bluuebunny/crossref_metadata_2025 huggingface dataset:
The Refinement of the Nanoporous Copper by Adding Third Elements
Authors: Dan Zhen Hua , Qin Feng Xiang , Hara Nobuyoshi
Published: May 2014

Fine nanoporous copper was fabricated from the amorphous Ti-Cu alloys with a minor addition of silver in 10 mM HF solutions. The pore sizes decreased from 100 nm to 12 nm with the increase of the Ag contents in comparison of Ti60Cu40 ribbons free of Ag. With increasing of the dealloying time, the sizes of the nanopores and ligaments increased for the nanostrucutres on Ti60Cu38Ag2 ribbons since the segregation of the Ag phase which triggered the galvanic dissolution of the adjacent Cu matrix in form of micro-couplings to further coarsen the nanoporous Cu. On the contrary, the trace formation of the Ag phase on the Ti60Cu39Ag1 ribbons had a weak ability to motivate the galvanic dissolution, indicating by the constant pore sizes and slight decrease in the ligament sizes with the increase in the dealloying time. The refinement of the nanoporous structures was ascribed to the drastic decrease in the surface diffusivity. The decrease in the surface diffusivity due to the involvement of Ag with a lower surface diffusivity in comparison of Cu was more than one order of magnitude. The involvement of Ag adatoms restricted the diffusion of Cu adatoms in the interface regions in the inward and outward directions.
On the Stress Development in SA508 Autogenous Weld
Authors: Abdolvand Hamidreza , Keavey Mike , Dai H. , Mark Alison , O’Meara N. , Walsh Joanna , Bate S. , Pellereau B. , Francis John A. , Withers Philip J.
Published: May 2014

Considering the significant role that residual stresses play in determining the lifetime-service of materials, it is mandatory to have a good understanding of and a means of predicting those that develop during welding processes. For this purpose, a User MATerial subroutine (UMAT) is developed to study the effects of various parameters that influence solid state phase transformations and residual stress evolution during welding of SA508 ferritic steel. The temperature dependent elastic and kinematic hardening parameters for each of the individual phases that can potentially develop during cooling from elevated temperatures are measured and are used for calculating stress development during low (75 mm/min) and high (300 mm/min) speed gas-tungsten arc welding (GTAW) on SA508 grade 3. These two speeds are selected to cover a wide range of cooling rates in the heat affected zone so that different phase proportions would be present. The results of the numerical simulations for residual stresses are compared against those measured by neutron diffraction. It is shown here that a low speed weld results in bainite formation whereas a high speed weld results in bainitic as well as subsequent martensitic phase transformations where each welding rate results in different residual stress development.
Density Functional Theory Study of H2O Molecules on Cr2O3 Surfaces
Authors: Nunomura Norio , Sunada Satoshi
Published: May 2014

In order to understand the reactivity of Cr2O3 surface towards H2O molecule, the optimized structure, electronic structure, and the behavior of adsorbates were examined using a first-principles calculation based on density-functional theory (DFT). H2O coverages varying from a quarter to two monolayers (MLs) were considered. At a low coverage, the oxygen atom of H2O adsorbs on the Cr atom of the outermost Cr2O3 surface layer, the entire H2O molecule is slanted at the direction of a hollow site, and a molecular plane is nearly parallel to the surface. The hydrogen bond is formed between the surface oxygen atom and the hydrogen atom of H2O molecule. From the optimized structure, the H2O dissociation mechanism which passes through a transition state is guessed. For 0.5ML coverage the obtained absorption energy is-82.5 kJ/mol. Our results are in good agreement with other reported theoretical and experimental results.
Microstructure Computation for Phase Transition in Steels
Authors: Qin Rong Shan
Published: May 2014

A computational method for fast and accurate reconstruction of steels microstructure has been developed. The method makes use of the physical description of phase transition kinetics and mathematical description of grain morphology, implements the spirit of symbolic dynamics for phase transition, and has produced realistic microstructure for steels. Using the known microstructure-property relationship of strong steels, this method enhances the design and optimum the chemical-thermomechanical processing conditions for the production of novel steels.
Discovery of New Materials and Heat Treatments: Accelerated Metallurgy and the Case of Ferrous and Magnesium Alloys
Authors: Toda-Caraballo I. , Galindo-Nava Enrique I. , Rivera-Díaz-del-Castillo Pedro E.J.
Published: May 2014

Traditionally, the discovery of new materials has been the result of a trial and error process. This has resulted in an extremely time-consuming and expensive process. Models for guiding the discovery of new materials have been developed within the European Accelerated Metallurgy project. The application of statistical techniques to large materials datasets has lead to the discovery of unexpected regularities among their properties. This work focuses on mechanical properties. In particular, the interplay between yield strength, ultimate tensile strength and elongation. A methodology based on principal component analysis, and Kocks-Mecking modelling has led to a tool for finding optimal compositional and heat treatment scenarios. The model is first presented for wide ranges of alloys, and the application to the discovery of new magnesium and ferrous alloys is outlined.
Simulation of Inhomogeneous Materials Evolution in Hot Rolling Using a Layer Model
Authors: Schmidtchen Matthias , Kawalla Rudolf , Rimnac Axel
Published: May 2014

A fast simulation of the inhomogeneous materials evolution during the deformation steps and its effect on subsequent processes is demanded for the development of new technologies for materials with a homogeneous microstructure. In the paper a layer model for flat hot and cold rolling is presented. A deepened understanding of the influence of inhomogeneities in material state and material flow on the whole process can be reached due to the introduction of a new computational concept for variable layer thickness distributions in the layer model. The concept will be explained and the additional information obtained concerning the influence of shear, local residual stresses as well as inhomogeneous stress and strain states in the roll gap on the microstructure evolution will be presented and discussed.
Limitations of ICME and ICMS due to Variability – Alternative Strategies for Alloy Design
Authors: Tancret Franck
Published: May 2014

Integrated Computational Materials Engineering (ICME), and Integrated ComputationalMaterials Science (ICMS) are developing fields with an aim of alloy design, by combining physicalmodels describing materials behavior through lengthscales and processing steps. It has beensuspected, however, that uncertainties in input parameters may cumulate in a hereditary way andyield to a high variability in the final output, independently of the quality of models themselves.Such a variability is however rarely quantified. In this aim, an illustrative example is here given,using a set of “cascade models”, each model being voluntarily very simple (grain growth,precipitation, hardening…) whereas assumed to be exact, so that only the effect of parameteruncertainties on the variability of the output (yield stress of a Ni-base superalloy) can be studied. Itis demonstrated that, with usual uncertainty levels in input parameters, the final dispersion (error)can become very high. Additionally, considering that models are not exact themselves would renderthe situation even worse. Besides, global and implicit models, like neural networks or Gaussianprocesses, have been shown to be able to perform reliable predictions and to be used for alloydesign, with acceptable levels of error, the latter being estimated by statistical methods. In addition,unlike ICME or ICMS, predictions are very fast so that automatic alloy composition optimisation ispossible using, for instance, genetic algorithms. Other fast predictive tools, like computationalthermodynamics (Thermo-Calc), can then be used as constraints during alloy optimisation.
Comparison of Material Flow Stress Models toward More Realistic Simulations of Friction Stir Processes of Mg AZ31B
Authors: Ammouri Ali H. , Hamade Ramsey
Published: May 2014

Utilizing a proper material model for describing the mechanical behavior of any material is key for a successful simulation of friction stir processing (FSP) where temperature, strain, and strain rate gradients vary abruptly within, and when moving away, from the stirring zone. This work presents a comparison of how faithfully do three different constitutive equations reproduce the state variables of strain, strain rate, and temperature in an FEM simulation of a test-case FSP (1000 rpm spindle speed, and 90 mm/min feed). The three material models considered in this comparison are namely: Johnson-Cook (JC), Sellars-Tegart (ST), and Zerilli-Armstrong (ZA). Constants for these constitutive equations are obtained by fitting these equations to experimental mechanical behavior data collected under a range of strain rates and temperatures of twin-rolled cast wrought AZ31B sheets.It is widely recognized that JC-based models over predicts stress values in the stir zone whereas ST-based models are incapable of capturing work hardening outside of the stir zone. Therefore, a ZA model, being a physical based-HCP specific model, is hereby investigated for its suitability as a material model that would overcome such drawbacks of JC-and ST-based models. The equations from the constitutive models under consideration are fed into an FEM model built using DEFORM 3D to simulate the traverse phases of a friction stir process. Amongst these three material models, comparison results suggest that the HCP-specific ZA model yield better predictions of the state variables: strain, strain rate, and temperature, and, consequently, the estimated values for flow stresses.
Performance of Modern DCI Materials – Investigation of Microstructural, Temperature and Loading Rate Effects on Mechanical and Fracture Mechanical Properties
Authors: Baer Wolfram
Published: May 2014

Design and safety assessment of advanced ductile cast iron (DCI) components like windturbines or transport and storage casks for radioactive materials require appropriate material data interms of strength and fracture toughness. Therefore, it is of vital importance to characterize andunderstand the deformation, damage and fracture behaviour of DCI which may substantially changefrom ductile to brittle by increasing loading rate, decreasing temperature and/or increasing stresstriaxiality. This paper reports on recent BAM investigations on different qualities of the widely usedDCI grade EN-GJS-400 with varying pearlite shares (none and 18 % respectively). The focus wason the influences of microstructure, temperature (ambient and -40 °C) and loading rate (quasi-staticto crash) on strength (YS, UTS, flow curve) and fracture mechanical properties (R-curve, crackinitiation toughness, fracture toughness). Systematic metallographical and fractographical analyseswere performed accompanying the whole test program and a systematics of specific damagebehaviour and fracture mechanisms was derived from the results.
Electrochemical Study of Diffusion Bonded Joints between Micro-Duplex Stainless Steel and Ti6Al4V Alloy
Authors: Bhola S.M. , Kundu S. , Mishra Brajendra , Chatterjee Subrata
Published: May 2014

In the present study, corrosion behavior of a diffusion bonded interface formed between micro-duplex stainless steel (MDSS) and a mixed titanium alloy (Ti6Al4V) formed at 900°C for 60 minutes under 4MPa uniaxial pressure in vacuum has been investigated in 1M HCl and 1 M NaOH solutions using various electrochemical measurements such as Equilibrium Potential (EP), Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PD). For comparison, corrosion behavior of base metal alloys, MDSS and Ti6Al4V have also been also characterized. Bonded interface has been characterized in light optical microscopy and scanning electron microscopy using back scattered electron. The layer wise σ phase and λ+FeTi phase mixture has been observed at the bond interface and the bond tensile strength and shear strength were ~556.4MPa and ~420.2MPa, respectively. The corrosion rates of the bonded joint are intermediate to the corrosion rates of MDSS and Ti6Al4V alloy.
Contribution of the Nanoindentation to the Study of HCP Metals
Authors: Lecomte Jean Sébastien , Nguyen L.T. , Abbès F. , Schuman C. , Raulot J.M.
Published: May 2014

This study combines nanoindentation experiments, electron backscatter diffraction (EBSD) and atomic force microscopy (AFM) topographic measurements to investigate the material anisotropy contribution to the indentation behaviour of individual grains of various hexagonal-close packed (HCP) polycrystals with different axial ratio (zinc, magnesium and titanium). The grain size was much larger than the indents size to ensure quasi-single-crystal indentation and when, combined with an EBSD mapping, a wide variety of crystal orientations can be probed, which provides mechanical characterization of materials at the micro/nanoscale. Experimental curves can be used to determine the mechanical properties of the indented material. Furthermore, by using data issued from AFM topographic measurements, one can analyze the dislocations arrangements below and around the indentation print, and thus characterize the most probably activated deformation systems.
Effects of Heat Treatments on Tungsten for Armours in NFR
Authors: Ciambella Laura , Donnini Riccardo , Montanari Roberto
Published: May 2014

Tungsten is a promising armour material for plasma facing components of nuclear fusion reactors (NFR) because of its low sputtering rate and favourable thermo-mechanical properties (high melting point and good thermal conductivity).
This paper reports some results of an experimental campaign carried out for investigating the microstructural characteristics and the mechanical properties of tungsten (99.97% purity; 5% porosity) for fusion applications.
Tungsten has been heat treated at 500 °C and 800 °C with increasing soaking time. The samples in as-supplied condition and after each step of the heat treatments have been examined by optical microscopy and TEM observations, X-ray diffraction (XRD) and micro-hardness tests.
The original material has a dislocation density of 1.5 x 1010 cm-2 and a mean grain size of 65 μm.
Grain size is not affected by the heat treatment at 500 °C which induces only a weak decrease of dislocation density leading to a little smaller hardness. The microstructure can be considered substantially stable even if a weak recovery of dislocations takes place.
On the contrary, grain growth is observed after heating at 800 °C: 10 hours of treatment nearly doubles the average grain size.
Effect of Thermal Treatments on the Mechanical Properties Enhancement of High Reliability Metallic Materials by Laser Shock Processing
Authors: Ocaña José Luis , Díaz M. , Porro J.A. , de Lara L. Ruiz , Correa C.
Published: May 2014

Laser shock processing (LSP) is increasingly applied as an effective technology for the improvement of metallic materials mechanical properties in different types of components as a means of enhancement of their fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses fields into metallic components allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Additional results accomplished by the authors in the line of practical development of the LSP technique at an experimental level (aiming its integral assessment from an interrelated theoretical and experimental point of view) are presented in this paper. Concretely, experimental results on the residual stress profiles and associated mechanical properties modification successfully reached in typical materials under different LSP irradiation conditions are presented. In this case, the specific behavior of a widely used material in high reliability components (especially in nuclear and biomedical applications) as AISI 316L is analyzed, the effect of possible “in-service” thermal conditions on the relaxation of the LSP effects being specifically characterized.
Controllable Electrostriction of Polyurethane Film
Authors: Kanda Masae , Yuse Kaori , Guyomar Daniel , Nishi Yoshitake
Published: May 2014

Although their experimental errors can be observed, pure polyurethane (PU) elastomers are one of the most important class of polymers due to some remarkable electromechanical characteristics such as large electric field induced strain, high specific energy and fast speed of response. In order to obtain the large strain at low electric field, a dependence of the solidification condition on strain was investigated for pure polyurethane films. Optimum solidification condition to get thin film with 19 μm thickness remarkably enhanced the strain at high electric field at high electric filed, although they show the low strain at low electric field at low electric filed. The starting point of the convergence occurred at a lower electric field for the solidification condition to get thick film with 150 μm thickness as opposed to for the optimum condition to obtain the thin film with 19 μm thickness. Based on results of crystalline volume fraction and crystalline periodicity, strongly attributed to not only polarization, but also electrostriction, the strain was controlled by the solidification condition. The optimum solidified samples do not have convergence until 20 MV/m. Based on the prediction and experimental results, the electrostriction of PU films depended on its solidification condition.
Geometric Modeling of Ceramics Dendrites to Modulate Energy and Material Flows by Using Stereolithography
Authors: Kirihara Soshu
Published: May 2014

Through computer aided design, manufacturing and evaluation, various ceramics dendrites with spatially ordered micro cavities were successfully fabricated by utilizing stereolithography. Micrometer order ceramic lattices were propagated spatially in computer graphic space. Ceramics nanoparticles were dispersed in to photo sensitive liquid resins to obtain thixotropic slurries. The paste material was spread on a grass substrate by using a mechanical knife edge, and an ultra violet micro pattern was exposed to create cross sectional solid layer. After the layer stacking process, the obtained composite precursor was dewaxed and sintered in an air atmosphere. By the micro patterning stereolithography, solid electrolyte dendrites of yttria stabilized zirconia with spatially ordered porous structures were fabricated for fuel cell miniaturizations. Gaseous fluid profiles and pressure distributions in the formed ceramic lattices with various porosity percent were visualized and analyzed by a finite element method. Subsequently, alumina micro photonic crystals with a diamond lattice structure were fabricated. Electromagnetic wave properties were measured by using a terahertz time domain spectroscopy. A complete photonic band gap was exhibited, and a localized mode to select the wavelength was obtained by introducing a defect cavity.
Effect of Zr Addition on Magnetostriction of Tb-Dy-Fe Alloys Prepared by Micro-Pulling-Down Method
Authors: Oikawa Katsunari , Shoji Tetsuo , Anzai Koichi
Published: May 2014

Effects of Zr addition and annealing on the magnetostriction of Tb-Dy-Fe alloy crystals were investigated. The (Fe1.9Tb0.27Dy0.73)1-xZrx (x: 0, 0.0125, 0.025, 0.05, 0.075) crystal fibers about 2 mm in diameter were grown by the micro-pulling-down (μ-PD) method. The grown crystals showed the low chemical segregation along longitudinal direction and the growth direction was oriented in the <311> direction. The saturation magnetostriction of the fiber increases with increasing the Zr content, annealing temperature and annealing time. The fiber-shape Tb-Dy-Fe crystals prepared by the μ-PD method are promising for the applications as sensors and actuators.
Polymer Matrix Composites with Shape Memory Properties
Authors: Quadrini Fabrizio
Published: May 2014

Shape memory composites and structures were produced by using carbon fiber reinforced prepregs and a shape memory epoxy resin. The matrix of the prepregs was an epoxy resin as well but without remarkable shape memory properties. This way, two different technical solutions were adopted. Shape memory composite tubes and plates were made by adding a shape memory layer between two carbon fiber reinforced skins. An optimal adhesion between the different layers was achieved thanks to the compatibility of the prepreg matrix and the shape memory material. Shape memory composite structures were also produced by joining composite shells with shape memory foams. Mechanical, dynamic mechanical and shape recovery tests were carried out to show the properties of the composite materials and structures. Results confirm the ability of this class of materials to easily change their shape without affecting the mechanical stiffness of the recovered structures.
Effect of Second Phase Particles on the Tensile Instability of a Nanostructured Al-1%Si Alloy
Authors: Huang Tian Lin , Wu Gui Lin , Liu Qing , Huang Xiao Xu
Published: May 2014

A nanostructured Al-1%Si alloy containing dispersed Si particles was produced by heavily cold-rolling to study the effect of second phase particles on the tensile instability of nanostructured metals. Tensile tests were conducted on the as-deformed sample and the samples after recovery annealing treatments. The structural features of deformed and annealed samples were characterized by transmission electron microscopy. By comparing with the behavior of nanostructured commercial purity Al without dispersed particles, a remarked improvement in the tensile stability was found. This is related to a prevention of localized deformation by the presence of finely dispersed Si particles in the nanoscale matrix structure.
Effect of Grain Refinement on Cold Formability Behavior on Medium C-Boron Steel
Authors: Salvatori Ilaria , Guarnaschelli Claudio , Coppola Tommaso
Published: May 2014

The effect of grain refinement on cold formability behavior on medium C-Boron steel has been studied. In particular a 30MnB4 steel long product has been considered to be used for screw production as final application.
One of the issues during the cold forming of screw heads is given by the possible material failure in the most strained area, like the flange tip in the head. The probability of having a high scrap rate is strictly linked to the material cold formability limits.
The study focused on the comparison between steel with conventional and ultrafine microstructure. Relationships between steel microstructure and plastic deformation behavior of the material were investigated by FEM modeling. Calibration of the model was carried out by analyzing the ultrafine grained steel, produced in pilot mill whose grain size was about 2-3 μm and the conventional steel industrially produced (grain size about 12 μm). Specific laboratory tests to characterize the material formability have been carried out. Finite element simulations have been performed to characterize the strain and stress state both in the forming process and in experimental tests to determine the material ductile fracture locus. Mechanical tests allowed to build the ductility curves related to the different microstructures to be used to simulate cold forming taking into account the material damage. Results put in evidence a significant improvement in the forming behavior of UFG steel, meaning that the refinement of grain size should produce a more evident effect in scrap reduction during the cold forming process.
Nano-Structuring of 316L Type Steel by Severe Plastic Deformation Processing Using Two-Dimensional Linear Plane Strain Machining
Authors: Wiezorek Jorg M.K. , Facco G. , Idell Y. , Kulovits A. , Shankar M.R.
Published: May 2014

Using a novel plastic deformation technique, termed linear plane-strain machining, large shear strains up to ~2.3 have been imparted to 316L stainless steel at rates of up to 1700/s. Combinations of hardness and magnetic measurements, X-ray diffraction (XRD) and transmission electron microscopy (TEM) experiments were used to monitor the microstructural and mechanical property changes for the room temperature plastic deformation processing. Grain refinements to the ultra-fine grained and even the nanocrystalline size regime have been achieved without formation of significant volume fractions of strain-induced martensite. The mechanical strength enhancements in the linear plane-strain machined 316L have been attributed to grain refinement and stored strain. The suppression of martensite formation has been correlated to significant adiabatic heating of the 316L during high strain rate plastic deformation processing.
Metallurgical Study of Friction Stir Welded High Strength Steels for Shipbuilding
Authors: Allart Marion , Benoit Alexandre , Paillard Pascal , Rückert Guillaume , Chargy Myriam
Published: May 2014

Friction Stir Welding (FSW) is one of the most recent welding processes, invented in 1991 by The Welding Institute. Recent developments, mainly using polycrystalline cubic boron nitride (PCBN) tools, broaden the range of use of FSW to harder materials, like steels. Our study focused on the assembly of high yield strength steels for naval applications by FSW, and its consequences on the metallurgical properties. The main objectivewas to analyze the metallurgical transformations occurring during welding. Welding tests were conducted on three steels: 80HLES, S690QL and DH36. For each welded sample, macrographs, micrographs and micro-hardness maps were performed to characterize the variation of microstructures through the weld.
Process Window for Friction Stir Lap Welding of Aluminum Alloy 6061
Authors: Larose Simon , Guérin Maxime , Wanjara Priti
Published: May 2014

Precipitation-hardenable 6xxx series aluminum alloys are incorporated in many structural components with due consideration of their good combination of properties including a relatively high strength, outstanding extrudability and excellent corrosion resistance. Accordingly, AA6061 has been identified as a very good candidate material for structural lightweighting of transportation vehicles. However, the weldability of aluminum alloy (AA) 6061 by means of conventional technologies such as GMAW and GTAW methods is limited by sensitivity to solidification cracking. In this respect, friction stir welding (FSW) presents a tremendous potential for assembly of aluminum structures for the transportation industry due to the low heat involved that can mitigate crack formation and, thus, translate into improved mechanical performance of the assembly.
In this work, FSW of 3.18 mm thick AA6061-T6 sheets in the lap joint configuration was investigated. This configuration is considered to be more challenging for assembly by FSW than the butt joint type due to the orientation of the interface with respect to the welding tools and the necessity to break the oxide layer on two aluminium alloy planar surfaces. Weld trials were performed to examine the influence of the FSW tool geometry and process parameters on the welding defects, microstructure, hardness and bend performance. Unacceptable material expulsion and/or significant thinning in one of the two overlapped sheets were produced under most conditions. A set of FSW tool geometries leading to a viable process operational window under which the risk of defects could be mitigated and/or eliminated was identified in this study.
Development of Homogeneity in an Al-6061 Alloy Processed by ECAP and ECAP-Conform
Authors: Xu Cheng , Langdon Terence
Published: May 2014

Equal-channel angular pressing (ECAP) has been established as an effective method to achieve ultrafine-grained materials and ECAP combined with the Conform process (ECAP-Conform) is considered a promising candidate to realize continuous processing by ECAP. This paper describes experiments conducted on samples of an Al-6061 alloy in order to evaluate the homogeneity development of the alloy processed by ECAP and ECAP-Conform. The samples of the Al-6061 alloy were processed by ECAP and ECAP-Conform at room temperature up to 4 passes via route BC. The microhardness measurements were recorded both in the cross-sectional planes and along the longitudinal directions of the samples. The results show the alloy obtained significant strengthening using both processes. There was reasonable plastic isotropy after 4 passes of ECAP-Conform in both the cross-sectional plane and the longitudinal direction and the alloy showed a homogeneous microhardness distribution in the cross-sectional plane after 4 passes of conventional ECAP.
Effect of Contraction Behaviors during Solidification of 7xxx Aluminum Alloys on Hot Tearing Susceptibility
Authors: Nagaumi Hiromi , Xue Guan Xia , Zhang Zheng Zheng , Ma Yu Li
Published: May 2014

Contraction behavior of 7xxx aluminum alloys was systematically investigated using a new device for measuring linear contraction during solidification. The effects of contraction behaviors and microstructure during solidification of three types of 7xxx series aluminum alloys on the hot tearing susceptibility were studied. It was found that the contraction behaviors of the three alloys showed extremely different shrinkage characters during solidification. The linear expansion coefficient (LEC) of 7050 and 7075 alloys shown an enormous increase from rigidity point (solid fraction is 0.69 and 0.73 respectively) to the peak value and then dropped to a constant value with the decreasing temperature. The LEC of 7022 alloy is different from the 7050 and 7075 alloys that it increases from rigidity point (solid fraction around 0.8) with a small fluctuation at the temperature little lower to the rigidity point and then they increase monotonously to the room temperature. The microstructure showed that the onset of the contraction process was the point which dendrites started coalescence. The profiles of thermal expansion coefficient of 7050 alloy were greater than the 7022’s during the solidification process, so the contraction behavior of the alloy during solidification could be used as a kind of criterion of hot tearing susceptibility.
Mechanical Properties of Al-10 Mass % Si-Mg High-Pressure Die-Casting Alloy with Different Mg Content
Authors: Yanagihara Emi , Orii Shin , Takeda Suguru , Iketani Takuya , Saikawa Seiji , Matsuda Kenji , Terayama Kiyoshi , Ikeno Susumu
Published: May 2014

The influence of Mg content on Al-10 mass % Si-0.05, 0.30 and 0.60 mass % Mg alloys castings were produced by high-pressure die-casting process, used by microstructure observation and evaluation of mechanical properties. With increasing Mg content, the main constituent phases (primary α-Al phase and eutectic phase) were not changed, but a small amount of phases crystallized at last stage of solidification (β-Al5FeSi, π-Al8Si6Mg3Fe and Mg2Si) were changed in the kind and the volume. In the mechanical property, 0.2%PS and UTS were increased, elongation and absorbed energy were decreased with increasing Mg content or difference of heat treatment. Because the fracture mode in primary α-Al phase was changed from ductile to brittle by precipitation strengthening.
Parameters Controlling High Temperature Deformability of Wrought Magnesium Alloys
Authors: Lhuissier Pierre , Salvo Luc , Blandin Jean Jacques
Published: May 2014

Due to limited deformability at room temperature, high temperature forming of magnesium alloys appears as an interesting alternative. Superplastic properties can be obtained in the case of fine grained magnesium alloys and in this regime, due to significant damage sensitivity, fracture strain is mainly controlled by nucleation, growth and coalescence of cavities. Magnesium alloys with large grained alloys can also exhibit interesting deformabilities at high temperature since dislocation movements can be controlled by a solute drag effect promoting plastic stability. Examples of such situations are presented in the case of wrought magnesium alloys, the associated damage mechanisms being investigated thanks to 3D X-ray micro tomography performed in continuous mode, namely directly during high temperature deformation tests.
The Orientation Dependence of Strain Hardening and Texture Development in an Extruded Magnesium Alloy
Authors: Sarker D. , Chen Dao Lun
Published: May 2014

Extruded magnesium alloys showed mechanical anisotropy due to the development of strong crystallographic textures during forming processes. In the present study the strain hardening behavior and texture evolution of an extruded AM30 magnesium alloy were studied in compression using cylindrical samples oriented at angles of 0°, 15°, 30°, 45° and 90° from the extrusion direction (ED). The yield strength decreased with increasing angle up to 45° and then increased at 90° from the ED, while the ultimate compressive strength exhibited a reverse trend. Both hardening capacity and fracture strain first increased from 0° to 45° and then decreased at 90° from the ED. The strain hardening behavior was directly related to the texture change and twinning, which played a key role in accommodating the compressive deformation, as the c-axes in most grains were observed to rotate always towards the anti-compression direction, irrespective of the sample orientation.
Effect of Thermomechanical Processes on Twin Roll Casted Magnesium Alloy Sheets
Authors: Duygulu Ozgur , Ucuncuoglu Selda , Secgin Gizem Oktay
Published: May 2014

6 mm thick and 1500 mm wide magnesium alloy AZ31, AZ61, AZ91, AM50 and AM60 sheets were produced by twin roll casting technique. Sheets were homogenized between 350-475oC for 1-24 h. AZ31 sheets were rolled down to 1 mm by symmetrical warm rolling and asymmetric warm rolling. Age hardening was also performed on magnesium alloy AZ91 sheets. Specimens were aged at 100-300oC for up to 100 h. Characterization was performed by light microscope, scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), transmission electron microscopy (TEM) and x-ray diffraction (XRD) after twin roll casting and also after each thermomechanical process including aging. Tensile tests and micro hardness tests were performed for mechanical properties. In addition to the room temperature tests, elevated temperature tensile tests were also performed at 100, 150, 200, 250, and 300oC at various deformation speeds. Forming limit diagram of the material was determined under warm forming condition.
Effect of Plane Strain on the Microstructure and Texture of AZ31 Sheet with Various Reduction Ratios
Authors: Kim Dae Guen , Kim Hak Young , Yoon Young Ok , Kim Shae K. , Lim Hyun Kyu
Published: May 2014

In this study, the effect of plane strain on the microstructure and texture of AZ31 sheet was investigated with various reduction ratios. To achieve plane strain, that is, to prevent shear deformation during warm-rolling, AZ31 sheet was capsuled by pure Cu tube. The large strain induced by simple one-pass warm-rolling led to the significant grain refinement and texture randomization. The two-dimensional finite-element method showed that the warm-rolling of AZ31 sheet capsuled by Cu tube imposed a uniform plane strain in the whole sheet thickness. The high reduction ratio caused the dynamic recrystallization during annealing of the rolled sheet.
On the Bonding Strength of Mg-Mg and Mg-Al Material Compounds
Authors: Reichelt Stephan , Saleh Haitham , Schmidtchen Matthias , Kawalla Rudolf
Published: May 2014

The dependence of different brushing parameters during surface preparation on the resulting bonding strength for the roll-bonding of Mg-Mg composites was investigated. A parameter study with different brushing parameters was used to analyze the effect on surface roughness as pre-step for roll-bonding trials with different roughness ratio. Furthermore, the influence of different Mg alloys and of a roll-bonded Al-Mg-Al sandwich composite on the obtained bonding strength was investigated.
Age-Hardening Behavior of Mg-Al-Zn Alloys Produced by Sand Mold Casting
Authors: Saikawa Seiji , Ebata Yuhei , Terayama Kiyoshi , Ikeno Susumu , Yanagihara Emi
Published: May 2014

In recent years, Mg-Al-Zn system alloy has been used for the parts in the automobile for weight reductions. The age-hardening behavior of Mg-6mass%Al (-1mass%Zn)-0.3mass%Mn alloys sand mold castings were investigated by Vickers hardness measurement and optical microscopic observation. Both alloys were solution-treated and then isothermal-aged at 473, 498 and 523K. For each aging temperature, both alloys were indicated age-hardening obviously, and decreased the value of maximum hardness and shorten time to maximum hardness with heighten aging temperature. Age-hardening curves for both alloys approximately showed the same change of hardness. However, these optical micrographs after aging treatment are observed different microstructure. In case of AM60 magnesium alloy, discontinuous precipitation preferentially occurred in aged sample. The volume fraction of discontinuous precipitation was larger than that of continuous precipitation. On the other hand, in case of AZ61 magnesium alloy, the volume fraction of continuous precipitation was larger than that of discontinuous precipitation. Furthermore, over-aged sample of both alloys were consisted of discontinuous precipitation, continuous precipitation and pre-precipitation area.
High Temperature Creep Behavior and Effects of Stacking Fault Energy in Mg-Y and Mg-Y-Zn Dilute Solid Solution Alloys
Authors: Suzuki Mayumi , Murata Yasuyuki , Yoshimi Kyosuke
Published: May 2014

Compressive creep behavior of hot-rolled (40%) Mg-Y binary and Mg-Y-Zn ternary dilute solid solution alloys are investigated in this study. Creep strength is substantially improved by the addition of zinc. Activation Energy for creep in Mg-Y and Mg-Y-Zn alloys are around 200 kJ/mol at the temperature range from 480 to 570 K. These values are higher than the activation energy for self-diffusion coefficient in magnesium (135 kJ/mol). Many stacking faults, which are planar type defects are observed on the basal planes of the magnesium matrix in Mg-Y-Zn ternary alloys. TEM observation has been revealed that the non-basal a-dislocation slip is significantly activated by these alloys. The rate controlling mechanism of Mg-Y and Mg-Y-Zn dilute alloys are considered to the cross-slip or prismatic-slip controlled dislocation creep with high activation energy for creep, more than 1.5 times higher than the activation energy for creep controlled dislocation climb.
Microstructural Characteristics and Mechanical Properties of Spray-Deposited Mg-Gd-Y-Zr Alloy
Authors: Wang Feng , Xiong Bai Qing , Zhang Yong An , Li Zhi Hui , Liu Hong Wei , Li Xi Wu
Published: May 2014

In this study, Mg-6.8Gd-4.5Y-0.5Zr alloy was fabricated by the spray atomization and deposition technique. The microstructure and mechanical properties of the alloy were studied using optical microscopy, scanning/transmission electron microscopy, X-ray diffraction, and tensile tests. The secondary phases in the microstructure of the spray-deposited alloy were examined. The tensile test results indicate that the spray-deposited Mg-6.8Gd-4.5Y-0.5Zr alloy displays superior tensile strength due to grain refinement and the presence of precipitating strengthening phases.
The Cube Recrystallization-Texture Related Component in the β-Fiber Rolling-Texture FCC Metals
Authors: Lee Dong Nyung , Han Heung Nam
Published: May 2014

The cold-rolling texture of fcc sheet metals with medium to high stacking fault energies is known to consist of the brass {011}<211>, Cu {112}<111>, Goss {011}<100>, S {123}<634>, and cube {100}<001> components. The recrystallization (Rex) texture of cold-rolled Al, Cu and their alloy sheets is well known to be the cube texture. The 40°<111> orientation relationship between the S and cube components, which has been taken as a proof of the oriented growth theory, has made one believe that the S orientation is responsible for the cube Rex texture. The oriented growth theory is claimed to be associated with grain boundary mobility anisotropy. However, some data indicate the Cu component is linked with the cube component. There is no 40°<111> orientation relationship between the Cu and cube components. The strain-energy-release-maximization model (SERM), in which the strain energy due to dislocations is importantly taken into account, suggests that the Cu and S components in the rolling texture are linked with the cube and ~{031}<100> components in the Rex texture, respectively.
ATI 425® Alloy Formability: Theory and Application
Authors: Bryan David
Published: May 2014

ATI 425® Alloy, nominal composition Ti-4.0Al-2.5V-1.5Fe-0.25O, is a new alpha/beta Ti alloy of significant commercial interest as a viable replacement for Ti-6Al-4V, CP-Ti, and other titanium alloys in a variety of aerospace applications. ATI 425® Alloy offers properties comparable to Ti-6Al-4V alloy with significant improvements in formability, both at room and elevated temperatures. The reasons for the improved formability, particularly at low temperatures, are not well understood. The development of a thorough understanding is complicated by the wide array of phases, microstructures, and deformation paths available via thermomechanical processing in alpha/beta titanium alloys.
In this paper, theories of strengthening and dislocation mobility in titanium and HCP metals will be reviewed and applied to better understand why ATI 425® Alloy offers a unique combination of strength and formability not obtainable by conventional alpha/beta titanium alloys. Subsequently, the application of the improved formability to a range of product forms including sheet, tubing, and forgings will be discussed.
Friction Stir Welding of Ti-6Al-4V Alloy
Authors: Leo Paola , Cerri Emanuela
Published: May 2014

Titanium (Ti) and its alloys are used extensively in aerospace industry where there is a critical need for material with high strength-to–weight ratio and high elevate temperature properties. Friction stir welding (FSW) is a new solid state welding process in which a cylindrical–shouldered tool with an extended pin is rotated and gradually plunged into the joint between the workpieces to be welded. The material is frictionally heated to a temperature at which it becomes more plastic but no melting of the blanks to be welded is reached therefore the presence of defects typically observed in and close to the welding seam is strongly reduced. The final result is the improvement of the mechanical performances of the welded joints even in some materials with poor fusion weldability. In this paper the authors analyze the microstructure of FSW joints of Ti-6Al-4V processed at the same travel speed (50 mm/min) and at different rotation speed (300-500rpm). The microstructure of base material (BM) is not homogenous. It is characterized by distorted α/ β lamellar microstructure together with smashed zone of fragmented β layer and β retained grain boundary phase. The BM has been welded in the as received state, without any previous heat treatment. The microstructure of the transverse section of joints is not homogeneous. Close to the top of weld cross sections a much finer microstructure than the initial condition has been observed while in the center of the joints the microstructure is mixed and less refined.
Effect of Zr Addition on High Temperature Mechanical Properties of Near Alpha Ti-Al-Zr-Sn Based Alloy
Authors: Jayaprakash Murugesan , Ping De Hai , Yamabe-Mitarai Y.
Published: May 2014

Titanium (Ti) alloys are widely used in aerospace industries successfully up to 600°C. Increasing the operating temperature and performance of these alloys would be very useful for fuel economy. Numerous numbers of research works has been focused on the improvement of the high temperature performances of Ti alloys. It has been well known that Zirconium (Zr) is one of the important solid-solution strengthener in Ti-alloys. In the present study, the effect of Zr addition on the microstructure and mechanical properties of the near–α Ti-Al-Zr-Sn based alloys has been investigated.The compression test results showed that Zr addition significantly improves both room temperature and high temperature strength. The results obtained were explained based on the microstructural observation, room temperature and high temperature compressive tests.
Effect of Si and Ge Addition on the Evolution of Microstructure in Near Alpha Titanium Alloy
Authors: Suresh K.S. , Kitashima T. , Yamabe-Mitarai Y.
Published: May 2014

Near α titanium alloys have found wide application as compressor blades, fins in aero engines [1]. In order to achieve better fuel economy, there is a major focus to increase the operating temperature of these components. Addition of small amount of silicon has been found to significantly improve creep resistance [2-7]. Highly stable grain boundary precipitates could reduce the grain boundary sliding and uniform precipitation could restrict the dislocation creep at high temperature. Applications of Si added titanium alloys are limited up to 600oC. Ge being analogous to Si shows better solid solubility, particularly at room temperature [8]. Consequently, it can lead to solid solution strengthening. It has also been reported that germanides have better thermal stability compared to silicides [8]. However, there is no investigation available on the effect of Ge on the microstructural evolution in near α titanium alloys. Therefore, the present study aims at understanding the effect of Si and Ge addition on the evolution of microstructure in near α titanium alloys.
Hybrid Fiber Laser – Arc Welding of High Strength Low Alloy Steel
Authors: Cao Xin Jin , Wanjara Priti , Bernard A. , Pudo Dominik , Munro Cameron , Nolting Allison E.
Published: May 2014

High strength low alloy (HSLA) grade 80 (HSLA-80) steel with a thickness of 9.1-mm was successfully welded in a single pass using a 5-kW fiber laser combined with an arc welding process. It was found that the maximum gap size in the Y-groove butt joint configuration should remain below 0.2 mm for a 9.1-mm section thickness. Sound butt joints with no welding cracks but some minor microporosity were successfully obtained. However, an underfill defect was frequently observed on the top surface of the weldments. Underfilling could be mitigated through increasing the filler wire addition so as to exceed the groove volume; however, due to significant evaporation and expulsion of the molten pool at the high laser power density, the underfill defect would be difficult to fully eliminate. At slow cooling rates, slight softening in the heat affected zone (HAZ) was present in the mid-thickness region but its elimination is possible at high welding speeds.
Heat Treatment Effects on Distortion, Residual Stress, and Retained Austenite in Carburized 4320 Steel
Authors: Clark Andrew , Bowers Randy J. , Northwood Derek O.
Published: May 2014

The effects of heat treatment on distortion, residual stress, and retained austenite were compared for case-carburized 4320 steel, in both the austempered and quench-and-tempered condition. Navy C-ring samples were used to quantify both size and shape distortions, as well as residual stress. The austempering heat treatment produced less distortion and a higher surface residual stress. Both hoop and axial stresses were measured; the difference between them was less than seven percent in all cases. Depth profiles were obtained for residual stress and retained austenite from representative C-ring samples for the austempered and quench-and-tempered heat treatment conditions. Austempering maintained a compressive residual stress to greater depths than quench-and-tempering. Quench-and-tempering also resulted in lower retained austenite amounts immediately beneath the surface. However, for both heat treatments, the retained austenite content was approximately one percent at depths greater than 0.5 mm.