NiCrBSi Coatings Research Articles

Milling of Complex Surfaces of EN 10060 Steel after HVOF Sprayed NiCrBSi Coatings

The high-velocity oxy-fuel spraying process was used to investigate and improve the surface properties of a workpiece. The research was focused on the spherical surface of a workpiece made of high-strength steel, a ball and socket assembly. After spraying with a nickel alloy, the surface was machined by milling. The coating was carried out as a process in which a very thin layer of coating of the required thickness and the required specific properties, i.e., high Vickers hardness, adhesion to the surface, wear resistance and other important characteristics, which must be respected in other machining methods, was applied to the already finished, heat-prepared metal substrate. This article deals with the milling of complex surfaces of steel substrate EN 10060 after spraying with NiCrBSi alloy. After spraying, a total of 15 milling experiments were performed in order to determine precisely the optimal cutting parameters of milling and surface adhesion, based on newly acquired prediction relations. The main presented results are new relations for the determination of optimal technological milling conditions based on the identification of adhesive sections using derived equations. The new relations were verified and also compared with the current literature in the field.

Microstructure and corrosion resistance of ERNiCrMo-13 and NiCrBSi coatings in simulated coal-fired boiler conditions: The effect of fly-ash composition

This work is devoted to the study of microstructure, corrosion behavior, and deposition formation of ERNiCrMo-13 and NiCrBSi coatings in simulated coal-fired boiler environments. It was found that these coatings applied to TP347 boiler steel by means of arc spraying were comprised of Cr1.12Ni2.88 compound. The hot corrosion tests were performed in simulated flue gases and synthetic fly ashes at 900 °C. The composition (wt%) of synthetic ashes was 75 fly ash + (25 − x) Na2SO4 + x NaCl with varying levels of Na2SO4 and NaCl (x = 0, 3.25, 7.99, and 25). The experimental results showed that NiCrBSi coatings had better corrosion resistance than ERNiCrMo-13 coatings. The corrosion kinetic of the coatings was composed of two stages including a rapid mass gain and a reduction of the mass gain rate due to selective oxidation (stage I) and a mass loss or a larger mass gain rate due to dissolving of oxide scales or deposition of fly ashes (stage II). The high level of NaCl in the fly ashes was responsible for the non-parabolic rate law of the corrosion kinetics, the accelerated corrosion of the coatings, and the internal oxidation of the substrates. The severe corrosion of ERNiCrMo-13 and NiCrBSi coatings occurred in the condition with a high content of NaCl. During corrosion tests, the different compounds such as NiO, Cr2O3, CrO2, NiSi2, and Fe3Cr2Si3O12 were formed on the coating surfaces. The protective Cr2O3 and/or CrO2 scales formed due to the selective oxidation acted as a corrosion barrier in the initial stage, and will lose the protection when the reaction between chromium oxides and NaCl occurs. The oxides and salts were found to be covered on the coatings due to the deposition of the fly ashes. The mechanisms of deposition formation, Cl-induced corrosion, and internal oxidation under the simulated coal-fired boiler conditions are discussed.

Splash involved deposition behavior and erosion mechanism of long laminar plasma sprayed NiCrBSi coatings

The behavior of low-velocity NiCrBSi particles with a high surface temperature of 1800 °C during the long laminar plasma spraying process was studied. During the experiment, the maximum length of the laminar plasma jet exceeded 600 mm, and coatings were obtained using a laminar plasma spray at a wide spray distance ranging from 250 to 500 mm. Interestingly, the coatings obtained at a short spray distance of 250 mm showed special alternate porous and compact lamellar structure with island-like bulges that were evenly distributed on the coating surface. This type of structure was possibly formed by a low-velocity splashes deposition process intensified by the furry-like structure, which can be attributed to vapor phase deposition. The coatings obtained at an extremely long spray distance of 500 mm showed massive cracks. Moreover, the medium-distance sprayed coatings of 350–450 mm showed similar lamellar-like microstructure and mechanical performance because of the similarity in the particle states in the low-energy-gradient laminar plasma jet. Thus, a laminar plasma spray shows great reproducibility and potential for improving the spraying efficiency on an uneven plane.

Wear and microstructural properties of coatings on Weldox 700 steel

Abstract In this study, the wear and microstructure properties of some coatings produced on Weldox 700 steel were investigated via a high-velocity oxygen fuel (HVOF) technique. For the coating types, NiCrBSi, WCCo and CoNiCrAlY-based coatings were selected. Microstructure and phase formation were examined via scanning electron microscopy (SEM), X-ray diffraction and X-ray energy dispersive spectrometry. Wear tests of the substrate and coatings were made using the ball-on-disc method. It can be seen from the SEM images that the coating layers are metallurgically/ mechanically connected to the substrate and have a mostly homogeneous structure. The hardness measurement was taken from the top of the coatings. The hardness values of the coatings were significantly higher than those of the substrate. The coated substrates exhibit a very good tribological performance compared with the substrate. Depending on the load, the wear rate and coefficient of friction of the coatings were much lower as compared with the Weldox 700 steel substrate.

The structural characteristics and contact loading behavior of gas powder laser clad CoNiCrW coating

The microstructure, phase composition, microhardness and micromechanical properties of the laser clad Co-31.8Ni-22.6Cr-4.1W coating, as well as its contact endurance under contact-fatigue loading according to the scheme of the pulsing non-impact “sphere-to-surface” contact, have been studied. It has been found that the phase composition of the coating is γ + CoB + Cr23C6 + Cr(B,C), with the size of the strengthening phases (chromium carbides and carboborides) ranging between 1 and 10 µm. The average microhardness of the coating surface is 810 HV0.1. The process of fatigue degradation of the coating is characterized by a pronounced periodicity, with alternating periods of increasing size of contact damages and periods when it remains unchanged. Using the microindentation data, the ability of the Co-31.8Ni-22.6Cr-4.1W coating to resist mechanical contact action has been estimated and compared with two laser clad NiCrBSi coatings. It has been shown that the microindentation method (single loading) can be used for estimating and comparing the ability of laser clad coatings from alloys of different systems to withstand repeated contact loads if the coatings have identical size of the strengthening phases.

High‐temperature corrosion behaviors of typical nickel alloy coatings in a simulated boiler coal ash/gas environment in the Zhundong region

AbstractThe high‐temperature corrosion behaviors of five nickel alloy coatings used in coal‐fired boilers in the Zhundong region (Xinjiang province) were investigated in simulated coal ash and coal‐combusted flue gas environment at 650°C for 250 and 500 hr. The samples were analyzed by weight gain experiment, X‐ray diffraction test, and scanning electron microscopy technique with energy‐dispersive spectroscopy. The results indicated that the corrosion level is in the order of NiCrMo13 ≈ Hastelloy C‐276 (276) > NiCrBSi > Inconel 718 (718) > 45CT. The compositions of the corrosion scale in five nickel alloy coatings mainly consist of NiO, Ni3S2, and Cr2O3. The enrichment of Cr in the corrosion scale in 45CT, 718, and NiCrBSi coatings inhibits the formation of oxide and sulfide on the coating surface. The presence of W and Mo in nickel alloy coatings accelerates the formation of corrosion products, thus weakening the corrosion resistance of NiCrMo13 and 276 in simulated coal ash and coal‐combusted flue gas environment.

Properties and High-Temperature Wear Behavior of Remelted NiCrBSi Coatings

Remelted NiCrBSi coatings were examined using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction analysis, microhardness and wear testing. After wear tests, the surfaces of the worn samples were examined by 3D profilometry and scanning electron microscopy to investigate the effects of load and temperature on the coefficient of friction and wear resistance. In all the wear experiments, there was a momentary increase in the wear volume and a momentary decrease in the average coefficient of friction values at the elevated test temperatures. This behavior was caused by the stable oxide layer formed on the surface as a consequence of the elevated test temperature. Three dominant wear mechanisms were observed with the NiCrBSi coatings: delamination at room temperature, spalling and adhesion at 250°C, and oxidation at 450°C, whereas in the uncoated samples there was delamination at room temperature, and micro-cracking and oxidation, both at 250°C and 450°C. Remelted NiCrBSi coatings provided better wear resistance and lower coefficient of friction than uncoated STKM-13A steel, especially at higher temperatures.

Particle Size-Dependent Microstructure, Hardness and Electrochemical Corrosion Behavior of Atmospheric Plasma Sprayed NiCrBSi Coatings

Particle size is a critical consideration for many powder coating-related industries since it significantly influences the properties of the produced materials. However, the effect of particle size on the characteristics of plasma sprayed NiCrBSi coatings is not well understood. This work investigates the microstructures, hardness and electrochemical corrosion behavior of plasma sprayed NiCrBSi coatings synthesized using different-sized powders. All coatings mainly consist of Ni, N3B, CrB, Cr7C3 and Cr3C2 phases. The coatings produced by small particles (50–75 μm) exhibit lower porosity (2.0 ± 0.8%). Such coatings show a higher fraction (15.5 vol.%) of the amorphous phase and lower hardness (700 HV0.5) than the counterparts (8.7 vol.% and 760 HV0.5, respectively) produced by large particles (75–100 μm) with higher porosity (3.0 ± 1.6%). Meanwhile, the coatings produced from smaller particles possess a larger number of non-bonded boundaries, leading to the easier penetration of corrosive medium, as well as a higher corrosion current density (0.254 ± 0.062 μA/cm2) and a lower charge transfer resistance (0.37 ± 0.07 MΩ cm2). These distinctions are attributed to particle size-induced different melting degrees and stackings of in-flight particles during deposition.

A Novel Strategy for Depositing Dense Self-fluxing Alloy Coatings with Sufficiently Bonded Splats by One-Step Atmospheric Plasma Spraying

Self-fluxing alloy coatings are usually utilized by spray fusing two-step process for fully dense microstructure and metallurgical bonding to the substrate. The fusing process brings out limitations for coating applications due to the need of high-temperature fusing. In this study, it is found for the first time that metallurgical bonding between NiCrBSi splats can be achieved by deposition of super-hot droplets created by plasma spraying. Thus, a sufficiently dense NiCrBSi coating can be prepared by one-step plasma spraying. NiCrBSi powders with a size range of 30-50 μm were used as typical material for plasma spraying. The particle temperatures were measured by a DPV-2000 thermal spray in-flight particle diagnostic system. The microstructure of coatings was characterized using scanning electron microscopy. Results show that particles can be heated to a significantly high temperature over 2400 °C by the optimal design of the nozzle internal structure, and the plasma-sprayed NiCrBSi coatings are almost fully dense with effective metallurgical interparticle bonding. Based on the numerical simulation result of the interfacial temperature evolution between spreading splat and NiCrBSi substrate, a self-fusing mechanism is proposed for plasma spraying of NiCrBSi. Furthermore, the coating prepared by one-step plasma spraying reveals superior abrasive wear resistance and corrosion resistance as compared with the flame spray and fusing counterpart. It is clearly demonstrated that the new approach to deposit highly dense coatings directly by plasma spraying with self-fusing effect could greatly expand the applications of fluxing alloy coating materials.

Influence on the Microstructure of Laser Cladding NiCrBSi Coatings with Electromagnetic Compound Field

A NiCrBSi coating was produced on a pure iron plate by laser cladding technology. Electric-magnetic compound field was applied in order to improve the quality of coating. The effect of electric-magnetic compound field on the microstructure and the phase composition of coating was investigated by OM and XRD, respectively. The results indicated that the phase composition of the coatings were γ-(Fe,Ni), Cr23C6, Cr7C3, CrB and Ni3B with and without electromagnetic field. Microstructural observation showed that the grains were refined obviously by electromagnetic stirring. The electromagnetic stirring could change the direction of the heat dissipation and changed the direction of the columnar crystal at the bottom of the coating. High qualitative coating without porosity were obtained under electromagnetic field.

EFFECT OF Cr3C2 ADDITION ON THE MICROSTRUCTURE AND PROPERTIES OF LASER CLADDING NiCrBSi COATINGS

In this paper, the enhancement of NiCrBSi coatings by adding Cr3C2 were investigated. The NiCrBSi coatings with different additions of Cr3C2 were produced by laser cladding. The microstructure, hardness and wear resistance of the coatings were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tester and M-200 wear tester. It is found that the main phases in the coatings are [Formula: see text]-Ni, Cr[Formula: see text]C6 and Cr7C3, and they also contain a small amount of CrB, Ni4B3 and Ni3Si2. Moreover, with the increase of Cr3C2 addition, the microhardness and wear resistance of coatings are obviously improved. When the addition of Cr3C2 is 20%, the wear resistance of the coating is the best, and the wear resistance of the coating increased by 191.2% than that of the Cr3C2-free coating. The wear resistance of coating decreases when the addition of Cr3C2 reaches 30%.

GTAW-Pulsed Refusion Patterns of NiCrBSi Thermal Sprayed Coatings

NiCrBSi coatings were produce by Flame Spray on a carbon steel substrate. The “as spray” coatings were refused by means of Pulsed Gas Tungsten Arc Welding (GTAW-P) process, following different patterns and welding procedure, with objective of optimize the coating characteristics and productivity. The patterns evaluated were oscillated triangular (OT) and oscillated sinusoidal (OS). Travel speed and workpiece-electrode distance were also analyzed. On each obtained sample the surface appearance, macro and microstructure on transverse cuts were evaluated, determining penetration, dilution and level of defects, among others features. Microhardness profiles and adherence were also evaluated. The OS pattern show a more uniform profile of the refused thickness, with less dilution with the base material. Travel speed and workpiece-electrode distance have both significant effect on the volume of refused material, affecting dilution and consequently the resultant coating hardness.

Failure Mechanism and Mechanical Characteristics of NiCrBSi Coating

Mechanical properties of NiCrBSi coatings on plain carbon steel substrate prepared by HVOF (High velocity flame spraying) were studied in this work. Sprayed coatings with average thicknesses of 0.25 mm, 0.5 mm and 1 mm were prepared on preheated steel strips and steel strips without preheating. Chemical analysis of the coatings cross‑section offered information about material structure and distribution of chemical elements within the coating. Hardness of the coating was measured with the aim to reveal the influence of coating thickness and coated substrate preheating on coating hardness. Similar hardness was observed regardless coating preparation conditions and thickness. Bend test was used for characterization of failure character of NiCrBSi thermally sprayed coatings under different thermal conditions. Higher coating thickness was beside cracking, accompanied also by coating delamination from the substrate, while also some influence of testing temperature (laboratory temperature vs. ‑50 °C) on coating failure characteristics were observed. No influence of the coating preparation conditions on the coating pull‑off strength was observed.

Effects of spraying conditions on the microstructure and properties of NiCrBSi coatings prepared by internal rotating plasma spraying

NiCrBSi alloy coatings were fabricated via internal rotating plasma spraying (IRPS) inside the cylinder liner and in open space using the same processing parameters. The effects of spraying condition on the microstructural, mechanical and tribological properties of the IRPS coatings were investigated. Simultaneously, the effects of the flow rate of primary gas (FRPG) on the coatings at a short spray distance were thoroughly evaluated. The microstructure, Vickers hardness, bond strength and tribological properties of the coatings were experimentally determined and characterized in detail. The results demonstrated that all coatings fabricated by IRPS had a dense structure and high microhardness. The bond strength and tribological properties were effectively promoted inside the cylinder, in contrast to open space condition. It is also found that coefficient of friction and wear volume of the coatings declined with the increasing of FRPG. Especially, the coatings prepared with FRPG at 100 L⸱min−1 exhibited the lowest friction and best wear resistance despite their higher porosity. The main wear mechanisms were abrasive and fatigue wear for the coatings deposited in open space, while the dominant wear mechanisms for the coatings prepared inside the cylinder were adhesive wear and tribolayer delamination.

Wear and Friction Behavior of NiCrBSi Coatings at Elevated Temperatures

In many hot forming operations, the dies are subjected to high temperatures and high contact pressures. To combat wear problem, it is essential to select the accurate die material, hardness and surface coating for increasing the die life. This paper is an investigation into the use of NiCrBSi coating as a wear-resistant material on the H11 tool steel. The coating was developed by high-velocity oxy-fuel spray and atmospheric plasma spray process. In-depth characterization of the as-sprayed specimens was done by field emission-scanning electron microscopy/energy-dispersive spectroscopy and x-ray diffraction techniques. The mechanical and physical properties of the as-sprayed coatings were measured. Thereafter, the tribological performances of the uncoated and coated specimens were studied on high-temperature pin-on-disk tribometer under two different loads and temperatures ranging from room temperature to 800 °C. Wear mechanisms were mainly oxidative and adhesive at 400 °C and a combination of oxidative wear, abrasive wear and adhesive wear at 800 °C for the HVOF-sprayed and the APS-coated specimens.

Characteristics of Thermally Sprayed Nicrbsi Coatings before and after Electromagnetic Induction Remelting Process

Characteristics of Thermally Sprayed Nicrbsi Coatings before and after Electromagnetic Induction Remelting Process

Automatic remelting and enhanced mechanical performance of a plasma sprayed NiCrBSi coating

Thermal sprayed NiCrBSi coatings often have some shortcomings such as poor cohesion and adhesion, which degrade their properties and are expected to be eliminated by the remelting process. However, there is still a lack of remelting methods combining the advantages of reliability, reproducibility and low-cost. This work developed a remelting method to remelt the as-sprayed NiCrBSi by plasma gun in an automatic mode using optimized parameters. The remelting process reduces the porosity, eliminates the lamellar boundaries and promotes the formation of metallurgical bonding at the coating/substrate interface. Therefore, the hardness (803 HV0.5) and bonding strength (165 MPa) of the remelted NiCrBSi coating are about 22% and 516% higher than the corresponding ones of the as-sprayed NiCrBSi counterpart (hardness: 657 HV0.5; bonding strength: 32 MPa). The remelted NiCrBSi coating also exhibit significantly enhanced wear resistance compared with the substrate and as-sprayed one. Comparison between the remelted NiCrBSi coatings prepared by various remelting methods indicates that the remelting process used in this work is prominently useful for wider industrial applications since it is reliable, reproducible and convenient.

Effect of WC–Co content on the microstructure and properties of NiCrBSi composite coatings fabricated by supersonic plasma spraying

This paper presents our detailed investigation into the effect of the WC–Co content on the microstructure and properties of supersonic plasma sprayed NiCrBSi composite coatings on Inconel 718. The results showed that the NiCrBSi/WC–Co composite consisted predominantly of Ni, Ni3Fe, Ni3B, CrB, WC, Cr7C3, and WFeB2, in addition to lesser amounts of W2C, Cr3Ni2Si, and Co3B. The coating containing 15 wt% WC–Co exhibited the most compact microstructure with the lowest number of defects, as well as the lowest porosity (i.e., 0.6%). The mechanical properties of the as-sprayed coatings were significantly enhanced by the addition of WC–Co. Upon increasing the WC–Co content, the friction coefficients of the as-sprayed coatings increased from 0.59 to 0.74. The main wear mechanisms transformed from abrasive wear coupled with spallation for the NiCrBSi coatings with a low WC–Co content to adhesive wear and fatigue fracture for coatings with a medium WC–Co content, to a combination of brittle fracture failure and slight abrasive wear for coatings with a high WC–Co content. Furthermore, the coating with 15 wt% WC–Co registered a higher microhardness (910.6 HV) and adhesive strength (44.7 MPa), and a lower wear rate (8 × 10−6mm3/(N m)) than the other as-sprayed coatings, indicating that this was the optimal WC–Co content for this type of NiCrBSi-based composite coating on Inconel 718. The synergy between the compact structure, higher microhardness, and adhesive strength was considered responsible for the excellent wear resistance of the NiCrBSi–based composite coating with a WC–Co content of 15 wt%.

Microstructure and Properties of NiCrBSi metal matrix composite coatings by laser processing

The NiCrBSi MMC coatings were formed on the surface steel using laser processing to reinforce the wear resistance of steel substrate. The NiCrBSi MMC layer were composed of the coating zone (CZ) and the bonding zone (BZ). The microstructures and properties of the coatings were investigated. The results showed that the NiCrBSi MMC coatings with no micro-cracks, lamella structures, pores and voids mainly consisted of reticulation structure of Fe-Cr solid solution and blocky structure of Fe-Ni solid solution, which were as solid solution strengthening in CZ. A small quantity of Ni3Si phases and carbide dispersed in interdendritic structure. Compared with the steel substrate, the wear properties of the NiCrBSi coatings significantly improved due to the high hardness chrome dendritic phase and contain hard particles. Consequently, the weight loss after wear test for the NiCrBSi coatings is much less than that of steel substrae.

Ultrafast laser induced NiCrBSi coatings

NiCrBSi composite coating was fabricated on 1045 steel substrate by ultrafast laser induced process. The composite layer consists of the coating zone (CZ) and the bonding zone (BZ). Microstructure and chemical compositions were investigated. The morphology of transverse section revealed that the microstructure of the substrate mingled with that of the coatings in BZ, it was showed that the substrate-coating interface was excellent metallurgical bonding. Reticulation structure of Fe-Cr solid solution and blocky structure of Fe-Ni solid solution were formed as solid solution strengthening in CZ. A small quantity of Ni3Si phases and carbide dispersed in interdendritic structure. Fine particles of carbide and boride precipitated in Fe-Cr reticulation solid solution. The microcracks and pores were eliminated in the homogeneous composite coating, while the coating efficiency was increased.