Chromium Coatings Research Articles

Development of Cr and Al Pack Cementation Coatings on Co-Based γ/γ′ Superalloys

Co-based superalloys have been developed as candidate materials to replace Ni-based superalloys in hot sections of turbine engines, however, their oxidation resistance is limited. Therefore, in this work chromium and aluminum diffusion coatings were developed via the pack cementation process for novel γ/γ′-strengthened superalloys of the Co–Ni–Al–W system. This alloy system also offers the opportunity to vary the cobalt-to-nickel ratio and the tungsten content systematically to investigate their influence on the coating process. The coating process was shown to successfully enrich the surfaces of such alloys either in aluminum or chromium. For Al, the result was the formation of (Co, Ni)Al on top of an interdiffusion zone, while for chromium a Cr-rich layer in solid solution with the substrate along with the formation of σ-phase were observed. The coating formation mechanisms are discussed for both coatings in the light of activities and phase formation.

Preliminary Analysis of Reactivity Feedbacks for Inner-Side Chromium Coating

Abstract Protective coatings were proposed as near-term concepts to enhance the accident tolerance of nuclear fuel claddings; it is expected to improve corrosion resistance in severe events, and enhance cladding performance during normal operation, without introducing major design changes. Various aspects such as corrosion resistance, thermal and neutronic performances are being evaluated. However, the fact that inner uncoated side of fuel cladding may expose to the oxidizing environment under some circumstances is still a concern. Thus, a complementary inner-side coating was proposed. Metallic chromium is extensively studied as a potential coating material, and showed promising performance. Neutronic penalties are expected if chromium used as protective coating. In this study, reactor's inherent safety feedback, when chromium coatings used for fuel claddings inner-side protection, is evaluated and compared with the case of using external coatings. These parameters have not been studied before. Five different coating thicknesses were used in this evaluation. Results showed that inner side coatings will induce less negative moderator temperature feed backs, while feedback to changes in fuel temperature will be more negative than the reference uncoated case. Boron coefficient was found to be less negative compared to the reference. It was found that each coating thickness will induce unique changes in neutrons flux; generally, there will be reduction in thermal portion of neutron flux, which will be less for the case of inner-side coatings, when compared to external coatings. The magnitude of feedback varies from thickness to another. Reactivity feedbacks also calculated for some cases where inner and external coatings used simultaneously, results showed similar behavior, with the magnitude varying from a combination to another. The presence of chromium coatings will introduce some changes in reactor's neutron flux; nevertheless, the reactor will still keep its inherent negative feedback to changes in different operation parameters studied.

Stabilizing the Unstable: Chromium Coating on NiMo Electrode for Enhanced Stability in Intermittent Water Electrolysis.

Hydrogen production through water electrolysis is a promising method to utilize renewable energy in the context of urgent need to phase out fossil fuels. Nickel-molybdenum (NiMo) electrodes are among the best performing non-noble metal-based electrodes for hydrogen evolution reaction in alkaline media (alkaline HER). Albeit exhibiting stable performance in electrolysis at a constant power supply (i.e., constant electrolysis), NiMo electrodes suffer from performance degradation in electrolysis at an intermittent power supply (i.e., intermittent electrolysis), which is emblematic of electrolysis powered directly by renewable energy (such as wind and solar power sources). Here we reveal that NiMo electrodes were oxidized by dissolved oxygen during power interruption, leading to vanishing of metallic Ni active sites and loss of conductivity in MoOx substrate. Based on the understanding of the degradation mechanism, chromium (Cr) coating was successfully applied as a protective layer to inhibit oxygen reduction reaction (ORR) and significantly enhance the stability of NiMo electrodes in intermittent electrolysis. Further, combining experimental and Molecular Dynamics (MD) simulations, we demonstrate that the Cr coating served as a physical barrier inhibiting diffusion of oxygen, while still allowing other species to pass through. Our work offers insights into electrode behavior in intermittent electrolysis, as well as provides Cr coating as a valid method and corresponding deep understanding of the factors for stability enhancement, paving the way for the successful application of lab-scale electrodes in industrial electrolysis powered directly by renewable energy.

Tribological Electroless Ternary Ni-B-W Coatings: A Suitable Alternative to Hard Chromium Coatings

Abstract Concerns raised about the environmental ramifications of electrodeposited hard chromium (EHC) plating are perhaps the paramount challenge posed to the finishing industries to find a suitable alternative. Electroless Ni-B coatings have attracted much attention due to their superior mechanical and tribological properties; those are enhanced further in electroless Ni-B-W coatings. Electroless Ni-B-W can be a suitable alternative for the replacement of EHC in a variety of engineering applications. In the present study, the changes in morphological features, deposition rates with respect to time, and deposition mechanisms of electroless Ni-B-W coatings are studied thoroughly. After heat treatment, all deposited coatings are characterized thoroughly for the evaluation of their mechanical and tribological characteristics. This is helpful in the comparison of characteristics with properties of industrial EHC coatings. To analyze the coating-substrate adhesion in the electroless depositions, scratch tests with progressive load and repetitions are carried out. Frictional behavior and failure mechanisms at the scratch tracks of all fabricated coatings are also studied through repetitive scratch tests. Heat treatment of electroless Ni-B-W coatings induced significant improvements in mechanical, tribological properties and adhesion behavior. The present study establishes beyond doubt that owing to a specific set of properties, electroless Ni-B-W coatings show tremendous potential to be recommended as a replacement for chrome coatings.

Vickers hardness of NiW coating as a potential replacement for Cr-VI: A methodology to consider size effect and tip defect in classical microindentation

Hard chromium coatings are widely used due to their excellent mechanical properties. However, they are historically obtained from hexavalent chromium (Cr-VI) solutions, which are classified as Carcinogenic Mutagenic Reprotoxic (CMR) material due to their very high toxicity. NiW coating is studied in this work as a possible replacement for Cr-VI coating. The substrate used is ST37 steel. The conventional commercial Cr-VI coating is considered here as reference material in terms of hardness.Usually in classical microindentation, the tip defect is always neglected and the indentation size effect (ISE) is studied disjointedly. However, these two aspects can interact together into the hardness measurement. Based on Vickers hardness measurements on steel substrate and both on a cross-section and on the top surface of the Cr-VI coating, 50 μm of thickness, we propose a discussion on the indentation size effect and the influence of the indenter tip defect on the hardness measurement. To validate our approach, the tip defect length was previously determined by SEM observation. Its value allows concluding that the apparent indentation size effect on the Cr-VI coating is only due to the tip defect. However, the corrected Vickers hardness for the steel substrate reveals always a residual ISE. This hardness-load dependence of steels is attributed to the strain hardening generated by the surface preparation.Starting from the methodology developed on the quasi-massive materials, we have corrected the raw indentation data obtained for the NiW coatings and we have applied the model of Jönsson and Hogmark to separate the contribution of the substrate on the hardness measurement to determine the hardness of the coating only. A discussion on the value of the constant involved in their model confirms that it should be cautiously considered. As a result, the macrohardness of the Cr-VI coating is determined around 8.0 GPa whereas for the NiW coating it is found to be from 4.5 to 5 GPa depending on the deposition parameters.

Chemical vapor deposition from metal (Cr, Mo, W) carbonyls in a conical spouted bed vacuum reactor with a downflow reactant feeding

A vacuum set-up with a conical spouted bed reactor for LPCVD of coatings onto powders, where a volatile solid substance is used as a CVD precursor (reactant), is developed. Structurally, the reactor is a cone with a vertical axis, fluidizing gas is supplied through the bottom branch, and reactant vapor is supplied from the evaporator through a thermostated nozzle into the top of the spouted particle bed (substrate powder). Examples given include the deposition of chromium, molybdenum, and tungsten coatings from carbonyls Cr(CO)6, Mo(CO)6, and W(CO)6 onto diamond powders with grain sizes from 150 to 500 μm, when coatings up to 1 μm thick were obtained at the reactor efficiency (the degree of the reactant conversion to the coating) within 42–77 %. In addition to the set-up design and process parameters, the saturated vapor pressure of carbonyls, chemical reactions during the deposition from carbonyls, and fluidized bed hydrodynamics are discussed.

The Atmospheric Corrosion of Trivalent Cr Metal / Cr Oxide Coatings for Packaging Steels

The superior mechanical properties associated with steel mean that it is heavily utilized in many industries including automotive, and construction (1). Although steel offers desirable mechanical properties such as toughness and tensile strength, it is known to corrode, this having cost implications and raising safety concerns, for instance within the food packaging industry. Thus, steel is often used in conjunction with a coating as a preventative measure for corrosion.Within the food packaging industry, steel is often coated with a thin (~20 nm thick) chromium metal-chromium oxide coating, the product being referred to as electro chromium coated steel (ECCS), which is produced during a continuous electrodeposition process whereby a low carbon steel strip passes through baths of chromic acid electrolyte containing hexavalent chromium, Cr(VI). The final coating consists of two distinct layers; a 20-110 mg.m-2 chromium underlayer and a 2-20 mg.m-2 native (hydr)oxide outer layer (2). REACH, a regulation associated with the restriction of chemicals that are harmful to human health and the environment, have made a legislation that has imposed a restriction on the use of Cr(VI) due to its carcinogenic nature (3). This impact has resulted in the drive of the steel packaging industry to find a suitable, non-toxic replacement for ECCS.Coatings made with Trivalent Chromium Coatings Technology (TCCT®) are currently being developed as a potential replacement for ECCS. TCCT® production has developed to consist of a two-electrolyte process involving an aqueous solution of Cr(III) sulphate, sodium sulphate, sodium formate and sulphuric acid leading to the formation/application of a bilayer coating. Various issues including coating inhomogeneity have previously been reported (4).Due to the low coating weights involved, packaging products such as ECCS and TCCT® are also used in conjunction with an organic coating. Thus, they could be susceptible to various modes of organic coating failure including corrosion-driven cathodic delamination, whereby a coating becomes physically separated from the underlying substrate, a key failure process that affects organically coated metal products in high humidity, such as those experienced during storage in the packaging industry. Cathodic delamination occurs when an electrolyte comes into contact with the metallic substrate at a flaw in the organic coating at which anodic metal dissolution occurs. This is coupled to the cathodic oxygen reduction reaction which takes place at the delamination front. The hydroxide ions produced during the cathodic reduction of oxygen, or a reaction intermediate, disturb the bonds between the substrate and coating leading to adhesion failure and delamination of the coating (5).To ensure that new products such as TCCT® are successfully incorporated into the market it is important that they are comparable in performance to existing products. For example, TCCT® must provide sufficient delamination resistance. The scanning kelvin probe (SKP) is a technique which measures corrosion potential under a thin electrolyte film and organic coatings, which can be used to create a surface potential map (6).This study makes use of the SKP to investigate the rate of cathodic delamination as a function of TCCT® Cr(III) oxide (varying from 1.8 mg.m-2 to 23.35 mg.m-2). The results will help to determine the minimum satisfactory chromium oxide coating weight needed for commercial TCCT®.It was found that higher Cr(III) oxide coating weights had a positive effect on inhibiting cathodic delamination, confirming the mechanism. The results were explained using complementary electrochemical data including OCP measurements as well as potentiodynamic polarisation which showed that higher TCCT® Cr(III) oxide coating weights were acting to supress the cathodic reaction.The results also highlighted that a TCCT® Cr(III) oxide coating weight of around 7 mg.m-2 is sufficient with regards to resisting cathodic delamination completely. This work has determined that the Cr(III) oxide coating weight value is very important with regards to improving coating coverage and resisting cathodic delamination.References Singh MK. Application of Steel in Automotive Industry Application of Steel in Automotive Industry. Int J Emerg Technol Adv Eng. 2016;6(7):2250–459.Wijenberg J, Steegh M, Penning JP, Portegies Zwart I. Wo 2014/079909 2014.Petry T, Knowles R, Meads R. An analysis of the proposed REACH regulation. 2007;44(2006):24–32.Allman A, Whiteside J, Jewell E, Griffiths C, McMurray N, de Vooys A. Surface modification of Cr(III) packaging substrates for enhanced adhesion via citric acid processing. Surfaces and Interfaces. 2020 1;20:100545.Øystein O, Knudsen AF. Corrosion Control Through Organic Coatings. Second. Schweitzer PA, editor. New York: Taylor & Francis; 2017.Stratmann M, Streckel H, Feser R. A new technique able to measure directly the delamination of organic polymer films. Corros Sci. 1991;32(4):467–70.

Effect of Ammonium Formate Addition on Corrosion Behavior of Trivalent Chromium Coatings Electrodeposited in Deep Eutectic Solvents

Effect of Ammonium Formate Addition on Corrosion Behavior of Trivalent Chromium Coatings Electrodeposited in Deep Eutectic Solvents

Chromium-coated cladding analysis under simulated LOCA burst conditions

Of the near-term accident-tolerant fuel concepts identified, chromium coatings have been shown to slow cladding oxidation without altering fuel system geometry or greatly affecting neutronic performance. To identify how coated cladding tubes perform under high-temperature accident conditions, pressurized-tube burst tests were conducted in the Severe Accident Test Station at Oak Ridge National Laboratory. To analyze how the coating affects cladding behavior, coated and uncoated cladding burst tests were simulated by using the BISON fuel performance code. Thermocouple data from these tests were fit into axial and azimuthal profiles and combined to generate 3D cladding surface temperatures, and pressure transducer data were compared until cladding failure. The cladding temperatures at failure and the internal gas pressure evolution show relatively good agreement between the simulation and experiment results. Simulations were then extrapolated to demonstrate the coatings effectiveness to increasing the cladding burst temperature by using a parametric evaluation of the initial tube gas pressure. This work demonstrates the possibility of an increased cladding failure margin under transient conditions due to the addition of chromium coating, and more pertinently, an increased cladding failure margin from more accurate experimental characterization.

Microstructural and Mechanical Characterization of Chromium Coating Deposed on Carbon Fibers

Microstructural and Mechanical Characterization of Chromium Coating Deposed on Carbon Fibers

Development of axial and ring hoop tension testing methods for nuclear fuel cladding tubes

• Axial Tube Tension (ATT) and Ring Hoop Tension (RHT) test methods were developed and used to evaluate tensile properties of Zircaloy-4 claddings with various conditions such as non-irradiated, Cr-coated, hydrided, and irradiated. • In RHT tests it was shown that the application of either PVD or cold spray chrome coatings with small (micrometer scale) thicknesses does not meaningfully affect the yield and ultimate tensile stresses in the unirradiated state.

Properties of Chromium Coatings Applied by Various Methods to Zirconium Alloy E110

Properties of Chromium Coatings Applied by Various Methods to Zirconium Alloy E110

Interface crack behavior of thermal protection coating of gun bores under transient convective cooling

Electroplating chromium coating is a common and critical surface coating technology for the artillery bore. In this study, the fracture behavior of interface cracks in the chromium coating-steel substrate system under transient convective cooling was studied by the finite element method. A two-dimensional model containing periodic segmented coatings was established, and the temperature dependence of material parameters was considered. The effects of convection strength, crack geometry and coating thickness on the delamination behavior of chromium coatings were discussed. It was found that the increase in crack density and coating thickness reduced the energy release rate. The shear mode dominates the fracture mode of the interface crack during the convection cooling period, and the crack closes once the convection stops. When the crack density and coating thickness reach a certain value, the proportion of the shear traction no longer changes. These results can provide references for artillery coating design.

Sliding wear behavior of a sustainable Fe-based coating and its damage mechanisms

The current industry demand is to identify suitable alternatives to the risk-of-supply prone and/or toxic, WC-Co and electrolytic hard chrome coatings without comprising the desired wear performance. Therefore, compositions based on abundantly available elements (e.g. ‘Fe’) that possess adequate wear resistance are desirable from health, sustainability and economic standpoints. In this work, crystalline Fe-based (Rockit-401) coatings were processed using two different thermal spray routes, i.e. HVOF and HVAF spraying. The influence of deposition route and processing conditions on the microstructure, porosity content, hardness and phase composition was examined. The as-deposited coatings were subjected to mild (5 N) and harsh (15 N) dry sliding wear test conditions by employing alumina ball as the counter surface material, and their wear performance was examined. Mild sliding wear test conditions (5 N) resulted in anomalous wear behavior, where the abrupt drop in CoF at several instances during the test was observed in all the investigated coatings. On the other hand, under harsh wear test conditions (15 N), such an abrupt dip in CoF was not observed. Detailed wear mechanisms of the coatings were revealed under different test conditions (5 N and 15 N). This work sheds light on processing, wear behavior and wear mechanisms of a sustainable and high-performance coating that fulfills non-toxic and sustainability goals in tandem for tribological applications.

NEUTRON: Neural particle swarm optimization for material-aware inverse design of structural color

SummaryDesigning optical structures for generating structural colors is challenging because of the complex relationship between the optical structures and the color perceived by human eyes. Machine learning-based approaches have been developed to expedite this design process. However, existing methods solely focus on structural parameters of the optical design, which could lead to suboptimal color generation because of the inability to optimize the selection of materials. To address this issue, an approach known as Neural Particle Swarm Optimization is proposed in this paper. The proposed method achieves high design accuracy and efficiency on two structural color design tasks; the first task is designing environment-friendly alternatives to chrome coatings, and the second task concerns reconstructing pictures with multilayer optical thin films. Several designs that could replace chrome coatings have been discovered; pictures with more than 200,000 pixels and thousands of unique colors can be accurately reconstructed in a few hours.

Surface roughness control in nanolaminate coatings of chromium and tungsten nitrides

Frictional forces arising during machining operations of cutting tools generate high temperatures at the tool-workpiece interface, promoting tool-wear phenomena. Surface roughness is acknowledged to contribute significantly to friction generation, and its control is therefore of paramount importance. Structural confinement of growth defects in multilayer coating architectures with individual layers thickness in the nanometric regime can help reduce surface roughness development. Here, a set of nanolaminate coatings consisting in an alternated repetition of cubic chromium nitride (CrN) and cubic tungsten nitride (c-WN) layers is fabricated via unbalanced DC magnetron Sputtering. The individual layers thickness range is between 100 and 10 nm. The reduction of surface roughness as a function of individual layers thickness is demonstrated by semi-contact Atomic Force Microscopy (AFM). Scherrer analysis performed on X-Ray Diffraction (XRD) crystallographic signals shows that the reduction in surface roughness is correlated to a reduction in crystallite size, modulated by the nanolaminate architecture. Conformity and uniformity of multilayer coatings is observed via FIB-SEM cross-section micrographs. The relative contribution of CrN and c-WN layers to the overall roughness development is investigated through a SEM cross-section micrograph-based analysis. The microstructural and topographical features of nanostructured CrN/c-WN multilayer coatings are correlated to the observations from the cross-section analysis and discussed in terms of the energy transfer to the growing surface during each deposition step. • Nanolaminate CrN/WN coatings are deposited via DC-magnetron sputtering. • Surface roughness decreases with the individual layers thickness. • The nanolaminate structure hinders the development of structural defects and asperities. • Roughness build-up is analyzed through a novel layer-by layer approach. • The contribution of the two materials is discussed in terms of sputtering yield differences.

Enhancing the Electroplated Chromium Coating for Corrosion Protection of Aluminum by Adding Graphene Oxide

Enhancing the Electroplated Chromium Coating for Corrosion Protection of Aluminum by Adding Graphene Oxide

Construction of chromium coatings with (200) preferred orientation and exploration the high-temperature steam oxidation properties

In order to improve the high-temperature steam oxidation resistance of Zircaloy-4 for accident tolerant fuel claddings (ATF), Cr coatings with (200) preferred orientation were deposited by changing argon flow using closed field unbalanced magnetron sputtering. The influences of the argon flow on the microstructure and high-temperature steam oxidation properties of Cr coatings were studied systematically. The results indicate that Cr coatings exhibit obvious preferred orientation of Cr (200) especially for 30sccm argon flow due to more adatom easy aggregation on Cr (200) plane under more ion collisions. With the argon flow increases, the grains of Cr coatings gradually becomes compact and homogeneous, which causes the formation of thicker Cr2O3 oxide layer and residual Cr layer on Cr coatings surface after 1200 °C high-temperature steam oxidation test at 8h. Above all, Cr coatings prepared by 30sccm argon flow still possess excellent steam oxidation resistance properties even after 12h exposure time. In addition, the high-temperature steam oxidation mechanism of 30sccm argon flow Cr coatings under different exposure time also was discussed in detail. The study about Cr (200) preferred orientation is expected to provide a new research idea for prolonging steam oxidation resistance and accident tolerant time.

Determination of the Elastic Modulus of Wear Resistant Coatings by Quantitative Acoustic Microscopy

Abstract For the quality assessment of coatings there is an increasing need of test methods which are able to fulfil the requirements to a high reliability of the test results. The exact knowledge of the coating properties and their objective assessment helps the coating industry for an optimum coating development as well as the user which will use the coated parts under a specific purpose. As part of an European project four laboratories deal with the determination of elastic moduli of hard coatings by means of quantitative acoustic microscopy. On titanium nitride coatings and C doped chromium coatings on M2 tool steel basic and continuing research studies were accomplished, guidelines have been developed and proofed in round-robin tests.

A Comparative Research on Corrosion Behavior of Electroplated and Magnetron Sputtered Chromium Coatings

Chromium deposits rank among the most widespread metal coatings for functional and decorative purposes. However, electrodeposition from Cr(VI) aqueous solution, which is the industrial process currently used to achieve thin chromium deposits, presents several environmental issues, urging the development of alternative solutions. In this study, which aims to compare the functional and aesthetical properties of decorative coatings, 800 nm thick chromium layers were deposited directly onto copper substrates by means of magnetron sputtering (MS) and direct current electrodeposition (ED). The obtained coatings were characterized regarding their thickness, morphology, color index, chemical composition, and corrosion resistance viewpoints. With respect to the electroplated samples, which constitute the benchmark, the magnetron sputtered ones appeared to be darker but showed a pleasing reflective appearance and superior thickness homogeneity, as well as the absence of voids and macrocracks, as evidenced by scanning electron microscopy (SEM) investigation. Regarding the anticorrosion performances of the chromium layers, electrochemical and standard salt spray test (NSS test) were carried out at room temperature in 3.5% NaCl solution, and evidenced similar, if not better, results for the magnetron sputtered coatings. On the whole, the data displayed here demonstrates the suitability of magnetron sputtering technology for use as an industrially feasible finishing technology for both aesthetic and mild-condition anticorrosion purposes.