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Showing papers in "Metals and Materials International in 2009"


Journal ArticleDOI
TL;DR: In this paper, a mathematical model was developed to predict the tensile strength of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters such as tool rotational speed, welding speed, axial force etc., and the tool pin profile.
Abstract: AA2219 aluminium alloy (Al-Cu-Mn alloy) has gathered wide acceptance in the fabrication of lightweight structures requiring a high strength-to-weight ratio and good corrosion resistance. In contrast to the fusion welding processes that are routinely used for joining structural aluminium alloys, the friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed, axial force etc., and the tool pin profile play a major role in determining the joint strength. An attempt has been made here to develop a mathematical model to predict the tensile strength of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters. A central composite design with four factors and five levels has been used to minimize the number of experimental conditions. The response surface method (RSM) has been used to develop the model. The developed mathematical model has been optimized using the Hooke and Jeeves search technique to maximize the tensile strength of the friction stir welded AA2219 aluminium alloy joints.

84 citations


Journal ArticleDOI
TL;DR: In this article, the effects of annealing conditions on microstructural evolution and mechanical properties have been investigated in low carbon, manganese TRIP (Mn TRIP) steel based on a 0.12C-6Mn-0.5Si-3Al alloy system.
Abstract: The effects of annealing conditions on microstructural evolution and mechanical properties have been investigated in low carbon, manganese TRIP (Mn TRIP) steel based on a 0.12C-6Mn-0.5Si-3Al alloy system. The microstructure of cold-rolled sheet subjected to annealing at 760 °C to 800 °C for 30 s to 1800 s consists of a recrystallized ferrite matrix and fine-grained austenite with a phase fraction of 25 % to 35 %. Variation of the annealing conditions remarkably influenced the characteristics of constituent phases and thus affected the tensile strength and elongation. Optimization of microstructural parameters such as grain size and fraction of constituent phases, which control the yield strength, overall work hardening, and the kinetics of strain-induced martensite formation, is thus critical for obtaining an exceptional mechanical balance of the alloy.

75 citations


Journal ArticleDOI
TL;DR: In this article, a non-dominated Sorting Genetic Algorithm (NSGA-II) was used to optimize the cutting conditions, yielding a nondominated solution set that is reported here.
Abstract: Optimization of cutting parameters is important to achieving high quality in the machining process, especially where more complex multiple performance optimization is required. The present investigation focuses on the multiple performance optimization on machining characteristics of glass fiber reinforced plastic (GFRP) composites. The cutting parameters used for the experiments, which were carried out according to Taguchi’s L27, 3-level orthogonal array, were cutting speed, feed and depth of cut. Statistical models based on second-order polynomial equations were developed for the different responses. The Non-dominated Sorting Genetic Algorithm (NSGA-II) tool was used to optimize the cutting conditions, yielding a non-dominated solution set that is reported here.

63 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the mechanism for the formation of inverted pyramidal Ag crystallites at the Si interface as well as the effect of the PbO content of the glass frit on Ag crystallite formation.
Abstract: The reactions between Ag pastes containing two types of PbO-based glass frits and an n-type (100) Si wafer during firing in air at 800 °C were investigated in order to understand the mechanism for the formation of inverted pyramidal Ag crystallites at the Si interface as well as the effect of the PbO content of the glass frit on Ag crystallite formation. Inverted pyramidal Ag crystallites were formed by the precipitation of Ag atoms dissolved in fluidized glass during the subsequent cooling process after firing. PbO in the glass frit did not participate directly in the reaction with the Si wafer. However, its content had a strong influence on the reaction rate at the glass/Si interface and, thus, on the size and distribution of the Ag crystallites. The effect of the PbO content in the glass could be understood from the higher Ag solubility and lower viscosity of the glass at the firing temperature with increasing PbO content. Based on the experimental results, a model was proposed for the formation of Ag crystallites at the glass/Si interface during the firing process of screen-printed thick-film Ag metallization.

62 citations


Journal ArticleDOI
TL;DR: In this article, a twin-roll cast (TRC) AZ31-0.7Ca alloy sheet has been subjected to TMT followed by annealing and its microstructure was evaluated.
Abstract: A twin-roll cast (TRC) AZ31-0.7Ca alloy sheet has been subjected to thermo-mechanical treatment (TMT) followed by annealing and its microstructure was evaluated. The as-cast microstructure of TRC AZ31-0.7Ca alloy is essentially similar to that of TRC AZ31 alloy, except for the presence of Al2Ca dispersoid particles. The presence of Al2Ca particles imparts significant changes to the microstructure of TMT-ed TRC alloy such as the refinement of grain size and evolution of textures different from those of ingot cast and TRC AZ31 alloys.

55 citations


Journal ArticleDOI
TL;DR: In this article, the effects of wire/flux combination on the chemical composition, tensile strength, and impact toughness of the weld metal were investigated and interpreted in terms of element transfer between the slag and the welding metal, i.e., Δ quantity.
Abstract: Submerged arc welding was performed using metal-cored wires and fluxes with different compositions. The effects of wire/flux combination on the chemical composition, tensile strength, and impact toughness of the weld metal were investigated and interpreted in terms of element transfer between the slag and the weld metal, i.e., Δ quantity. Both carbon and manganese show negative Δ quantity in most combinations, indicating the transfer of the elements from the weld metal to the slag during welding. The amount of transfer, however, is different depending on the flux composition. More basic fluxes yield less negative Δ C and Δ Mn through the reduction of oxygen content in the weld metal and presumably higher Mn activity in the slag, respectively. The transfer of silicon, however, is influenced by Al2O3, TiO2 and ZrO2 contents in the flux. Δ Si becomes less negative and reaches a positive value of 0.044 as the oxides contents increase. This is because Al, Ti, and Zr could replace Si in the SiO2 network, leaving more Si free to transfer from the slag to the weld metal. Accordingly, the Pcm index of weld metals calculated from chemical compositions varies from 0.153 to 0.196 depending on the wire/flux combination, and it almost has a linear relationship with the tensile strength of the weld metal.

53 citations


Journal ArticleDOI
TL;DR: In this paper, the hardness characteristics of constituent micro-phases (ferrite and bainite) in a dual-phase API X100 pipeline steel were analyzed by nanoindentation experiments.
Abstract: The hardness characteristics of constituent micro-phases (ferrite and bainite) in a dual-phase API X100 pipeline steel were analyzed by nanoindentation experiments. The measured nano-hardness of the bainite phase is from 3.8 GPa to 4.9 GPa, which is much higher than that of the ferrite phase, which ranged from 1.75 GPa to 2.3 GPa. With the hardness and volume fraction of each micro-phase, attempts were made to predict the overall hardness by applying a simple rule-of-mixture. A comparison between the predicted overall hardness value and the experimentally measured value revealed that the rule-of-mixture can be successfully applied for prediction purposes. The results are discussed in terms of the grain boundary strengthening effect and the indentation size effect.

52 citations


Journal ArticleDOI
TL;DR: In this article, the macro-performance of the automotive TWIP sheet in conjunction with springback was evaluated using simple tension and tension-compression tests to determine anisotropic properties, as well as the Bauschinger, transient, and permanent softening behaviors during reverse loading.
Abstract: In an effort to reduce the weight of vehicles, automotive companies are replacing conventional steel parts with light weight alloys and/or with advanced high strength steels (AHSS) such as dual-phase (DP), twinning induced plasticity (TWIP), and transformation induced plasticity (TRIP) steels. The main objective of this work is to experimentally and numerically evaluate the macro-performance of the automotive TWIP sheet in conjunction with springback. In order to characterize the mechanical properties, simple tension and tension-compression tests were performed to determine anisotropic properties, as well as the Bauschinger, transient, and permanent softening behaviors during reverse loading. For numerical simulations, the anisotropic yield function Yld2000-2d was utilized along with the combined isotropic-kinematic hardening law based on the modified Chaboche model. Springback verification was performed for the unconstrained cylindrical bending and 2D draw bending tests.

51 citations


Journal ArticleDOI
TL;DR: In this article, the performance of the organic radical battery (ORB) with a lithium metal anode and a cathode consisting of a nitroxide radical polymer poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) with 1M LiPF6 as an electrolyte in ECC/DMC was evaluated at room temperature.
Abstract: The electrochemical properties of the organic radical battery (ORB) having a lithium metal anode and a cathode consisting of a nitroxide radical polymer poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) with 1M LiPF6 as an electrolyte in ethylene carbonate (EC)/dimethyl carbonate (DMC) have been evaluated at room temperature. The cell, with a thin cathode of 17 µm thickness incorporating 40 wt.% of PTMA, exhibited the full theoretical specific capacity at current densities up to 10 C (∼1 mA/cm2). However, a decrease in the specific capacity and an increase in the ohmic resistance were observed at higher current densities. The cell performance was good even on repeated charge-discharge cycles as an excess of 85 % retention of the initial discharge capacity was observed. This was true even after 400 cycles. However, a gradual decrease in capacity, an increase in charge-discharge voltage separation, and an electrode/electrolyte interfacial resistance have been observed after a large number of cycles. The examination of the scanning electron micrographs of the cathode material revealed that prolonged cycling resulted in the agglomeration of PTMA particles. These in turn increased the resistance and decreased the capacity of the cell.

50 citations


Journal ArticleDOI
TL;DR: In this article, a 3D cellular automaton-finite element (CAFE) model was used to predict the axial texture evolution of a single-crystal (SX) casting.
Abstract: The solidification grain structure and texture evolutions during single crystal (SX) casting of the advanced Ni-base superalloy CMSX-4 have been investigated. In order to understand the development of the solidification grain structure, SX casting experiments were carried out with a specially designed grain selector in a Bridgman directional solidification (DS) furnace. In addition to casting trials, the SX casting process was simulated by a 3-D cellular automaton-finite element (CAFE) model. The predicted solidification grain structure and the texture evolutions were validated by comparison with the microstructural observation and the electron back scattered diffraction (EBSD) results. It was shown that the overall grain structure, crystallographic texture evolution, and the location where the final selection of the single crystal occurs can be predicted well by the present CAFE model. The axial texture evolution of the single crystal was found to be significantly influenced by the grain density at the chill surface. The CAFE predictions also revealed that the geometry of the grain selector plays a significant role in the final selection of the single crystal.

44 citations


Journal ArticleDOI
TL;DR: The corrosion behavior of pure magnesium that has different content ratio of impurities (such as Fe/Mn ratio) in Hanks' solution was investigated in order to tailor the lifetime of biodegradable implant made of pure Mg as mentioned in this paper.
Abstract: The corrosion behavior of pure magnesium that has different content ratio of impurities (such as Fe/Mn ratio) in Hanks’ solution was investigated in order to tailor the lifetime of biodegradable implant made of pure magnesium. Two distinct stages of corrosion were observed: a slow corrosion rate stage and a subsequent fast corrosion rate stage. The first stage was characterized by uniform corrosion that produced magnesium hydroxide and calcium phosphate film on a magnesium surface, resulting in a slow corrosion rate. The second stage with an abrupt increase in the corrosion rate was induced by Fe precipitates and was stimulated by an increase in the Fe/Mn ratio. This corrosion was developed to a preferred crystallographic pitting corrosion where the pits propagated along the preferred crystallographic plane and several layers of Mg planes with narrow interplanar space remained uncorroded. From this study, it is expected that the lifetime of the biodegradable implant made of pure Mg can be tailored by controlling the amount and ratio of the impurities.

Journal ArticleDOI
TL;DR: In this article, an attempt has been made to study the effect of FSW process parameters on the tensile strength of A319 alloy welded joints, which were made using different combinations of tool rotation speed, welding speed, and axial force, each at four levels.
Abstract: Fusion welding of cast A319 (Al-Si-Cu) alloy will lead to many problems including porosity, micro-fissuring, and hot cracking. Friction Stir Welding (FSW) can be used to weld A319 alloy without these defects. In this investigation, an attempt has been made to study the effect of FSW process parameters on the tensile strength of A319 alloy welded joints. Joints were made using different combinations of tool rotation speed, welding speed, and axial force, each at four levels. The quality of weld zone was analyzed using macrostructure and microstructure analysis. Tensile strength of the joints were evaluated and correlated with the weld zone microstructure. The joint fabricated with a 1200 rpm tool rotation speed, 40 mm/min welding speed, and 4 kN axial force showed superior tensile strength compared with the other joints.

Journal ArticleDOI
TL;DR: In this article, a semi-empirical thermodynamic model for size dependency of melting point of nano particles and wires has been proposed by introducing a size dependence of surface energy, which is applicable to a wider range of materials.
Abstract: A semi-empirical thermodynamic model for size dependency of melting point of nano particles and wires has been proposed by introducing a size dependency of surface energy. The model predicts the size dependency of melting point of nano particles and wires for a wide range of elements: fcc (Au, Pt, Ni), hcp (Mg), and bcc (W), all in good agreement with experimental data and/or molecular dynamics simulations. Since the model is free from adjustable parameters, it is applicable to a wider range of materials.

Journal ArticleDOI
TL;DR: In this paper, the influence of Cu addition on the corrosion resistance of low-alloy steel in an acid-chloride solution was investigated by electrochemical methods, such as potentiodynamic polarization tests and an electrochemical impedance spectroscopy (EIS).
Abstract: The influence of Cu addition on the corrosion resistance of low-alloy steel in an acid-chloride solution was investigated by electrochemical methods, such as potentiodynamic polarization tests and an electrochemical impedance spectroscopy (EIS). The XPS analysis of the corroded surfaces indicated the formation of protective Cu2O and Cu(OH)2 layers on the surface. The formation of Cu products on the surface reduced the uniform corrosion rate of the steel, but promoted localized corrosion due to the galvanic interaction between the covered areas of copper oxide/hydroxide and the uncovered areas on the surface of steel.

Journal ArticleDOI
TL;DR: In this paper, the effect of steel fibers on the speed sensitivity of the friction coefficient was investigated and the results indicated that the friction material containing steel filbers was more sensitive to sliding speed, exhibiting a highly negative µ-ν relation.
Abstract: The tribological properties of brake friction materials with and without steel fibers were investigated. The focus of this study was determining the effect of steel fibers on the speed sensitivity of the friction coefficient. The speed sensitivity of the friction coefficient is closely associated with the stick-slip phenomenon. The results indicate that the friction material containing steel filbers was more sensitive to sliding speed, exhibiting a highly negative µ-ν relation. In particular, the friction material with steel fibers showed a larger vibration amplitude during brake applications, suggesting that the µ-ν relation was strongly related to the friction-induced vibration. On the other hand, the wear resistance of the friction materials containing steel was significantly better than that without steel fibers, suggesting longer service life. A possible mechanism of the stick-slip by the steel fibers is discussed in terms of the physical properties of the steel fiber and the gray iron rotor.

Journal ArticleDOI
TL;DR: In this paper, high-ordered TiO2 nanotube arrays were prepared using a self-templating multi-step anodic oxidation process in a fluoride-containing electrolyte.
Abstract: Highly ordered TiO2 nanotube arrays were prepared using a self-templating multi-step anodic oxidation process in a fluoride-containing electrolyte. The microstructures, chemical compositions, and phases of the self-organized TiO2 nanotube arrays were analyzed by FESEM, XPS, and XRD, respectively. Hexagonal packing density in TiO2 nanotube arrays significantly improved after the the multi-step anodic oxidation. The area densities of the hexagonal TiO2 nanotube arrays increased approximately 3 times from the first to second step in the anodic oxidation steps process (4.9 μm−2 to 16.4 μm−2), but there was no difference between the second and third step (16.4 μm−2 to 16.0 μm−2). The as-anodized TiO2 nanotube array had an amorphous structure and it transformed to an anatase phase during the annealing process at 450 °C for 1 h. The as-anodized TiO2 nanotube arrays adsorbed the fluoride, hydrocarbon groups (CH), hydroxyl groups (OH, C-OH), and carboxyl groups (O = C-OH) on their surfaces.

Journal ArticleDOI
TL;DR: The phase diagram of the CaO-SiO2-CrOx-MgO-MnO system at moderately reducing oxygen partial pressure was calculated using a commercial thermochemical program and compared with the phase analysis for converter slags taken from the stainless steelmaking process as discussed by the authors.
Abstract: The phase diagram of the CaO-SiO2-CrOx-MgO-MnO system at moderately reducing oxygen partial pressure was calculated using a commercial thermochemical program and compared with the phase analysis for converter slags taken from the stainless steelmaking process. It was found that a (Mn,Mg)Cr2O4 solid solution and Ca2SiO4 phase are in equilibrium with the oxidation slags after the oxygen blowing period, which is consistent with thermodynamic calculations. Furthermore, it could be proposed that the thermodynamic properties of a MgCr2O4-MnCr2O4 binary spinel make it close to an ideal solution.

Journal ArticleDOI
TL;DR: In this paper, a systematic study on the conversion of zinc sulfide to zinc oxide nanoparticles as a function of annealing temperature is presented, which reveals that the as-synthesized powder is a mixture of ZnS and ZnO, which later converts to the zinc oxide phase only.
Abstract: A systematic study is presented on the conversion of zinc sulfide to zinc oxide nanoparticles as a function of annealing temperature. Zinc acetate dihydrate (Zn(CH3COO)2.2H2O) and thiourea (NH2CSNH2) are used as precursors to synthesize ZnS and then ZnO. The aqueous solution of the precursor was refluxed at 90 °C for over 12 h. The synthesized complex was then annealed at 300 °C, 500 °C, 700 °C, and 900 °C in air for one hour. From elemental analyses, it was found that the as-synthesized powder is a mixture of ZnS and ZnO, which annealing later converts to the zinc oxide phase only. The morphological observations revealed spherical particles of various sizes (20 nm to 300 nm) while increasing the annealing temperatures. A drastic change in the vibration bands is noticed with annealing. Photoelectron peaks related to sulfur and carbon are observed for synthesized powder, whereas, these peaks disappeared when annealed at 500 °C.

Journal ArticleDOI
TL;DR: In this article, the authors presented MD simulations for the radiation damage of single and nano-poly-crystalline tungsten and showed that the recombination rate of self-interstitial atoms (SIAs) and vacancies is faster in the single-crystal that in the poly-polycrystal structure.
Abstract: This study presents MD simulations for the radiation damage of single- and nano-(poly)crystalline tungsten. The nano-(poly)crystalline microstructure was constructed using a new construction method combined with the phase field model. At the maximum damage state, the recombination rate of self-interstitial atoms (SIAs) and vacancies is faster in the single-crystal that in the poly-crystal structure. In the steady state, the number of SIAs is twice as large in the nano-crystal, as caused by the attractive interaction between the grain boundary and the SIAs.

Journal ArticleDOI
TL;DR: In this article, the magnetic properties of vanadium-doped single crystalline silicon carbide nanowires were reported, and it was shown that the vanadium carbide phase can exhibit half-metallic ferromagnetic properties that are essential for the realization of spintronic devices.
Abstract: This study reports the magnetic properties of vanadium (V) doped single crystalline silicon carbide nanowires The first principle calculation indicated that the V-doped cubic SiC phase can exhibit half-metallic ferromagnetic properties that are essential for the realization of spintronic devices Based on this calculation, V-doped SiC nanowires were fabricated in a chemical vapor deposition process The single crystalline β-SiC nanowires, which are doped with ca 4 at% of V, had diameters of < 100 nm and a length of several µm High-resolution transmission electron microscopy observations revealed vanadium carbide (VC) phases in the nanowires, even at this low concentration of dopants Magnetic characterization implies that the nanowires are a mixture of the diamagnetic phase of VC and ferro- or paramagnetic phases of V-doped SiC These results suggest that the doping of transition metal having high solubility to the SiC phase can lead to the realization of dilute magnetic semiconductor behavior at very low temperature

Journal ArticleDOI
TL;DR: In this article, the effects of processing parameters including the precursor ratio, calcination time, temperature and atmosphere on the surface microstructure of synthesized TiO2 nanofibers were investigated.
Abstract: TiO2 nanofibers were synthesized by an electrospinning technique using polyvinyl pyrrolidone and titanium tetraisopropoxide as precursors. The effects of processing parameters including the precursor ratio, calcination time, temperature and atmosphere were investigated. The calcination temperature determines the TiO2 phases as either anatase or rutile. The diameter of the synthesized TiO2 nanofibers is not sensitive to the calcination atmosphere or the time. However, the surface microstructure of the synthesized nanofibers depends highly on calcination atmosphere. Calcination in an N2 atmosphere produces smooth surfaces. In contrast, surfaces that are more granular evolve when they are calcined in an O2 atmosphere. In addition, less Ti precursor in the electrospinning solution results in slim nanofibers.

Journal ArticleDOI
TL;DR: In this paper, a continuous wave Nd:YAG laser was used to make the Sn-3.5 wt.%Ag solder joint formed using a laser heat source.
Abstract: Microstructure and shear strength were assessed for a Sn-3.5 wt.%Ag solder joint formed using a laser heat source. A continuous wave Nd:YAG laser was used to make the Sn-3.5 wt.%Ag solder joint. Solder balls of 400μm diameter were used and the laser beam spot diameter at focus was approximately 120μm. The UBM (Under Bump Metallurgy) on a FR4-PCB consisted of Cu/Ni/Au from bottom to top with a thickness of 15μm/5μm/0.05μm, respectively. In order to position solder balls on the UBM, RMA (rosin mildly activated) type flux for a BGA (Ball Grid Array) was used. Selected optimal conditions were as follows: a laser power of 2W and heating time of 0.3 s, 0.5 s, and 0.7 s; a laser power of 3 W and heating time of 0.1 s and 0.3 s; and a laser power of 4 W and a heating time of 0.1 s. Under all conditions, the shear strengths of the solder joint of (CuNi)3Sn4 at the interface between the pad and solder were larger than 554.37 gf (i.e. the shear strength obtained from hot plate reflow). When the laser power was set at 2 W, the microstructure of IMC (intermetallic compound) was recrystallized regularly due to active convection, which was caused by increased heating time. Under a laser power of 4 W and heating time of 0.7 s, the microstructure was recrystallized irregularly due to violent convection caused by excessive energy input (=laser power (W) ×heating time (s)). The IMC layer increased in thickness as a result of increasing the energy input, and was affected by laser power more than by heating time.

Journal ArticleDOI
TL;DR: In this paper, the microstructural evolution of titanium alloy under isothermal and non-isothermal hot forging conditions was predicted using artificial neural networks (ANN) and finite element (FE) simulation.
Abstract: The microstructural evolution of titanium alloy under isothermal and non-isothermal hot forging conditions was predicted using artificial neural networks (ANN) and finite element (FE) simulation. In the present work, the change in phase volume fraction, grain size, and the volume fraction of dynamic globularization were modelled considering hot working conditions. Initially, an ANN model was developed for steady-state phase volume fraction. The input parameters were the alloy chemical composition (Al, V, Fe, O, and N) and the holding temperature, and the output parameter was the alpha/beta phase volume fraction at steady state. The non-steady state phase volume fraction under non-isothermal conditions was subsequently modelled on the basis of 4 input parameters such as initial specimen temperature, die (or environment) temperature, steady-state phase volume fraction at die (or environment) temperature, and elapsed time during forging. Resulting ANN models were coupled with the FE simulation (DEFORM-3D) in order to predict the variation of phase volume fraction during isothermal and non-isothermal forging. In addition, a grain size variation and a globularization model were developed for hot forging. To validate the predicted results from the models, Ti-6Al-4V alloy was hot-worked at various conditions and then the resulting microstructures were compared with simulated data. Comparisons between model predictions and experimental data indicated that the ANN model holds promise for microstructure evolution in two phase Ti-6Al-4V alloy.

Journal ArticleDOI
TL;DR: In this paper, the high-temperature corrosion resistance of plasma-sprayed ceramic oxide coatings has been evaluated in a LiCl-Li2O molten salt under an oxidizing environment.
Abstract: In this study, the high-temperature corrosion resistance of plasma-sprayed ceramic oxide coatings has been evaluated in a LiCl-Li2O molten salt under an oxidizing environment. Al2O3 and YSZ coatings were manufactured by atmospheric plasma spraying onto a Ni alloy substrate. Both the plasma-sprayed Al2O3 and YSZ coatings had a typical splat quenched microstructure which contained various types of defects, including incompletely filled pores, inter-splat pores and intra-splat microcracks. Corrosion resistance was evaluated by the thickness reduction of the coating as a function of the immersion time in the LiCl-Li2O molten salt at a temperature of 650 °C. A linear corrosion kinetic was found for the Al2O3 coating, while no thickness variation with time occurred for the YSZ coating. The ceramic oxide coatings were reacted with LiCl-Li2O molten salt to form a porous reaction layer of LiAl, Li5AlO4 and LiAl5O8 for the Al2O3 coating and a dense reaction layer of non-crystalline phase for the YSZ coating. The reaction products were also formed along the inside coating of the porous channel. The superior corrosion resistance of the YSZ coating was attributed to the formation of a dense protective oxide layer of non-crystalline reaction products on the surface and at the inter-splat pores of the coating.

Journal ArticleDOI
TL;DR: In this article, the hardness and tensile properties of the friction stir welded A5052/A5J32 joint were investigated according to the fixing location and the welding conditions.
Abstract: The joining of dissimilar A5052 and A5J32 alloy sheets with thicknesses of 1.5mm and 1.6mm, respectively, was carried out using the Friction Stir Welding (FSW) technique. The tool rotated at a speed in a range of 1000 rpm to 1500 rpm with a welding speed ranging from 100 mm/min to 400 mm/min. The hardness and tensile properties of the friction stir welded A5052/A5J32 joint were investigated according to the fixing location. In the case where the A5J32 aluminum alloy was fixed on the retreating side, defect-free welds were obtained under all welding conditions. However, in the case where the A5052 aluminum alloy was fixed on the retreating side, some welding defects were observed at the joint under certain welding conditions with a lower heat input. However, the welding defects had no effect on the mechanical properties. A good correlation between the hardness distribution and the welding zones was observed. The experimental results showed that the tensile properties differed depending on the fixing location of the materials and were also affected by the welding conditions.

Journal ArticleDOI
TL;DR: In this article, a two-step procedure based on the miscibility gap between two elements, produced an in-situ bulk metallic glass matrix composite, which exhibits a large immiscible region in solid state, formed a two phase mixture of Zr- and Ta-rich solid solution by phase separation.
Abstract: An original two-step procedure, based on the miscibility gap between two elements, produced an in-situ bulk metallic glass matrix composite. The Zr-Ta binary alloy, which exhibits a large immiscible region in solid state, formed a two-phase mixture of Zr- and Ta-rich solid solution by phase separation. When the Zr-Ta binary alloy was remelted with Cu, Zr, and Ti, the Ta-rich solid solution, which has a high melting temperature, did not melt, while the remaining melt containing Zr-rich solid solution mixed with the other elements and solidified into an amorphous phase at lower temperatures. The improvement of strength in the composite indicates that the interfaces between the Ta-rich particles and the BMG matrix formed by phase separation are strong enough to hold a high interfacial cohesion strength.

Journal ArticleDOI
TL;DR: In this paper, the effect of prior microstructures on the behavior of cementite particles in conjunction with microstructural changes of the matrix during subcritical annealing was investigated by changing the initial micro-structures into ferrite + coarse pearlite, ferrite-pearlite, bainite, and martensite.
Abstract: The effect of prior microstructures on the behavior of cementite particles in conjunction with microstructural changes of the matrix during subcritical annealing was investigated by changing the initial microstructures into ferrite + coarse pearlite, ferrite + fine pearlite, bainite, and martensite, in medium carbon steels. While the coarsening of cementite particles in martensite proceeded rapidly with the growth of large cementite particles at boundaries with the dissolution of smaller particles within martensite laths, the coarsening rate of cementite particles in bainite was found to be much slower than that in martensite. This could be attributed to the thermal stability of cementite particles, the smaller amount of carbon in solution, and the lower driving force for solute diffusion due to the uniform size distribution of cementite particles in bainite. The controlling coarsening kinetics in medium carbon steels with ferrite-pearlite, bainite and martensite, were found as boundary diffusion, diffusion along dislocation, a combination of boundary diffusion and diffusion along dislocation, respectively.

Journal ArticleDOI
D. B. Park1, J. W. Lee1, Y. S. Lee1, Kyoung-Tae Park, Wonjong Nam1 
TL;DR: In this article, the effects of alloying elements and initial interlamellar spacing on tensile strength and the occurrence of delamination in cold-drawn hyper-eutectoid steel wires were investigated under equivalent drawing conditions.
Abstract: The effects of alloying elements and initial interlamellar spacing on tensile strength and the occurrence of delamination in cold-drawn hyper-eutectoid steel wires were investigated under equivalent drawing conditions. The initial interlamellar spacing showed little influence on the occurrence of delamination. The addition of Cr effectively increased attainable tensile strength, since the added Cr not only increased tensile strength but also delayed delamination. The addition of Ni also increased attainable tensile strength, since the effect of the added Ni on delaying delamination prevailed over the tendency to decrease tensile strength and work hardening. The addition of Cr increased the attainable tensile strength more effectively than the addition of Ni in cold-drawn hyper-eutectoid steel wires, although the added Ni markedly delayed delamination-associated strain.

Journal ArticleDOI
TL;DR: In this article, the effects of various types of inclusions on the glass forming ability of the alloy Fe68.8C7.0Si3.5B5.0P9.6Cr2.1Mo2.0Al2.
Abstract: For the mass production of bulk metallic glasses, the use of industrial raw materials that contain certain amounts of inclusions is inevitable. The glass-forming ability of bulk metallic glasses, i.e., the critical cooling rate for glass formation upon solidification, is closely related to the nature of heterogeneous nucleation offered by inclusions during the solidification process. Significantly different effects of various types of inclusions on the glass forming ability of the alloy Fe68.8C7.0Si3.5B5.0P9.6Cr2.1Mo2.0Al2.0 are demonstrated in this study. The origins of the effects of different inclusions on the glass forming ability are analyzed through thermodynamic, crystallographic and classical heterogeneous nucleation kinetic theories.

Journal ArticleDOI
TL;DR: In this paper, the optimum condition of compaction and sintering for PEO coatings was established based on the investigation of microstructure, microhardness, and corrosion properties of coatings which were compared to those of cast Mg-6 wt.%Al alloy.
Abstract: Mg-6 wt.%Al-1 wt.%Zn alloy powders were produced by gas atomization, and subsequently compacted and sintered under various conditions of temperature, time, and pressure. The bulk Mg-6 wt.%Al-1 wt.%Zn alloy was coated by the plasma electrolytic oxidation (PEO) method. The optimum condition of compaction and sintering for PEO coatings was established based on the investigation of microstructure, microhardness, and corrosion properties of coatings which were compared to those of cast Mg-6 wt.%Al alloy. The coatings on Mg-6 wt.%Al and Mg-6 wt.%Al-1 wt.%Zn alloys consisted of MgO, MgAl2O4, and Mg2SiO4. The Mg-6 wt.%Al-1 wt.%Zn alloy compacted at room temperature for 10 min and sintered at 893 K for 3 h showed the most porous and nonuniform coating layer because the coatings had grown through grain boundaries that resulted from poor bonding between powder particles in the substrate. However, the coated Mg-6 wt.%Al-1 wt.%Zn alloy hot-compacted at 593 K for 10 min had the thickest coating layer and the highest microhardness. In addition, it demonstrated the best corrosion resistance as verified by polarization curves in 3.5% NaCl solution.