Iron Substrate Research Articles

Hard-yet-tough high-vanadium hierarchical composite coating: Microstructure and mechanical properties

In this work, we report a high-vanadium hierarchical coating prepared on the surface of nodular cast iron substrate by a low-cost plasma transferred arc (PTA) surface alloying process. The coating consists of a graded layer with an alloyed zone (AZ) rich in submicron sized granular (V-Ti-Nb-Cr-Mo) composite carbides on top of intermediate melted zone characterized by refined ledeburite and martensite. The dense spherical particles in the AZ are FCC structured MC-type (M = V, Ti and Nb) carbides which tend to aggregate while M7C3 and M2C carbides nucleate on MC. The super-lattice V8C7 maintains its cube-on-cube orientation relationship with TiC. The hardness of the AZ is 9.6 ± 1.0 GPa, ~ 4 times that of the substrate. Nano- and micro-indentations point at a superior strength-toughness in the AZ, where cracks are deflected and bridged by the spherical MC carbides in a compressive residue stress state. The fracture mode appears to be rather ductile in the AZ whereas brittle failure appears in both the melted zone and substrate. TEM and EDS results confirm that such a microarchitecture design, assisted by the rapid solidification rate of the PTA process, concurrently activates various strengthening micromechanisms including the precipitation hardening and grain refinement.

Anaerobic ammonium oxidation coupled to iron reduction in constructed wetland mesocosms

Acidimicrobiaceae sp. A6 (referred to as A6) was recently identified as playing a key role in the Feammox process (ammonium oxidation coupled to iron reduction). Two constructed wetlands (CW) were built and bioaugmented with A6 to determine if, under the right conditions, Feammox can be enhanced in CWs by having strata with higher iron content. Hence, the solid stratum in the CWs was sand, and one CW was augmented with ferrihydrite. Vertical ammonium (NH4+) concentration profiles in the CW mesocosms were monitored regularly. After four months of operation, when reducing conditions were established in the CWs, they were inoculated with an enrichment culture containing A6 and monitored for an additional four months, after which they were dismantled and analyzed. During the four-month period after the A6 enrichment culture injection, 25.0 ± 7.3% of NH4+ was removed from the CW with the high iron substrate whereas 11.0 ± 9.7% was removed from the CW with the low iron substrate on average. Since the CW with high NH4+ removal had the same plant density, same bacterial biomass, same fraction of ammonium oxidizing bacteria (AOB), a higher biomass of A6, and a higher pH (NH4+ oxidation by Feammox raises pH, whereas NH4+ oxidation by aerobic AOB decreases pH), this difference in NH4+ removal is attributed to the Feammox process, indicating that wetlands can be constructed to take advantage of the Feammox process for increased NH4+ removal.

Tribological behavior of thin film coating-a review

An automotive industry sectors are facing major challenges to produce materials of high hardness, low wear rate and corrosive resistant due to international intrinsic norms. Scientist and researchers are developing new materials with different surface properties to come over the international intrinsic norms and hence, they are trying to enhance tribological behavior and increase the life of automotive parts, make the parts corrosive resistant. Therefore, it has become essential to explore the new combinations of coating materials. A tribome-chanical effect of hard metal (WC-12 % Co and Cr3C2-25 % NiCr) coating on the cast iron and steel substrate were compared. Micro hardness, porosity, microstructure, corrosion and economical factor were compared and concluded that the hardness of WC-12%Co & Cr3C2-25NiCr coated on mild steel substrate were comparatively superior but the Cr3C2-NiCr coated cast iron substrate was better over WC-12%Co because it was more economical and corrosive resistant and competitive wear characteristics and as the temperature and load are increased, the Cr3C2-NiCr shows excellent wear resistances.

Optimisation of fluorapatite coating synthesis applied to a biodegradable substrate

ABSTRACT Fluorapatite was synthesised using the sol–gel route at three different pH values and aged for a number of days. The coating that was determined to be of optimal morphology was then applied to a pure iron substrate and to an austenitic stainless steel, the latter serving as a control. Deposited fluorapatite coatings were characterised by means of X-ray diffraction and Fourier transform infrared spectroscopy. Crystalline fluorapatite was successfully produced at temperatures as low as 250°C. Temperatures of 250°C and higher caused carbonated fluorapatite, present at 150°C, to transform into fluorapatite. Neutralisation of the sol before coating was found to give rise to a less soluble product when immersed in Hank’s solution at 37°C and 5% CO2. Coatings on pure iron and stainless steel substrates were produced by neutralising the sol to pH 7 and heat treatment at 250°C. This generated a morphology which could potentially aid in cellular attachment.

Corrosion engineering towards efficient oxygen evolution electrodes with stable catalytic activity for over 6000 hours

Although a number of nonprecious materials can exhibit catalytic activity approaching (sometimes even outperforming) that of iridium oxide catalysts for the oxygen evolution reaction, their catalytic lifetimes rarely exceed more than several hundred hours under operating conditions. Here we develop an energy-efficient, cost-effective, scaled-up corrosion engineering method for transforming inexpensive iron substrates (e.g., iron plate and iron foam) into highly active and ultrastable electrodes for oxygen evolution reaction. This synthetic method is achieved via a desired corrosion reaction of iron substrates with oxygen in aqueous solutions containing divalent cations (e.g., nickel) at ambient temperature. This process results in the growth on iron substrates of thin film nanosheet arrays that consist of iron-containing layered double hydroxides, instead of rust. This inexpensive and simple manufacturing technique affords iron-substrate-derived electrodes possessing excellent catalytic activities and activity retention for over 6000 hours at 1000 mA cm-2 current densities.

Influencing the anticorrosion efficiency of pigments based on zinc ferrite by conductive polymers

Abstract Generally, organic coatings which contain zinc ferrites are able to protect metal substrate, most often low-carbon steel, by inhibition mechanism. Conductive polymers are using a system of conjugated double-bonds to transfer a charge over the chain thereby providing their own electrical conductivity in the organic coatings. The charge from the chain in combination with the iron substrate generates electrons to the formation of passivation products on the surface of paint film. This paper is focused on combination of zinc ferrite with conductive polymer and using of synergic effect of these two components. The organic coatings were formulated from hematite and specularite on pigments concentration line 5, 10, 20 and 25 wt.% for better recognizing of the effectiveness of zinc ferrite component. The content of the conductive polymer was consistently set at 3 wt.% in each organic coating. A solvent-based epoxy-ester resin was used as a binder. The physico-mechanical and corrosion tests were performed for all samples. The corrosion signs were evaluated on the surface of coating and also on the surface of metal substrate. In the end, the efficiency was compared alone zinc ferrite and alone polymers and also their combinations.

Microstructure and wear behaviour of Ni-based alloy coated onto grey cast iron using a multi-step induction cladding process

Abstract The purpose of this work was to develop an innovative approach to remanufacturing grey cast iron cylinder liners. Ni-based alloy coatings were fabricated on HT 300 cast iron substrates using a multi-step induction cladding technique. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD) were employed to analyse the microstructure, elemental distribution and phase composition of the coating. The results indicated that the coatings were metallurgically bonded to the substrate, and there were no visible defects and cracks at the interface resulting in failure of the coating. The portion closest to the substrate was rich in γ-Ni solid solution, whereas the intermediate and top portions consisted of boride-, carbide- and Ni-based solid solution eutectics. The microhardness from the top layer of the coating to the interface exhibited a gradual decrease, and the average microhardness of the coating is 877.12 HV0.2, which was four times higher than that of the substrate. The results of dry sliding wear tests showed that the friction coefficient of the Ni-based alloy coating was much more consistent than that of the HT 300 substrate, and the wear loss and roughness of the coating was lower than that of the substrate. The wear mechanism for the coating is light abrasive wear, whereas for the substrate, the wear mechanism is a mixture of severe abrasive and adhesive wear.

Synthesis of large-area multilayer hexagonal boron nitride sheets on iron substrates and its use in resistive switching devices

Hexagonal boron nitride (h-BN) is an attractive insulating material for nanoelectronic devices due to its high reliability as dielectric and excellent compatibility with other two dimensional (2D) materials (e.g. graphene, MoS2). Multilayer h-BN stacks have been readily grown on Cu and Pt substrates via chemical vapor deposition (CVD) approach, confirming its potential for wafer scale integration. However, the growth of h-BN on other substrates needs to be also achieved in order to expand the use of this material. Recently, the CVD growth of monolayer h-BN on Fe substrates was reported, but it just focused on material structure characterization. Here we present the first fabrication of electronic devices using multilayer h-BN dielectric stacks grown on Fe foils. We fabricate and characterize resistive switching (RS) devices based on Au/Ag/h-BN/Fe nanojunctions, and observe the coexistence of both volatile and non-volatile RS depending on the electrode to which the bias is applied. The characteristics measured agree well with those simulated via SIM2RRAM software and QPC modeling, and the cycle-to-cycle variability is slightly lower than that of transition metal oxide based RS devices.

A Versatile Strategy for Characterization and Imaging of Drip Flow Microbial Biofilms.

The inherent architectural and chemical complexities of microbial biofilms mask our understanding of how these communities form, survive, propagate, and influence their surrounding environment. Here we describe a simple and versatile workflow for the cultivation and characterization of model flow-cell-based microbial ecosystems. A customized low-shear drip flow reactor was designed and employed to cultivate single and coculture flow-cell biofilms at the air-liquid interface of several metal surfaces. Pseudomonas putida F1 and Shewanella oneidensis MR-1 were selected as model organisms for this study. The utility and versatility of this platform was demonstrated via the application of several chemical and morphological imaging techniques-including matrix-assisted laser desorption/ionization mass spectrometry imaging, secondary ion mass spectrometry imaging, and scanning electron microscopy-and through the examination of model systems grown on iron substrates of varying compositions. Implementation of these techniques in combination with tandem mass spectrometry and a two-step imaging principal component analysis strategy resulted in the identification and characterization of 23 lipids and 3 oligosaccharides in P. putida F1 biofilms, the discovery of interaction-specific analytes, and the observation of several variations in cell and substrate morphology present during microbially influenced corrosion. The presented workflow is well-suited for examination of both single and multispecies drip flow biofilms and offers a platform for fundamental inquiries into biofilm formation, microbe-microbe interactions, and microbially influenced corrosion.

A Stable and Electrocatalytic Iron Electrode for Oxygen Evolution in Alkaline Water Electrolysis

Iron electrodes disintegrate in alkali at the anodic potentials needed for oxygen evolution. Hence, relatively expensive nickel-based electrodes and substrates have been the workhorse of materials for industrial water electrolysis. We report here a novel surface-modification method that transforms iron into an electrocatalytically-active and robust oxygen evolution electrode for alkaline water electrolysis. This surface modification consists of an electrochemical oxidation step followed by a thermal decomposition step. The electrochemical oxidation of the iron substrate in alkali transformed the surface to high surface area iron(II) hydroxide with a coral-like morphology that converted to magnetite upon heat treatment. On this high-surface area substrate an electrocatalytic layer of amorphous nickel hydroxide was produced by the thermal decomposition step. Such a surface-modified iron electrode exhibited an extremely low overpotential of 195 mV at 10 mA/cm2 and a low Tafel slope of 43 mV/decade. The electrochemical oxidation step during preparation results in doubling of the electrochemically active area. Even after 1500 h of oxygen evolution at 10 mA/cm2, there was no noticeable change in the electrode potential, morphology, or surface composition of these iron electrodes. This durability was attributed to the conductive oxide layer of magnetite that protects iron surface at the anodic potentials of oxygen evolution. The remarkable electrocatalytic activity was attributed to the amorphous layer of nickel hydroxide. Development of such a robust and electrochemically-active iron electrode presents a unique opportunity for the advancement of alkaline water electrolysis.

Corrosion influence on the evaporation of sessile droplet

The influence of the corrosion on the evaporation of sessile droplet of sodium chloride solution was quantitatively investigated at a relative humidity of 0%. On planar surface, sessile saline droplets evaporated in the pinned, constant contact area mode. The time of evaporation of a sessile saline droplet is much longer on iron substrate than on silicon. This is due to the initiation of corrosion phenomenon. At low and intermediate salt concentrations, the inverse of the classical Evans model is observed due to the evaporation time which is fast and the hydrodynamic flows linked to evaporation. Increasing salt concentration leads to the same evaporation rate for iron and silicon. This study shows that the conditions of evaporation will influence both the evaporation itself and the corrosion phenomenon.

DLC deposited onto nitrided grey and nodular cast iron substrates: An unexpected tribological behaviour

Abstract In the pursuit of suitable alternative substrate materials for DLC coatings, grey cast iron (GCI) and nodular cast iron (NCI) stand out due their vast industrial applications, consequence of its sufficient mechanical strength associated with low cost. However, graphite flakes and nodules introduce critical discontinuities on these metallic surfaces. In the present work, the effect of graphite morphology on the tribological behaviour of DLC (a-C:H) obtained via PECVD is analyzed. Scuffing resistance was accessed using dry reciprocating sliding tests, where GCI presented a friction coefficient of 0.06 during a lubricious regime whereas NCI presented μ=0.14. Thus, active friction reduction mechanisms were investigated using additional interrupted tests. The wear tracks were analyzed revealing how tribolayers morphology and chemical nature modified friction.

Structure and Corrosion Behavior of Arc-Sprayed Zn-Al Coatings on Ductile Iron Substrate

In this research, four coatings including pure zinc, pure aluminum, a double-layered coating of zinc and aluminum, and a coating produced by simultaneous deposition of zinc and aluminum were deposited on a cast iron substrate using electric arc-spraying technique. The coatings were characterized by XRD, SEM and EDS map and spot analyses. Adhesion strength of the coatings was evaluated by three-point bending tests, where double-layered coating indicated the lowest bending angle among the specimens, with detection of cracks at the coating–substrate interface. Coatings produced by simultaneous deposition of zinc and aluminum possessed a relatively uniform distribution of both metals. In order to evaluate the corrosion behavior of the coatings, cyclic polarization and salt spray tests were conducted. Accordingly, pure aluminum coating showed susceptibility to pitting corrosion and other coatings underwent uniform corrosion. For double-layered coating, SEM micrographs revealed zinc corrosion products as flaky particles in the pores formed by pitting on the surface, an indication of penetration of corrosion products from the lower layer (zinc) to the top layer (aluminum). All coatings experienced higher negative corrosion potentials than the iron substrate, indicative of their sacrificial behavior.

Comparative Analysis of the Microstructural Features of 28 wt.% Cr Cast Iron Fabricated by Pulsed Plasma Deposition and Conventional Casting

The effect of pulsed plasma deposition (by an electrothermal axial plasma accelerator) followed by post-heat treatment on the structure and microhardness of a 28 wt.% Cr white cast iron is analyzed and discussed with respect to the microstructure of the conventionally cast monolithic counterpart. The cast iron (as deposited on a 14 wt.% Cr cast iron substrate) had a microhardness of 630-750 HV0.05; it had layered light contrast/dark contrast structure where dark contrast layers contain fine carbide network. Pulsed plasma deposition followed by heat treatment resulted in a substantial refinement of the microstructure: eutectic M7C3 coarse acicular plates in the conventional cast iron were replaced by fine M7C3, M3C2, M3C particles (Cr depleted in favor of Fe), while the initial carbide particle of 2-3 μm was reduced to 0.6 μm. Secondary dendrite arm spacing decreased from 15 to 1.3 μm, accordingly. The carbide volume fraction in the post-heat-treated coating remarkably increased with respect to the conventional counterpart resulting in a substantial increase in the coating hardness (1300-1750 HV0.05). The heat-treated coating displayed higher resistance to three-body abrasion than the as-deposited coating and similar resistance with that of the conventionally cast iron.

An Efficient and Robust Surface-Modified Iron Electrode for Oxygen Evolution in Alkaline Water Electrolysis

Iron is unstable as an oxygen evolution electrode in alkaline media. Thus, relatively expensive nickel-based electrodes are used in industrial alkaline water electrolysis. We show that an iron substrate can be rendered stable and electrocatalytically active for the oxygen evolution reaction by nano-scale surface modification with nickel. The electrocatalytic activity of such a surface-modified iron electrode is comparable to the recently-reported nickel-based catalysts. The electrocatalytic activity is due to a 50-nanometer layer of a high-surface area α-nickel hydroxide on the iron electrode. The nickel modification renders the iron electrode electrically-conductive, prevents dielectric breakdown, and thus endows anodic stability. The electrocatalytic activity is unchanged even after 1000 hours of continuous operation. The temperature of preparation is critical, as excessive dehydration of the hydroxide layer results in nickel ferrite formation and a drastic reduction in electrocatalytic activity. We report significant insight into the surface chemical composition and structure of the catalyst layer by X-ray Absorption Spectroscopy, Photoelectron Spectroscopy, and Transmission Electron Microscopy. Electrochemical kinetics analysis suggests that surface hydroxo-intermediates react with the hydroxide ions from the solution to evolve oxygen. Thus, the surface-modified iron substrates present an opportunity for improving the performance and reducing the cost of alkaline water electrolysis systems.

Influence of Graphene Oxide Content on the Zn-Gr Composite Layer Prepared by Pulse Reverse Electro-plating

The Zinc (Zn)-graphene (Gr) composite layer was prepared successfully by using a pulse reverse electro-plating method on the iron substrate. Effect of GO content in the electrolyte on the microstructures of the composite layer and the corrosion behaviors in the 3.5 wt% NaCl solution were also investigated in detail by using scanning electron microscope (SEM), X-Ray Diffraction (XRD) and a series of electrochemical measurements. The results revealed that: 1) GO can be reduced into Gr during the co-deposition of electro-plating; 2) adding GO in the electrolyte changed the Zn growth mechanism in the composite layer, i.e., gradually transforming from the main preferred orientations of (112) and (101) crystal planes into (103), (102) and (110) planes 3) there is an optimal GO adding amount in a range 0.3–0.5g/L in the electrolyte, at which the Zn-Gr composite layer exhibited the highest corrosion resistance and corrosion current density just be a hundredth comparing with that of pure Zn layer in simulated seawater environment; 4) the Zn-Gr composite layer is of a strong adhesion with the substrate. The present work is expected to provide basic data for future practical applications in galvanized steel used for corrosion environment.

The Effect of Phase Continuity on the Cathodic Delamination Resistance of Polyaniline Based Coatings

Organic coatings based on electrically conducting polyaniline emeraldine salts (ES) and electrically insulating polyvinyl butyral (PVB) are applied to an iron substrate. An investigation is made into how ES phase continuity, and in-coating charge percolation, affect the kinetics and mechanism of corrosion driven cathodic coating delamination. Bilayer coatings are prepared by solution casting continuous ES films onto the substrate, then overcoating with PVB. These are compared with composite coatings of decreased phase continuity, prepared using ES powders dispersed in PVB. Coating delamination is followed using scanning Kelvin probe potentiometry and optical spectrophotometry. At ES coating weights < 0.05 mg.cm−2, delamination rate was inversely proportional to coating weight and slower for bilayer coatings. The same trend was found at higher coating weights for ES doped using camphorsulfonic acid. However, for ES doped with phenylphosphonic acid, bilayer coating delamination rates became independent of ES coating weight > 0.05 mg.cm−2 and were greater than for dispersion coatings. The relationship between cathodic delamination rate and PAni ES continuity is proposed to depend strongly upon the nature and continuity of the interphase formed between the PAni ES coating and iron, and therefore on the dopant anion identity.

Effect of Surface Textures of Iron substrate on the Crystal Orientation Relationship between Electrodeposited Zinc and Iron

Effect of Surface Textures of Iron substrate on the Crystal Orientation Relationship between Electrodeposited Zinc and Iron

Electrochemical Hydrogen Permeation Properties of MoS2 and Ni80Cr20 Films Prepared by Magnetron Sputtering on Pure Iron

Single-layer MoS2 and Ni80Cr20, as well as a double-layer Ni80Cr20/MoS2, films were fabricated on pure iron substrate by magnetron sputtering, and their hydrogen permeation properties were investigated by electrochemical hydrogen permeation experiments. It was found that the single-layer MoS2 or Ni80Cr20 could act as a barrier effectively retarding hydrogen permeation toward the substrate due to their lower diffusion coefficient. Using the overpotential stepping hydrogen permeation test (OSHPT), the lattice diffusion coefficient (DL) of hydrogen in MoS2 and Ni80Cr20 films was determined to be 8.35 × 10−8 and 1.76 × 10−9 cm2/s, respectively. Furthermore, it was observed that the use of Ni80Cr20 as the intermediate layer not only could improve the surface state of MoS2 after hydrogen permeation but also enhanced the effect of retarding hydrogen permeation in the double-layer Ni80Cr20/MoS2 film. In addition, the influences of MoS2 and Ni80Cr20 films on the hydrogen evolution reaction (HER) were also investigated.

Effect of NiCr on dry sliding wear of high carbon iron-molybdenum composite plasma spray coating

The primary area of research under consideration is the wear behaviour of the cylinder liner and piston ring. Since coating can increase hardenability, toughness and wear resistance of the substrate (piston ring), the thermal spray techniques were used for piston ring coatings. In this study, a powder mixture of the iron-molybdenum composite, NiCr, CrC, and molybdenum was deposited by atmospheric plasma spray method on cast iron substrate with increasing NiCr composition from 10 to 50 wt.% in the interval of ten. With the increase of NiCr percentage, the coefficient of friction (CoF) and specific wear rate of the coating decreases. This reduction was due to excellent resistance to high-temperature oxidation, corrosion and good wear resistance of NiCr. The cylinder liner (cast iron) was used as the counter body for the test. The pin-on-disk test was used to investigate the tribological property of piston ring coatings.