Aluminum Brass Research Articles

低濃度亜硝酸塩環境における銅合金の応力腐食割れ感受性

低濃度亜硝酸塩環境における銅合金の応力腐食割れ感受性

Indentation size effect in polycrystalline F.C.C. metals

High purity aluminum and alpha brass samples were tested for the indentation size effect (ISE) using a combination of microhardness (high load) and nanoindentation (low load). We employed rate effects to study low temperature deformation mechanisms using nanoindentation creep and load relaxation. Based on these rate effects which are conspicuous in terms of the rate sensitivity of the hardness, ∂H /∂ ln ε ̇ eff , we calculated the activation volume, V ∗ , and compared data from indentation creep with data from uniaxial loading. The data from nanoindentation for alpha brass when plotted, V∗ vs H or τ (flow stress) , extrapolated into literature data from conventional tensile testing, while the aluminum nanoindentation data exhibited an offset. We propose some mechanisms for this offset. We demonstrate that the trend of V ∗ vs H, resulting from the ISE in a single specimen, concurs with that obtained from testing specimens with various levels of work hardening. This suggests that the ISE is driven by a dislocation mechanism. Additionally, when the results are fitted to a strain gradient plasticity model (SGP), the data at deep indents (microhardness and large nanoindentation) exhibited a straight-line behavior closely identical to literature data. However, for shallow indents (nanoindetation data), the slope of the line severely changes, decreasing by a factor of ten, resulting in a “bilinear behavior”. We also propose some possible mechanisms for this behavior.

Nanoindentation and the indentation size effect: Kinetics of deformation and strain gradient plasticity

A study of the indentation size effect (ISE) in aluminum and alpha brass is presented. The study employs rate effects to examine the fundamental mechanisms responsible for the ISE. These rate effects are characterized in terms of the rate sensitivity of the hardness, ∂H/ ∂ ln ε ̇ eff , where H is the hardness and ε ̇ eff is an effective strain rate in the plastic volume beneath the indenter. ∂H/ ∂ ln ε ̇ eff can be measured using indentation creep, load relaxation, or rate change experiments. The activation volume V ∗ , calculated based on ∂H/ ∂ ln ε ̇ eff which can traditionally be used to compare rate sensitivity data from a hardness test to conventional uniaxial testing, is calculated. Using materials with different stacking fault energy and specimens with different levels of work hardening, we demonstrate how increasing the dislocation density affects V ∗ ; these effects may be taken as a kinetic signature of dislocation strengthening mechanisms. We noticed both H and ∂H/ ∂ ln ε ̇ eff (V ∗) exhibit an ISE. The course of V ∗ vs. H as a result of the ISE is consistent with the course of testing specimens with different level of work hardening. This result was observed in both materials. This suggests that a dislocation mechanism is responsible for the ISE. When the results are fitted to a strain gradient plasticity model, the data at deep indents (microhardness and large nanoindentation) exhibit a straight-line behavior closely identical to literature data. However, for shallow indents (nanoindentation data), the slope of the line severely changes, decreasing by a factor of 10, resulting in a “bilinear behavior”.

The influence of the surface condition on the adhesion of Pseudomonas fluorescens (ATCC 17552) to copper and aluminium brass

The adhesion of P. fluorescens (ATCC 17552) to copper, zinc and aluminium brass in the absence and presence of a surface oxide layer was evaluated performing comparative batch experiments with various times of exposition. The adhesion of this strain to bare copper and aluminium brass was extremely low even after 120 min of exposition. On aged samples, on the other hand, adhesion increased with time on both metals. The degree of bacterial adhesion to aged metals was found to follow the sequence zinc>aluminium brass>copper, and the differences were related to the composition of the oxide layer. The presence of ZnO in the layer strongly increased the adhesion due to the large co-ordination capacity of Zn 2+ ions. Correlation was found between the water contact angle of the metal surface and the degree of bacterial adhesion showing that adhesion increases with the decrease in the contact angle. Bacteria were found to have a hydrophilic surface with a water contact angle of 23.5±2° as determined by the sessile drop method.

New evidences on the catalase mechanism of microbial corrosion

Changes on the oxygen reduction rate induced on aluminium brass by cell-free bacterial cultures of an isolate belonging to the genus Pseudomonas were studied in relation to the bacteria phase of growth and to the surface oxide layer composition after various electrochemical pre-treatments of the metal samples. Cultures isolated from the stationary phase of growth strongly influenced the oxygen reduction kinetics. Cathodic currents increased throughout the potential range tested when Cu 2O and CuO were present simultaneously in the surface film (so-called aged surfaces). In this case, the maximum increment (35%) was observed within the oxygen reduction limiting current region. On pre-oxidised surfaces, when the oxide film was composed mainly by CuO, the effect induced by stationary phase cultures was even higher, with the limiting current density increasing by almost 60%. On pre-reduced surfaces on the other hand, when only a submonolayer of Cu 2O was covering the surface, there was no effect as current density values were similar to those obtained in control experiments. Exponential phase cell-free cultures did not modify the limiting current values in any of the surfaces investigated. Results were in agreement with the participation of catalase as a bacterial catalyst for the oxygen reduction process. The normalised catalase activity from different stationary phase cell-free cultures ranged from 0.88 to 4.02 mg ml −1 U −1, while there was no observable activity in exponential phase cultures. The incidence of the catalase mechanism in microbiologically influenced corrosion processes induced by aerobic biofilms is highlighted on the basis of the results obtained using metabolites from planktonic cells and their agreement with most of the experimental evidences so far reported by other authors.

1,2,4,5 tetrazo spiro (5,4) decane‐3 thione as a corrosion inhibitor for arsenical aluminium brass in 3.5% NaCl solution

The influence of a newly synthesised organic compound on the inhibition of corrosion of arsenical aluminium brass in a NaCl solution has been investigated using weight loss measurements, potentiodynamic polarization studies and impedance measurements. Different corrosion kinetic parameters obtained from polarisation studies reveal that the inhibition of corrosion of arsenical aluminium brass in NaCl is under mixed control. UV‐reflectance, X‐ray diffraction and scanning electron microscopic studies have also been carried out to understand the mechanism of inhibition of corrosion, and also the morphological changes on the surface of the alloy. The adsorption of this compound on the metal surface from 3.5% NaCl solution is found to obey Temkin’s adsorption isotherm.

Corrosion inhibition of aluminium–brass in 3.5% NaCl solution and sea water

Electrochemical characteristics of Al–brass are investigated in both 3.5% NaCl and sea water. At active potential, the alloy is dissolved directly or through an adsorbed metastable CuCl layer. At higher applied anodic potential, the active–passive transition leads to the formation of a thicker and more stable CuCl salt layer. With further increase in the anodic potential, the formation of CuO and/or Cu(OH)2 will take place. The inhibition of the corrosion process is studied by adding SDBS, DPh(EO)9, and LAPACl as anionic, nonionic, and cationic surfactants. It is found that the inhibition efficiency increases in the following order SDBS>LAPACl>DPh(EO)9, and increases with increasing their concentrations.

ROTATABLE-TORSION-BALANCE EQUIVALENCE PRINCIPLE EXPERIMENT FOR THE SPIN-POLARIZED HoFe3

We use a rotatable torsion balance to perform an equivalence principle test on a magnetically shielded spin-polarized body of HoFe 3. With a rotation period of one hour, the period of possible signal is reduced from one solar day by 24 times, and hence the 1/f noise is greatly reduced. Our present experimental results give a limit of (-0.68 ± 0.90) × 10-9 on the Eötvös parameter [Formula: see text] and a limit of (1.8 ± 5.3) × 10-9 on the Eötvös parameter [Formula: see text] of equivalence of the polarized body compared with unpolarized aluminum–brass cylinders in the solar gravitational field, and a limit (-0.24 ± 0.55) × 10-9 on the Eötvös parameter [Formula: see text] in the earth gravitational field. This improves the previous limit on the Eötvös parameter [Formula: see text] for polarized electrons in the solar gravitational field by one order of magnitude.

Comparative study of the Effect of Oxygen and Oxygen/Ozone mixtures on the Electrochemical behaviour of different Metals

The effect of dissolved ozone on the electrochemical behaviour of heat exchanger structural materials (carbon steel, stainless steel, copper, 70:30 copper–nickel, aluminium brass and titanium grade 1) was studied to evaluate the possibility of using ozone as sole biocide in cooling water treatment. With this purpose, voltammetric and open circuit potential (OCP) against time measurements at different ozone concentrations between 0.1 and 1.2 ppm were made. Results show different electrochemical responses according to the metal characteristics and the solution composition. First, the passivity of titanium and stainless steel was not affected by ozone. A linear OCP against log time relationship was found for titanium, suggesting the growth of a barrier film in both O2 and O2/O3 solutions. Mild steel does not passivate in synthetic cooling water either with O2 or O2/O3 in the solution. In the presence of ozone the breakdown of passivity is facilitated and makes the repassivation difficult. Ozone enhances the dissolution of Cu2O and the formation of Cu(II) species leading to less protective films. Both processes are strongly influenced by the pH. Finally, the dissolution of aluminium brass is higher than that of copper or copper–nickel.

Localized corrosion of copper alloys by optical interferometry and other techniques

An optical corrosion meter has been developed for materials testing and evaluation of different corrosion phenomena. The idea of the optical corrosion meter was established based on principles of 3D-holographic interferometry for measuring microsurface dissolution, i.e., mass loss, and on those of electrochemistry for measuring the bulk electronic current, i.e., corrosion current of metallic samples in aqueous solutions. In the present work an early stage of crevice corrosion and pitting corrosion of an aluminium brass and ure copper samples in seawater and tap water, respectively, were monitored in situ by the optical corrosion meter during the cyclic polarization test. The observations of pitting corrosion were basically interferometric perturbations detected on the surface of both alloys. However, the observations of crevice corrosion were basically interferometric perturbations detected on the surface of both alloys underneath a crevice assembly, made of Teflon bolt, Teflon nut, and Teflon washer. The crevice assembly used on all tested samples to crevice corrosion to create a differential aeration cell between the surface of the sample and areas underneath the crevice assembly in seawater. Each Teflon washer contained radial grooves and had 20 plateaus which formed crevices (shield areas) when pressed against the surface of the sample. The interferometric perturbations interpreted as a localized corrosion in a form of an early crevice corrosion or pitting corrosion of a depth ranged between 0.3 μm to several micrometers. Consequently, results of the present work indicate that holographic interferometry is a very useful technique as a 3D-interferometric microscope for monitoring crevice corrosion and pitting corrosion at the initiation stage of the phenomena for different metallic samples in aqueous solutions.

Crevice corrosion of copper alloys by optical interferometry

In the present investigation, an optical corrosion-meter has been developed for testing of materials and evaluation of different corrosion phenomena. The idea of the optical corrosion-meter was established based on principles of 3D-holographic interferometry for measuring microsurface dissolution, i.e. mass loss, and on those of electrochemistry for measuring the bulk electronic current, i.e. corrosion current of metallic samples in aqueous solutions. In the present work, an early stage of crevice corrosion of an aluminium brass and a pure copper sample in seawater and tap water, respectively, was monitored in situ by the optical corrosion-meter during the cyclic polarization test. The observations of crevice corrosion were basically interferometric perturbations detected on the surface of both alloys underneath a crevice assembly, made of a Teflon bolt, a Teflon nut, and a Teflon washer. The crevice assembly was used on all tested samples to create a differential aeration cell between the surface of the sample and areas underneath the crevice assembly in seawater. Each Teflon washer contained radial grooves and had 20 plateaus which formed crevices (shield areas) when pressed against the surface of the sample. The interferometric perturbations were interpreted as a localized corrosion in the form of an early crevice corrosion of depth ranging between 0.3 μm and several micrometers. Consequently, results of the present work indicate that holographic interferometry is a very usefull technique as a 3D-interferometric microscope for monitoring crevice corrosion at the initiation stage of the phenomenon for different metallic samples in aqueous solutions.

Utilization the concentrated solar energy for process of deformation of sheet metal

Superplastic forming (SPF) is an important industrial process that has found application in sheet metals which saves energy, reduces cost and enhances structural properties in a single operation. One of the essential share of the process is heating of a preform. Due to utilization the concentrated solar energy this operation can be made more simply and cheaper. The goal of this work was to apply the renewable solar energy to current really effective technology. Deformation experiments were performed at schemes both forming with a punch and negative forming. Several aluminum alloys, brass and iron alloy were employed as sheet preforms to obtaining the parts of convex and concave shape. The sheet metals had thickness from 30 μm to 1,5 mm and has been produced by thermal treatment and rolling. The punches were applied of steel and ceramics, the vacuum pump was employed to the negative forming. The mirror dish concentrators both with diameter of 1500 mm and with diameter of 5000 mm were used for heating the metals by solar radiant energy. The solar plant operated in an automatic regime of the Sun tracking to stability the heating. The parts of different shapes were obtained at the temperatures up to 500 °C (Al alloys), 600 °C (brass) and 700 °C (iron alloy) and strain rates from 10 −4 to 10 −2 s −1. Utilization the concentrated solar energy to heating during forming of sheet metals gives the gain and has the perspectives for the places which are distanced from conventional power sources.

In-situ monitoring of pitting corrosion of copper alloys by holographic interferometry

Early stages of pitting corrosion of pure copper and an aluminium–brass alloy in tap water were monitored in situ by the optical corrosion-meter during the cyclic polarization test. The observations of pitting corrosion were basically interferometric pertubations detected only on the surface of the pure copper in tap water. The interefrometric pertubations are interpreted as a localized corrosion in the form of early pittings, of a depth ranging between 0.3 μm to several micrometers. Results of the present work indicate that holographic interferometry is a useful technique as a 3D-interferometric microscope for monitoring pitting at the initiation stage of the phenomenon for different metallic samples in aqueous solutions.

Exploration of a Helium Inductively Coupled Plasma/Mattauch—Herzog Mass Spectrometer for Simultaneous Multielement Analysis

A helium inductively coupled plasma (He ICP) was coupled with a low-resolution Mattauch–Herzog mass spectrometer (MHMS) for simultaneous ion detection. The potentials and limitations of the system were explored for the introduction of aqueous samples and for laser ablation sampling of solid materials including aluminum alloy, brass, fused ore, and glass standard reference materials. Compared to the data obtained with an Ar ICP on the same instrument, the detection limits were approximately 10 and 100 times worse for samples in solid and solution forms, respectively, partly due to the presence of a strong secondary discharge for the He ICP used with this instrument. In general, the ICP detection limits measured with the MHMS were 10–1000 times inferior to the data obtained with a quadrupole-based instrument.

The corrosion-trend monitoring with the impedance technique

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Electrical contact resistance of titanium nitride coatings for electromagnetic shielding applications

Coating materials are typically applied to aluminum alloys, steel, and brass components used in electromagnetic shields in order to provide better corrosion and wear protection for the substrates, and to produce low contact resistance at mated contact joints. This is especially important for contacts which are periodically operated in aggressive environments, such as the doors and access panels on mobile communications facilities used by the military in the field. In this work, the contact resistance of titanium nitride (TiN) coated aluminum alloy 6061-T6, prepared using reactive ion plating, is compared to chromate conversion coated and bare aluminum alloy 6061-T6 contacts when mated to a typical electromagnetic gasket as a function of cyclic make-and-break loading of the contacts. An outline of the coating process and contact resistance test method is presented, along with details of comparative contact resistance results of the coated contacts. It is concluded that 5 μm thick TiN coatings have significantly lower contact resistance than comparable chromate conversion coated or bare aluminum alloy 6061-T6 contacts when cycled through several thousand contact closures.

Computation of the polarization resistance by a series expansion

The definition of the polarization resistance, Rp, as the reciprocal of the first derivative of the function i = i(ΔE) at the point ΔE = 0 is introduced by considering the kinetic law of a system where more than two elementary electrochemical reactions occur. The importance of establishing a direct relationship between Ic and Rp is stressed. The theory of this new formulation, based on the Maclaurin series expansion of the ideal response f(ΔE), is expounded and some considerations on the numerical calculation of definite integrals are also given. Finally, some experimental applications of this theory are presented. They refer to different electrochemical systems and show that, even if their response close to the mixed potential is of the non-linear type, it is always possible to obtain a well-defined value of Rp. The systems examined are: iron and 1 N H2SO4 solutions at 25 °C containing KCl at various concentrations; five carbon steels in solutions having 100 g 1−1 of EDTA at pH 9 and 100 °C; aluminium brass in a solution containing 35 g 1−1 of NaCl at 35 °C. The definite integrals were computed using ΔE = 0 mV as lower bound and 15, 20 and 30 mV or −25, 15 and 25 mV as upper bounds. Usually experimental data were best-fitted with a polynomial of the fourth degree over the ΔE interval [−50, 50]mV. It was observed that the polynomial of the fourth degree reproduced very faithfully the values of i(ΔE) inside the interval [−30, 30]mV. Examination of the results shows that a good agreement between the proposed and other methods exists and stresses the self-consistence and accuracy of the experimental data (ΔEk, ik) (k = 1, 2,…, n) obtained with different electrochemical techniques.

Processing of materials—monolithic to composites

A multimillion rupee 500-ton hydraulic extrusion/forging facility established at NPL, New Delhi, has been used to undertake extensive studies in forming, the process of plastically deforming, which is the most important way of shaping materials. Wrought materials are used extensively for making useful products employing extrusion and forging, the two important secondary processing techniques used to convert materials into useful shapes and sizes and also to improve the mechanical and metallurgical properties. The success of these processes depends on the proper control and eventual optimization of different process variables.Different ferrous and non-ferrous materials including 316 and 321 stainless steels (using glass lubrication), aluminium brass, admiralty brass and 70/30 and 90/10 cupro nickels have been extruded at a lab-scale production level to determine the influence of different extrusion variables such as temperature, strain rate, extrusion ratio, different die design and several different compositions of lubricants on pressure requirement and surface quality of the products.In the case of ferrous extrusions, the choice of billet-container lubricant has a marked effect on the shape of pressure-distance curves by influencing the effective coefficient of friction and heat transfer coefficient. Temperature, extrusion ratio and strain rate mainly influence the level of pressure-distance curves. Significance of specially designed dish shaped dies, avoiding the dead metal zone and the importance of extrusion limit diagrams for different materials on the available press capacity has also been highlighted.Deformation behaviour of the hi-tech materials; discontinuously reinforced metal matrix composites (MMCs) and aluminium-lithium alloys using hot extrusion and closed die forging, have been carried out. Parameters have been optimized to extrude rods and thin walled circular MMC tubes of aluminium alloy (2124/6061)-SiCp MMCs having varying volume fractions of SiCp. This developmental work has been carried out using powder metallurgy, liquid metallurgy and spray atomization and deposition routes, in joint collaboration with several R & D organizations.Hot extrusion being an important production technique, results of these experiments can be directly transferred to industries. Similar deformation studies either by closed die or by isothermal forging have been made to develop components.The pilot plant level facility is available for any industry for carrying out developmental R & D work. NPL welcomes such collaboration.

A kinetic equation for damage during superplastic deformation

In this paper a kinetic equation for the isotropic damage during superplastic deformation is proposed, based on the thermodynamic theory of irreversible processes with internal state variables and the normality criterion. The damage variable D during superplastic deformation is non-linear with the equivalent plastic strain ξ P, and it is shown that D is affected strongly by the triaxiality stress ratio (σ m/σ eq). Furthermore, in order to demonstrate the efficiency to the proposed equation, superplastic deformation experiments were performed on aluminum alloy LY12CZ and brass H62 without any pre-treatment. The comparision with the experimental results is presented on the influence of the triaxiality stress ratio on the equivalent strain to rupture: good correlation is found between the theoretical and experimental results. Therefore, this equation for damage may reflect successfully superplastic damage behaviour during superplastic deformation processes.

Fracture Behavior and Strength of Stepped-Lap Bonded Joint with Adhesive Resin Under Tensile Loading.

Nonlinear fracture behavior of stepped-lap bonded joints is studied. The joints used have adherends of eight kinds of metals : three types of carbon steel, and four types of aluminum alloy and brass. The joints also have various thicknesses, lap lengths and step numbers. The effect of Young's modulus and yield strength of adherend material on the joint strength is calculated by means of elasto-plastic finite element method analysis. It is found that the strength of the joint which yields at an adherend corner is nearly equal to the yield strength of the adherend material, because the displacement of the adhesive layer increases abruptly after the adherend yield, and exceeds the layer's deformation capacity. The joint strength diagrams obtained by the strength prediction method applying our adhesion criteria show good agreement with the experimental results for all the present joins having various dimensions and materials.