Codeposition Of Cr Research Articles

Exploration of electrodeposited process of Ni-Co-Cr coating and investigation of Cr doping strengthening mechanism by indentation simulation

Ni-Co-Cr coating with excellent mechanical properties was successfully prepared by the electrodeposition process. Compared with the binary Ni-Co alloy coating, the hardness of the ternary coating is increased to 1247HV, an increase of 61%. The wear rate decreased by 40.7%. The exploration of the deposition process found that sodium formate and urea can effectively dissociate [Cr(H 2 O) 6 ] +3 complexes to realize the co-deposition of Cr 3+ . The strengthening mechanism of Cr doping was then investigated by molecular dynamics indentation simulation. It is found that grain refinement and solid solution strengthening contribute 20% (0.33 GPa) and 80% (1.33 GPa) to the hardness, respectively. The enhanced covalent character between Cr and solvent atoms improves the elastic modulus and promotes the dislocation nucleation, which originates from body-centered cubic-like (BCC-like) defect clusters. In the plastic deformation stage, Cr doping reduces the stacking fault energy of the alloy and makes the release of the plastic strain more uniform and stable. The denser 3D stacking fault network structures hinder the further propagation of dislocation loops and increase the dislocation reaction probability. More Lomer-Cottrell and Hirth Locks are generated and improve the strength of the coating. • An electrodeposited Ni-Co-Cr coating with excellent mechanical properties was developed. • The contribution of grain refinement and solid solution strengthening to hardness was quantitatively investigated. • The strengthening in the elastic stages comes from the enhanced covalent character between Cr and solvent atoms. • The strengthening in the plastic stages comes from the increase in the number of immobile dislocations.

Electrochemical and surface chemistry of amorphous chromium-zirconium film prepared by magnetron sputtering

The foremost failure of several protective films, including Cr films, is corrosion at susceptible areas such as grain boundaries and intercolumnar areas. In this work, corrosion inhibition is introduced to eliminate the susceptible areas, by modifying the film structure. Consequently, an amorphous featureless film, without grain boundaries and intercolumnar areas, is successfully fabricated by co-deposition of Cr and Zr to form a CrZr film. Applying electrochemical impedance spectroscopy (EIS) test in 3.5 wt.% NaCl solution reveals that film crystallinity as well as its microstructure strongly affect corrosion behavior. The amorphous featureless CrZr film effectively inhibits solution penetration, resulting in passivity and the highest film resistance (Rfilm). Apart from promoting amorphization, the addition of Zr retards corrosion reaction by the formation of ZrO2 on the film surface, as seen by the high impedance of film capacitance (Qfilm). X-ray photoelectron spectroscopy (XPS) confirms the coexistence of Cr and Zr in the film, which reduces the dissolution of ZrO2 and results in the high value of the oxide/hydroxide ratio. Thus, both the high oxide/hydroxide ratio in the CrZr film together with low interfacial defects contribute to good corrosion resistance. Tailoring the structure of the CrZr film offers an alternative solution for the protection of many kinds of material from attacks of corrosion.

Light-Induced Synthesis of Heterojunctioned Nanoparticles on a Semiconductor as Durable Cocatalysts for Hydrogen Evolution.

This work attempted to synthesize heterojunctioned nanoparticles consisting of a transition metal and Cr on powdered SrTiO3, an n-type semiconductor exhibiting photocatalytic activity for overall water splitting. This was performed via band gap irradiation of SrTiO3 (λ > 300 nm) in an aqueous methanol solution containing a transition metal precursor and K2CrO4. The resulting multicomponent nanoparticles were examined as promoters for photocatalytic overall water splitting. Among the transition metals examined, Au and Pd became effective promoters for overall water splitting upon codeposition of Cr. In the case of Au, which is stable in its metallic state, the resulting (Au+Cr) nanoparticles had a core/shell structure consisting of metallic Au (the core) and amorphous Cr2O3 (the shell), similar to Au/Cr2O3 prepared by a stepwise photodeposition method. However, when using a core transition metal with a tendency to form an oxide, such as Pd, the nanoparticles had different morphologies and electronic states, depending on the proportion of Cr. In the case of a combination of Pd and Cr, the photocatalytic activity for overall water splitting was strongly dependent on the structure and electronic state of the (Pd+Cr) multicomponent cocatalyst. Increasing the proportion of Cr was found to suppress the reverse reaction (that is, H2-O2 recombination), an effect that is not realized when employing a conventional impregnation method.

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La0.6Sr0.4Co0.2Fe0.8O3-δ Cathodes of Solid Oxide Fuel Cells

The presence of both chromium and sulfur (Cr/S) contaminants on the microstructure and electrocatalytic activity properties of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) electrodes of solid oxide fuel cells (SOFCs) is studied, using Confocal laser Raman spectroscopy, XRD, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and electrical conductivity relaxation (ECR) methods. LSCF dense bar samples were heat treated in the presence of Cr2O3 and 20 ppm SO2 and in the temperature range of 600–900°C. The deposition and reaction products between LSCF and Cr/S depend on the temperature: SrCrO4 only forms on LSCF samples at 900°C and 800°C, while formation of SrSO4 phase occurs at all temperatures studied. The results indicate that sulfur shows a higher activity with LSCF, as compared to gaseous Cr species. Segregated SrO is more likely to react with gaseous Cr species at higher temperatures, however, reaction with SO2 is more pronounced at lower temperatures, forming SrSO4. ECR results indicate that co-deposition of Cr and sulfur significantly deteriorates the surface exchange and diffusion processes for the O2 reduction reaction on LSCF electrodes.

Vapor phase codeposition of Cr and Si on Nb-base in situ composites by pack cementation process

In order to identify suitable halide activators and pack compositions for codepositing Cr and Si to form diffusion coatings on Nb-base in situ composites by the pack cementation process, thermochemical calculation was taken to analyze the vapor pressure of halide species generated at high temperatures. NH4Cl, NaF and CrCl3·6H2O were selected as the halide salts. The results of thermochemical calculations suggested that the pack powder mixtures, which contained Cr, Si, halide salts and Al2O3, may be activated by NH4Cl and NaF. According to the thermochemical calculations, the pack powder mixture of 12Cr–6Si–5NH4Cl–77Al2O3 (wt%) activated by NH4Cl was formulated and coating deposition experiments were carried out at 1200 and 1300°C. With adequate control of pack compositions and deposition conditions, it was found that codeposition of Cr and Si could indeed be achieved at these temperatures. The coating has a three-layer structure, of which was mainly composed of Cr2(Nb,X) (X represents Ti and Hf elements), Nb5Si3 and (Nb,Cr)3Si. Then the kinetics of coating growth process affected by temperature was studied. The experimental results of the oxidation showed that the coating can efficiently prevent substrate from oxidizing.

Ti substrate coated with composite Cr–MoO2 coatings as highly selective cathode materials in hypochlorite production

The aim of this work was to investigate the possibility of preparation of the composite Cr–MoO2 coatings onto steel and titanium substrates as cathode materials with high selective properties which imply the suppression of hypochlorite reduction as a side reaction during hypochlorite commercial production. The electrodes were prepared by simultaneous deposition of chromium and suspended MoO2 particles on titanium substrate from acid chromium (VI) bath. The current efficiency for electrodeposition of the composite coatings did not vary significantly with the concentration of suspended MoO2 particles. The content of molybdenum in the deposits was relatively low (0.2–1.5at.%) and increased with increasing the concentration of suspended MoO2 particles in the bath, in the range from 0 to 10gdm−3. With further increase in the concentration of MoO2, the content of molybdenum in the coating varied insignificantly.X-ray photoelectron spectroscopy-XPS and EDS analysis were applied to analyze elemental composition and chemical bonding of elements on the surface and in the sub-surface region of obtained coatings. When the concentration of MoO2 particles in the bath was raised above 5gdm−3, the appearance of the coating changed from the typical pure chromium deposit to needle-like deposit with the appearance of black inclusions on the surface. XPS analysis and corresponding Cr 2p spectra showed the presence of chromium oxide, probably Cr2O3 with Cr(3+) valence state on the surface and in the sub-surface region of Cr–MoO2 coatings.Investigation of the current efficiency for the hydrogen evolution reaction (HER) on Cr–MoO2 cathodes showed that it increased with the increase of the content of MoO2 particles in the coating, exceeding the value of 97% in the solution with the hypochlorite concentration of 0.21moldm−3. Under the same conditions, the current efficiency for the HER on Ti and Ti/Cr cathodes is very low (≈20%), and corresponding polarization curves confirmed the fact that the side reaction of hypochlorite reduction takes place in the diffusion-controlled regime on these electrodes. The high selectivity of Cr–MoO2 coating is probably caused by the presence of chromium oxide (hydroxide) formed at the surface of the coating during co-deposition of Cr and MoO2 particles, which prevents hypochlorite reduction on the cathode during the HER.

Compressive property and energy absorption characteristic of 3D open-cell Ni–Cr–Fe alloy foams under quasi-static conditions

Reticulated open-cell Ni–Cr–Fe foams were manufactured by gas-phase codeposition of Cr and Fe onto the struts of pure Ni foam at 1050 °C, and then the samples were homogenization treated at 1200 °C in a vacuum atmosphere. The quasi-static compressive behavior and energy absorption characteristics of the Ni–Cr–Fe alloy foams with different Cr and Fe contents were discussed. The mechanical properties of these open-cell Ni–Cr–Fe alloy foams were also comparable with the pure Ni foams or the hypothetical Ni–Cr–Fe foam model. The results show that although the alloy foam struts show the similar hardness, the compressive strengths and energy absorption properties of the open-cell Ni–Cr–Fe alloy foams increase with increasing the Cr and Fe contents. The stress–strain behaviours of the Ni–Cr–Fe alloy foams are as smooth as those of nickel foams, indicating that the Ni–Cr–Fe alloy foams are the characteristic of typical ductile metallic foam. The energy absorption capabilities of the Ni–Cr–Fe alloy foams exhibit 22 times higher than that of the pure Ni foams. Simultaneously, the compressive strength of the Ni–Cr–Fe alloy foams at ambient temperature is in agreement with theoretical prediction by Gibson–Ashby model.

Synthesis and properties of open-cell Ni–Cr–Fe–Al alloy foams by pack co-deposition process

A pack cementation process for the co-deposition of Cr, Fe and Al onto open-cell nickel foam was developed. The reticulated open-cell Ni–Cr–Fe–Al foams were annealed to homogenize the material with 18.8wt.% Cr, 11.3wt.% Fe and 7.7wt.% Al. The microstructure and phase composition of the Ni–Cr–Fe–Al foams were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive analysis (EDS). The results show that the coating is uniform and dense along the perimeter of the Ni strut, and consists of three layers: a Cr–Fe outer layer, an inner layer containing mostly Al and a transition zone. After homogenization annealing, the alloyed foams retain the hollow struts structure of the original pure nickel foams and the low relative densities. The Ni–Cr–Fe–Al alloy foams exhibit enhancement in absolute strength as compared to the pure nickel and Ni–35.2Cr foams. Furthermore, the Ni–Cr–Fe–Al alloy foams show excellent oxidation resistance and outperform the chromia-forming Ni–35.2Cr alloy foam after oxidation at 900 and 1000°C, which is mainly due to its high aluminum and chromium content leading to the formation of a continuous and adherent duplex oxide layer.

Texture and microstructure of Cr 2O 3 and (Cr,Al) 2O 3 thin films deposited by reactive inductively coupled plasma magnetron sputtering

Cr 2O 3 and (Cr,Al) 2O 3 films were grown using reactive dc and inductively coupled plasma magnetron sputtering at substrate temperatures of 300–450 °C. For pure chromia, α-Cr 2O 3 films with fiber texture were grown; the out-of-plane texture could be controlled from < 0001> to < 101̅4>. The former texture was obtained as a consequence of competitive growth with no applied bias or inductively coupled plasma, while the latter was obtained at moderate bias (− 50 V), probably due to recrystallization driven by ion-bombardment-induced strain. By reactive codeposition of Cr and Al, a corundum-structured metastable solid solution α-(Cr,Al) 2O 3 with Cr/Al ratios of 2–10 was grown with a dense, fine-grained morphology. Hardness and reduced elastic modulus values were in the ranges 24–27 GPa and 190–230 GPa, respectively.

Structure and mechanical properties of Cr–B–N films deposited by reactive magnetron sputtering

Cr–B–N films with various B contents were deposited by reactive magnetron sputtering from the co-deposition of Cr and B targets in the presence of the reactive gas mixture. Comparative studies on microstructure and mechanical properties between CrN and Cr–B–N films with various B contents were conducted. The addition of B to CrN films caused a decrease of the crystallization of the films, while the B existed mainly as amorphous phase of BN compound in the CrBN films. The mechanical properties were also improved. And the Cr–B–N films with 6.1 at.% B content showed highest hardness and lowest wear rate.

Structure and mechanical properties of reactive sputtering CrSiN films

CrSiN films with various Si contents were deposited by reactive magnetron sputtering using the co-deposition of Cr and Si targets in the presence of the reactive gas mixture. Comparative studies on microstructure and mechanical properties between CrN and CrSiN films with various Si contents were carried out. The structure of the CrSiN films was found to change from crystalline to amorphous structure as the Si contents increase. Amorphous phase of Si 3N 4 compound was suggested to exist in the CrSiN film. The growth of films has been observed from continuous columnar structure, granular structure to glassy-like appearance morphology with the increase of silicon content. The film fracture changed from continuous columnar structure, granular structure to glassy-like appearance morphology with the increase of silicon content. Two hardness peaks of the films as function of Si contents have been discussed.

Electrodeposition of α-Fe2O3 Doped with Mo or Cr as Photoanodes for Photocatalytic Water Splitting

Electrochemical methods for the codeposition of Cr or Mo with α-Fe2O3 (hematite) have been developed to produce doped iron oxide films with varying compositions of Cr and Mo which are active photoanodes for photoelectrochemical (PEC) water decomposition (“water splitting”). The films were characterized by scanning electron microscopy, X-ray diffraction, UV−vis optical spectroscopy, and X-ray photoelectron spectroscopy to determine the effect of the dopants on the hematite structure and PEC performance. Upon doping, the microstructures of the films varied; however, no preferred crystallographic orientation or dopant phase segregation was observed. The best performing samples were 5% Cr and 15% Mo doped which had Incident Photon Conversion Efficiencies (IPCE’s) at 400 nm of 6% and 12%, respectively, with an applied potential of 0.4V vs Ag/AgCl. These IPCE values were 2.2× and 4× higher than the undoped sample for the 5% Cr and 15% Mo samples, respectively. The increase in performance is attributed to an improvement in the charge transport properties within the films and not due to significant changes in the electrocatalytic rates due to dopants residing at the surface. The onset potential for photocurrent in all the samples was approximately −350 mV vs Ag/AgCl. The optical absorption spectra of the films showed bandgaps of approximately 2.0−2.1 eV for all samples regardless of doping.

Electrochemical studies on Zn deposition and dissolution in sulphate electrolyte

The electrochemical deposition and dissolution of Zn on Pt electrode in sulphate electrolyte was investigated by electrochemical methods in an attempt to contribute to the better understanding of the more complex Zn–Cr alloy electrodeposition process. A decrease of the Zn electrolyte pH (from 5.4 to 1.0) so as to minimise/avoid the formation of hydroxo-products of Cr in the electrolyte for deposition of alloy coatings decreases the current efficiency for the Zn reaction, but the rate of the cathode reaction increases significantly due to intense hydrogen evolution. The results of the investigations in Zn electrolytes with pH 1.0–1.6 indicate that Zn bulk deposition is preceded by hydrogen evolution, stepwise Zn underpotential deposition (UPD) and formation of a Zn–Pt alloy. Hydrogen evolution from H2O starts in the potential range of Zn bulk deposition. Data obtained from the electrochemical quartz crystal microbalance (EQCM) measurements support the assumption that electrochemical deposition of Zn proceeds at potentials more positive than the reversible potential of Zn. Anodic potentiodynamic curves for galvanostatically and potentiostatically deposited Zn layers provide indirect evidence about the dissolution of Zn from an alloy with the Pt substrate. The presumed potential of co-deposition of Cr (−1.9 V vs. Hg/Hg2SO4) is reached at a current density of about 300 mA cm−2.

Deposition of Zn–Cr alloy coatings from sulfate electrolyte: effect of polypropylene glycol 620 and glycine and combinations thereof

The effect of polypropylene glycol with molecular mass 620 (PPG 620) and glycine as additives in electrodeposition of Zn–Cr alloy coatings from acidic sulfate electrolyte containing (NH4)2SO4 and H3BO3, at ambient temperature, without agitation is investigated. PPG 620 inhibits the Zn reaction causing significant proximity of the deposition potentials of Zn and Cr, and a co-deposition at a less negative potential of −1.8 V (vs. Hg/Hg2SO4) as compared to the case when polyethylene glycol 1500 (PEG 1500) is used. Depending on the deposition conditions, alloy coatings containing up to 23 mass % Cr can be obtained. Glycine itself does not facilitate the co-deposition of Cr and Zn. Added to the electrolyte containing PPG 620, glycine causes a decrease of the Cr content in the alloy. However, the alloy coatings deposited in the presence of both additives are denser, have better overall appearance and good adherence to the steel substrate. Moreover, glycine increases the buffer capacity of the electrolyte. At short deposition times, the alloy coatings consist mainly of bcc Γx-(Zn, Cr) phase with lattice parameter about 3.035 (3) A and mean crystallite size of the order of 25 nm. Cr content in the coatings can be controlled by changing the concentration of Cr(III) and pH of the electrolyte as well as the current density. Depending on the working conditions, the cathode current efficiency is within 35–55%.

Structure of thin CrSi2 films on Si(0 0 1)

The morphology and texture of CrSi2 films grown on Si(001) is reported. The films have been prepared under ultra high vacuum conditions by reactive codeposition and by the template method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses have been performed to investigate the influence of the substrate temperature and the template thickness on the silicide texture and morphology. XRD evidences that the major part of CrSi2 crystallites grows with an orientation of CrSi2(001)[100]∥Si(001)[110] within all present experiments.Considering the morphology and preferred orientation of the crystallites the substrate temperature of 700°C is determined to be optimal for the codeposition growth method. A further improvement of the CrSi2(001) texture and an increase of the grain size by an order of magnitude is observed after deposition of 0.5nm Cr onto the Si(001) substrate at room temperature prior to the codeposition of Cr and Si at 700°C.

Nonequilibrium Structures in Codeposited Cr-Fe-Ni Films

ABSTRACTTernary libraries are prepared by codeposition of Cr, Fe, and Ni on single-crystal Si and Al2O3 (sapphire) substrates at ∼100°C. The varying proximity to the three metal sources produces a spread of compositions in the films, which are analyzed both as-deposited and after annealing in vacuum for 2 h at 500°C. Structural maps are produced using synchrotron radiation and simultaneous detection of 2D diffraction patterns and x-ray fluorescence spectra. Four phases are identified in the as-deposited films. Three phases occur in equilibrium: bcc (α), fcc (γ), and intermetallic (σ). The fourth phase does not correspond to any equilibrium phase in the Cr-Fe-Ni system; it is tentatively identified as isomorphic to the α-Mn (A12) structure. After annealing, the nonequilibrium phase is no longer observed, but the occurrence of the three equilibrium phases is still far from the equilibrium phase boundaries. The particle size measured by x rays is small (9–15 nm), suggesting that higher annealing temperatures are required for the growth of equilibrium phases.

The effect of a coating heat-treatment on Cr–Si and heat-treatment on the mechanical properties of Cr17Ni2 stainless steel

The in-situ co-deposition of Cr–Si into Cr17Ni2 stainless steel (similar to AISI 431) was achieved using a pack cementation process. Through the optimum parameters, a coating containing approximately 27 wt.% Cr and 2 wt.% Si was obtained, with a layer thickness of approximately 120 μm. Studies showed that the thermal treatment of the coating resulted in a reduction of tensile strength, but the improvement of impact toughness, although the coating had little effect on the mechanical properties of the bulk. Tempering at 300 or 450°C improved the tensile strength and the impact toughness of the steel at 9 and −55°C, while tempering at 550°C reduced these mechanical properties.

Magnetic anisotropy and chemical long-range order in epitaxial ferrimagnetic CrPt 3 films

Thin films of CrPt 3 were prepared by molecular beam epitaxy on both Al 2O 3(0 0 0 1) and MgO(0 0 1) substrates, either directly by co-deposition of Cr and Pt at high temperatures or after in situ annealing of superlattices [Cr(2 Å)/Pt(7 Å)]. In situ RHEED observations and X-ray diffraction measurements have allowed us to check the single-crystal quality of CrPt 3 films and to determine the degree of L1 2-type long-range order (LRO). In films co-deposited between 850°C and 950°C a nearly perfect LRO has been observed. As in bulk alloys, such ordering yields a ferrimagnetic order, while the disordered films are non-magnetic. In contrast with the ferromagnetic L1 2-type ordered CoPt 3(1 1 1) films, the ferrimagnetic CrPt 3(1 1 1) films exhibit perpendicular magnetic anisotropy with quality factors, K u / K d , as large as 5 and large coercivities around 450 kA/m. Such anisotropy could be related to the arrangement of Cr atoms, which owing to their large magnetic moment, oppositely directed to the small Pt moment, drive the magnetization. Since the six Cr nearest neighbours around a Cr atom are along the 〈0 0 1〉 directions, making an angle of 54.74° with the [1 1 1] growth direction, the overlap of their electron distribution favors an easy axis of magnetization normal to the film plane. This idea is supported by the absence of magnetic anisotropy in ferrimagnetic CrPt 3(0 0 1) films.

Simultaneous chromizing and aluminizing using chromium oxide and aluminum: (II) on austenitic stainless steel

The codeposition of Cr and Al on 304 stainless steel has been investigated, using the conversion reaction of Cr 2O 3 to halide. An increase in ratio of Cr 2O 3 to Al in the pack composition tends to form a chromide coating, which is very poor in high temperature oxidation resistance. A codeposited coating layer, which shows high oxidation resistance, is mainly characterized by three zones: an outer layer of iron aluminide, a nickel-rich iron aluminide, and an interdiffusion zone consisting of alpha ferrite and nickel aluminide precipitates. Oxidation resistance increased as the thickness of the outer iron aluminide layer increased. This means that the aluminum in the outer layer, rather than that in nickel aluminide precipitates or alpha ferrite, acts as a strong aluminum source forming a protective Al 2O 3 scale at the coating surface. Using a pack mixture containing 10 wt.% Cr 2O 3 and 10 wt.% Al, a coating, which shows excellent oxidation resistance at 1100°C, was obtained after codeposition of aluminum and chromium on 304 stainless steel at 1050°C for about 6–8 h.

An X-ray absorption near-edge spectroscopy study of the oxidation state of chromium in electrodeposited oxide films

The oxidation state of chromium incorporated into simulated corrosion films of nickel has been investigated using the technique of `in situ' X-ray Absorption Near-Edge Spectroscopy (XANES). The films were prepared by electrochemical deposition of the appropriate oxide (hydroxide) onto a graphite substrate. Cathodic deposition from a 0.01 M Cr(NO 3) 3 solution at constant current results in a Cr 3+ oxide (hydroxide) film. Deposition from a 0.01 M K 2CrO 4 solution produces a film which is predominantly Cr 3+ but with some Cr 6+. This material is air-sensitive and the ratio of Cr 6+ to Cr 3+ increases with time of exposure to ambient. Cathodic codeposition of Cr 3+ with nickel hydroxide from Cr(NO 3) 3 solution results in a film with chromium in the 3+ oxidation state. On the other hand, cathodic codeposition from a Cr 6+ solution of K 2CrO 4 with nickel hydroxide leads to a film containing Cr 6+.