Corrosion resistance of new copper alloy containing 29Zn, 10Ni and up to 5Mn vis-a-vis Cu-10Ni in sulphide polluted synthetic seawater

Cu-10 Ni alloy suffers from accelerated corrosion in sulphide-polluted seawater. New copper alloys containing 29% Zn, 10Ni and 3 or 5% Mn have been found to be more corrosion resistant than Cu-10Ni alloys in sulphide polluted synthetic seawater. The studies were carried out in synthetic seawater (ASTM D 114–75) and sulphide was added through Na₂S (1 gpl ≈ 41ppm S²⁻). Testing was carried out using cathodic and anodic potentiodynamic polarization methods. Corrosion product film formed on the Cu-29Zn-10Ni-5Mn alloy in sulphide polluted synthetic seawater was characterized using SEM and XRD. The film was found to contain Cu₂O, Cu₂S, NiS and ZnS. Better corrosion resistance of new alloys as compared to that of Cu-10Ni alloy is attributed to formation of ZnS, a bad conductor, in the film and incorporation of Mn³⁺ cations in Cu₂O and Cu₂S lattice.     

Development of single-phased copper alloy for seawater applications: As a cost-effective substitute for Cu-10Ni alloy

Cu-10Ni alloy is a standard material for seawater application. Under Indian scenario, where half of copper and whole of Ni (and Cu-Ni) requirement is met by imports, search for a cheaper substitute is obvious. An attempt has been made to develop a single-phased copper alloy containing 10 wt% Ni, 29 wt% Zn, up to 5 wt% Mn and 1 wt% Fe as a substitute to Cu-10wt% Ni-1wt% Fe alloy. Studies on Corrosion resistance of test alloys were carried out in synthetic seawater (ASTM D 114-75) by electro-chemical methods (cathodic and anodic polarization). Corrosion product film formed on alloy containing 5wt% Mn was characterized by SEM and XRD. A film of Cu₂O was found to form on the surface of the alloy, which accords corrosion protection. The test alloys containing 29 wt% Zn and 3 or 5 wt% Mn have exhibited better corrosion resistance in synthetic seawater than Cu-10Ni alloy. The role of Mn and Zn addition has been discussed.     

Effect of zinc addition to copper in improving its corrosion resistance in sulfide polluted synthetic seawater

In an endeavor to develop a cost effective substitute of Cu-10Ni alloy for seawater application (especially for sulfide polluted seawater) few Cu-Ni-Zn-Mn alloys were developed in our laboratory. The Cu-Ni-Zn-Mn alloy was found to have better corrosion resistance than Cu-10Ni both in clean and sulfide polluted synthetic seawater. Resistance to sulfide in Synthetic Seawater was attributed to the formation of ZnS. To ensure that the resistance to sulfide attack is due to Zn alone, a series of studies were carried out with binary alloys of Cu and Zn with increasing weight percentage of Zn (12% and 36%). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) was used for the purpose. Polarization studies gave the corrosion data and EIS was effective in depicting the nature of corrosion product (film). It was found that among the test alloys, Cu-36Zn is most corrosion resistant in sulfide polluted seawater due to formation of ZnS in the film. As it is a binary alloy, the corrosion resistance against sulfide is attributed to Zn alone.     

Combined effect of chloride and pH on corrosion resistance of Cu-10Ni alloy

Cu-10Ni alloy is a standard heat exchanger material for saltwater (including seawater) applications owing to its excellent thermal conductivity and corrosion resistance. The excellent corrosion resistance is due to formation of Cu₂O film, which accords protection. However, when varying amount of H⁺, OH^? and Cl^? ions are present, CuCl₂ ^? may also form. The CuCl₂ ^? is not protective as Cu₂O and hence corrosion resistance may be affected. Present paper investigates combined effect of chloride ion and pH on corrosion resistance of Cu-10Ni alloy. Cathodic and anodic polarization test results are presented for saltwater containing various amounts of NaCl at pH 6 and 8. It is found that, i_corr increases with increasing chloride concentration. The results are discussed using dissolution mechanisms, semi-conducting behaviour of Cu₂O film and deterioration of the film in presence of chloride ions.     

Hot corrosion of Fe-10Cr-18Ni-5Mn-5Al-Si-N steels in molten sulfate deposits

The effect of Na₂SO₄ coating on the corrosion behaviour of 5 steel alloys as well as two commercial alloys - type 304 stainless steel and Inconel 690 - were tested in air at 900 °C under atmospheric pressure. Corroded samples were analysed by XRD, SEM and EDX. A newly developed alloy (No. 5) having the composition Fe-10.4Cr-15.43Ni-5.52Mn-5.52AI-1.5Si showed almost comparable corrosion resistance with Inconel 690. Stainless steel 304 failed catastrophically. Other newly developed alloys (no. 1-4) showed intermediate resistance. The results have been interpreted in the light of the nature of scales formed and on the premise that Na₂SO₄ decomposes to give S^2- ions which delay the formation of an internal protective film.     

Layered Coating of Zn–Co Alloys on Mild Steel using Triangular Current Pulses for Better Corrosion Protection

Cyclic multilayer alloy (CMA) coatings of Zn–Co were electrodeposited on to mild steel (MS) from acid sulphate bath having thiamine hydrochloride and citric acid as additives. Depositions were carried out galvanostatically from a single bath containing Zn⁺² and Co⁺² ions. The triangular current pulses cycling between two cathode current densities were used for gradual change in composition in each layer. CMA coatings were developed under different sets of cathode current densities and number of layers, and their corrosion resistances were evaluated by potentiodynamic polarization and Electrochemical Impedance Spectroscopy method, and results were compared with that of monolayer Zn–Co alloy coatings. At optimal configuration, CMA coating represented as (Zn–Co)_3.0/5.0/300 was found to exhibit ~11 times better corrosion resistance compared to monolayer, (Zn–Co)_4.0, deposited for same length of time from same bath. The formation of layered and corrosion mechanism was analyzed using Scanning Electron Microscopy. The corrosion protection of layered coatings of Zn–Co alloy was attributed to the different phase structure of the alloys in alternate layers, evidenced by XRD analysis.     

High strength microduplex Cu-Ni-Zn alloys

High ambient temperature tensile and fatigue strengths have been obtained in two-phase α-β Cu-Ni-Zn alloys (nickel silvers) by controlled thermomechanical working. The thermomechanical working operation involves cold working of solution annealed stock, followed by annealing in the two-phase region. This results in simultaneous recrystallization and precipitation yielding a fine-grained two phase microstructure termed “microduplex”. The high mechanical properties obtained are attributed to the fine-grained two-phase microduplex microstructure. Compositional variations studied included 10 to 40 pct Ni, 35 to 40 pct Zn, balance Cu. On the basis of ease of processing and mechanical properties, a particularly attractive composition is Cu-15Ni-37.5Zn, designated IN-836. Typical room temperature properties of IN-836 in the microduplex condition include 100 ksi (690 MN/m²) yield strength with 25 pct elongation and 40 ksi (275 MN/m²) fatigue limit (10⁷ cycles). Finally, superplastic behavior has been observed in IN-836. F. J. ANSUINI was formerly with The International Nickel Company, Inc., Paul D. Merica Laboratory, Sterling Forest, Suffern, N. Y. 10901.     

Stress corrosion of Cu- Zn and Cu- Zn- Ni alloys: The role of dealloying

Evidence is presented to demonstrate the occurrence of strain induced dealloying during stress corrosion of Cu-Zn alloys with 15-30 pct Zn and a Cu-28 pct Zn-12 pct Ni alloy. The binary Cu-Zn alloys cracked intergranularly in the ammoniacal solutions used, whereas cracking was transgranular in the ternary alloy. Dealloying was thus found to be a common feature of both modes of cracking. The results further indicate that this dealloying occurs only during crack propagation and not during the incubation period before crack initiation. Additional support for these observations was provided by slow strain rate stress corrosion tests on the Cu-30 pct Zn alloy. These results are consistent with a dealloying model for stress corrosion cracking. The possible mechanisms for the enhanced room temperature transport of solute atoms, required in this model, are discussed.     

Effects of transient carbon deposition on the sodium sulfate-induced corrosion of nickel-base alloys

The role of solid carbon in accelerating the Na₂SO₄-induced corrosion of nickel-base alloys at high temperature has been investigated. Corrosion rates of salt-coated IN 738 alloy in an oxidizing atmosphere containing 0.1 pct SO₂ were much increased when the alloy was initially exposed to a low concentration of methane for a short time at 1273 K (1000°C). Crucible tests carried out with Ni-5 Al, Ni-30 Al, Ni-20Cr-15 Al and IN 738 specimens immersed in Na₂SO₄-carbon mixtures showed that corrosion of these alloys was dramatically enhanced if the carbon persisted long enough to form a Na₂S phase by reaction with the Na₂SO₄. In an oxidizing environment a graphitic carbon had a more pernicious effect on alloy corrosion resistance than a finely dispersed carbon black which burnt away more readily. Corrosion rates in air were also accelerated in the presence of carbonized crude oil residue such as might be formed as a result of incomplete fuel combustion in a gas turbine.     

The corrosion of lead anodes in copper electrowinning

The steady-state corrosion rate of 0.4 pct As-10 pct Sb-Pb anodes in H₂SO₄ copper electro-winning electrolytes was studied. The corrosion rate increases markedly with increasing acid strength and current density, although the corrosion per pound of copper electrowon is affected only slightly by current density. Several ions such as Cu⁺², Mg⁺², Al⁺³, SiO₃ ^-2 and Na+ have no effect on the corrosion while Fe+S and Ni+2 ions have moderate inhibiting effects. Strong corrosion inhibition is brought about by introducing small amounts of Co*2 into the solution or by substituting a Ca-Pb alloy for the conventional antimonial lead anodes.     

New Economical 19Cr Duplex Stainless Steels

New economical duplex stainless steels (DSSs) containing 19Cr-6Mn-xNi-1.0Mo-0.5W-0.5Cu-0.2N (x = 0.5 to 2.0) were developed, and the microstructure, impact property, and corrosion resistance of the alloys were studied. The ferrite content increases with the solution treatment temperature, but decreases with an increase in nickel. The sigma phase is not found precipitating in the alloys treated with solution from 1023 K to 1523 K (750 °C to 1250 °C). The low-temperature impact energy of the experimental alloys increases first and then decreases rapidly with an increase in nickel, which is mainly due to the martensite transformation with an increase in austenite. The alloys have a better mechanical property and pitting corrosion resistance than AISI 304. Among the designed DSS alloys, 19Cr-6Mn-1.3Ni-1.0Mo-0.5W-0.5Cu-0.2N is found to be an optimum alloy with proper phase proportion, a better combination of mechanical strength and elongation, and higher pitting corrosion resistance compared with those of the other alloys.     

Effect of rare earths on corrosion resistance of Cu-30Ni alloys in simulated seawater

Cu-30Ni-xRE(x=0-0.213 wt.%) alloy was prepared by adding rare earths(RE) in melted Cu-30Ni alloy using metal mould casting method.The effects of RE on corrosion resistance of the alloy in simulated seawater were investigated using optical microscope,scanning electronic microscope with energy-dispersive spectrometer and electrochemical measurement system.The results showed that the corrosion resistance of Cu-30Ni alloy was greatly improved by adding proper amount of RE,whereas excess addition of RE worsened ...     

The diffusivity of oxygen in liquid copper-lead alloys

The oxygen diffusivity in liquid copper-lead alloys at 1403 K (1130‡C) was measured us-ing the electrochemical cell: Ni-NiOJZrO₂(+CaO)/O in liquid Cu-Pb alloy(I)/ZrO₂(+CaO)/O in liquid Cu-Pb alloy(II). Oxygen in liquid Cu-Pb alloy(I) was transferred to the right by applying a preselected voltage between the two liquid Cu-Pb alloys. The oxygen diffusivity in liquid Cu-Pb alloy(I) was calculated from the emf change with time between the Ni-NiO and liquid Cu-Pb alloy (I) electrodes. The results were: D_o (in pure Cu) = 8.14 (^+0.70 _-0.43) × 10⁵ cm²/s, D_o (in Cu-25 at. pct Pb) = 11.4(^+0.4 _-0.6) × 10^-5 cm²/s, D_o (in Cu-50 at. pct Pb) = 12.9(^+1.9 _-1.5) × 10^-5 cm²/s, D_o (in Cu-75 at. pct Pb) = 11.0(^+2.4 _-1.2) x 10^-5 cm²/s, D_o (in pure Pb) = 26.3(^+4.8 _-3.7) × 10^-5 cm²/s. It was found that the oxygen diffusivity in liquid copper-lead alloys did not change dras-tically over the entire composition range, in contrast with that reported by other investi-gators for liquid copper-nickel alloys. The oxygen diffusivity in pure liquid lead agreed with the results of our previous work using an FeO-Fe₃O₄ mixture as a sink for oxygen.     

Diffusion of titanium in copper

Interdiffusion coefficients in copper-titanium alloys have been determined by Matano's method in the temperature range between 973 and 1283 K on (pure Cu)-(Cu-1.98 at. pct Ti alloy) and (pure Cu)-(Cu-2.91 at. pct Ti alloy) couples. Temperature dependence of the impurity diffusion coefficient of titanium in copper, determined by extrapolation of the concentration dependence of the interdiffusion coefficient to zero mole fraction of titanium, is expressed by the following Arrhenius equation along with the probable errors:D _Ti/Cu=(0.693 _−0.135 ^+0.169 )×10⁻⁴exp[−(196±2)kJ mol⁻¹/RT] m²/s. The difference in the activation energies for the impurity diffusion of the 3d-transition metals and self-diffusion in copper has been calculated by applying LeClaire's model with the oscillating potential of the impurity atom in copper. The calculated values agree well with the experimental values including the present one. Kazutomo Hoshino, formerly Graduate Student, Tohoku University     

Mechanical properties of Ir-Nb alloys containing Ni and Al

Two alloys made by adding 5 or 10 at. pct, respectively, of Ni-18.9 at. pct Al to an Ir-15 at. pct Nb alloy were investigated. The microstructure and compressive strength at temperatures between room temperature and 1800 °C were investigated to evaluate the potential of these alloys for ultra-high-temperature use. Their microstructural evolution indicated that the two alloys formed fcc and L1₂-Ir₃Nb two-phase structures. The fcc and L1₂ two-phase structures were examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The 0.2 pct flow stresses were above 1000 MPa at temperatures up to 1200 °C, about 150 MPa at 1500 °C, and over 100 MPa at 1800 °C. The strength of the quaternary Ir-base alloys at 1200 °C was even higher than that of Ir-base binary and ternary alloys. And the strength of quaternary Ir-Nb-Ni-Al was equivalent to that of the Ir-15 at. pct Nb binary alloy at 1800 °C. The compressive ductility of quaternary (around 20 pct) was improved drastically compared with that of the Ir-base binary alloy (lower than 10 pct) and the ternary Ir-base alloys (about 11 pct). An excellent balance of high-temperature strength and ductility was obtained in the alloy with 10 at. pct Ni-18.9 at. pct Al. The effect of Ni and Al on the strength of the Ir-Nb binary alloy is discussed.     

Optimization of bright zinc-nickel alloy bath for better corrosion resistance

Optimization of an acid chloride bath for electrodeposition of smooth Zn-Ni alloy on to mild steel was studied using thiamine hydrochloride (THC) as brightener. The influence of deposition current density, temperature, composition, and corrosion properties of Zn-Ni alloy coatings was investigated. The effect of bath composition and operating parameters on deposits characters like composition, micro-hardness, thickness and adhesions were tested. Under no conditions of current density employed in the present study, the anomalous type of co-deposition has changed to normal type. Electrolytically deposited Zn-Ni alloys were characterized by electrochemical AC and DC techniques. The experimental results revealed that coatings having ∼ 3.16 wt. % Ni at 3.0 A/dm² was the most corrosion resistant. The better corrosion resistance at optimal current density was attributed to the formation of n-type semiconductor film at the interface using Mott-Schottky (M-S) analysis. The effect of THC on plating process was investigated through cyclic voltammetry techniques. X-ray diffraction (XRD) studies of the coatings showed the presence of γ-Phase with composition of Ni₅Zn₂₁, responsible for it extended orrosion resistance. The change in the surface morphology of the coatings, with current density was analyzed using scanning electron microscopy (SEM).     

Corrosion Study of Zinc, Nickel, and Zinc-Nickel Alloys in Alkaline Solutions by Tafel Plot and Impedance Techniques

The article describes the use of Tafel plot and electrochemical impedance spectroscopy (EIS) techniques, in order to study the corrosion process of pure zinc, nickel, and synthetic Zn-Ni alloys in various concentrations (0.25 to 1 M) of KOH solution in a temperature range 298 K to 328 K (25 °C to 55 °C). The corrosion rate increases with increasing both concentration of KOH and temperature for all investigated electrodes. The results showed that the increase in Ni content improves the corrosion resistance and increases the barrier of activation energy, and the higher value of corrosion resistance is obtained at 10 pct Ni. The electrochemical measurements using two mentioned techniques are in good agreement with the results of microhardness in that the microhardness gradually increases with increasing Ni content in the alloy. Thus, the corrosion rate of these alloys is significantly reduced compared with that of pure zinc. It is observed that the Warburg tail at low frequency completely disappears at the applied potentials in the case of alloy IV (10 pct Ni) only. This indicates that the diffusion of Zn ion species is strongly reduced. Therefore, addition of Ni to Zn has a beneficial effect, because it leads to lower loss of anode material. The results obtained at certain positive potential (+420 mV vs SCE) exhibited that the semicircle diameter in the case of alloys is lower compared with that of pure zinc. This result means that the values of the charge transfer resistance (R _ct ) in the case of alloys are decreased, due to the breakdown of the oxide layer at this potential. This behavior can be considered as an important criterion for a good battery anode, due to reactivation of the alloy surface at certain positive potential (+0.420 V vs SCE) and suppression of hydrogen gas compared with those of pure zinc.     

Microstructure and corrosion behavior of as-cast and heat-treated Al-4.5 Wt pct Cu-2.0 wt pct Mn alloys

The microstructure and corrosion behavior of as-cast and heat-treated Al-4.5 pct Cu-2.0 pct Mn alloy specimens solidified at various cooling rates were investigated. The equilibrium phases Al₆Mn and θ-Al₂Cu, which are observed in the conventionally solidified alloy in the as-cast condition, were not detected in rapidly solidified (melt-spun) material. Instead, the ternary compound Al₂₀Cu₂Mn₃ was present in addition to the α phase, which was present in all cases. The morphological and kinetic nature of corrosion was investigated metallographically and through potentiostatic techniques in 3.5 wt pct NaCl aqueous solution. Corrosion of the as-cast material was described by two anodic reactions: corrosion of the intermetallic phases and pitting of the α-Al solid solution. The corrosion rate increased with cooling rate from that for the furnace-cooled alloy to that for the copper mold-cast alloy and, subsequently, decreased in the rapidly solidified alloy. In the heat-treated material, corrosion could be described by two anodic reactions: corrosion of Al₂₀Cu₂Mn₃ precipitate particles and pitting of the α-Al matrix. S.M. Skolianos, formerly Graduate Student, Department of Metallurgy, University of Connecticut     

Phase transformations at high pressures and temperatures and the structure of a hypoeutectic 1Ni-99Al alloy

The phase transformations in a hypoeutectic 1Ni-99Al alloy are studied by differential barothermal analysis in the temperature range up to 750°C at a compressed argon pressure up to ～100 MPa. The Al matrix of the initial alloy is found to be saturated by micropores at a concentration of 3.7 × 10¹⁰ cm^?3. After melting and solidification in a compressed argon atmosphere, the micropore concentration increases to 3.2 × 10¹¹ cm^?3. As a result of melting and solidification at a high pressure, the initial fine-grained structure of the alloy with an average grain size of 16 μm transforms into a coarse-grained structure during dendritic solidification. The processing of electron-microscopic images is used to determine the volume content of intermetallic compound Al₃Ni in the Al matrix. The liquidus temperature of the alloy at 100 MPa increases by 10°C, and the solidus temperature is 5°C higher than the eutectic transformation temperature in aluminum-rich Al-Ni alloys. The solid-phase decomposition of the supersaturated solid solution of nickel in aluminum occurs at 630°C. At 100 MPa, the field of solid solutions of nickel in aluminum extends to 1.2 at % Ni as compared to the Al-Ni system at atmospheric pressure. The lattice parameters of Al and Al₃Ni are found to increase in the alloy solidified at 100 MPa. The microhardness of the Al matrix in the alloy is measured after a barothermography cycle. A portion of the Al-Ni phase diagram is proposed for a pressure of 100MPa in the nickel content range 0–4.3 at %.