Iron Substrate Research Articles

Electrochemical Corrosion Behavior and Microstructural Characterization of HVOF Sprayed Inconel-718 Coating on Gray Cast Iron

In the present work, Inconel-718 (IN718) coating was developed on a gray cast iron (C.I) substrate by utilizing a high-velocity oxy-fuel spray technique. The microstructural analysis was performed to know the topological characteristics of the deposited IN718 coating. Corrosion testing of bare and coated samples was carried out at an ambient temperature in a NaCl solution (3.5 wt.%) using potentiodynamic polarization technique. The kinetics of corrosion and surface characteristics of the as-sprayed and corroded coatings were studied by scanning electron microscopy/energy-dispersive spectroscopy techniques. The different phases in the feedstock powder and as-sprayed coating were determined through X-ray diffraction analysis. The reported average microhardness value of the developed IN718 coating was 563 ± 15 HV0.2. The increased hardness of the IN718 coating is credited to the existence of Mo and Ti elements in the IN718 coatings. Corrosion testing showed that the IN718 coating exhibited the maximum corrosion resistance compared to a C.I. substrate due to a stable passive layer in the IN718 specimen.

Electroless Deposition of Ni-Sn Layers Having High Sn Content（＞30 at.%）on Fe Substrates（2）

Electroless deposition of nickel-tin（Ni-Sn）layers on iron（Fe）substrates from baths containing sodium hypophosphite（NaH2PO2）as a reducing agent was examined. In a bath containing both sodium citrate（Na3C6H5O7）and sodium gluconate（HOCH2 （CHOH）4COONa）as com plexing agents, the Ni-Sn layer having 1 μm thickness and atomic Sn content of 30-40 at.% was formed. The bath stability was maintained until the 10th deposition process. Optimizing the concentration ratios of sodium citrate to sodium gluconate and to sodium stannate（Na2SnO3）was important to ascertain the Ni-Sn layer properties for this study. The main component of the Ni-Sn layer was found to be Ni1.5Sn. A small amount of the Ni layer was included in the layer. Results confirmed that the Ni-Sn layer formed from the optimized bath with NaH2PO2/ Na3C6H5O7/ HOCH2 （CHOH）4COONa had nearly perfect chemical resistance properties against hydrogen peroxide and sodium hydroxide aqueous solutions.

STRUCTURAL TRANSFORMATION OF THE NICRMNSI – FE NANODISPERSE SYSTEM IN A CORROSIVE ENVIRONMENT

Structural changes in the NiCrMnSi nanodisperse system deposited on a metal Fe substrate by the HVOF method in a CORROSIVE H2S medium (pH-2,4) were studied. Structural transformation in the NiCrMnSi - Fe system is caused by the oxidation process in a hydrogen sulfide-containing medium. It was found that 216 hours later, when interacting with a corrosive medium, the boundary zone of the interfacial boundaries of the iron substrate with the NiCrMnSi nanodisperse system was destroyed. The evolution of the destruction of the border zone is studied using the IMAGEJ software package.

Tribological Properties of Chromium Nitride on the Cylinder Liner under the Influence of High Temperature.

The chromium nitride coating is a hard coating used to improve the sliding friction and wear behavior and is applied to engine components in various operating conditions even at an elevated temperature. In this study, chromium nitride was deposited by a physical vapor deposition process onto the cast iron substrate. All tribological tests were performed on linear reciprocating tribometer with a stroke length of 5 mm in a dry condition at variable temperature levels of 28 °C, 100 °C, 200 °C, and of 300 °C corresponding to loads of 10 N, 20 N, 30 N, and 40 N against the cylinder liner material. The worn surfaces of chromium nitride(CrN) coatings after friction tests were analyzed by scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS). The results showed that friction coefficients (COF) ranged from 0.93 to 0.34 from room temperature to 300 °C against the cylinder liner material as a counter-body of 6 mm in diameter; higher temperature results in the positive tribological performance of CrN, with at least 0.34 COF at 300 °C. The wear mechanisms of CrN and counter-body surfaces are abrasive wear accompanied by the slight oxidation. This study guides the wear behavior of cylinder liner coatings in an environment similar to the engine.

Inexpensive and robust iron-based electrode substrates for water electrolysis and energy storage

The instability of iron under anodic conditions makes iron-based electrode substrates unsuitable for alkaline electrolyzers and rechargeable alkaline batteries. Therefore, significantly more expensive substrates such as nickel foam or sintered nickel are used. Nickel adds a significant cost to electrolysis and energy storage systems. We show that iron substrates can be stabilized using a unique protective thermal coating. These coatings can also yield some of the most electrocatalytically active electrodes in addition to showing no notable change in performance even after 1500 h of anodic polarization. Besides sintered iron, low-carbon steel mesh can be stabilized similarly. Low-carbon steel protected by a thin layer of lithium-doped cobalt spinel was found to be an excellent current collector for positive nickel hydroxide electrodes in alkaline batteries. Thus, surface-modified iron substrates, 40 times less expensive than nickel, are promising for lowering the material costs of alkaline water electrolyzers and rechargeable alkaline batteries.

A study on processing and hot corrosion behaviour of HVOF sprayed Inconel718-nano Al2O3 coatings

In the present work, processing and hot corrosion behaviour of Inconel718-nano-Al2O3 based composite coatings with varying nano-Al2O3 contents (10, 20 and 30 wt. %) was studied. The nano-Al2O3 powders were synthesised by using manual granulation technique. The composite coatings were deposited on grey cast iron (GCI) substrate by using a high-velocity oxy-fuel process (HVOF). Hot corrosion behaviour of bare and coated specimens was determined at 900 °C in a high-temperature furnace for 50 h. The weight change data was used to establish the oxidation kinetics of bare and coated specimens. The coating with the highest proportion of nano-Al2O3 content exhibited the maximum hardness and corrosion resistance. The nano-sized alumina particles enhanced the hardness of the coatings by posing a higher constraint to the plastic deformation during the indentation. The presence of nano-Al2O3 and various protective oxides (Cr2O3, NiCr2O4, and TiO2) resulted in the improved corrosion resistance of coatings in comparison to the GCI substrate.

Tribological properties of PDA + PTFE coating in oil-lubricated condition

In this study, the tribological properties of 45 ± 2 μm-thick polytetrafluoroethylene (PTFE) and polydopamine (PDA) + PTFE coatings in oil-lubricated conditions were investigated under a normal load of 10 N and a linear reciprocating speed of 0.1 m/s. Both the PTFE and the PDA + PTFE coatings were deposited using an in-house spray-coating method. The PDA + PTFE coating was five times more durable compared to the PTFE coating in oil-lubricated conditions. Both PTFE and PDA + PTFE coatings showed lower COF in oil-lubricated conditions than in dry conditions. The nanomechanical properties measured by PeakForce Quantitative Nanomechanical (PFQNM) characterization method showed an increase in Young’s modulus and adhesion force for the PDA + PTFE coatings compared to the PTFE coatings. Chemical analysis showed that the cross-linking between PDA and PTFE polymer chains occurred during the high-temperature sintering procedure. The higher adhesion of PDA + PTFE coating to the cast iron substrate and the stronger cohesion due to the cross-linking between PDA and PTFE contributed to the higher durability of the PDA + PTFE composite coatings.

An ultra-stretchable glycerol-ionic hybrid hydrogel with reversible gelid adhesion

Functional hydrogels have attracted enormous interest as wet adhesives for biomedical research and engineering applications. However, reversible hydrogel adhesives that can be used for gelid conditions were rarely reported. In this work, we have developed a freezing-tolerant (freezing temperature < −50 °C), ultra-stretchable (stretch strain > 30000% at 25 °C) glycerol-ionic hydrogel via the ultraviolet curing of acrylamide monomer and hyper-branched polyethylenimine polymer in CaCl2-water-glycerol solution. The fabricated hydrogel exhibited reversible gelid adhesion, rapid self-healing (recover in 3 s) and weight-retaining (>2 weeks) properties. The hydrogel allows two iron substrates to adhere together at −40 °C with the lap-shear adhesion strength as high as ~1 MPa. Such strong adhesion measured was reversible, specifically achieving ~100% of initial adhesion strength at 25 °C and ~36% at −40 °C. Additionally, decreasing the testing temperature significantly improved the tensile strength but decreased the fracture strain of the hydrogel. Interestingly, lap-shear adhesion tests suggested that the gelid adhesion strength was enhanced by 130 times as the testing temperature decreased from 25 °C to −40 °C, which was mainly attributed to the enhanced mechanical strength of the bulk hydrogel as well as the increased surface interaction at gel-substrate interfaces. More importantly, the adhesion failure gradually changed from cohesive failure to adhesive failure as the temperature decreased. This work provides new practical and fundamental insights into developing multifunctional freezing-tolerant hydrogel adhesive for gelid conditions.

Diamond Deposition on Iron and Steel Substrates: A Review.

This article presents an overview of the research in chemical vapor deposition (CVD) diamond films on steel substrates. Since the steels are the most commonly used and cost-effective structural materials in modern industry, CVD coating diamond films on steel substrates are extremely important, combining the unique surface properties of diamond with the superior toughness and strength of the core steel substrates, and will open up many new applications in the industry. However, CVD diamond deposition on steel substrates continues to be a persistent problem. We go through the most relevant results of the last two and a half decades, including recent advances in our group. This review discusses the essential reason of the thick catalytic graphite interlayer formed on steel substrates before diamond deposition. The high carbon diffusion in iron would induce severe internal carburization, and then voluminous graphite precipitated from the substrate. In order to hinder the catalytic graphite formation, various methods have been applied for the adherent diamond film deposition, such as pre-imposed various interlayers or multi-interlayers, special controls of the deposition process, the approaches of substrate alloying and so on. We found that adherent diamond films can be directly deposited on Al alloying steel substrates, and then the role of Al alloying element was examined. That is a thin dense amorphous alumina sublayer in situ formed on the alloying substrate, which played a critical role in preventing the formation of graphite phase and consequently enhancing diamond growth and adhesion. The mechanism of Al alloying suggests that the way used to improve hot corrosion resistance is also applicable. Then, some of the hot corrosion resistance methods, such as aluminizing, siliconizing, and so on, which have been used by some researchers examining CVD diamond films on steel substrates, are reviewed. Another way is to prepare diamond-like carbon (DLC) films on steel substrates at low temperature, and then the precipitated graphite from the internal carburization can be effectively avoided. In addition, based on some new findings, the understanding of the diamond nucleation and metastable growth is discussed.

Effect of Vacuum Annealing on the Nickel-Based Coatings Deposited on a CGI Cast Iron through Atmospheric Plasma Spraying

Plasma-sprayed nickel-based self-fusion alloy coatings were annealed in a vacuum at 990, 1020 and 1050 °C for 20 min to increase the bonding between the compacted graphite cast iron substrate and coating, as well as the inner cohesion of the coatings. It was found that nickel and chromium diffused between nickel-based alloy coatings and compacted graphite cast iron substrate. A metallurgical translation zone with a thickness up to 1145 μm formed during the vacuum annealing, which resulted in an enhancement of the adhesion between the coating and substrate. The adhesion strength at room temperature was increased from the as-sprayed coating of 33.4 MPa to the annealed one of 163 MPa. Meanwhile, the adhesion strength at 500 °C reached 146 MPa. Conversely, the inner cohesion of the coating was improved with the particles’ interfaces healed after vacuum annealing. The micro-hardness of the annealed coatings was increased to 902 HV from the as-sprayed one of 578 HV.

Tuning the magnetic properties of cobalt tetraphenylporphyrin films with oxygen exposure

A single molecular layer of cobalt tetraphenylporphyrin grown on top of an iron substrate is exposed to oxygen to investigate the limits of molecule/substrate magnetic coupling.

The evolution of configuration and final state of graphene on rough iron surface

Molecular dynamics simulations are performed to investigate the evolution of configuration and morphology defects, the final strain and strain induced energy state of graphene on rough iron substrate. A series of randomly rough surfaces are modeled to simulate the real iron surface for the first time. The results show that the formation of morphology defects in graphene are mainly caused by the rapid normal displacement and the following shrinking along lateral directions that are both induced by the strong adhesion between graphene and iron. Fortunately, this strong adhesion cannot lead to global strain in whole graphene layers, i.e., the C–C strain are almost localized around the peaks of the asperities. Thus, the deformation energy (~20 meV/C atom) is mainly induced by bond angle bends and dihedral rotations rather than the expansion or compression of bond length. Through statistical analysis, we further find that the strain and deformation energy are linearly dependent on the substrate roughness. Our findings provide insight into tuning the morphology of graphene and the substrate designing of graphene-based devices. As the photoelectric performance of graphene is largely influenced by strain, our study also provides a guiding direction for evaluating the performance of graphene devices.

Fabrication of TiC-Reinforced Surface Layers on Ductile Cast Iron Substrate by Laser Surface Alloying

This chapter presents a novel method for analysis and optimization of the in-situ formation of TiC-reinforced composite surface layers (TRL) on a ductile cast iron substrate during the laser surface alloying process, combining the experimental approach with the computational thermodynamics. The microstructure of the TRLs has been assessed by light optical microscopy, scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction. The results of thermodynamic calculations with the Scheil-Gulliver model showed a good agreement with the experimental results, indicating that the actual solidification path for the analyzed Fe-C-Si-Ti alloy systems under the investigated range of laser processing conditions is close to the Scheil-Gulliver assumption.

Interfacial effect between graphite and iron substrate on basal plane orientation and lubricity of graphite

The role of graphite/substrate interface in low-friction behavior of graphite was investigated. Iron and graphite powder mixtures were plastically deformed in either Ar–H2 or air atmospheres to obtain bare iron or iron oxide surface. Then, graphite particles adhered to and formed interfaces with surfaces. Friction force microscopy revealed that friction on particle surface milled in Ar–H2 atmosphere was obviously higher. X-ray absorption near-edge structure and transmission electron microscopy revealed that although the basal plane of graphite oriented along the oxidized surface, it did not occur along the bare iron surface, which explains the difference in lubricity on each surface.

Intermetallic formation of Al-Fe and Al-Ni phases by ultrafast slurry aluminization (flash aluminizing)

Aluminizing of Fe and Ni-based substrates is a conventional process often made by gas phase related techniques (CVD, pack cementation and above the pack), whereby the coating thickness is controlled by solid-state diffusion. Similar coatings can be achieved by slurry aluminizing where self-propagating high temperature synthesis and solid-state diffusion mechanisms are involved. The present work investigates ultrafast (5 min annealing) aluminization to reduce coating time and compares the results on pure iron and nickel substrates with a conventional slurry aluminizing treatment (2 and 5 h). The use of fast heating ramps (25 and 100 °C/min) led to outwardly diffused coatings even with very high Al slurry activities. On nickel, the coatings were homogeneous while on iron, Kirkendall porosity occurred in the outermost layers due to the great dissolution of Fe in the Al melt and its subsequent outward diffusion towards to the Al source.

The investigation on friction and wear properties of cast iron matrix surface compact vanadium carbide layer

To enhance the wear resistance of cast iron, a cast iron matrix compact vanadium carbide layer was fabricated by two step in-situ solid-phase diffusion processes. The vanadium carbide layer consist of V2C dense layer, V8C7 dense layer, and V8C7/α-Fe gradient transition layer with 7.6 μm, 35.7 μm, and 86.3 μm in thickness, respectively. The friction and wear properties of the compact vanadium carbide layer and the cast iron substrate were evaluated using the pin-on-disc abrasive wear tests and ball-on-flat dry sliding wear tests. Abrasive wear results show that the wear resistance of the compact vanadium carbide layer is 11.67 times higher than that of matrix. The main abrasive wear mechanism is fracture and peel off of vanadium carbide particle. Ball-on-flat dry sliding wear results show that the friction coefficient of the layer increased first and then decreased with the temperature changing from 25 °C to 800 °C. The main friction wear mechanism is spalling at 25 °C, forming mechanical mixture layer at 400 °C, and delamination wear at 800 °C.

Trivalent Chromium Based Conversion Coating Contains Zinc/Zn(OH)2 on Iron Substrates for the Detection of Uric Acid in Biological Samples and Control of Dyeing

Trivalent Chromium Based Conversion Coating Contains Zinc/Zn(OH)2 on Iron Substrates for the Detection of Uric Acid in Biological Samples and Control of Dyeing

Trivalent Chromium Based Conversion Coating Contains Zinc/Zn(OH)2 on Iron Substrates for the Detection of Uric Acid in Biological Samples and Control of Dyeing

Trivalent Chromium Based Conversion Coating Contains Zinc/Zn(OH)2 on Iron Substrates for the Detection of Uric Acid in Biological Samples and Control of Dyeing

Early period corrosion and scaling characteristics of ductile iron pipe for ground water supply with sodium hypochlorite disinfection

The corrosion and scaling phenomenon have crucial impact on drinking water distribution systems (DWDS), which might lead to pipe blockage or leakage, colored water and other chemical stability issues. In this study, a simulating pipe system with continuous water flow was prepared to investigate the characteristics of corrosion and scaling on ductile iron pipe transporting ground water with sodium-hypochlorite (NaOCl) disinfection. Electrochemical assays, such as polarization curves and electrochemical impedance spectra were applied to monitor the corrosion and scaling process. Results showed the morphology and components of scale were closely related with the electrochemical analysis results. The corrosion current density decreased continuously as corrosion and scaling proceeded. The process could be divided into three stages. During Stage I (0–20 days), the corrosion current intensity of low NaOCl dosage experiments (1, 2 mg/L) were higher than those of high NaOCl dosage experiments (5, 10 mg/L). The difference could be explained by different oxidation potentials, pH and CaCO3 deposition. During Stage II (20–80 days), higher proportions of Fe3O4 in scale in experiments with no or low NaOCl dosages restrained the corrosion process and presented smaller corrosion current. Subsequently, the ductile iron surface became passivated and the difference of various NaOCl dosages affecting corrosion and scaling process turned to be negligible during Stage III (80–90 days). A negative linear relationship between the proportion of stable scale component and the corrosion current density was established. Besides the direct corrosion reaction with iron substrate, NaOCl dosing was accompanied by an increase in pH and calcium carbonate precipitation potential values, which affected the early period corrosion and scaling phenomenon greatly.

Graphene Oxide Coatings on Amino Acid Modified Fe Surfaces for Corrosion Inhibition

An effective solution for corrosion protection of metallic carbonyl iron (CI) substrates in strong saline environment (3 M KCl) is demonstrated in this work. A thin layer coating of graphene oxide ...