High-Strength Weldable Corrosion-Resistant Aluminum Alloy for Bearing Building Structures

A weldable corrosion-resistant alloy based on the Al - Zn - Mg system has been developed. The alloy has high strength characteristics (σ_r ≥ 500 MPa and σ_0.2 ≥ 450 MPa) and is well weldable (the factor of weld concavity is 0.8 – 0.95). The substrate metal and welded joints of this metal are characterized by high corrosion resistance, good ductility and fracture toughness, and high fatigue resistance. The alloys and the process of its production are based on known scientific achievements of the All-Russia Institute of Light Alloys (VILS) in the field of alloys of the Al - Zn - Mg system and in the field of alloying of aluminum alloys with scandium. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 30 – 35, August, 2005.     

Kinetics and mechanism of interaction of aluminum and magnesium of Al-Mg-Bi ternary system with water

The kinetics and mechanism of interaction of aluminum and magnesium of an Al-Mg-Bi ternary system with water were obtained using the method of high-temperature volumetry at high pressures and temperatures of 225–325°C. The kinetic parameters of the reaction, i.e., the rate constant, activation energy, and degree of conversion, were calculated and the mechanism of corrosion dissolution of activated by bismuth aluminum and magnesium in water with the release of hydrogen at high rates was suggested. The kinetic parameters during the interaction of aluminum activated by bismuth and magnesium in boehmite (AlOOH), and magnesium hydroxide (Mg(OH)₂) with water with the release of hydrogen at a rate of 3196–4033 l/(m² min) in the investigated temperature range were determined. The nanostructured particles of Al-Mg-Bi alloys were detected using a JSM6490 LV electron microscope (Japan).     

Carburization resistance of nickel-base, heat-resisting alloys

Cast heat-resisting alloys containing 45 or 60 wt% nickel were isothermally carburized in flowing gas mixtures of H₂–5CH₄ (volume percent) at temperatures of 900–1,100 °C, and their performance compared with that of standard commercial grades containing 30–35% nickel. Chromium-rich M₇C₃ and M₂₃C₆ precipitated internally in all materials, to depths which increased according to parabolic kinetics. Comparison of the rate constants with those predicted from Wagner’s diffusion theory showed that carbon diffusion through a chromium-depleted alloy matrix was the rate-controlling process. The 45% nickel alloys carburized more slowly than the 30–35% nickel grades as a result of decreased carbon solubility and diffusivity at the higher nickel level. The 60% nickel alloys also contained aluminum. At higher temperatures, diffusion of aluminum to the surface led to A1₂O₃ scale formation and enhanced carburization resistance. The degree of protection obtained depended on alloy aluminum content. P. Becker—On secondment from Schmidt & Clemens GmbH, Post Fach 1140, 51779 Lindlar, Germany.     

Silicon as an alloying element in ferrite stainless steels containing 8–13% Cr

A jumpwise improving of the passivation ability and pitting-resistance of the Fe-(8–13)% Cr-(0.32–2.7)% Si alloys upon surpassing the limit of ∼14–15 at % by the chromium and silicon summary concentration is found. It is suggested that the nature of the critical summary concentration C _Cr + C _Si is identical to that in Fe-Cr binary alloys; it is caused by the silicon building-in to the alloy’s crystal lattice and its substitution for chromium in the statistical proportion to its atomic part in alloys. When the summary concentration C _Cr + C _Si approaches ∼14–15 at %, each elementary cell in the Fe bcc lattice must necessarily contain either a Cr atom or the proportional number of Si atoms. The improved passivation ability and pitting-resistance of the Fe-Cr-Si alloy, compared with the Fe-Cr alloys, is explained by the fayalite formation at the alloy surface. Original Russian Text ? I.I. Reformatskaya, I.G. Rodionova, A.N. Podobaev, I.I. Ashcheulova, E.V. Trofimova, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 6, pp. 591–597.     

Critical potential of the surface development of Ag-Au alloys

Based on the model taking into account the appearance of a morphological instability and the evolution of a surface with time during the selective anodic dissolution of a homogeneous A-B alloy with the predominant content of the electrochemically negative metal A, equations for the critical potential E _cr and overpotential η_cr of the surface development are derived. Criteria of the nature of chemical hindrances of the selective dissolution in the over-critical range are formulated. The E _cr and η_cr values corresponding to the breakage of the morphological stability of the A-B alloy surface (with the atomic silver part X _Ag = 0.65 to 0.95) in an acidic nitrate solution containing diverse amounts of silver ions (10⁻⁴ to 10⁻² M) are experimentally found. The character of the effect of the atomic gold content in the alloy and the concentration of silver ions in the solution on η_cr and E _cr values of the alloys is determined. The nature of the kinetic limitations of the selective dissolution in the over-critical potential range is clarified. Original Russian Text ? A.V. Vvedenskii, O.V. Koroleva, O.A. Kozaderov, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 1, pp. 28–37.     

Tunnel scanning microscopy and spectroscopy in studying Fe-Cr stainless steels

Scanning tunnel microscopy (STM) and scanning tunnel spectroscopy (STS) are used in studying highly pure iron and chromium and Fe-x%Cr (2.4 ≤ x ≤ 60 wt %) alloys at the air boundary, as well as some of the alloys in 0.01 N H₂SO₄. The obtained probability coefficients (α) of the electron tunnel transfer from a specimen to the needle and the slopes (β) of the logarithmic U _t /log (I _t ) dependences as functions of the chromium content in Fe-Cr alloys confirm the critical compositions of the alloys containing ∼6.5 and 10–13% chromium, which is in accord with the results of the steady-state and transient electrochemical measurements. A correlation between these critical compositions of the alloys and sharp changes in the histograms of α and β values is observed. Pronounced extreme properties of the Fe-25.2% Cr alloy surface, which corresponds to the inclusion of Cr atoms in tetrahedral voids of the alloy crystal lattice, are noticed. Original Russian Text ? E.V. Trofimova, E.V. Kasatkin, I.I. Reformatskaya, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 3, pp. 245–255. The work was financially supported by the Russian Foundation for Basic Research, project no. 04-03-32337.     

The Effect of Cr on the Oxidation of Ni–10 at% Al in 1 atm O2 at 900–1000°C

The oxidation of three Ni–xCr–10Al alloys with a constant Al content of 10 at% and containing 3, 5, and 10 at% Cr was investigated at 900–1000°C in 1 atm of pure oxygen and compared to the behavior of Ni–10Al. At both temperatures, an external NiO scale overlying a zone of internal-oxide precipitates formed on Ni–10Al and Ni–3Cr–10Al: in addition, a discontinuous Al₂O₃ layer formed at the front of the internal oxidation for Ni–3Cr–10Al. An exclusive external scale of Al₂O₃ formed at most places on Ni–5Cr–10Al at 900°C, while, at some sites, the same alloy formed an outer NiO layer overlying an internal oxidation zone. The scales formed on Ni–5Cr–10Al at 1000°C were complex, but eventually a protective Al₂O₃ layer developed either at the alloy surface or beneath a region containing a mixture of different oxides. Finally, an exclusive external Al₂O₃ layer formed on Ni–10Cr–10Al at both temperatures. Thus, the addition of sufficient chromium to Ni–10Al produced a classical third-element effect, inducing the transition between internal and external oxidation of aluminum under a constant Al content. A possible mechanism for the effect of chromium on the oxidation of Ni–10Al is discussed on the basis of an extension to ternary alloys of a criterion first proposed by Wagner for the transition between internal and external oxidation of the most-reactive component in binary alloys.     

Deposition of amorphous phosphate coatings on aluminum

Amorphous phosphating of aluminum and its alloys AДH, Д1, and Д16 is studied. It is found that uniform coatings are deposited at pH 4.5 at a temperature of 50°C from the solution containing MoO ₄ ²⁻ promoting ions. By using the x-ray photoelectron spectroscopy, it is shown that phosphates of aluminum and Mo(IV, V) are the predominant components of phosphate coating. By the “thin layer” method, it is found that, in the near-surface layer, alkalization of solution takes place depending on the initial pH value. The dependence pH_dep = pH_in ± 0.3 is linear. Phosphate coatings, which are deposited in the solution pretreated with magnetic field (MF), differ in their properties from the coatings obtained by the conventional procedure. MF can increase or decrease the corrosion resistance of phosphate coating depending on the aluminum alloy. Original Russian Text ? V. Burokas, A. Martushene, A. Ruchinskene, A. Sudavichyus, G. Bikul’chyus, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 4, pp. 373–378.     

IncoMAPAl—9052合金在3.5%NaCl溶液中的应力腐蚀行为

采用双悬臂梁试样,实验研究了IncoMAP Al-9052合金在3.5％NaCl溶液中的应力腐蚀开裂(SCC)行为。结果表明该种合金的裂纹扩展机制有别于常规的铝合金。其初期阶段的裂纹扩展过程可划分为三个阶段,在每一阶段的裂纹扩展机制可能是不同的,但其裂纹扩展的主要机制为氢脆。     

Low-Temperature Interface Reaction Between Titanium and the Eutectic Silver-Copper Brazing Alloy

Reaction zones formed at 790 °C between solid titanium and liquid Ag-Cu eutectic alloys (pure and Ti-saturated) have been characterized. When pure Ag-Cu eutectic alloy with 40 at.% Cu is used, the interface reaction layer sequence is: αTi/Ti₂Cu/TiCu/Ti₃Cu₄/TiCu₄/L. Because of the fast dissolution rate of Ti in the alloy, the reaction zone remains very thin (3-6 μm) whatever the reaction time. When the Ag-Cu eutectic alloy is saturated in titanium, dissolution no longer proceeds and a thicker reaction zone with a more complex layer sequence grows as the reaction time increases. Four elementary chemical interaction processes have been identified in addition to Ti dissolution in the liquid alloy. These are growth of reaction layers on Ti by solid state diffusion, nucleation and growth from the liquid of TiCu₄, isothermal solidification of silver and, finally, chemical conversion of the Cu-Ti compounds by reaction-diffusion in the solid state. A mechanism combining these processes is proposed to account for the constitution of Ti/Ag-Cu/Ti joints brazed at 780-800 °C.     

Influence of Pre-oxidation on the Corrosion and Mechanical Strength of Fe–25Cr and Fe–25Cr–20Ni Alloys at 973 K

The influence of pre-oxidation on the corrosion and mechanical strength of Fe–25Cr and Fe–25Cr–20Ni alloys was investigated in N₂–0.1SO₂ at 973 K with and without mechanical loadings. About 0.1μm-thick Cr₂O₃ scales formed on the Fe–25Cr alloy by pre-oxidation in Ar. However, spinel oxides of (Fe,Cr)₃O₄ remained on the Cr₂O₃ and voids formed at the oxide/metal interface on Fe–25Cr–20Ni after pre-oxidation in Ar. The preformed oxides are very effective in preventing corrosion of the alloy surfaces. The preformed oxides are also beneficial to increase the strength of the alloys in corrosive environments. The effects of pre-oxidation on Fe–25Cr are stronger than those of Fe–25Cr–20Ni due to the different characteristics of the preformed oxides.     

High-temperature chloride corrosion of industrial ЭИ827 and BЖ-85 nickel alloys

High-temperature chloride corrosion (ChC) of ЭИ827 and BЖ-85 nickel alloys was investigated in a temperature range of 773 to 1173 K and exposure time of 1 to 50 h in the MgCl₂-KCl-NaCl ternary eutectic and oxidation in air (at 873 to 1273 K for 500 h). The ChC is intergranular, intensely develops starting from a temperature of 973 K, and results in softening due to the strong extraction of chromium and aluminum from the base alloy. Other things being equal, the ChC rate exceeds the oxidation rate in air by two to three orders of magnitude. Original Russian Text ? I.V. Oryshich, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 6, pp. 640–644.     

Comparison of Oxidation Behavior and Electrical Properties of Doped NiO- and Cr2O3-Forming Alloys for Solid-Oxide, Fuel-Cell Metallic Interconnects

The goal of this paper was to determine if NiO-forming alloys are a viable alternative to Cr₂O₃-forming alloys for solid-oxide fuel-cell (SOFC) metallic interconnects. The oxide-scale growth kinetics and electrical properties of a series of Li- and Y₂O₃-alloyed, NiO-forming Ni-base alloys and La-, Mn-, and Ti-alloyed Fe–18Cr–9W and Fe–25Cr base ferritic Cr₂O₃-forming alloys were evaluated. The addition of Y₂O₃ and Li reduced the NiO scale growth rate and increased its electrical conductivity. The area-specific-resistance (ASR) values were comparable to those of the best (lowest ASR) ferritic alloys examined. Oxidation of the ferritic alloys at 800°C in air and air+10% H₂O (water vapor) indicated that Mn additions resulted in faster oxidation kinetics/thicker oxide scales, but also lower oxide scale ASRs. Relative in-cell performance in model SOFC stacks operated at 850°C indicated a 60–80% reduction in ASR by Ni+Y₂O₃, Ni+Y₂O₃, Li, and Fe–25Cr+La,Mn,Ti interconnects over those made from a baseline, commercial Cr₂O₃-forming alloy. Collectively, these results indicate that NiO-forming alloys show potential for use as metallic interconnects.     

Hydrogenation properties and crystal structures of Ti−Mn-V BCC solid solution alloys

We have proposed new hydrogen absorbing alloys of the ‘Laves phase related BCC solid solution alloy’, the hydrogen capacity of which reaches almost double that of conventional rare-earth based AB₅ alloys. We have reported the hydrogen absorbing properties of Ti−V−Mn, Ti−V−Cr and T−V−Mn−Cr alloys. It has been accepted that the crystal structural change of BCC hydrogen absorbing alloys is the same as that of V metal. The mono-hydride (H/M=1) of V metal has a BCT structure and the di-hydride (H/M=2) has an FCC structure. However, we recently found that the Ti−V−Mn alloy shows different behaviors in phase transformation with hydrogenation to V metal. We found three hydride phases with a BCC, a deformed FCC and an FCC structure in the Ti−V−Mn solid solution alloy-H₂ system. The deformed FCC hydride phase has not yet to our knowledge been reported. The lattice constant of the deformed FCC was 0.407 nm, one axis of which is reduced by about 4%. Its single-phase region appeared at a hydrogen content between 0.8 H/M and 1.0 H/M in absorption at 298 K. The lower plateau observed due to formation of the deformed FCC hydride phase gives an increase of effective hydrogen capacity by decreasing hydrogen remaining in the alloy in the desorption process. This article based on a presentation made in the symposium “The 2nd KIM-JIM Joint Symposium: Hydrogen Absorbing Materials”, held at Hanyang University, Seoul, Korea, October 27–28, 2000 under the auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Ti55合金电子束焊缝氢致延迟裂纹的扩展机理

钛合金广泛应用于军事航空领域 ,但是一些钛合金在焊接条件下 ,焊缝会产生氢致延迟裂纹 ,其致裂机理尚不十分清楚。通过充氢CT(Compacttension)试件的恒载拉伸试验 ,研究了氢浓度对Ti5 5合金电子束焊缝裂纹尖端应力强度因子门槛值Kth及裂纹扩展速率da/dt的影响规律 ,分析了氢致延迟裂纹扩展的机理。结果表明 ,氢在Ti5 5合金焊缝中的固溶度约为 79× 10 -4%。当充氢浓度C0 低于 79× 10 -4%时 ,随着焊缝氢浓度C0 的增大 ,裂纹开始扩展的应力强度因子门槛值Kth迅速减小 ,而裂纹扩展速率da/dt随着C0 的增大而增大 ;C0 为 79× 10 -4%时 ,Kth为最小值并呈恒值特征。裂纹尖端应力场诱导氢原子扩散导致氢化物TiH2 析出是Ti5 5合金电子束焊缝氢致延迟裂纹扩展的主要机制     

The effect of Si addition on crystallization behavior of amorphous Al-Y-Ni alloy

This article reports the effect of silicon (Si) addition upon the crystallization behavior and mechanical properties of an amorphous AlYNi alloy. An amount of 1 at.% Si was added to a base alloy of Al₈₅Y₅Ni₁₀ either by substitution for yttrium (Y) to form Al₈₅Y₄Ni₁₀Si₁, or by substitution for nickel (Ni) to form Al₈₅Y₅Ni₉Si₁. Differential scanning calorimetry (DSC) of all three alloys showed three exothermic peaks. Comparing the peak temperature for the first exothermic peak, a significant shift occurs toward the lower temperature. This indicates that 1 at.% substitutions of Y or Ni by Si decreases the stability of the amorphous phase. DSC study of these amorphous alloys during isothermal annealing at temperatures about 5–15 K lower than their first crystallization peaks showed that the formation of α-Al nanocrystals via primary crystallization occurred without an incubation period. The Avrami time exponent (n) of the primary crystallization from the amorphous structure was determined to be 1.00–1.16 using the Johnson-Mehl-Avrami (JMA) analysis. This suggested a diffusion-controlled growth without nucleation. However, a DSC study of these amorphous alloys during isothermal annealing at higher temperatures between 585 and 605 K showed a clear incubation period during the formation of the Al₃Ni and Al₃Y intermetallic phases. An n value of 3.00–3.45 was determined using JMA analysis. This suggested that the transformation reaction involved a decreasing nucleation rate and interface-controlled growth behavior. The tensile strength σ_f and Vickers hardness for these amorphous alloys are in the range 1050–1250 MPa and 380–398 diamond pyramid hardness number (1 diamond pyramid hardness number=1 kg/mm²=9.8 MPa), respectively.     

Influence of Al-Ti-B addition on the microstructure and mechanical properties of A356 alloys

The mechanical properties (σb,σ0.2,and δ) and fracture behavior of tensile specimens of the refined A356 alloys were investigated as a function of the addition level of Al-Ti-B master alloy under both as-cast and T6 heat-treated conditions. The results show that as the addition level of Al-5Ti-1B master alloy increases from 0.1 wt.% to 5.0 wt.%,the mechanical properties of refined A356 alloys improve steadily and then decrease slightly under both as-cast and T6 heat-treated conditions. Also,they display exc...     

Mechanisms of grain refinement in aluminum alloys in the process of severe plastic deformation

A study of the mechanisms of grain refinement in the process of severe plastic deformation of two aluminum alloys, i.e., 2219 bearing nanometric particles of Al₃Zr and low-alloy Al-3% Cu, is described. The alloys are deformed by the method of equal channel angular pressing at 250°C to a maximum strain degree of about 12. The angles of (sub)grain boundaries in alloy 2219 are determined with the help of transmission electron microscopy by the method of Kikuchi lines. The evolution of the microstructure in alloy Al-3% Cu is studied with the help of grain-boundary maps obtained by the method of electron back-scattered diffraction. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 14–19, February, 2006.     

Relation between phase transformations and mechanical properties of alloys in the Ti−Al−W−Zr system

Conclusions  

Mechanical properties of the cast intermetallic alloy Ti-43Al-7(Nb,Mo)-0.2B (at %) after heat treatment

A new approach to obtaining fine-grained structure in intermetallic-compound alloys such as γ-TiAl + α₂-Ti₃Al has been suggested. This approach is based on the use of alloys that solidify as the β phase, which contain β-stabilizing additives such as Nb and Mo and are characterized by the small size of crystallites already in the cast state; in these alloys, a simple heat treatment makes it possible to substantially decrease the fraction of the lamellar component and to increase the content of the β(B2) phase. It is shown on the example of the Ti-43Al-7(Nb,Mo)-0.2B (at %) alloy that this heat treatment ensures superplastic properties in the material in the temperature range of T = 1050–1130°C at a deformation rate $ \dot \varepsilon A new approach to obtaining fine-grained structure in intermetallic-compound alloys such as γ-TiAl + α₂-Ti₃Al has been suggested. This approach is based on the use of alloys that solidify as the β phase, which contain β-stabilizing additives such as Nb and Mo and are characterized by the small size of crystallites already in the cast state; in these alloys, a simple heat treatment makes it possible to substantially decrease the fraction of the lamellar component and to increase the content of the β(B2) phase. It is shown on the example of the Ti-43Al-7(Nb,Mo)-0.2B (at %) alloy that this heat treatment ensures superplastic properties in the material in the temperature range of T = 1050–1130°C at a deformation rate = 1.7 × 10⁻⁴ K⁻¹. Under these temperature-strain-rate conditions, relative elongations such as δ = 160–230% and low flow stresses such as σ = 36–100 MPa characteristic of superplastic flow have been obtained. It has been shown for the first time for the intermetallic γ-TiAl + ga₂-Ti₃Al alloy that a sheet semifinished product cut out from an ingot subjected only to heat treatment can have plasticity acceptable for press forming. Original Russian Text ? V.M. Imayev, R.M. Imayev, T.G. Khismatullin, 2008, published in Fizika Metallov i Metallovedenie, 2008, Vol. 105, No. 5, pp. 516–522. The author is also known by the name Imayev. The name used here is a transliteration under the BSI/ANSI scheme adopted by this journal.—Ed.