bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformation Microstructures of Two-Phase Intermetallic Alloy Composed of Ni3Al and Ni3V in Single Crystalline Form
Authors: Moronaga T. , Kaneno Yasuyuki , Tsuda Hiroshi , Takasugi Takayuki
Published: January 2012

Two-phase single-crystal intermetallic alloys composed of Ni3Al (L12) and Ni3V (D022) with some orientations were compressed at various temperatures, and their deformation microstructures were observed by transmission electron microscopy (TEM). The deformation at room temperature was governed by the glide motion of dislocations in the primary Ni3Al precipitates and the activation of the microtwins in the Ni3V variant structures in the channel regions. The interfaces between the primary Ni3Al precipitates and the Ni3V variant structures are suggested to work as the barriers to the dislocation motion. While, at temperature above the peak temperature (873 K), the deformation microstructures of the two-phase intermetallic alloy exhibited the ribbon-like deformation microstructures penetrating the constituent phases i.e. through the interfaces between primary Ni3Al precipitates and the Ni3V variant structures in the channel regions. It was also suggested that the superior strength in the two-phase intermetallic alloys is due to the high flow strength of the Ni3V phases and to the interfacial hardening receiving when the dislocations activated in the primary Ni3Al precipitates propagate to the channel regions.
Friction and Wear Properties of Fe7Mo6-Based Alloy under Various Sliding Conditions
Authors: Murakami Takashi , Matsuzaki Kunio
Published: January 2012

In this study, the friction and wear properties of the Fe7Mo6-based alloy/Al2O3 tribopair were investigated at high temperatures in air and at 298 K in water. The Fe7Mo6-based alloy/Al2O3 tribopair exhibited friction coefficients as low as 0.5 at 298 K and 873 K in air. On the other hand, this tribopair exhibited higher friction coefficients at 573 K than at 298 K and 873 K. It was also found that the friction coefficients of this tribopair were approximately 0.5 in water. The Fe7Mo6-based alloy disk specimens and their paired Al2O3 ball specimens exhibited the highest specific wear rates at 873 K in air. Oxygen-rich phase was observed on the worn surfaces of all the disk specimens. Concerning the friction and wear tests at high temperatures in air, the amount of the oxygen-rich phase increased with increasing the testing temperature. In addition, a little larger amount of the oxygen-rich phase was observed on the worn surface formed at 298 K in water than that formed at 298 K in air.
Microstructural Refinement of Boron Containing β-Solidifying γ-Titanium Aluminide Alloys
Authors: Oehring Michael , Stark Andreas , Paul Jonathan D.H. , Lippmann Thomas , Pyczak Florian
Published: January 2012

β solidifying γ titanium aluminide alloys exhibit fine and homogeneous microstructures in the cast condition, in particular if the alloys contain B as a grain refining agent. Following work in the literature [1], it is demonstrated that the grain refining effect due to B is solely attributed in such alloys to its effect on the solid-state β/α transformation. The results further show that grain refinement in these materials can be obtained by a simple heat treatment, even if the microstructure has been extensively coarsened through prior heat-treatment.
Density Functional Theory and Ab Initio Molecular Dynamics Study of the Effect of Ti and Zr Transition Metals in D03 Fe3Al
Authors: Chentouf Sara , Raulot Jean Marc , Aourag Hafid , Grosdidier Thierry
Published: January 2012

The formation energies of the T.M impurities Ti and Zr were calculated using DFT calculations at absolute zero and ab initio MD simulations at 300 K. We found that, with increasing temperature, Zr impurities become more stable and prefer to segregate at the interface of ∑5 (310)[001] grain boundary. In the case of Ti, the results show that it remains a stable defect when temperature increases.
The Microstructure, Creep, and Hardness Properties of Powder Metallurgy Beta Gamma TiAl-4Nb-3Mn Alloy
Authors: Sawatzky Trevor , Seo Dongyi , Saari H. , Laurin D. , Kim Young Won
Published: January 2012

Pre-alloyed beta gamma titanium aluminide powder with a nominal composition of TiAl-4Nb-3Mn is consolidated by hot isostatic pressing. After consolidation, a step cooled heat treatmentis performed to homogenize the material and produce a fully lamellar microstructure. Various agingheat treatments are then performed with the goal of forming interfacial beta phase precipitates alonglamellar interfaces. The step cooled heat treatment produces a relatively fine microstructure with alamellar spacing of 0.04 μm and an average lamellar colony size of 60 μm. The aging heat treatmentsgenerate beta phase precipitates along lamellar colony boundaries but not along lamellar interfaces,and result in lamellar degredation and grain growth. Constant load tensile creep and room temperaturehardness tests are performed on step cooled heat treated and step cooled heat treated and aged specimens.Creep resistance, generally, improves with aging time, even with no interfacial precipitation,and the lamellar degredation that occurs with aging. The microstructures of the as-tested specimensare characterized and related to the creep properties. The hardness values are also compared as afunction of selected heat treatment condition and microstructural features.
First Principles Investigation of Interaction of Oxygen with Low Index Surfaces of γ-TiAl
Authors: Song Yan , Dai J. H. , Yang Rui
Published: January 2012

A first principles study of adsorption of oxygen atom on surfaces of γ-TiAl was performed to investigate the intrinsic mechanism dominated the adsorption behaviours. First surface stability was evaluated. It was shown that the (100) surface is the most stable surface followed by (111), (110), and (001) surfaces. Then adsorption of oxygen on the (100) and the (111) surfaces was studied. Oxygen atom prefers the Ti-rich environment and has high potential to generate TiO2. Competition between the O-Al bonding and the O-Ti bonding was observed. However, the O-Ti interaction dominates the adsorption behaviours in all considered systems. A linear relationship between adsorption energy and integration of orbital overlaps of O and metals was observed, which indicates that the electronic structure controls adsorption behaviours of oxygen on surfaces of γ-TiAl and provides a guidance to improve the oxidation resistance of γ-TiAl based alloys.
The Effect of EMS on the Microstructure of LPSO Mg-Zn-Y Cast Alloy
Authors: Akiyama H. , Kawamura Yoshihito
Published: January 2012

In this study, long period stacking ordered structure (LPSO) type magnesium alloys have been developed. They consist of LPSO phase and α-Mg phase and have excellent mechanical properties at both ambient and elevated temperatures. In the present study, the influence of electromagnetic stir (EMS) on the structure of LPSO type Mg96Zn2Y2 (at. %) billets of φ200 mm in diameter was investigated in order to establish the large-scale casting technology of LPSO type Mg alloy. EMS refined the grain size of α-Mg up to approximately 1/3.5, and reduced the size difference between the surface and the center of the billets. By applying EMS, it was found possible to provide large-scale casting billets with fine and homogeneous microstructure.
Plastic Deformation Behavior in Magnesium Alloy Single Crystals
Authors: Ando Shinji , Tsushida Masayuki , Kitahara Hiromoto
Published: January 2012

Zn and Al are major alloying elements of Mg alloys. Main slip system of Mg is a basal slip and the CRSS increases with Zn or Al content. According to von-Mises criterion, five kinds of independent slip systems are required for uniform deformation, so it is necessary to activate non-basal slip systems to show good ductility. However, it has not become clear the effect of Zn or Al for non-basal slip systems yet. To investigate deformation behavior of magnesium crystal by non-basal slip, Mg-Zn and Mg-Al single crystals were stretched in the [110] direction and Mg-Zn single crystals were compressed in the [0001] direction. {112}<23> second order pyramidal slip was activated in Mg-0.1at%Zn and Mg-0.5at%Al. On the other hand, {101} twin was mainly activated in Mg-1.0at%Al alloy. Yield stress due to the pyramidal slip of magnesium decreased by 0.1at%Zn addition, however they increased with addition of aluminum..
High Temperature Deformation and Associated 3D Characterisation of Damage in Magnesium Alloys
Authors: Lhuissier Pierre , Villanueva Fernandez A. , Salvo L. , Blandin Jean Jacques
Published: January 2012

A way to overcome the low deformability of magnesium alloys at room temperature is toincrease the temperature of forming operations. The stress exponent n, which is known to be a keyparameter in the control of plastic stability, generally decreases when temperature increases.Nevertheless, low n-values are not enough to ensure large capacity of deformation since fracturecan also result from strain induced cavitation. In the present investigation, both the mechanisms ofhigh temperature deformation and damage were studied in selected Mg alloys. Since damage datacan also give information on the deformation mechanisms, the strain induce cavitation behaviourwas mainly studied thanks to X-ray micro tomography which provides 3D information like thecavity shapes or the variation with strain of the number of cavities. Moreover, additionally toconventional post mortem analyses, it was attempted to perform the 3D damage characterisation inin situ conditions, namely directly during high temperature deformation tests.
Ternary Intermetallic Compounds across the Mg-NiY Line at 673 K
Authors: Mezbahul-Islam Mohammad , Kevorkov Dmytro , Essadiqi Elhachmi , Medraj Mamoun
Published: January 2012

The phase relationship of the Mg-Ni-Y system along the Mg-NiY line has been investigated using electron probe micro analysis (EPMA) at 673 K. Three two phase regions (Mg2Y+τ6, Mg2Y+ MgNiY(τ3), MgY+Mg3Ni2Y4(τ1)) and two three phase regions (Mg2Y+Mg3Ni2Y4(τ1)+ MgNi2Y2(τ2) and NiY+Mg3Ni2Y4(τ1)+MgNi2Y2(τ2)) have been identified. One new ternary compound Mg5NiY(τ5) was found and reported for the first time. Ternary solubility of the Mg8-13NiY(τ6) compound has been established which extends from 77.10 at.% Mg until 86.77 at.% Mg along the Mg-NiY section. Solubility of the third element in the binary compounds, NiY, Mg2Y and MgY has also been determined. Keywords: Mg alloy, phase identification, phase equilibrium, isothermal section.
Intragranular and Grain Boundary Precipitations with Aging Treatment in Mg-Al System Alloys Poured into Gravity Mold
Authors: Furui Mitsuaki , Ikeno Susumu , Saikawa Seiji
Published: January 2012

It is well-known that age hardening occurs in Mg-Al system alloys, when the alloy containing aluminum exceeds 6mass%. This precipitation reaction depends on aluminum content and aging temperature. The aging behavior in AZ91 magnesium alloy was investigated and it is the subject of this paper. However, for the Mg-Al system alloys, the influence of aluminum content on aging hardening characteristics has not been researched in detail so far. In this study, continuous and discontinuous precipitations during aging in Mg-Al system alloys cast into sand and iron molds were investigated by means of hardness measurement and microstructure observation with optical microscopy and transmission electron microscopy. Variation of hardness with aging was found to be caused mainly by the discontinuous precipitation along the grain boundaries from the composite rule in hardness. In iron mold castings, It was found that the variation of hardness with aging was found to be caused mainly by the continuous precipitation inside the crystal grain.
Microstructure Evolution of AS21 Magnesium Alloy via the SIMA Process
Authors: Karimi Majid Bigdeli , Heidary Mostafa Hajian , Samei Javad , Green Daniel E.
Published: January 2012

AS is a relatively new series of Magnesium alloys. The microstructure of this alloy can be improved for semisolid processing. The current research is concerned with the microstructure evolution of AS21 under the strain induced melt activated (SIMA) process. For this purpose, the AS21 alloy is cast and compressed 10-40% at 200 °C. The semisolid heat treatment is completed in a carbonate salt bath at different temperatures between 600-620 °C. The microstructure studies show that there is no favourable microstructure evolution between 600-610 °C. At 615 °C fine globular grains are obtained with the most desired mean grain size and sphericity of 67 µm and 81%, respectively. At 620 °C an undesirable coarsening phenomenon occurs that damages the microstructure globularity. SEM micrographs show that in a successful SIMA processing, the Mg2Si phases are broken into fine particles distributed within the grains and grain boundaries.
Microstructural Factors Affecting the Deformation Behavior of Mg12ZnY LPSO-Phase Alloys
Authors: Hagihara Koji , Kinoshita Akihito , Fukusumi Yoshihiro , Yamasaki Michiaki , Kawamura Yoshihito
Published: January 2012

Microstructural factors that govern the plastic deformation of the long-period stacking ordered (LPSO) phase were clarified. The decrease in length of the long-axis for the plate-like shape of LPSO-phase grains increases the yield stress of the alloy in which basal slip is predominant in deformation. On the other hand, the yield stress tended to increase as the thickness of the plate-like shapes of the grains decreased for the alloy in which the formation of deformation kinks carried the strain.
Experimental Study on Phase Diagram in the Vicinity of X or W Phase in the Mg-Zn-Y Ternary System
Authors: Horiuchi T. , Ikee H. , Hamaya A. , Minamoto S. , Nomoto S. , Miura Seiji
Published: January 2012

To elucidate the phase equilibria in the vicinity of the X or W phase in the Mg-Zn-Y ternary system, five Mg-Zn-Y ternary alloys containing the X or W phase were prepared and isothermally heat-treated to reach thermodynamic equilibrium. The microstructure and chemical compositions of the equilibrium phases of the alloys were analyzed. Furthermore, the crystal structure of the W phase was investigated, and the liquidus temperatures of the alloys were examined using differential thermal analysis. The results showed that the X phase can be crystallized not by a eutectic reaction, as reported previously, but by a peritectic reaction. They also showed that the W phase has the Heusler-type crystal structure with a stoichiometric composition of Mg1Zn2Y1, and that Mg and Zn in the W phase can be substituted for each other. The Mg-Zn-Y ternary phase diagram was calculated using an assessed CALPHAD thermodynamic database based on the experimental results of the present study, and compared with a recently reported phase diagram.
Deformation Behavior of Mg-Ni-Y Alloy with Long Period Stacking Ordered Phase
Authors: Itoi Takaomi , Ichikawa Ryu , Hirohashi Mitsuji
Published: January 2012

Microstructures of the long period stacking ordered (LPSO) phase deformed by compression test or rolling at room temperature were investigated. The Mg85Ni6Y9 (at.%) alloy was composed mostly of plate-type phase with 10H-type LPSO structure. The Mg85Ni6Y9 alloy exhibited compression yield stress of 365 MPa and fracture strain of 30 % at room temperature. After compression test with applied stress of 25 %, a bend, delamination between basal planes and crack initiation at boundary of the LPSO phase were observed. From these microstructural features, it was considered that the deformation of the LPSO phase significantly influenced by a kink deformation. The Mg85Ni6Y9 alloy could be rolled with 30 % reduction at room temperature. The kink deformation was frequently observed in the LPSO phase of the alloy sheet. The basal plane texture was formed in plane sheet of the alloy sheet. However, it was more difficult to form basal plane texture in the LPSO phase than in the pure-Mg due to introduce the kink deformation. Therefore, it was considered that better rollability of the Mg85Ni6Y9 alloy compared with the pure-Mg was brought for the kink deformation.
Dynamic Strain Aging Behavior of a Mg-Ce Alloy and its Implications for Extrusion
Authors: Jiang Lan , Jonas John J. , Mishra Raja K.
Published: January 2012

Compression tests were employed to characterize the DSA behaviour of Mg-Ce alloys. Samples were taken from cast billets and extruded bars of Mg-0.5 wt.% Ce. The DSA behavior was examined at temperatures from 150°C to 400°C at strain rates of 0.001/s to 1.5/s. A rate equation was fitted to the experimental results, which is employed to predict whether or not DSA will occur at the strain rates and temperatures involved in the formation of the RE texture component during extrusion.
Microstructure and Mechanical Properties of Extruded Mg-Zn-Ce-Zr Alloy Rods
Authors: Jin Li , Li Guang , Dong Jie , Ding Wen Jiang
Published: January 2012

Mg-Ce based alloy is a significant extrusion alloy for high ductility and Zn is a promising element for the increase of strength in the alloys. The effects of Zn addition to the Mg-0.5%Ce-0.5%Zr alloy and the extrusion parameters on the microstructures and mechanical properties of Mg-Zn-Ce-Zr alloy have been investigated. The results suggest that Zn element addition will enhance alloy strength and save accepted ductility. The extrusion parameters have been optimized to get the fine grain size, random texture, and therefore to develop a higher ductility and lower yield asymmetry alloy.
HRTEM Observation of Precipitates in Mg-Gd-Zr and Mg-Y-Zr Alloys Aged at 423 K
Authors: Kawabata Tokimasa , Matsuda Kenji , Ikeno Susumu
Published: January 2012

High resolution transmission electron microscopy (HRTEM) observation was performed to clarify the early stage of precipitation in Mg-Gd (-Zr) alloy and Mg-Y(-Zr) alloy aged at 423 K. At the early stage of agigng at 423 K, the intensity of the diffuse spots become higher at the 1/2 distance of 1100 or 2110 corresponding to magnesium matrix spots with aging time. Contrasts of mono layers on {100}Mg planes, and the feature of D019 type structure, precipitates with five layers corresponding the feature of (020)b' plane and b' phase co-existed and b' phase formed predominantly in the peak aged Mg-Gd (-Zr) alloy at 423 K, wheres in the peak aged Mg-Y(-Zr) alloy at 423 K, monolayer and precursor of precipitates with five layers corresponding the feature of (020)b' plane formed predominantly.
Improving Corrosion Resistance of MRI 230D Mg Alloy by Hybrid Coating of Laser Surface Alloying and Plasma Electrolytic Oxidation
Authors: Rapheal G. , Kumar Subodh , Blawert Carsten , Dahotre Narendra B.
Published: January 2012

A permanent mould cast creep resistant MRI 230D Mg alloy was laser surface alloyed (LSA) with Al and Al2O3 in order to improve its wear and corrosion resistance. However, this treatment was successful only in improving wear resistance but not corrosion resistance due to the presence of micro−cracks in the coated layer, which has been discussed in an earlier paper. The LSA coated Mg alloy has been further subjected to plasma electrolytic oxidation (PEO) treatment in alkaline silicate electrolyte in order to cover those micro−cracks and improve corrosion resistance, which is discussed in the present manuscript. For comparison, the PEO coating has also been applied on the as−cast MRI 230D Mg alloy. The microstructural characterization of coatings and corroded surfaces was carried out by scanning electron microscope and X−ray diffraction. Electrochemical corrosion tests were conducted in 3.5 wt% NaCl solution having neutral pH to investigate the corrosion behavior. The LSA coatings consisted mainly of β (Mg17Al12) phase, the coatings produced by PEO treatment on MRI 230D Mg alloy consisted mainly of Mg2SiO4 phase, and hybrid coatings of PEO on LSA consisted of Mg2SiO4 and MgAl2O4 phases in the PEO layer. Scanning electron micrographs of the cross−section revealed that the PEO treatment covered the micro−cracks present in the LSA and corrosion tests revealed that it improved the corrosion resistance, though not to the extent of the corrosion resistance of the PEO coated MRI 230D Mg alloy. All the samples exhibited localized form of corrosion.
Scale/Physics/Time Properties and Functions in Bioartificial Systems
Authors: Bidone Tamara C. , Deriu Marco A. , Falvo D’urso Labate Giuseppe , Massai Diana , Morbiducci Umberto , Montevecchi Franco Maria
Published: January 2012

Recent research on biological materials and bioartificial systems has created one of the most dynamic field at the confluence of physical sciences, molecular engineering, cell biology, materials sciences, biotechnology and (nano) medicine. This field concerns better understanding of living systems, design of bio-inspired materials, synthesis of bioartificial technologies with new properties depending on their multi-scale architectures. Biological and man-made systems show the first level of organization at the nanoscale, where the fundamental properties and functions are settled (e.g., proteome and genome). The nanoscale properties reflect on larger scales: mesoscale, microscale, and continuum. Mechanisms by which phenomena at the different length and time scales are coupled and influence each other is the central issue in linking properties to functionalities, with a dramatic impact in designing and engineering biosystems. To get insights into the progressive trough-scales cascade effects-from molecular to macroscale level and from nanoseconds to life expectancy duration-multiscale/multiphysics models are required, dealing with inorganic, biological and hybrid matter. Thus, bioartificial systems technology depends upon our ability in assembling molecules into objects, hierarchically along several length scales, and in disassembling objects into molecules, in a tailored manner. As a peculiar feature, in bioartificial systems, the definition of the interactions between artificial and biological components needs to incorporate the “time” variable, in order to reproduce the evolution of the overall system, and to simulate complex phenomena as biodegradation and tissue remodeling. Herein, a number of paradigmatic multiscale models that attend the investigation of biological systems and the engineering of bioartificial systems is reviewed and discussed.
A Differential Scanning Calorimetric Study of the Mg-Cu-Y System
Authors: Mezbahul-Islam Mohammad , Essadiqi Elhachmi , Medraj Mamoun
Published: January 2012

The Mg-Cu-Y system has been experimentally investigated using differential scanning calorimetry (DSC). Vertical sections and phase assemblage diagrams are calculated using thermodynamic modeling. Solidification behavior of the key alloys was discussed in light of the thermodynamic calculation. Melting temperatures of two of the ternary compounds; Mg18CuY and Mg4CuY, are predicted using the modified thermodynamic database of this system. Key words: Mg alloys, Bulk metallic glass, Differential scanning calorimetry, Thermodynamic modeling.
C Fibres - Mg Matrix Composites Produced by Squeeze Casting and Friction Stir Processing: Microstructure & Mechanical Behaviour
Authors: Mertens Anne , Simar Aude , Delannay Francis
Published: January 2012

Mg-Al-Zn alloys have been reinforced with carbon fibres using either the liquid state process of squeeze casting (SC), or friction stir processing (FSP), a solid state process developed more recently and that appears as a promising alternative for the large-scale production of C-Mg composites. Both processes have shown their ability to produce sound composites with enhanced strength compared to the non-reinforced alloys. In SC composites, the unsized woven C fabric remains intact while in the FSP composites the sized C fabric is fragmented in short fibres, with an aspect ratio typically equal to 4, homogenously distributed in the Mg alloy matrix.
Improvement in Mechanical Properties of Coarse-Grained AZ61 Mg Alloy by Multidirectional Forging and Ultrafine Grain Refinement
Authors: Miura Hiromi , Ito M.
Published: January 2012

A commercial AZ61 magnesium (Mg) alloy composed of coarse initial grains was multi-directionally forged (MDFed) under decreasing temperature conditions from 673 K to 463 K up to a cumulative strain of ΣΔε = 6.4 at a true strain rate of 3 × 10-3 s-1. A pass strain of Δε = 0.8 was employed. The average grain size decreased gradually with an increase in the cumulative strain. After straining to ΣΔε = 6.4 (i.e., after 8 passes of MDF), equiaxed ultrafine grains (UFGs) with an average size of approximately 0.8 μm were uniformly produced. These grains were relatively coarse as compared with MDFed Mg alloys having initially finer grains. The hardness of the AZ61 Mg alloy increased monotonically up to 910 MPa with decreasing grain size. The Hall-Petch relationship held within this experimental condition.
Effect of Grain Size on Fatigue Crack Propagation in Extruded AZ31 Magnesium Alloys
Authors: Morita Shigeki , Ohno Nobuyoshi , Tamai Fujio , Kawakami Yuji
Published: January 2012

This paper describes the fatigue crack propagation behavior of extruded AZ31B magnesium alloys (average grain size: approximately 15 and 119 μm, respectively). Fatigue crack propagation tests were performed on center cracked tension (CCT) specimens at a stress ratio of R=0.1 and a frequency of 10 Hz at room temperature. Loading axis was parallel to the extrusion direction; crack face was perpendicular to basal plane of each grain. The crack growth rate (da/dN) of the coarse-grained specimen was approximately 5 times higher than that of the fine-grained specimen. Fracture surfaces of the fine-grained and coarse-grained specimens showed various directional steps independent of macroscopic crack growth direction.
Effect of Long-Period Stacking Order Phase and α-Mg Phase on Strength and Ductility of Mg-Zn-Y Alloy
Authors: Noda Masafumi , Kawamura Yoshihito
Published: January 2012

Mg alloys are lightweight structural alloys that normally have a good castability and machinability as well as an excellent specific strength and rigidity. However, the mechanical properties of Mg alloys are inferior to those of Al alloys, and their range of industrial applications is limited. Recently, Mg–Zn–Y alloy has been found to show a high tensile yield strength with a good elongation. The alloy has a long-period stacking order (LPSO) phase as the secondary phase in an α-Mg phase. In general, the tensile yield strengths of LPSO-type Mg alloy are known to be markedly enhanced by the formation of kink bands in the LPSO phase and by microstructural refinement of the α-Mg phase during plastic deformation. The separate roles of the LPSO phase and the α-Mg phase in relation to the mechanical properties of high-strength LPSO-type Mg alloy were investigated at ambient and high temperatures. For high strengths at ambient and high temperatures, it was important that the α-Mg phase consisted of a fine-grain region and a nonrecrystallized region, and that the LPSO phase remained as a block-type phase. On the other hands, it was necessary to change the LPSO phase from a block-type phase into a plate-type phase by heat treatment before tensile testing to improve the ductility of the alloy while maintaining its tensile yield strength. Microstructural control of the LPSO phase and the α-Mg phase is necessary to obtained Mg–Zn–Y alloy with superior mechanical properties at ambient-to-high temperatures.
Microstructure of the High-Strength Magnesium Alloy on Cylinder Upsetting
Authors: Ruan Li Qun , Noda Masafumi , Marumo Yasuo , Kawamura Yoshihito
Published: January 2012

Magnesium alloys are known for its light weight. Due to the desirable properties,magnesium is required in the fields such as transportation from the point of significant energy savings.Magnesium alloys are also being expected as an alternative for the next generation materials in fieldsof variety. At present, casting and thixomolding process are the main manufacturing methods formagnesium alloy parts. The major problem for forging of magnesium alloy is the lack of basicprocess data, such as strength and ductility.Mg96Zn2Y2 is a high strength magnesium alloy material newly developed by Dr. Y. Kawamurain Japan. It has attracted much attention recently. The name of this alloy is called as 'Kumadai Goukin'.'Kumadai Goukin' of high strength magnesium alloy material is expected as forged parts of theautomobile and materials for aerospace applications. It is necessary to clarify forging processcharacteristics of this material.The purpose of the present study is to evaluate the processing property of Mg96Zn2Y2 material.In this study, cylinder upsetting tests were performed under various deformation temperatures andspeeds for 'Kumadai Goukin'. Furthermore, the dependence of flow stress and ductility of thesematerials to processing temperature and speed was evaluated. We performed microstructureobservation to examine mechanism. We were analyzed that ductility of this material had improved.
Evolution of Texture and Microstructure of AZ31 Mg Alloy Sheet at High Strain Rates
Authors: Ulacia I. , Dudamell N.V. , Esnaola J.A. , Yi Sang Bong , Pérez Prado María Teresa , Galvez F. , Letzig Dietmar , Hurtado I.
Published: January 2012

The high strain rate behaviour of magnesium alloys is of great interest to automotive,aerospace and/or defence industries because some critical components should have the propermechanical properties to work under crash or impact conditions. In the current study, resultsfrom an extensive experimental program are presented. The uniaxial mechanical behaviour ofAZ31 sheet under dynamic conditions (ε=103 s-1) is analyzed and compared with that observedat low strain rates. AZ31 sheets have been tested in tension and compression using Hopkinsonbar apparatus at 25°C and 250°C. Moreover, interrupted tests were also performed in orderto relate the evolution of deformation mechanisms with strain. Finally, detailed microstructureand texture examination by electron backscatter di raction (EBSD) and neutron di ractionhas been carried out in order to elucidate the predominant deformation and recrystallizationmechanisms.
Microstructure and Mechanical Properties of Magnesium Alloy Prepared by Repetitive Upsetting
Authors: Guo Wei , Wang Qu Dong , Liu Man Ping , Liu Xin Tao , Zhou Hao
Published: January 2012

Repetitive upsetting (RU) was applied to a commercial AZ31 Mg alloy. The samples were processed at temperatures of 230 °C, 250 °C and 300 °C up to 3 passes. Effects of processing temperature on the microstructure and mechanical properties were investigated. The results indicate that the microstructure was effectively refined by RU and an average grain size of ~1.9 μm was obtained at 250 °C. Increasing the temperature resulted in larger mean grain size and higher microstructural homogeneity. Both the strength and hardness were significantly improved. It was also found that increasing the processing temperature led to increase in the strength but decrease in the ductility. The sample after RU 3 passes at 230 °C had tensile strength of 330 MPa compared with 173 MPa prior to the processing.
Grain Refinement of Mg-Al-Zn Alloy Bar during Hot Compression
Authors: Watazu Akira , Hakamada Masataka , Iwasaki Hajime , Shigematsu Ichinori , Saito Naobumi
Published: January 2012

Grain refinements during hot compression of continuous casting AZ80 alloy bars and extrusive AZ61, AZ80 alloy bars were observed. The hot compression true stress-true strain curves of extrusive AZ61 and AZ80 alloy had similar tendencies, which were that the true stress increased and had a peak around 0.2 true strain, and then the stress decreased and was almost even from about 0.4 true strain. The stress peaks shifted to the high strain side as the compression speed, true strain speed, increased. However, the stress peaks did not shift at different compression temperatures. Fine grains were obtained under the condition of high strain speed and low temperature, but the grain sizes were uneven at low temperature compression. The stress peaks in the hot compression true stress-true strain curves of continuous casting AZ80 did not shift at different compression temperatures. AZ80 forging products with fine grains are expected to be formed under various conditions by using continuous casting AZ80.
Hot Deformation and Dynamic Recrystallization of the Beta Phase in Titanium Alloys
Authors: Montheillet Frank , Pallot L. , Piot David
Published: January 2012

Due to the high rate of dynamic recovery associated with the large stacking fault energy of the bcc structure, classical "discontinuous" dynamic recrystallization, occurring by nucleation and growth of new grains is not observed in the β phase of titanium alloys. Instead, the following mechanisms take place: at low and moderate strains (ε < 1), the original flattened (compression) or sheared (torsion) grains are still recognizable, although their boundaries are strongly serrated. In this strain range, grain size (thickness) results from both the convection and the migration of grain boundaries. At intermediate strains, "geometric" dynamic recrystallization leading to "pinching off" events of the original grains is observed, whereas at larger strains (ε > 5), grain fragmentation occurs by the generation of new grain boundaries ("continuous" dynamic recrystallization). The associated flow stress often exhibits pronounced softening and the resulting (equiaxed) grain size can be much smaller than the initial one. It is worth to note that a very similar sequence of mechanisms takes place in ferritic steels, as well as in aluminium alloys, in spite of their different crystallographic structure. In this paper, the above mechanisms will be illustrated by a set of data pertaining to titanium alloys.
Process-Structure-Property Relationships for Magnesium Alloys
Authors: Weiler Jonathan P. , Wood J.T. , Basu I.
Published: January 2012

Gravity step-casting experiments were performed to investigate process-structure-property relationships in three different die-cast magnesium alloys – AM60, AZ91 and AE44. The step-cast mold was instrumented to capture temperature profiles of the solidification of molten magnesium. This paper investigates the structure-property relationships of these magnesium alloys, specifically the dependence of the fracture properties upon the porosity that forms during the casting process. Sixteen tensile specimens were cut from the step-casting perpendicular to the solidification front, for each alloy examined. Correlations from X-ray tomography data were used to estimate the maximum area fraction of porosity from the average volumetric porosity in the specimens, assuming a typical size and spatial distribution of porosity. This relationship can be used in the absence of more accurate measure of porosity (i.e. serial sectioning, computed x-ray tomography). A failure model for die-cast alloys – which depends upon the strain-hardening coefficient and the maximum area fraction of porosity in the specimen – was used to predict fracture strains for each specimen. The experimental tensile elongation of each specimen was compared with predicted values. The resulting mechanical properties determined from these cast magnesium alloys will be used to develop process-structure-property relationships.
Effect of Process Variables on Microstructural Features during Solidification of AM60B Magnesium Alloy
Authors: Basu I. , Wood J.T. , Weiler Jonathan P.
Published: January 2012

In this study, commercial AM60B magnesium alloy was studied under different solidification conditions to understand the influence of cooling rate, thermal gradient, growth velocity, Niyama criterion, solidification time and mold dimensions on microstructural features such as secondary and tertiary dendrite arm spacing, grain size, porosity, pore shape and size, local morphological and phase variations. Porosity, grain size and dendrite arm spacing were measured as functions of the process variables. It was realized that the process of mold filling and solidification are simultaneous in nature and they significantly affect the microstructure development trends and its dependency on the process parameters. A significant effect, of the above mentioned, was found on the obtained porosity values and their variation along the casting. The results clearly indicate that rate of filling, nature of flow of liquid and shape of the mold greatly affect the solidification process and thereby the microstructure.
Evolution of Precipitated Phases during Ageing in High Alloyed Mg-Al Based Alloys
Authors: Yakubtsov Igor , Niewczas Marek
Published: January 2012

The artificial ageing treatments have been performed in the commercial magnesium alloys AZ80 (Mg-8.2Al-0.5Zn) with different grain size in the temperature interval 150-250 °C. The comprehensive microstructure observations through ageing were carried out by light microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. Solid solution decomposition proceeds in non-deformed materials by two modes of precipitated γ – Mg17Al12 phase: discontinuous (grain boundary) and continuous (intragranular) precipitation. A competitive formation of precipitation is influenced by either initial grain size or applied cold deformation before ageing. The electrical resistivity measurements have allowed evaluating some kinetic parameters of precipitated γ - Mg17Al12 phase. The good agreements of the obtained volume fractions of γ - Mg17Al12 phase after different ageing time by electrical resistivity and a XRD technique were observed.
Microstructural Evolution during Recrystallization of Magnesiun Alloys
Authors: Yi Sang Bong , Bohlen Jan , Sandlöbes Stefanie , Zaefferer Stefan , Letzig Dietmar , Kainer Karl Ulrich
Published: January 2012

Microstructural evolution during the annealing of cold rolled Mg, Mg-1.5Nd and Mg-3Y sheets has been examined. The experimental results show a significant difference in recrystallization kinetics and grain growth between pure Mg and Mg-RE alloy sheets. Pure Mg sheet shows rapid recrystallization and grain growth, whereas recrystallization is considerably retarded in the Mg-RE alloys. Although recrystallized grains which are triggered at shear bands in the cold rolled pure Mg sheet show a relatively weak texture with a basal pole split into the sheet rolling direction, rapid grain growth is accompanied by re-strengthening of the basal-type texture. In contrast, a weak texture appears in the early recrystallization stage in Mg-RE alloys and is retained during annealing due to retarded recrystallization and grain growth.
Effect of Cold Deformation on Microstructure and Mechanical Properties of Mg-8Gd-3Y-0.5Zr Alloy
Authors: Li De Jiang , Zeng Xiao Qin , Su Xin , Xie Yan Cai , Ding Wen Jiang
Published: January 2012

Pre-cold rolling with the reduction of 15% was employed on Mg-8Gd-3Y-0.5Zr (wt.%) (GW83K) alloy in different initial states: as-extruded (state 1) and extruded followed by annealing (state 2) with the aim to investigate the effects on microstructure and mechanical properties. Microstructure observation revealed that there are more amounts of mechanical twins in the alloy in state 2 than that of the alloy in state 1 after cold rolling, which indicates the different deformation mechanisms. Further investigation through EBSD has elucidated the grain boundary structure and types of twins in the alloys. Pre-cold deformation greatly promotes the age hardening response and the peak aging time at 200°C was found to be nearly 12h for the alloy in both state 1 and state 2, which were about 24h and 80h less than that of their non-deformed counterparts, respectively. Tensile tests at temperatures lower than 250°C showed that the alloy in state 1 has a predominant mechanical property than that of the alloy in state 2, while at 300°C, it displayed a reverse tendency.
Elastic Constants, Equation of State and Mechanical Relaxations of some Metallic Glasses at High Pressure
Authors: Aniya Masaru
Published: January 2012

One of the fundamental physical quantities necessary to describe the mechanical properties of the materials is the bulk modulus. In the present report, a simple method to estimate the values of the bulk modulus and its pressure derivative of metallic glasses is presented. The method which is based on a jellium model of metals provides a good agreement with measured data. The estimated values of the elastic constants have been used to determine the equation of state of bulk metallic glasses. It is found that the usual Murnaghan equation of state deviates considerably from the experimental results at high pressures. The deviation has been interpreted to arise from the structural relaxations. The effect of pressure on the fragility of bulk metallic glasses is discussed briefly.
Effect of Inhomogeneity of Zr-Based Bulk Metallic Glass Plate on Fatigue Strength under Torsion
Authors: Nakai Yoshikazu , Nakagawa Kenichi , Mikami Kohei
Published: January 2012

Fatigue tests of Zr-based bulk metallic glass plates were conducted under cyclic-torsion, and the results were compared with those obtained under cyclic-bending and axial-loading. The fatigue strength of axial-loading was lower than that under cyclic-bending because the fatigue strength depends on the cooling rate in the casting process of the material, which is different in the thickness direction. The fatigue strength of plane-bending reflects the strength at the specimen surface while that of axial-loading is determined by the weakest strength in the thickness direction. For cyclic torsion of specimens with rectangular cross-section, the fatigue crack initiation site must be determined by the ratio of specimen width to specimen thickness, and fatigue strength depends on the ratio. Therefore, the criteria for fatigue limit under combined stress for metallic glass should be constructed considering the crack initiation site.
Molecular Dynamics Simulations Based on Plastic Crystal Model with Introducing United Atom Scheme Demonstrated for Zr2Ni Metallic Glass
Authors: Takeuchi Akira , Inoue Akihisa
Published: January 2012

Molecular dynamics (MD) simulations were performed for a Zr2Ni alloy by referring to crystallographic features of a metastable Zr2Ni phase. Simulation method was identical to our previous studies named plastic crystal model (PCM), which includes crystallographic operations for an intermetallic compound in terms of the random rotations of hypothetical clusters around their center of gravity and subsequent annealing at a low temperature. On the basis of MD-PCM, the present study considers an additional refinement named united atom scheme (UAS) on the motions of atoms in the hypothetical clusters. In MD-PCM-UAS, Dreiding potential was assigned for atomic bonds in a cluster whereas Generalized Embedded Atom Method potential for the other atomic pairs. The simulation results by MD-PCM-UAS yield a liquid-like structure. However, annealing did not cause subsequent structural relaxation, which differs from the results by MD-PCM and conventional MD simulations. Further simulations based on MD-PCM-UAS were performed for a nanostructure comprising clusters and glue atoms, leading to the best fit with the experimental data.
Development of Cu-Clad Metallic Glass for Soldering
Authors: Terajima Takeshi
Published: January 2012

Soldering is a potential technique for joining metallic glasses. It can be performed at far below the crystallization temperature of various metallic glasses; thus, there is no possibility of crystallization. However, Cu-Zr-based metallic glass displays poor wettability to Pb-free solder, because a strong native oxide film prevents direct contact between the solder and the glass. To overcome this problem, Cu-Zr-based metallic glass clad with a thin film of Cu has been developed. This was produced by casting the melt of a Cu36Zr48Al8Ag8 pre-alloy into a Cu mold cavity, inside which a thin film of Cu with a thickness of 2 μm was placed. Cu36Zr48Al8Ag8 metallic glass was successfully formed and welded to the Cu thin film. From microstructure analysis, it was found that a reaction layer was formed at the interface between the Cu and the Cu36Zr48Al8Ag8 metallic glass. However, no oxide layer was observed in the Cu-clad layer. It was found that the Cu cladding played an important role in preventing the formation of the surface oxide film. Consequently, solderability to the Cu-Zr-based metallic glass was drastically improved.
Precipitation in Zr-Based Ternary Alloys during Quenching
Authors: Yamamoto Tokujiro , Yokoyama Yoshihiko , Inoue Akihisa
Published: January 2012

The crystal structure of the phase precipitated in a Zr-Cu-Al ternary alloy during quenching was investigated. The crystal structure is constructed by stacking several atomic layers periodically and is similar to that of the Laves phases. The reason why a Zr-Cu-Al alloy tends to crystallize into Laves-like periodic stacking order structure is discussed.
Unusual Effect of Oxygen on the Mechanical Behavior of a β-Type Titanium Alloy Developed for Biomedical Applications
Authors: Niinomi Mitsuo , Nakai Masaaki
Published: January 2012

Oxygen enhances the strength of titanium alloys in general; however, excess oxygen can make titanium alloys brittle. On the other hand, oxygen enhances the precipitation of the α phase and suppresses the formation of the ω phase. Thus, using the optimal amount of oxygen is important to improve the mechanical properties of titanium alloys. The role of oxygen in titanium alloys is still not well understood. The effect of oxygen on the mechanical behavior of a β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (referred to as TNTZ), which is used for biomedical applications, was investigated in this study. Oxygen was found to stabilize the ω phase in TNTZ. This behavior of oxygen is unusual considering the known behavior of oxygen in titanium alloys: oxygen is known to suppress the formation of the ω phase in titanium alloys. A small amount of oxygen increases the tensile strength but decreases the ductility of TNTZ. On the other hand, a large amount of oxygen, of around 0.7 mass%, increases both the tensile strength and the ductility of TNTZ. This phenomenon is unexpected.
An Analytical Technique for Optimization of Mechanical Performance of Foam Core Sandwich Structures
Authors: Montazeri Hanif , Azarmi Fardad , Coyle Tom W. , Mostaghimi Javad
Published: January 2012

Sandwich structures are widely used, especially in areas where the performance of conventional materials is simply not adequate. Sandwich components achieve the same structural performance as conventional materials with weight savings of up to 75 %. They are basically made from two thin skins (faces) and a lightweight thicker core. Their structural, physical, and mechanical characteristics can be tailored based on service requirements by selection of different materials and manufacturing processes. In this study, the geometry and property of each separate component is utilized to the structural advantage of the whole assembly. Although Lagrangian method has been widely applied in other engineering disciplines, it has received less attention for optimization of sandwich components. The Lagrangian method is therefore introduced and expanded to find solutions for multipurpose design problems. This new optimization approach will enable us to find analytical solutions for complicated design problems which were conventionally solved by utilizing graphical methods. This paper aims to present a generic optimization method which can be used in the variety of applications in this field.