NiCr Coatings Research Articles

The Mechanical and Tribological Properties of Cold-Sprayed Cermet Coatings—Al Alloy Substrate Systems

AbstractThe article describes the influence of a solid lubricant such as graphite on the coating-substrate adhesion, susceptibility to cracking during three-point bending tests and tribological properties of the cermet coating-substrate systems. Two types of deposits Cr3C2-25(Ni20Cr) and (Cr3C2-25(Ni20Cr))-5(Ni25C), cold-sprayed on the Al 7075 alloy substrate, were analyzed. The Cr3C2-25(Ni20Cr) coatings showed a homogeneous microstructure with evenly distributed ceramic particles in a Ni20Cr matrix. The (Cr3C2-25(Ni20Cr))-5(Ni25C) deposits also contained graphite placed both between metallic particles and near the crushed ceramic Cr3C2 particles. The force required for the crack that appeared in the coating-substrate system during the three-point bending test under constant velocity was significantly higher in the case of (Cr3C2-25(Ni20Cr))-5(Ni25C) deposit than in that without the solid lubricant. The cracks were observed perpendicular to the coating-substrate interface. The graphite embedded in the cermet coating structure prevented the formation of crack nuclei during three-point bending test under cyclic load at room temperature and reduced the size of cracks in the deposit at 200 °C. Both cermet coatings revealed the same adhesion. The addition of graphite not only did not deteriorate the adhesion of the deposits and thus their quality but also improved their other properties, such as flexural strength and wear resistance. Coatings containing the solid lubricant showed a lower wear index than the Cr3C2-25(Ni20Cr) deposits examined at both room and elevated temperatures. This recommends their use in industry as deposit working in heavy wear conditions. The presented results of mechanical tests effectively fill the gap regarding the properties of the cold-sprayed cermet coatings.

STUDIES ON PHYSICAL, MICRO-STRUCTURAL, AND SLURRY EROSION BEHAVIOR OF COLD-SPRAYED Ni–20Cr+TiC+Re COATINGS ON SA516 STEEL FOR HIGH-TEMPERATURE APPLICATIONS

In this paper, three kinds of Ni–20Cr coatings were deposited on SA516 substrate steel by cold-sprayed coating technique. Physical properties (such as hardness, surface roughness, and residual stress) and slurry erosion behavior (with impingement angles of 30∘ and 90∘) of cold-sprayed substrates have been evaluated. Moreover, a scanning electron microscope (SEM) examination has been performed to evaluate the morphological characterization of various coatings. It has been found that the residual stresses induced in the coated specimens exhibited compressive nature. Further, micro-hardness and surface roughness was observed to proliferate with the incorporation of titanium carbide (TiC) and rhenium (Re) in Ni–Cr coatings. Micro-hardness for Ni–20Cr+TiC and Ni–20Cr+TiC+Re was observed at 233.67 and 278.9 Hv, respectively, where Surface roughness for Ni–20Cr+TiC and Ni–20Cr+TiC+Re was observed at 9.86 and 11.68[Formula: see text][Formula: see text]m, respectively. All types of Ni–20Cr coatings were quite efficient in reducing the erosion rate of the SA516 steel as compared to uncoated SA516 and most prominent of all was Ni–20Cr+Tic+Re coating. It was observed that at 30∘, weight loss for Ni–20Cr, Ni–20Cr+TiC and Ni–20Cr+TiC+Re was up to 0.00027, 0.00015 and 0.00012 g/mm2, whereas at 90∘, weight loss was for Ni–20Cr, Ni–20Cr+TiC and Ni–20Cr+TiC+Re was up to 0.00024, 0.00014 and 0.00012 g/mm2.

Structural characteristics and wear, oxidation, hot corrosion behaviors of HVOF sprayed Cr3C2-NiCr hardmetal coatings

It is of great importance to determine the wear, oxidation, and hot corrosion behavior of thermally sprayed Cr3C2-NiCr hardmetal coatings under different conditions, which are widely used in the different industrial applications. In this study, the influence of damage mechanisms such as oxidation, hot corrosion, and wear of Cr3C2-NiCr hardmetal coatings on stainless steel substrates at different temperatures and time periods was investigated. The properties of the coated samples were examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and 3D-optical surface profilometry. Increased time at oxidation tests has indicated that different oxide formations was accelerated by the effect of temperature. It is identified that changes have occurred in the microstructure of the Cr3C2–NiCr coatings depending on high temperature and time. At the oxidation tests, the oxidation layer was increased as a function of time. As a result of the hot corrosion effect, the Na2SO4 and V2O5 powder mixtures melted with the effect of temperature, leaked from the micro cracks, pores and moved from the coating surfaces to the inner regions. The Cr2O3 structure formed as a result of the temperature effect on the coating surface showed a protective feature, increasing the resistance of the coating against oxidation and delaying the formation of damage. Findings from the wear test indicated that the relative sliding motion of the surfaces in contact with the movement of the applied load results in shear stress, which causes friction force to be generated. The friction coefficients increase depending on the load, and as the load increases, resulting in volume losses.

Effect of HVOF processing parameters on [formula omitted] hard coatings deposited on AISI 4140 steel

High Velocity Oxygen Fuel (HVOF) thermal spray coating is a deposition process that is widely employed at present to improve surfaces and the remanufacturing of components subject to severe wear, offering an alternative to reduce the cost of spare parts and used as a substitute for electro-chromium, also generating greater thickness than chemical vapor deposition and physical vapor deposition. This study evaluates the influence of the projected application parameters for Cr3C2-20(Ni20Cr) coatings on AISI 4140 steel using the HVOF technique. To do so, a 24 factorial experimental design was used to evaluate the effect on the thickness, porosity, surface hardness, and microhardness in the cross-section, produced by four of the main operational factors in the HVOF process: the fuel/oxygen (F/O) ratio entering the combustion chamber, powder flow, the roughness of the substrate before deposition, and spray gun speed. The morphology of the Cr3C2-20(Ni20Cr) powders and the microstructure of the coatings were studied through a scanning electron microscope and energy dispersive spectroscopy, while the composition were analyzed by X-ray diffraction. It was determined that: (i) the F/O ratio is the operation parameter with the most significant influence on the properties studied; (ii) the gun speed has a significant effect on the thickness generated and porosity; and (iii) the powder flow and roughness of the substrate have a greater effect on the surface hardness and microhardness. Finally, it was determined that coatings with great thickness, low porosity, and great hardness, ideal for the recovery of parts, can be achieved from a F/O ratio of 0.45 and a powder flow with the system feeder rotating at 12 rpm, applied to a substrate with a roughness of Ra=18μm, combined with a spray gun speed of 5 mm/s.

SLIDING WEAR BEHAVIOR OF MARBLE DUST PRE-MIXED WITH NiCr COATINGS ON MILD STEEL SUBSTRATES AT ELEVATED TEMPERATURE

In this research, microsized marble dust is spray-coated on mild steel substrates through a well-designed high-velocity oxy-fuel (HVOF) spraying route. For this, a standard spray set up Hipojet 2700 is used. Marble dust is an ornamental stone waste generated in huge quantities during the depletion and processing of ornamental stones to make them usable. Commercially available spray-grade NiCr powder is added with a proportion of 10% by weight in the marble dust prior to deposition to increase its flowability and adherence. The coating on the mild steel substrates is deposited with a spray distance of 200[Formula: see text]mm and a fuel (LPG) feed rate of 55–60[Formula: see text]g/min. Dry-sliding wear trials under controlled conditions on the deposited coatings are conducted as per ASTM G 99-05 using a tribometer capable of operating at a wide temperature range. A parametric analysis of the test results using MINITAB 18 software shows that the control factors such as sliding velocity, specimen temperature, sliding distance and normal load, in the declining sequence, are significant in affecting the specific wear rate (SWR) of the coatings. Based on this, further experimentations are carried out separately for a wider range of the sliding velocity and specimen temperature keeping all other factors constant to study their individual effects on the wear rate more precisely. The morphologies of the worn surfaces are studied to ascertain the possible mechanisms taking place during the wear process leading to coating mass loss.

Electrochemical corrosion and solid particle erosion response of Y2O3 dispersed FeAl coatings deposited by detonation spray

The electrochemical corrosion and erosion wear behaviors of detonation sprayed ODS FeAl powder coatings on T91 substrate were investigated. Electrochemical corrosion resistance of the deposited coatings was evaluated in three different aqueous media, namely 3.5 wt% (0.61 M) NaCl, 2 N (1 M) H2SO4 and 3.5 wt% (0.25 M) Na2SO4 and are compared with T91 substrate and detonation sprayed Cr3C2–25NiCr coatings (on T91 substrate). The ODS FeAl coatings shown improved corrosion resistance in 3.5 wt% Na2SO4 than T91 substrate. However, the Cr3C2–25NiCr coatings have shown consistently better corrosion resistance than T91 substrate and ODS FeAl coatings in all the aqueous media. The corrosion mechanisms investigated imply that the higher corrosion rate of FeAl coatings as compared to the Cr3C2–25NiCr coatings is well compensated by the uniform corrosion in the case of former than the localized and intense corrosion in the case of later coatings and substrate material. In contrast, the solid particle erosion wear studies conducted at two different temperatures namely, room temperature (25 °C) and 400 °C have revealed that the ODS FeAl coatings exhibited 4 to 5 times improved wear resistance than that of Cr3C2–25NiCr coatings at room temperature and 1.5 to 2.5 times at a higher temperature (400 °C). Also, the ODS FeAl coatings have performed marginally better than the T91 substrate at both the test temperatures. The results obtained together with the observations made demonstrate a leap step towards the development of novel thermal spray grade feedstock materials as an alternative to industrially well-known Cr3C2–25NiCr coatings and open up a new avenue of techno-economic benefits that can be further explored.

Effect of stoichiometry conditions on the erosion and sliding wear behaviors of Cr3C2-NiCr coatings deposited by a novel ethanol-fueled HVOF process

In this work, a novel ethanol-fueled HVOF process, as the most recently developed liquid fuel HVOF technology, was employed to prepare Cr3C2–25wt%NiCr hard-metal coatings on 304 stainless steel substrates. The influence of different stoichiometry conditions, defined as the oxygen/ethanol ratio, on the evolution of the coating microstructure was investigated in order to correlate with the properties of as-deposited Cr3C2–NiCr coatings. The results showed that the varied stoichiometry factors have little effect on the phase composition of the coating. However, they have a great influence on the microstructure and performances, including porosity, microhardness, fracture toughness, erosion resistance and sliding wear resistance. A denser Cr3C2–NiCr coating with higher erosion resistance is obtained when the stoichiometry factor is <1, being markedly different compared with the results obtained using kerosene-fueled HVOF processes. The stoichiometry factor of kerosene-fueled HVOF processes is generally slightly >1 allowing to obtain a higher quality Cr3C2–NiCr coating. The sliding wear mechanism of Cr3C2–NiCr coatings is attributed to abrasive grooving, peelings induced by cracking, fragmentation and pull-out of carbide grains, as well as delamination and tribo-oxidation.

Study of the Tribological Properties of HVOF-Sprayed Ni-Based Coatings on Ti6Al4V Titanium Alloys

In aviation, the relative sliding between titanium alloy components causes varying degrees of wear. This work aimed at reducing abrasion between titanium alloy parts and improving their service life. Three different Ni-based coatings, WC-10Ni, Ni45, and NiCr coatings, are sprayed on the surface of Ti6Al4V alloy by HVOF. Test results of the mechanical and tribological properties of such coatings show that the hardness of the Ni45 and NiCr coatings are 673 HV0.1 and 438 HV0.1, respectively, which are lower than that of the WC-10Ni coating. When subjected to a high load, the Ni45 and NiCr coatings suffer a cracking of flat particle interfaces due to the low hardness, which lowers the fracture toughness more than that of the WC-10Ni coating. The specific wear rates of the coatings gradually decrease with the increase in the coating hardness and fracture toughness. However, the cutting of Ti6Al4V by the WC-10Ni coating and the adhesion of the NiCr coating to Ti6Al4V result in severe wear loss of the Ti6Al4V friction pair. The moderately hard Ni45 coating has a weaker cutting and adhesion effect on Ti6Al4V than the WC-10Ni and NiCr coatings, respectively, and the Ti6Al4V friction pair has the lowest wear loss. This study is a viable scheme for the design of wear-resistant coatings on titanium alloy surfaces and for improving the tribological properties between titanium alloy components.

Research on Optimizing Spray Parameters for Cr3C2 - NiCr Coating Created on Alloy Steel by Plasma Spraying Technique

Research on Optimizing Spray Parameters for Cr3C2 - NiCr Coating Created on Alloy Steel by Plasma Spraying Technique

Influence of the content of aluminum on the structure of gradient detonation coatings based on NiCr-Al

This paper studies the effects of aluminium content in the composite powder on the structure of detonation gradient coatings based on NiCr-Al. Gradient coatings were obtained by detonation spraying with a gradual stepwise decrease in the barrel filling volume with an acetylene-oxygen gas mixture from 50% to 25%. The elemental and phase composition, microstructure and surface roughness of coatings based on NiCr-Al with different aluminium content of 15%, 20%, and 30% were investigated. By varying the aluminium content in the powder composition, coatings with a gradient structure were obtained. The study results showed that the phase composition of the gradient coating strongly depends on the mass fraction of Al. In the case of an aluminium content of 30% in the composition of the composite powder, the formation of aluminium oxide was detected. It is established that under the same detonation deposition modes, the formation of the gradient structure of coatings will strongly depend on the aluminium content in the NiCr-Al composition. The study results showed that the optimal composition of the powder is NiCr – 80% and Al – 20% to obtain NiCr-Al coatings with a gradient structure.

Corrosion resistance of NiCr(Ti) coatings for metallic bipolar plates

In the present work, the electrochemical behavior of various NiCr(Ti) protective coatings manufactured using laser cladding were studied. The coatings were obtained by adding Ti in different wt% to the NiCr-based feedstock material. Thus, the coatings are investigated as new materials with potential applications for metallic bipolar plates used in polymer electrolyte membrane fuel cell (PEMFC) applications. The electrochemical tests were carried out at room temperature in a solution of H2SO4 0.5 M (pH = 0.3) + 2 ppm F- used as electrolyte. Chronoamperometry measurements were first employed in simulated anodic and cathodic conditions for 6 h. Afterward, electrochemical impedance spectroscopy (EIS) studies were performed in the frequency range of 100 mHz − 100 kHz with an alternative voltage amplitude of 10 mV. The recorded EIS data were fitted with an equivalent electrical circuit (EEC). Furthermore, the potentiodynamic polarization curves were recorded at a scan rate of 1 mV/s in the potential range of −250 mV to + 250 mV versus to the OCP values. Finally, the obtained data were analysed and compared. The studies showed that the corrosion behavior of the studied materials increase with the content of Ti addition.

Ceria-Doped Cr3C2–NiCr Coatings on Austenite Steel for Investigation in Actual Boiler Environment

Ceria-Doped Cr3C2–NiCr Coatings on Austenite Steel for Investigation in Actual Boiler Environment

Laser Surface Alloying of Sintered Stainless Steel.

A characteristic feature of sintered stainless steel (SSS) is its porosity. Porosity results in a lower density of steel, making attractive components for producing lightweight structures and materials used in industry (e.g., the automotive industry or aerospace). Scientists also observe that porosity adversely affects steel’s properties, especially its strength properties. One of the proposals for improving the discussed properties is the use of surface treatment of sintered stainless steels, e.g., with the use of concentrated energy sources such as plasma beams or laser beams. However, this proposal is an incidental subject of research, which is not justified from the point of view of the obtained research results presented by a few research groups. In this study, the surface modification (surface treatment) of sintered stainless steel was presented. The authors proposed the use of two surface treatments in order to compare them and obtain the best results. The first treatment was the deposit of Cr3C2–NiCr coatings on SSS surfaces using the atmospheric plasma spraying (APS) method. The second treatment was to create surface layers on SSSs by laser alloying the surface with a CO2 laser. Due to high precision and ease of automation, the most common methods in surface alloying treatment are laser technologies. This research’s main aim was to analyze the microstructure and strength properties of the SSS surface layer. The research confirms that applying the Cr3C2–NiCr coating and modifying the surface layer through the laser alloying method improves the mechanical properties of SSSs.

Deposition mechanisms and characteristics of nano-modified multimodal Cr3C2–NiCr coatings sprayed by HVOF

Abstract Nano-modified multimodal and conventional Cr3C2–NiCr coatings were fabricated by high-velocity oxygen-fuel spraying deposited on CuCrZr substrates. Results showed that individual nano-modified multimodal Cr3C2–NiCr particles were composed of nano (25−180 nm), submicron (200 nm to 0.5 μm), and micron (2–4.5 μm) Cr3C2 grains, NiCr binder phases, and a tiny amount of rare earth oxide additives. The nano-modified multimodal Cr3C2–NiCr coatings maintained a unique structure: submicron Cr3C2 grains embedded in the voids formed by micron Cr3C2 grains, NiCr binder phases and nano Cr3C2 grains imbedded in the voids formed by submicron and micron Cr3C2 grains, and nano Cr3C2 grains are dispersed in NiCr metal binder phases. A few discontinuous elongated amorphous and nanocrystalline phases existed in them. The mechanical interlocking was the dominant bonding mechanism accompanied by local metallurgical bonds. Compared to the conventional coating, the multimodal coating was uniform and dense (porosity was 0.3 ± 0.12%) as well as not obvious lamellar structures, the adhesive strength was 75.32 ± 1.21 MPa, exhibiting a 65 pct increase, and the microhardness was increased by about 18%. The lower porosity and higher strength of nano-modified multimodal structure coating were mainly related to dispersion distribution and synergistic coupling effects of Cr3C2 hard grains with different scales.

Oxidation performance of TP347H superheater steel after depositing ceria-doped Cr3C2–25NiCr coatings

Oxidation performance of TP347H superheater steel after depositing ceria-doped Cr3C2–25NiCr coatings

Slurry erosion behavior of thermally sprayed ceramic nanocomposite coatings on turbine steel

AbstractThe aim of the present study is to investigate the slurry erosion behavior of nano‐yttria‐stabilized zirconia (YSZ) reinforced Cr3C2–25NiCr ceramic nanocomposite coatings deposited on turbine steel. The Cr3C2–25NiCr coating powder, 95% (Cr3C2–25NiCr) + 5% YSZ, and 90% (Cr3C2–25NiCr) + 10% YSZ nanocomposite coating powder deposited on CA6NM steel samples by using high‐velocity oxy‐fuel coating technique. L9 orthogonal array Taguchi method was used to design the experiment. Erosion tests were performed on erosion test rig under hydro accelerated conditions at different levels of various parameters. Erosion tests and analysis of variance resulted that for coated samples, velocity is the major influencing factor followed by slurry concentration, impact angle, and particle size. Velocity was the largest contributor to the mass loss, whereas particle size has the least contribution to mass loss of the coated samples. The scanning electron microscopy analysis of eroded samples revealed that craters, micropores, platelets, plowing, spalling, and so on were responsible for the mass loss of uncoated and coated samples. The incorporation of YSZ nanoparticles decreased the porosity; erodent particles cannot penetrate more deeply inside the workpiece and resulted in less erosion. It has been resulted that 95% (Cr3C2–25NiCr) + 5% YSZ and 90% (Cr3C2–25NiCr) + 10% YSZ ceramic nanocomposite coatings exhibited better erosion resistance as compared to Cr3C2–25NiCr coatings due to high microhardness and low porosity.

Hot-corrosion behaviour of CNT reinforced Cr3C2-NiCr coatings working under high-temperature sprayed by HVOF method

The thermal power plant boiler tubes experience degradation of their surfaces due to oxidation and molten salt corrosion while working at elevated temperatures. The formation of protective coating layers can overcome such surface degradation. In the current research, protective coated layers composed of Cr3C2-25% NiCr/Carbon nanotube coatings are deposited on the ASTM SA-213T12 boiler tube substrate by the High-Velocity Oxy-Fuel (HVOF) thermal method. The coating powder Cr3C2-25%NiCr is reinforced with 3, 5 and 7 wt% of Multi-Wall Carbon Nano-Tube (MWCNT) prior to deposition. The uncoated and coated specimens are evaluated for hot corrosion behaviour in the molten salt environment (Na2SO4 + 60%V2O5) for 50 cycles, constituting 1 h of heating at 600 °C. Thermogravimetric analysis is used to investigate the kinetics of hot corrosion behaviour in both coated and uncoated samples. Coatings are characterized with the help of X-ray diffraction and Scanning Electron Microscope/Energy Dispersive Spectroscopy (SEM/EDS) techniques. Microstructural investigations with the help of SEM/EDS and X-ray diffraction of coated and uncoated samples revealed that 7 wt% of CNT coated samples minimized the voids and pores of the coatings, leading to better interlocking with the substrate surface. Furthermore, it is observed in the studies that the appreciable corrosion resistance of 7 wt% of CNT composite coatings is higher than 3 and 5 wt% of CNT-coated and uncoated samples.

A novel strategy to apply metallic nanoparticles to manufacture NiCrAl composite coatings smartly growing chromia and alumina

Formation of external scale rather than internal particles of chromia and alumina is of great importance for Cr- and Al-containing metallic materials to resist oxidation at high temperatures. Here we report a new strategy to apply metallic nanoparticles rich in Cr and Al to manufacture oxidation-resistant NiCrAl coatings with a well-designed structure, which can not only make the external oxide scale formation a quick and easy process but also be manufactured by simple electroplating and electrophorestic deposition following an established oxide map, so as to allow the composite coatings to smartly develop the best oxide scale against specific oxidizing environments. The method can be used to economically and systematically manufacture the MCrAlY (M = Ni, Co, or their combinations) coatings on superalloys and the metal-ceramic diffusion barriers between them.

Effect of heat treatment on corrosion resistance of supersonic atmospheric plasma-sprayed Cr3C2–NiCr coating

Supersonic atmospheric plasma spraying (SAPS) is a newly developed technique in preparing high-performance Cr3C2–NiCr coatings with a high deposition efficiency. In this work, the effect of post-heat treatment on carbide precipitation and corrosion property of the SAPS Cr3C2–NiCr coatings was investigated. The results suggested that heat treatment induced the precipitation of secondary carbide grains, and the size of these carbides increased with the increasing heat treatment temperature. In addition, the self-corrosion current density of the coatings thermally treated at 500∘C was seven times smaller than that of the coating without heat treatment. The corrosion morphology showed that significant corrosion cracks were present on the as-sprayed coating. In contrast, the heat-treated coatings demonstrated small corrosion holes due to the formation of small corrosion galvanic cells between the precipitation of carbides and the substrate.

Resistance to slurry erosion by WC-10Co-4Cr and Cr3C2 − 25(Ni20Cr) coatings deposited by HVOF stainless steel F6NM

Hydroelectric turbine machinery experience extreme wear and tear due to slurry erosion and is one of the leading causes for the unplanned shutdown of hydro power plants. The coatings produced by High-velocity oxy-fuel (HVOF) thermal spray process on different hydro-turbine parts is known for improving wear resistance. In the present study, WC-10Co-4Cr and Cr3C2 − 25(Ni20Cr) coatings were sprayed by HVOF process on F6NM stainless steel of Dul-Hasti hydro-power plant turbine material. The slurry erosive wear studies of developed coatings was performed using high speed slurry erosive wear tester. Sediments collected from Dul-Hasti power plant dam site was taken as erodent material. The effect of four parameters specifically rotational speed (500–1250 rpm), slurry concentration (25–40 wt%), sand particle size (125–425 μm), and test duration (450–900 min) on slurry erosion of coated materials was studied. It was observed that among all the developed three coatings, the WC-10Co-4Cr coated samples has shown superior erosion resistance compared to Cr3C2 − 25(Ni20Cr) coated samples due to its improved micro-hardness. Both the developed coatings were observed to be useful in enhancing the erosion resistance of F6NM steel significantly. Erosion mechanism were studied in detail using SEM. The properties such as hardness and porosity were also examined.