Electrodeposition of Ni–Co alloys from a deep eutectic solvent

Pure Ni and three Ni–Co alloys films, i.e. Ni–4 wt.%Co, Ni–18 wt.%Co, and Ni–40 wt.%Co, are electrodeposited at room temperature from the choline chloride/ethylene glycol deep eutectic solvent dissolved by nickel or/and cobalt chlorides. Electrodeposition mechanism, microstructure, and corrosion properties of the films are investigated. Surface morphology and chemical composite of the films are significantly dependent on the Ni²⁺ and Co²⁺ concentrations in the electrolytes. Interestingly, it is found that the amount of cobalt in the Ni–Co alloy films is significantly lower than that present in the electrolytes, which indicates an absence of anomalous codeposition process for the non-aqueous electrolytes. However, anomalous codeposition of Ni–Co deposits is frequently observed for the aqueous electrolytes. The Ni–Co alloy films possess face-centered cubic structures and refined grains revealed by X-ray diffractometer and scanning electron microscope. Potentiodynamic polarization measurements show that the Ni film exhibits the noblest corrosion potential and the lowest corrosion current compared with the Ni–Co alloys films. Moreover, the more Co content the Ni–Co films have, the more negative corrosion potential and the higher corrosion current the films exhibit.     

TEM study of structural and microstructural characteristics of a precipitate phase in Ni-rich Ni–Ti–Hf and Ni–Ti–Zr shape memory alloys

The precipitates formed after suitable thermal treatments in seven Ni-rich Ni–Ti–Hf and Ni–Ti–Zr high-temperature shape memory alloys have been investigated by conventional and high-resolution transmission electron microscopy. In both ternary systems, the precipitate coarsening kinetics become faster as the Ni and ternary element contents (Hf or Zr) of the bulk alloy are increased, in agreement with the precipitate composition measured by energy-dispersive X-ray microanalysis. The precipitate structure has been found to be the same in both Hf- and Zr-containing ternary alloys, and determined to be a superstructure of the B2 austenite phase, which arises from a recombination of the Hf/Zr and Ti atoms in their sublattice. Two different structural models for the precipitate phase were optimized using density functional theory methods. These calculations indicate that the energetics of the structure are not very sensitive to the atomic configuration of the Ti–Hf/Zr planes, thus significant configurational disorder due to entropic effects can be envisaged at high temperatures. The precipitates are fully coherent with the austenite B2 matrix; however, upon martensitic transformation, they lose some coherency with the B19′ matrix as a result of the transformation shear process in the surrounding matrix. The strain accommodation around the particles is much easier in the Ni–Ti–Zr-containing alloys than in the Ni–Ti–Hf system, which correlates well with the lower transformation strain and stiffness predicted for the Ni–Ti–Zr alloys. The B19′ martensite twinning modes observed in the studied Ni-rich ternary alloys are not changed by the new precipitated phase, being equivalent to those previously reported in Ni-poor ternary alloys.     

Effects of boron concentration on the corrosion resistance of Fe-B alloys immersed in 460 °C molten zinc bath

In order to investigate the effects of boron concentration on the corrosion resistance of Fe-B alloys in molten zinc, Fe-B alloys, with the boron concentrations of 1.5 wt.%, 3.5 wt.% and 6.0 wt.% respectively, were dipped into a pure molten zinc bath at 460 °C and kept in different time intervals. The results show that, in comparison with 1Cr18Ni9Ti stainless steel, Fe-B alloy with 3.5 wt.%B exhibits excellent corrosion resistance, due to the dense continuous network or parallel Fe₂B phase which hinders the Fe/Zn interface reaction in Fe-B alloys. The energy dispersive spectrum (EDS) results indicate that the coarse and compact δ phase with the length about 40 μm generates near the matrix of Fe-B alloy and massive ζ phase occurs close to the liquid zinc. The corrosion process includes Fe/Zn reaction and the isolation and fracture of Fe₂B. The failure of boride is mainly caused by the microcrack.     

V-Ni-Ti multi-phase alloy membranes for hydrogen purification

Hydrogen-selective membranes formed from body centred cubic alloys can exhibit very high hydrogen permeability, but are prone to brittle failure due to excessive hydrogen absorption. Until issues associated with this are overcome, these materials will not provide a viable alternative to Pd-based membranes. Multi-phase V-Ni-Ti alloys which contain a significant proportion of a BCC component show promise for this application. In order to examine this system in greater detail, alloys of the general form V_85−xTi_xNi₁₅, in which x was varied between 0 and 30 (at.%), were fabricated via arc melting and electrical-discharge wire cutting. Hydrogen permeation measurements of Pd-coated samples at 400 °C showed a monotonic increase in permeability with increasing Ti, reaching a maximum of 1.0 × 10⁻⁷ mol H₂ m⁻¹ s⁻¹ Pa^−0.5 for the V₅₅Ti₃₀Ni₁₅ alloy at 400 °C. The driving force for hydrogen transport is provided by hydrogen absorption, which varies non-linearly with Ti content, and is dependent on the volume fraction of BCC phase, and levels of Ti and Ni solution in the BCC phase. Diffusion coefficients of atomic H through the bulk alloys alloys are dependent largely on microstructure. Whereas the V₈₅Ni₁₅ alloy forms a single phase microstructure, progressive substitution of V with Ti introduced several minor phases; a NiTi-type phase (formed when x ≥ 5), and a NiTi₂-type phase (formed when x ≥ 10), both as V-containing solid solutions. These minor phases act as barriers to hydrogen diffusion, resulting in a significantly reduced diffusion coefficient compared to single-phase BCC alloys. Importantly, the mechanical stability of these alloys appears to be enhanced by the multi-phase microstructure. These alloys therefore show great promise for meeting future flux, cost and durability targets.     

Performance studies of bare and Co-plated titanium alloy as cathode current collector in Molten Carbonate Fuel Cell (MCFC)

The corrosion characteristics of bare, heat treated and cobalt coated titanium alloys were studied and compared with that of SS 316 in molten carbonates (Li/K = 62/38 vol.%) at 650 °C under oxygen atmosphere using electrochemical and surface characterization techniques. Immersion test of titanium alloys conducted in cathode environment followed by atomic absorption spectroscopy (AAS) indicated leaching of molybdenum from the alloy. Coating the alloy with Co was found to decrease the molybdenum dissolution rate. X-ray diffraction results showed the formation of LiTiO₂ and Li₂TiO₃ on the surface of the titanium alloys and formation of LiFeO₂ and Fe₂O₃ in the case of SS 316. SEM and EDAX analysis of the post-test samples revealed the loss of Mo, Sn and Zr from the titanium alloys and loss of Cr and Ni from SS 316. Electrochemical studies showed that the conductivity of the corrosion scale was higher for cobalt electroplated alloy when compared to other titanium alloys and lower than that of SS 316. Cobalt coated titanium alloy exhibited higher polarization resistance than other alloys. The present study confirmed that the surface modification of titanium alloy lead to the formation of a protective layer with better corrosion barrier properties and better electronic conductivity in molten carbonate fuel cell cathode operating conditions.     

Corrosion behaviour of different hot rolled steels

The oxidation-corrosion behaviour of hot rolled alloys was examined by electrochemical impedance spectroscopy. The corrosion behaviour of the non-oxidised alloys was first determined in order to have a reference behaviour. Then, each alloy was oxidised for 1 and 3 days at 650 °C in air and its corrosion behaviour was also determined. For all the alloys, Fe₂O₃ was formed at the scale-gas interface. However, the Fe₂O₃ crystallographic structures varied as a function of the alloy composition. Differences in the corrosion behaviour are due to the thickness, the microstructure and the porosity of the scale. The new graphite chromium iron alloy (Hi-Cr + C) have an oxidation-corrosion behaviour close to the indefinite chill double paired (ICDP) one and is therefore thought to be a good candidate to replace the ICPD alloy. In the case of the high speed steel (HSS) alloy, the oxidation-corrosion kinetics are too slow to prevent sticking problems. The Co addition decreases the corrosion-oxidation rates for the non-oxidised and oxidised samples but this effect is limited in time.     

Characterization of the martensitic transformation in Ni50−xTi50Cux alloys through pure thermal measurements

The addition of a third element to the Ni-Ti system often changes the product and the path of the martensitic transformation of the alloy, which is a direct B2-B19′ transformation for the NiTi alloy in the fully annealed state. In this study we investigate the martensitic transformation of fully annealed Ni_50−xTi₅₀Cu_x (x = 3-10 at%) shape memory alloy (SMA) samples using differential scanning calorimetry (DSC) and the four-probe electrical resistance (ER) measurements under stress-free conditions. DSC and ER data show that the ternary alloy goes through a direct B2-B19′ transformation for Cu content between 3 and 7 at% and through the two-stage B2-B19-B19′ transformation for Cu content between 8 and 10 at%. We find good agreement between the two techniques as regards the detection of the phase transformation temperatures. B19′ starting and finishing temperatures decreases with the increases of Cu content and show a significant reduction starting from 7 at%; the range of temperatures in which B19 is stable increases with increasing Cu content.     

Incorporation of transition metal ions and oxygen generation during anodizing of aluminium alloys

Enrichment of nickel at the alloy/film interface and incorporation of nickel species into the anodic film have been examined for a sputtering-deposited Al-1.2at.%Ni alloy in order to assist understanding of oxygen generation in barrier anodic alumina films. Anodizing of the alloy proceeds in two stages similarly to other dilute aluminium alloys, for example Al-Cr and Al-Cu alloys, where the Gibbs free energies per equivalent for formation of alloying element oxide exceeds the value for alumina. In the first stage, a nickel-free alumina film is formed, with nickel enriching in an alloy layer, 2 nm thick, immediately beneath the anodic oxide film. In the second stage, nickel atoms are oxidized together with aluminium, with oxygen generation forming gas bubbles within the anodic oxide film. This stage commences after accumulation of about 5.4 × 10¹⁵ nickel atoms cm⁻² in the enriched alloy layer. Oxygen generation also occurs when a thin layer of the alloy, containing about 2.0 × 10¹⁹ nickel atoms m⁻², on electropolished aluminium, is completely anodized, contrasting with thin Al-Cr and Al-Cu alloy layers on electropolished aluminium, for which oxygen generation is essentially absent. A mechanism of oxygen generation, based on electron impurity levels of amorphous alumina and local oxide compositions, is discussed in order to explain the observations.     

Surface modification of Zr-based bulk amorphous alloys by using ion irradiation

Surfaces of the [Zr_0.65Cu_0.18Ni_0.09Al_0.08]₉₈M₂ (M = Er and Gd) bulk amorphous alloys were modified by irradiation with energetic singly charged argon (Ar⁺) ions. Samples of both the alloys were irradiated with 2.17 × 10¹⁷ argon ions of 10 keV energy. As cast and ion irradiated samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Mechanical properties like Vicker's hardness, nanohardness, elastic modulus and elastic recovery were measured. Considerable increase in elastic modulus and hardness was observed because of ion irradiation in these alloys. The ion irradiated samples of the [Zr_0.65Cu_0.18Ni_0.09Al_0.08]₉₈Er₂ alloy showed better properties as compared to [Zr_0.65Cu_0.18Ni_0.09Al_0.08]₉₈Gd₂ alloy. CuZr₂ phase was detected in ion irradiated alloys by XRD and confirmed by EDS. The range of Ar⁺ ions was found to be approximately 9.3 ± 5.4 nm in both alloys.     

Effect of heat treatment on the microstructures and damping properties of biomedical Mg-Zr alloy

In this study, we elucidated the effect of heat treatment on the microstructures and damping properties of the biomedical Mg-1 wt% Zr (K1) alloy by optical microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry, and experimental model analysis. The following microstructural transformation occurred when the as-quenched (AQ, i.e., solution heat treated and quenched) K1 alloy was subjected to aging treatment in the temperature range 200-500 °C: α-Mg → (α-Mg + twin_dense) → (α-Mg + twin_loose) → (α-Mg + α-Zr). This microstructural transformation was accompanied by variations in the damping capacity. The damping properties of the AQ K1 alloy subjected to aging treatment at 300 °C for 16 h were the best among those of the alloys investigated in the present study. The presence of twin structures in the alloy matrix was thought to play a crucial role in increasing the damping capacity of the K1 alloy. Hence, we state that a combination of solution treatment and aging is an effective means of improving the damping capacity of biomedical K1 alloys.     

Electrodeposition of Co–Sb thermoelectric film from ethylene glycol–CoCl2–SbCl3 solution

The electrodeposition of cobalt–antimony thermoelectric semiconductor films was investigated in a non-aqueous solution of ethylene glycol (EG)–CoCl₂–SbCl₃ at 393 K. By controlling the bath composition and cathodic current density, Co–Sb alloys containing 0–94 mol% of Co were obtained at 50–300 Am^− 2. The resistance polarization caused by the formation of semiconductor film was observed in the polarization curve measured in the EG–CoCl₂–SbCl₃ (90.0–9.3–0.7 mol%) bath. In this bath, the Co–Sb (23.6–76.4 mol%) alloy was obtained by maintaining the constant potential electrolysis at 0.1 V. This alloy included CoSb₃ and exhibited a p-type thermoelectric conversion by the given temperature difference.     

The effect of boron on the thermal fatigue behavior of Iron-chromium-carbon-silicon alloy

The effect of boron on the thermal fatigue behavior of Fe-20Cr-1.7C-1.0Si-xB (x = 0, 0.3 and 0.6 wt.%) hardfacing alloys was investigated using a high frequency induction heating/water cooling system. Formation and growth of thermal fatigue cracks in tested alloys was also investigated, and the effect of the strain-induced martensitic transformation on cracking was analyzed by means of optical microscopy and by nondestructive testing using ultrasonic elastic waves. These experiments demonstrated that the alloy exhibits sustained resistance to thermal fatigue in its early stages since the strain-induced martensitic transformation interfered with the propagation of fatigue cracks.     

Electrochemical deposition of gold-tin alloy from ethylene glycol electrolyte

The possibility of Au-Sn alloy deposition from the ethylene glycol electrolyte has been shown. Deposited alloys contain 27-54 at.% of tin and include AuSn₂, Au₅Sn, AuSn crystalline phases together with amorphous gold. The coatings consist of tightly packed submicron grains grown up into agglomerates 2-4 μm in diameter. The rate of the alloy deposition can be varied from 1 to 5 μm h^− 1 at current density 5-50 mA cm^− 2_. The process of Au-Sn electroplating is characterized by the absence of noticeable cathode passivation, diffusion limitations and hydrogen reduction. The rate of electrodeposition is greatly dependent on Au(III) and Sn(IV) concentration in solution that allows to control Au:Sn ratio in the alloy.     

An investigation on hydrogen storage kinetics of nanocrystalline and amorphous Mg2Ni1−xCox (x = 0-0.4) alloy prepared by melt spinning

In order to improve the hydrogen storage kinetics of the Mg₂Ni-type alloys, Ni in the alloy was partially substituted by element Co, and melt-spinning technology was used for the preparation of the Mg₂Ni_1−xCo_x (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The structures of the as-cast and spun alloys are characterized by XRD, SEM and TEM. The hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the as-spun alloys is tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys are calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves are plotted by an electrochemical workstation. The results show that the substitution of Co for Ni notably enhances the glass forming ability of the Mg₂Ni-type alloy. Furthermore, the substitution of Co for Ni, instead of changing major phase Mg₂Ni, leads to forming secondary phases MgCo₂ and Mg. Both the melt spinning treatment and Co substitution significantly improve the hydrogen absorption and desorption kinetics. The high rate discharge ability, the hydrogen diffusion coefficient and the limiting current density of the alloys significantly increase with raising both the spinning rate and the amount of Co substitution.     

Influence of oxygen ion irradiation on the corrosion aspects of Ti-5%Ta-2%Nb alloy and oxide coated titanium

The corrosion resistance of Ti-5%Ta-2%Nb alloy and DOCTOR (double oxide coating on titanium for reconditioning) coated titanium by O⁵⁺ ion irradiation were compared and investigated for their corrosion behaviour. O⁵⁺ ion irradiations were carried out at a dose rate of 1 × 10¹⁷, 1 × 10¹⁸ and 1 × 10¹⁹ ions/m² at 116 MeV. The surface properties and corrosion resistance were evaluated by using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray (EDX), glancing-angle X-ray diffraction (GXRD) and electrochemical testing methods. The results of electrochemical investigations in 11.5 N HNO₃ indicated that the open circuit potential (OCP) of DOCTOR coated titanium is nobler than Ti-5%Ta-2%Nb alloy. The potentiodynamic polarization study of Ti-5%Ta-2%Nb alloy and DOCTOR coated specimen indicated decrease in passive current density with increase in ion doses (1 × 10¹⁷ to 1 × 10¹⁹ ions/m²) indicating decrease in anodic dissolution. Nyquist arc behaviour in the electrochemical impedance study substantiated the enhancement in oxide layer stability by O⁵⁺ ion irradiation. AFM results revealed that the DOCTOR coated Ti surface was dense without gross voids, and the surface roughness decreased by O⁵⁺ ion irradiation, but increased after corrosion test. EDX and GXRD patterns of DOCTOR coated Ti sample indicated that the coating was mainly composed of rutile TiO₂. Based on the above results, the O⁵⁺ ion irradiation effect on corrosion behavior of Ti-5%Ta-2%Nb alloy and DOCTOR coated titanium are discussed in this paper.     

The effect of Si additions on the high temperature oxidation of a ternary Ni-10Cr-4Al alloy in 1 atm O2 at 1100 °C

The oxidation of four Ni-10Cr-ySi-4Al alloys was studied at 1100 °C to examine the effects of Si additions (from 2 to 6 at.%) on the behavior of the alloy Ni-10Cr-4Al. Addition of 2 at.% Si prevented completely nickel oxidation, but could not form alumina scales. Larger Si additions produced alumina only over part of the alloy surface (about 20% with 4 at.% Si and 30% with 6 at.% Si), but could not prevent completely the internal oxidation of Al. The results are interpreted by extending to quaternary alloys the mechanism of the third-element effect already proposed for ternary alloys.     

The influence of imposed strain on the development of microstructure and transformation characteristics of Ni-Ti shape memory alloys

Presented paper describes the influence of imposed strain on the development of microstructure (substructure) in Ni-Ti materials during the application of ECAE (equal channel angular extrusion). The interrelationship between imposed strain and resulting transformation characteristics is in the main point of interest while the chemical composition, namely the occurrence of secondary phases such as TiC and Ti₄Ni₂O resulting from the technology used for the sample alloy preparation is also investigated. The alloy Ni50.6-Ti (at.%) was prepared by melting in the HF vacuum induction furnace using a graphite crucible. The deformation was carried out via ECAE combined with prior rotary forging/swaging. ECAE was carried out at 280 °C. The imposed strain had the value ∼2. The alloy was processed by deformation route Bc. It was established the high dislocation density generated by the imposed strain stabilized the B2 and R phases and shifted the transformation R ↔ B19′ towards the lower temperature region. Direct effect of the deformation stress was demonstrated in samples after the second pass when the occurrence of the deformation induced transformation B2 → B19′ was confirmed. Deformation induced transformation also represents contribution to the overall deformation of the samples during the process.     

Fabrication, microstructure and property of cellular CuAlMn shape memory alloys produced by sintering-evaporation process

Cellular CuAlMn shape memory alloys with open-cell or closed-cell structure have been manufactured successfully by sintering-evaporation process. This process consisted of mixing CuAlMn and NaCl powders, hot pressing and final high-temperature sintering to evaporate the filler material of NaCl powders. NaCl was eliminated completely during vacuum sintering, and strong metallurgical bonding in the cell walls was achieved. The pores’ structural parameter (pore size, shape, and direction) and porosity (25-70%) have been controlled effectively. The compressing deformation behavior and phase transformation behavior of the cellular CuAlMn shape memory alloy has been investigated. It was found that the maximum stress of the cellular CuAlMn shape memory alloys increased with the decrease in porosity, and the energy absorption per unit volume approached the maximum value of 35.81 MJ/m³ (the compression direction parallel to the cross-section) and 25.71 MJ/m³ (the compression direction perpendicular to the cross-section) as the porosity of the alloys was 60% and the pore size was between 355 and 800 μm.     

The effect of substrate composition on the electrochemical and mechanical properties of PEO coatings on Mg alloys

Plasma electrolytic oxidation (PEO) is a unique surface treatment technology which is based on anodic oxidation forming ceramic oxide coatings on the surface of light alloys such as Mg, Al and Ti. In the present study, PEO coatings prepared on AZ91D, AZ31B, AM60B and AM50B Mg alloys have been investigated. Surface morphology and elemental composition of coatings were determined using scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). SEM results showed that the coating exhibited a porous top surface layer and a subsequent dense layer with micro-pores and shrinkage cracks. Phase analysis of coatings was carried out by X-ray diffraction (XRD). XRD analyses indicated that PEO coatings on AZ alloys had higher amount of Periclase (MgO) followed by the presence of Spinel (MgAl₂O₄) e.g. on the AZ91D alloy compared to that on AM series alloys. In order to examine the effect of substrate composition on adhesion strength of PEO coating scratch tests were carried out. Electrochemical corrosion tests were undertaken by means of potentiodynamic polarization technique in 3.5% NaCl solution at room temperature (20 ± 2 °C). Corrosion test results indicated that the corrosion rates of coated Mg alloys decreased by nearly two orders of magnitude as compared to bare Mg alloys. PEO coatings on AZ series alloys showed better corrosion resistance and higher adhesion properties than AM series alloys. In addition to the PEO processing parameters, such are mainly attributes of the compositional variations of the substrate alloys which are responsible for the formation, phase contents and structural properties of the PEO coatings.