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Publisher: Springer-Verlag (Total: 2573 journals)

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 Acta Metallurgica Sinica (English Letters)Journal Prestige (SJR): 0.576 Citation Impact (citeScore): 2Number of Followers: 7      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1006-7191 - ISSN (Online) 2194-1289 Published by Springer-Verlag  [2573 journals]
• Temperature Effects on the Microstructures of Mg–Gd–Y Alloy Processed
by Multi-direction Impact Forging
• Abstract: Abstract A high strain rate multi-directional impact forging (MDIF) was applied to a solutionized Mg–Gd–Y–Zr alloy in the temperature range of 350–500 °C. Results demonstrate that the dominant deformation mode is twinning at a temperature below 400 °C, whereas at a medium temperature of 450 °C considerable continuous dynamic recrystallization was promoted by {10–12} extension twins. At a higher temperature of 500 °C, twinning activation was suppressed. New DRX grains were observed but their sizes were much bigger than those resulting from the MDIFed 50 passes at 450 °C, which are ascribed to the larger grain boundary mobility and atomic diffusion at 500 °C. Moreover, a non-basal weak texture was gained afterward MDIF at each temperature, which is credited to the MDIF process and the minor strain applied in each pass.
PubDate: 2019-12-02

• Effect of Sleeve Plunge Depth on Interface/Mechanical Characteristics in
Refill Friction Stir Spot Welded Joint
• Abstract: Abstract Refill friction stir spot welding was employed to produce 6061-T6 aluminum alloy joints with different sleeve plunge depths. The interface characteristics of joint-line remnant and hook are investigated by optical and scanning electron microscopy. The joint-line remnant consists of primary bonding region and secondary bonding region, and two types of hook can be identified as downward hook and upward hook. Tensile shear results demonstrate that joint-line remnant and hook make interaction effects on tensile shear properties. The optimal joint is achieved when sleeve plunge depth was 2.0 mm with the corresponding failure load of 8673.4 N. Three different types of fracture mode are exhibited in joints produced at different sleeve plunge depths, which are closely related with the morphology of interface characteristics.
PubDate: 2019-12-02

• Influence of Yttrium Addition on the Reduction Property of Tungsten Oxide
Prepared via Wet Chemical Method
• Abstract: Abstract W–Y2O3 composite nanopowders prepared via wet chemical method exhibit unique morphologies and microstructures. The yttrium addition during chemical reaction process affects not only the composition of tungsten acid hydrate precursors, but also the reduction property of tungsten oxide transformed from precursors. In this study, the morphology evolution of the samples with and without yttrium during reduction process has been studied, and it is found that the addition of yttrium can exert a strong influence on the reduction route of tungsten oxide and the final morphology of tungsten particles. The cause of the difference of reduction route and tungsten particle morphology is also analyzed. It is suggested that the composition of the samples with yttrium at the beginning of reduction is pure cubic system WO3(c-WO3), and the c-WO3 particles have c-WO3 whiskers attached to the surface. This kind of whiskers is essential for c-WO3 to be reduced directly to tungsten and also helpful to obtain W–Y2O3 powders with small size and good uniformity.
PubDate: 2019-12-02

• Ultra-fine-Grained Ferrite Prepared from Dynamic Reversal Austenite During
Warm Deformation
• Abstract: Abstract The ultra-fine-grained ferrite (UFGF) with the size of less than 1 μm is often difficult to be obtained for low-alloyed steel in practical production processing. In this study, considering the rod and wire production process, a new method for preparing the UFGF with submicron scale is proposed by warm deformation of six passes with total strain of 2.6, followed by the cooling process in Gleeble-3500 thermo-mechanical simulator. The results show that the UFGF with an average size of 0.64 μm could be obtained via the phase transformation from austenite grains with an average size of 3.4 μm, which are achieved by the deformation-induced reversal austenization during the high strain rate warm deformation. The main driving force for the reversal transformation is the stress. And the interval between the passes also plays an important role in the reversal austenization.
PubDate: 2019-12-02

• Microstructure, Texture Evolution, and Mechanical Properties of
ECAP-Processed ZAT522 Magnesium Alloy
• Abstract: Abstract In this work, the high-strength Mg–5Zn–2Al–2Sn (ZAT522, in wt%) Mg alloys was obtained at 220 °C and 130 °C by a two-step equal channel angular pressing (ECAP). For each stage, two passes were used. The results showed a remarkable grain refinement after the first stage of ECAP (A2 samples), leading to a fine-grained structure with average size of 1.40 μm. The additional stage (A4 samples) caused further grain refinement to 1.18 μm, and an ultra-fine grain structure (700 nm) appeared in the precipitate-rich region. The grain refinement mechanism for both samples was discussed in detail. To this end, the original extrusion fiber texture evolved into a new strong texture characterized by the base planes tilted toward the ECAP shear plane, with a higher Schmid factor value of 0.34. Compared with the as-extruded alloy, the yield strength of the A2 samples increased from 180 to 245 MPa, which was mainly attributed to the combined effects of grain boundary strengthening and precipitation strengthening. In the case of A4 samples, the dislocation strengthening resulted in a net increase in yield strength to 335 MPa, while the ductility was significantly reduced.
PubDate: 2019-12-02

• Friction Stir Processing of Magnesium Alloys: A Review
• Abstract: Abstract Magnesium (Mg) alloys have been extensively used in various fields, such as aerospace, automobile, electronics, and biomedical industries, due to their high specific strength and stiffness, excellent vibration absorption, electromagnetic shielding effect, good machinability, and recyclability. Friction stir processing (FSP) is a severe plastic deformation technique, based on the principle of friction stir welding. In addition to introducing the basic principle and advantages of FSP, this paper reviews the studies of FSP in the modification of the cast structure, superplastic deformation behavior, preparation of fine-grained Mg alloys and Mg-based surface composites, and additive manufacturing. FSP not only refines, homogenizes, and densifies the microstructure, but also eliminates the cast microstructure defects, breaks up the brittle and network-like phases, and prepares fine-grained, ultrafine-, and nano-grained Mg alloys. Indeed, FSP significantly improves the comprehensive mechanical properties of the alloys and achieves low-temperature and/or high strain rate superplasticity. Furthermore, FSP can produce particle- and fiber-reinforced Mg-based surface composites. As a promising additive manufacturing technique of light metals, FSP enables the additive manufacturing of Mg alloys. Finally, we prospect the future research direction and application with friction stir processed Mg alloys.
PubDate: 2019-12-02

• Effect of laser power and deposition environment on the microstructure and
properties of direct laser metal-deposited 12CrNi2 steel
• Abstract: Abstract Direct laser metal deposition was used for preparing blocks of steel 12CrNi2 using four different laser powers under two different deposition environments including atmospheric environment and Ar-protected chamber. The results showed that microstructures and mechanical properties were significantly affected by different laser powers. Increasing laser power and deposition in Ar chamber will lead to a decrease in the quantity and size of the voids, which brings more elongation to the samples. Bainitic microstructure was replaced by Widmanstatten ferrite and pearlite, and the amount of proeutectoid ferrite increased with increasing laser power. Moreover, microstructures of previous layers were completely altered in high laser power. Excessive heat accumulation by using high heat input can produce equiaxed ferritic grains with the pearlites in previously deposited layers. Hardness of deposited samples increased from the bottom layer toward the top layer. By using a diode laser with a spot diameter size of 2 mm, the 900-W laser power is suitable for producing crack- and void-free samples. However, post-deposition heat treatment is necessary for obtaining homogeneous desired microstructure and grain size in the manufactured samples.
PubDate: 2019-12-02

• Oxidation Performance and Interdiffusion Behavior of a Pt-Modified
Aluminide Coating with Pre-deposition of Ni
• Abstract: Abstract To refrain the interdiffusion of elements while holding good oxidation resistance, a (Ni,Pt)Al/Ni composite coating was prepared by sequential treatments of electroplating Ni and Pt and successive gaseous aluminization. In comparison with normal (Ni,Pt)Al coating, high-temperature performance of the composite coating was evaluated in isothermal oxidation test at 1100 °C. Both the two coatings exhibited good resistance against high-temperature oxidation, but the interdiffusion of elements between composite coating and single-crystal (SC) superalloy substrate was greatly relieved, in which the thickness of secondary reaction zone (SRZ) and the amount of precipitated topologically close-packed phase in the SC alloy matrix were significantly decreased. Mechanisms responsible for delaying rate of coating degradation and SRZ growth/propagation are discussed.
PubDate: 2019-12-01

• Site Occupation of Nb in γ -TiAl: Beyond the Point Defect Gas
Approximation
• Abstract: Abstract Microalloying is an effective approach to improve the mechanical properties of γ-TiAl intermetallic compound. Knowledge about the site occupancy of the ternary alloying element in the crystal lattice of γ-TiAl is highly demanded in order to understand the physics underlying the alloying effect. Previous first-principle methods-based thermodynamic models for the determination of the site occupancy were based on the point defect gas approximation with the interaction between the point defects neglected. In the present work, we include the point defect interaction energy in the thermodynamic model, which allows us to predict the site occupancy of the ternary alloying element in γ-TiAl beyond the point defect gas approximation. The model is applied to the γ-TiAl–Nb alloy. We show that, at low temperature, the site occupancy of Nb atoms depends on the composition of the alloy: Nb atoms occupy the Al sublattice for the Ti-rich alloy but occupy Ti sublattice for the Al-rich alloy. The fraction of Nb atoms occupying Al sublattice in the Ti-rich alloy decreases drastically, whereas the fraction of Nb atoms on the Ti sublattice in the Al-rich alloy decreases slightly with increasing temperature. At high temperature, Nb atoms occupy dominantly the Ti sublattice for both the Ti-rich and Al-rich alloys. The interaction between the point defects makes the Ti sublattice more favorable for the Nb atoms to occupy.
PubDate: 2019-12-01

• Effect of Cl − Concentration on the SCC Behavior of 13Cr Stainless Steel
in High-Pressure CO 2 Environment
• Abstract: Abstract An effect of Cl− concentration on the stress corrosion cracking (SCC) behavior of 13Cr stainless steel was investigated by employing electrochemical measurements and the slow strain rate tensile tests. These tests were conducted in various solutions with different concentrations of NaCl at 90 °C under 3 MPa CO2 with 3 MPa N2. The results indicate that the passive film of the specimen formed in the 10% NaCl solution has the best protective effect on the matrix. The SCC susceptibility does not increase with increasing the chloride ion concentration, the lowest SCC susceptibility occurs when the NaCl concentration is 10%, and the specimens show higher SCC susceptibility in the 5% NaCl and 20% NaCl solutions.
PubDate: 2019-12-01

• Stern–Geary Constant for X80 Pipeline Steel in the Presence of Different
Corrosive Microorganisms
• Abstract: Abstract The Stern–Geary constant (B value) is indispensable to measure the corrosion rate in the microbiologically influenced corrosion (MIC) systems. Linear polarization resistance (LPR) and weight loss methods were used to study the variation of B values for X80 pipeline steel in the presence of Pseudomonas aeruginosa, Acetobacter aceti and Desulfovibrio vulgaris. The results showed that B values in the presence of three different bacteria were 35.60 ± 0.55 mV, 33.00 ± 1.00 mV and 58.60 ± 0.55 mV, respectively, suggesting that the change of corrosion system significantly affected the B values of X80 pipeline steel. This work further indicated that the determination of B values is necessary to accurately measure the MIC rate by LPR method.
PubDate: 2019-12-01

• Growth of Gallium Nitride Films on Multilayer Graphene Template Using
Plasma-Enhanced Atomic Layer Deposition
• Abstract: Abstract In this work, the GaN thin films were directly deposited on multilayer graphene (MLG) by plasma-enhanced atomic layer deposition. The deposition was carried out at a low temperature using triethylgallium (TEGa) precursor and Ar/N2/H2 plasma. Chemical properties of the bulk GaN and GaN–graphene interface were analyzed using X-ray photoelectron spectroscopy. The sharp interface between GaN and graphene was verified via X-ray reflectivity and transmission electron microscope. The microstructures and the nucleation behaviors of the GaN grown on graphene have been also studied. The results of grazing incidence X-ray diffraction and Raman spectrum indicate that the as-deposited sample is polycrystalline with wurtzite structure and has a weakly tensile stress. Optical properties of the sample were investigated by photoluminescence (PL) at room temperature. The successful growth of GaN on MLG at a low temperature opens up the possibility of ameliorating the performance of electronic and optical devices based on GaN/graphene heterojunction.
PubDate: 2019-12-01

• Effects of Dissimilar Alumina Particulates on Microstructure and
Properties of Cold-Sprayed Alumina/A380 Composite Coatings
• Abstract: Abstract In this study, alumina/A380 composite coatings were fabricated by cold spray. The influence of alumina particulates’ morphology (spherical and irregular) and content on the deposition behavior of the coatings (including surface roughness, surface residual stress, cross-sectional microstructure and microhardness) was investigated. Results revealed that the spherical alumina mainly shows micro-tamping effect during deposition, which result in remarkable low surface roughness and porosity of the coatings. In addition, very low deposition efficiency and good interfacial bonding between the coating and the substrate were achieved. For irregular alumina particles, the embedding of ceramic particulates in the coating was dominant during deposition process, resulting in high retention in the final deposit. However, it showed limited influence on porosity, surface roughness and interfacial bonding of the deposit. The coatings containing irregular alumina particulates exhibited much higher microhardness than those containing spherical alumina due to the higher load-bearing capacity of deposited alumina.
PubDate: 2019-12-01

• Effect of Co on Microstructure and Stress Rupture Properties of K4750
Alloy
• Abstract: Abstract The effects of substituting Co for Fe on the microstructure and stress rupture properties of K4750 alloy were studied. The microstructure of the alloy without Co (K4750 alloy) and the alloy containing Co (K4750-Co alloy) were analyzed. Substitution of Co for Fe inhibited the decomposition of MC carbide and the precipitation of η phase during long-term aging treatment. In K4750-Co alloy, the morphology of MC carbide at the grain boundary (GB) remained dispersed blocky shape and no η phase was observed after aging at 750 °C for 3000 h. However, in K4750 alloy, almost all the MC carbides at GBs broke down into granular M23C6 carbide and needle-like η phase. The addition of cobalt could delay the decomposition of MC carbides, which accordingly restricted the elemental supply for the formation of η phase. The stress rupture tests were conducted on two alloys at 750 °C/430 MPa. When Co is substituted for Fe in K4750 alloy, the stress rupture life increased from 164.10 to 264.67 h after standard heat treatment. This was mainly attributed to increased concentration of Al, Ti and Nb in γ′ phase in K4750-Co alloy, which further enhanced the strengthening effect of γ′ phase. After aging at 750 °C for 3000 h, substitution of Co for Fe can also cause the stress rupture life at 750 °C/430 MPa to increase from 48.72 to 208.18 h. The reason was mainly because MC carbide degradation and η phase precipitation in K4750 alloy, which promoted the initiation and propagation of micro-crack during stress rupture testing.
PubDate: 2019-12-01

• Effects of Temperature on Fretting Corrosion Between Alloy 690TT and 405
Stainless Steel in Pure Water
• Abstract: Abstract In pressurized water reactor, fretting corrosion has become the main reason for the failure of 690TT heat exchanger tubes. The effect of temperature on the fretting corrosion behavior between 690TT tube and 405 stainless steel (SS) bar has been studied during 106 fretting cycles. The overall average coefficient of friction (COF) values descends with an increase in test temperature, while the width of worn scar becomes wider. The severest fretting corrosion happens when the test temperature is at 100 °C. The wear mechanism differs at different test temperatures, from adhesive wear at room temperature to abrasive wear and delamination at 100 °C, to abrasive wear at 200 °C. Deformation slips, high residual strain concentration, and micro-cracks are found which are disadvantageous for the further service performance of the tubes.
PubDate: 2019-12-01

• Effect of Cooling Rate on Microstructure and Mechanical Properties of
Sand-Casted Al–5.0Mg–0.6Mn–0.25Ce Alloy
• Abstract: Abstract This study examines the relationship among cooling rate, microstructure and mechanical properties of a sand-casted Al–5.0Mg–0.6Mn–0.25Ce (wt%) alloy subjected to T4 heat treatment (430 °C × 12 h + natural aging for 5 days), and the tested alloys with wall thickness varying from 5 to 50 mm were prepared. The results show that as the cooling rate increases from 0.22 to 7.65 K/s, the average secondary dendritic arm spacing (SDAS, λ2) decreases from 94.8 to 27.3 μm. The relation between SDAS and cooling rate can be expressed by an equation: $$\lambda_{2} = 53.0R_{\text{c}}^{ - 0.345}$$. Additionally, an increase in cooling rate was shown not only to reduce the amount of the secondary phases, but also to promote the transition from Al10Mn2Ce to α-Al24(Mn,Fe)6Si2 phase. Tensile tests show that as the cooling rate increases from 0.22 to 7.65 K/s, the ultimate tensile strength (UTS) increases from 146.3 to 241.0 MPa and the elongation (EL) increases sharply from 4.4 to 12.2% for the as-cast alloys. Relations of UTS and EL with SDAS were determined, and both the UTS and EL increase linearly with (1/λ2)0.5 and that these changes can be explained by strengthening mechanisms. Most eutectic Al3Mg2 phases were dissolved during T4 treatment, which in turn further improve the YS, UTS and EL. However, the increment percent of YS, UTS and EL is affected by the cooling rate.
PubDate: 2019-12-01

• Hot Deformation Behavior and Processing Map of a Cu-Bearing 2205 Duplex
Stainless Steel
• Abstract: Abstract The hot deformation behavior and processing map of Cu-bearing 2205 duplex stainless steel (2205-Cu DSS) were investigated at temperatures of 950–1150 °C and strain rates of 0.01–10 s−1. The effects of Cu addition and different deformation parameters on deformation behavior were, respectively, characterized by analyzing flow curves, constitutive equations and microstructures. The results indicated that the shapes of flow curves strongly depended on the volume fraction of two phases. When deformed at low strain rate, DRV in ferrite was prompted with increase in the temperature and was further developed to continuous DRX. At high strain rate, flow localization preferentially occurred in ferrite at low deformation temperature due to the strain partitioning and relatively less fraction of ferrite. The activation energy for 2205-Cu DSS was 452 kJ/mol and was found to connect with the variation of strain, strain rate and deformation temperature. The optimum hot deformation parameters for 2205-Cu DSS were obtained in the temperature range of 1100–1150 °C and strain rate range of 0.1–1 s−1 with a peak power dissipation efficiency of 41%. Flow localization was the main way to lead to flow instability. Meanwhile, the Cu-rich precipitates were generated within a few ferrite grains when deformed at temperature lower than 1000 °C. The interaction between dislocations and Cu-rich precipitates at high strain rate, as well as the limited DRV in ferrite and DRX in austenite, contributed to the complex microstructure and flow behavior.
PubDate: 2019-12-01

• Microstructure and Corrosion Behavior of Friction Stir Welded Al Alloy
Coated by In Situ Shot-Peening-Assisted Cold Spray
• Abstract: Abstract To improve the corrosion resistance of friction stir welded (FSW) joints, in situ shot-peening-assisted cold spray coating was applied to the surface of FSW joints. The microstructure and corrosion behavior of the coatings were investigated. The results showed that a dense coating was obtained by cold spraying technology. Moreover, the use of in situ shot-peening-assisted technology significantly reduced the porosity of the coating, which has a positive impact on the microstructure and the mechanical performance. Exfoliation corrosion tests showed that the coating affected positively on the corrosion resistance. On the coated surface, the craters caused by shot-peening particles were corroded in the form of exfoliation corrosion, while the exposed particles were corroded in the form of intercrystalline corrosion. This work provides a new approach to the corrosion protection of FSW joints.
PubDate: 2019-11-22

• Torsional Fatigue Cracking and Fracture Behaviors of Cold-Drawn Copper:
Effects of Microstructure and Axial Stress
• Abstract: Abstract The fatigue cracking and fracture behavior of cold-drawn copper subjected to cyclic torsional loading were investigated in this study. It was found that with increasing stress amplitude, the fracture mode of cold-drawn copper gradually changes from a shear fracture on transverse maximum shear stress plane to a mixed shear mode on both transverse and longitudinal shear planes and finally turns to the shear fracture on multiple longitudinal shear planes. Combining the cracking morphology and the relationship between torsional fatigue cracking and the grain boundaries, the fracture mechanism of cold-drawn copper under cyclic torsional loading was analyzed and proposed by considering the effects of the microstructure and axial stress caused by torsion. Because of the promotion of the grain boundary distribution on longitudinal crack propagation and the inhibition of axial stress on transverse crack grown, the tendency of crack propagation along the longitudinal direction increases with increasing stress levels.
PubDate: 2019-11-02

• Corrosion and Cavitation Erosion Behaviours of Cast Nickel Aluminium
Bronze in 3.5% NaCl Solution with Different Sulphide Concentrations
• Abstract: Abstract The effect of sulphide (Na2S) concentration (SC) on the corrosion and cavitation erosion behaviours of a cast nickel aluminium bronze (NAB) in 3.5% NaCl solution is investigated in this study. The results show that when the SC exceeds 50 ppm, the hydrogen evolution reaction dominates the cathodic process, and a limiting current region appears in the anodic branch of the polarisation curve due to the formation of a copper sulphide film, which is a diffusion-controlled process. After long-term immersion, the increased mass loss rate of NAB with the sulphide additions of 20 and 50 ppm is attributed to the less protective films, which contains a mixture of copper oxides and sulphides. Moreover, NAB undergoes severe localised corrosion (selective phase corrosion, SPC) at the β′ phases and eutectoid microstructure α + κIII. By comparison, NAB undergoes general corrosion and a copper sulphide film is formed in 100 and 200 ppm sulphide solutions. Cavitation erosion greatly increases the corrosion rate of NAB in all solutions and causes a negative potential shift in 3.5% NaCl solution due to the film destruction. However, a positive potential shift occurs in the solutions with SC higher than 50 ppm due to the accelerated mass transfer of the cathodic process. The cavitation erosion mass loss rate of NAB increases with the increase of SC. The occurrence of severe SPC decreases the phase boundary cohesion and causes brittle fracture under the cavitation impact. The corrosion–enhanced erosion is the most predominant factor for the cavitation erosion damage when the SC exceeds 50 ppm.
PubDate: 2019-11-02

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