publication.The Cr2O3 and Cr3C2–NiCr coatings were supplied having been applied to Inconel 625 substrates using high velocity oxy fuel (HVOF) and thermal detonation gun spray techniques, respectively. A ball-on-flat sliding wear configuration was used with three environments: dry, deionised water, and borated water to partially simulate nuclear reactor water chemistry. Wear rates were measured using both volume and mass standard metrics. The wear surface samples were characterised using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) in order to establish the operative wear mechanisms.All three candidate coating materials exhibited similar wear performance to HCP in the three test environments. There was, however, enough of a difference between performance in deionised and borated water, to merit the use of borated water in future testing. The data gathered using SEM and XPS provided insight into the wear mechanisms. These include both particle pull-out and tribolayer formation. The XPS data revealed that Cr3C2 is preferentially removed from the Cr3C2–NiCr coating during wear testing in a borated water environment.

Erosion wear behavior of NiCr+Cr3C2–NiCr coating under multi–impact angle and novel coating structure design

Despite advances in NiCr + Cr 3 C 2 –NiCr coating improving the erosion wear resistance at low impact angles, the deterioration at medium and high impact angles has not been solved for the impeller subjecting to multi–impact angle. Herein the conflict is circumvented by combining the erosion performance of the NiCr and Cr 3 C 2 –NiCr under different impact angles and proposing a novel coating structure. First, the NiCr + Cr 3 C 2 –NiCr coating specimens with different NiCr content were prepared using the plasma spraying system. Second, the erosion rate of NiCr + Cr 3 C 2 –NiCr coatings in relation to the impact angle and the concentration of NiCr was measured by an air jet erosion test system, the microhardness was measured on the polished cross-section, and the erosion morphology was observed by SEM and analysed. Erosion behavior analysis showed that the NiCr + Cr 3 C 2 –NiCr coatings exhibited the coupling erosion wear mechanism of high toughness and high hardness, where the dominant characteristic was depending on the concentration of NiCr. Then, a tangential functional gradient coating structure was proposed by combining the excellent erosion wear resistance of ductile and brittle materials at varying impact angles, and a semi-theoretical erosion rate model considering the influence of the NiCr concentration was established based on the deformation wear theory. The erosion rate model was validated by experiments which showed the error was within 9.15%. Consequently, the erosion rate can be regulated on demand along the entire eroded surface, which significantly improves the erosion resistance of cermet at medium and high impact angles, thus prolonging the residual life of remanufactured impeller.

Study of the Microstructure and Properties of Cold Sprayed NiCr Coating

Study of the Microstructure and Properties of Cold Sprayed NiCr Coating

Properties of protective NiCr coatings, deposited by Cold Spray technology

The NiCr coatings, deposited by modern Cold Spray technology, and by well-established Twin Wire Arc Spraying and High Velocity Oxygen Fuel technologies, was studied in terms of microstructure, mechanical, tribological and corrosion properties. Compared to other thermal spraying technologies, CS coatings achieve higher cohesive strength and associated tribological properties. The dense structure is responsible for the coatings’ high corrosion protection ability. The influence of CS technological parameters was found negligible, except the usage of nozzle for internal diameter spraying, which results to significant increase of coatings porosity.

Optimization of operating parameters by SEM in HVOF deposition of NiCr coatings.

Optimization of operating parameters by SEM in HVOF deposition of NiCr coatings.

Enhanced Mechanical, Electrochemical, and Passive Performance of Laser-Clad NiCrAl Coating by Laser Remelting

Enhanced Mechanical, Electrochemical, and Passive Performance of Laser-Clad NiCrAl Coating by Laser Remelting

Obtaining multilayer coatings by the detonation spraying method

This work were studied the effect of technological parameters of detonation spraying on the phase composition and tribological characteristics on the bases of NiCr and Al2O3 coatings. As well as there was obtained and investigated multilayer coating on the bases of NiCr/NiCr- Al2O3/Al2O3 . It was determined that during detonation spraying the phase composition of Al2O3 coatings strongly depends on the degree of filling the borehole with a gas mixture. The a - Al2O3 -phase content in the coatings increases when the degree of filling is 63% and 54%. Only one CrNi3 phase is observed on the diffractograms and only increase of reflex intensity (020) at barrel filling by 58% is observed by sputtering on the bases of NiCr coatings in different degrees of barrel filling. The results of the coating nanohardness study showed that the hardness of the Al2O3 coating increases depending on the content of a- Al2O3 in it. Al2O3 coating has the maximum nanohardness values and is 16.42 GPa at the borehole is filled to 63%. The nanohardness of NiCr coating has the maximum values at barrel filling by 58% and consisting of 8.02 GPa.

Production of TiC – Co and TiC – NiCr Composite Powders and Study of Their Interaction with a Target under Cold Spray Conditions

In the first part of the paper, the effect of mechanical treatment of particles of reacting Ti + C + Me (Me = NiCr or Co) mixtures on the process of self-propagating high-temperature synthesis (SHS) is investigated. It is shown that as a result of SH-synthesis in the free burning mode, a metal-ceramic sinter of high porosity is formed, which is easily destroyed by mechanical action. An increase in the volume fraction of the metal binder (NiCr or Co) leads to a redistribution of the sizes of carbides towards smaller values.In the second part of the paper, the results of cold spraying nickel-chromium alloy particles and cermet particles of the TiC – NiCr composition on an aluminum substrate are presented. Produced NiCr coatings have a high porosity (up to 10 %) and a layered structure with clearly defined contours of individual deformed particles (splats). Due to the high hardness and low plasticity of metal – ceramic particles of the TiC – NiCr composition, during their interaction with the surface of aluminum substrate, continuous coating cannot be produced, only individual adhered particles are observed. With prolonged exposure to the flow of such particles, erosion of the substrate takes place.

Comparative hot corrosion performance of APS and Detonation sprayed CoCrAlY, NiCoCrAlY and NiCr coatings on T91 boiler steel

Hot corrosion performance of Atmospheric Plasma Spray (APS) and Detonation spray (DSC) CoCrAlY, NiCoCrAlY, and NiCr coatings on T91 steel were investigated at 650 °C for 100 cycles under Na2SO4-K2SO4-Fe2O3 mixed salt deposit in ambient air. The hot corrosion resistance of DSC coatings was found to be superior to their APS counterparts. Chromia and spinel oxides provided excellent corrosion resistance while no α-Al2O3 was observed. DSC NiCr and APS NiCoCrAlY offered the most and the least corrosion resistance, respectively. DFT calculation was performed to validate the thermodynamic stability of each oxide and identify the precise oxide formation.

Novel suspension route to incorporate graphene nano-platelets in HVAF-sprayed Cr3C2–NiCr coatings for superior wear performance

Graphene nano platelets (GNP) have several attractive properties, including excellent lubricity that can be used to develop wear-resistant coatings. Thermally sprayed chromium carbideenickel chromium (Cr3C2eNiCr) coatings are widely employed to impart wear resistance to engineering components. This work attempts to improve the wear resistance of high velocity air fuel (HVAF) sprayed Cr3C2eNiCr coatings by incorporating GNP using a hybrid approach in which Cr3C2eNiCr (powder) and GNP (suspension) are co-axially injected. Two different powder-to-suspension delivery ratios were employed in this study that utilizes a liquid feedstock in tandem with a HVAF system. Furthermore, for comparison, a pure (without graphene) Cr3C2eNiCr reference coating was deposited by the HVAF process using identical spray parameters. The as-sprayed coatings were characterized for their microstructure and phase constitution by SEM/EDS and X-Ray Diffraction. Mechanical properties such as hardness and fracture toughness were evaluated using micro-indentation technique. The hybrid coatings were subjected to dry sliding wear tests and wear performance was compared with reference Cr3C2eNiCr. The GNP incorporated hybrid coatings exhibited lower CoF and lower wear rates than the reference Cr3C2eNiCr coating. Post wear SEM/EDS analysis revealed different wear mechanisms predominant in the investigated coatings. Utilizing the above as a case study, this work provides key insights into a new approach to produce GNP incorporated coatings for mitigating wear.

Improving the corrosion resistance of ferritic-martensitic steels at 600 °C in molten solar salt via diffusion coatings

Molten salt corrosion in the receiver's piping system and storage tanks is still one of the major drawbacks of concentrated solar power (CSP) plants and is currently covered by using expensive high-alloyed steels or Ni-base alloys. The employment of cheaper structural materials combined with protective coatings is an attractive alternative to increase cost-efficiency. The present study investigates the corrosion resistance of three different coatings (a pure Ni, a Cr and a combined Ni + Cr coating) deposited on ferritic-martensitic X20CrMoV12-1 steel during isothermal immersion in molten solar salt in comparison to uncoated Ni-base alloy Haynes 230. Exposure tests were conducted at 600 °C for up to 1000 h. To identify the individual role of the main elements, exposure tests of pure Fe, Ni and Cr were undertaken as well. In addition to the cross-sectional investigations via light-optical microscopy and EPMA, X-ray diffraction measurements were conducted to identify the corrosion products. These were complemented by weight change measurements and chemical analysis of the salts after the exposure tests. The study reveals differences between the corrosion behaviour of the different coating approaches, which is discussed as a function of coating composition and degradation mechanisms. Whereas pure Cr or pure Ni coatings offer hardly any improved protection of the uncoated X20CrMoV12-1 substrate, the combined Ni + Cr coating performs very well and improves the scaling behaviour of X20CrMoV12-1 significantly. The outcome highlights the correlation between the solubility of the pure metals Fe, Ni and Cr in molten solar salt and the corrosion resistance of the investigated coatings.

Developing partially oxidized NiCr coatings using the combined flame spray and plasma spray process for improved wear behaviour at high temperature

The powders of NiCrBSiFe and NiCr are partially oxidized using a flame spray process and are deposited on MDN321 steel substrate using a plasma spray process. The effect of partial oxidization on microstructure, microhardness, density, bond strength, and porosity of the coatings is analyzed. The friction and wear behaviour of the coatings was assessed using a pin-on-disc tribometer by varying loads (10, 20 and 30 N), sliding velocities (1, 2 m/s) and temperatures (RT, 200, 400 and 600 °C). Worn surfaces of NiCrBSiFe and NiCr coatings consist of oxide phases of SiO2, NiO, Cr2O3 and NiCr2O4 at elevated temperatures. These phases contributed to reducing the wear rate by five folds in coated steels compared to uncoated steels at 600 °C. The wear rate in coating decreases with an increase in temperature. The coefficient of friction was reduced gradually with the temperature in coatings and substrate. The wear rate coefficient of NiCr coating was 1.7 times higher than the NiCrBSiFe coating.

Structure and Tribological Properties of Ni–Cr–Al-Based Gradient Coating Prepared by Detonation Spraying

In this paper, Ni–Cr–Al coatings were deposited using the detonation spraying method. The aim was to investigate how technological parameters influence coating structure formation, phase composition and tribological performances. We observed that the degree to which the barrel is filled with an O2/C2H2 gas mixture strongly influences the chemical composition of manufactured coatings. High degrees of barrel filling led to a decrease in aluminum content in the coating. Filling degrees of 40% and 50% produced sprayed coatings in which only Ni–Cr phases could be found. When the filling degree was reduced up to 25%, Ni–Al phases began to form in the sprayed coatings. Gradient Ni–Cr–Al coatings were produced by gradually reducing the filling degree from 50% to 25%. These coatings are characterized by Ni–Cr near the substrate level with Ni–Cr and Ni–Al phases at higher levels. The results obtained confirm that gradient Ni–Cr–Al coatings exhibit high hardness as well as good wear resistance.