Showing papers in "Materials Transactions in 2008"

Phase Equilibria and Microstructure on γ' Phase in Co-Ni-Al-W System

Abstract: Phase equilibria between the y and y' phases at 900°C in the Co-(10-70)Ni-Al-W system were determined by electron probe microanalysis (EPMA) and X-ray diffractometry (XRD). It was found that the "/ phase with L1 2 structure continuously exists from the Co side to the Ni side in Co-Ni-Al-W system and that it widens to the low W region with increasing Ni content. The partition of Al into the y' phase increased with Ni content, while the W changed from a y' former to a y former by increase of Ni content. Differential scanning calorimetry (DSC) measurements also revealed that the y' solvus temperature increases with Ni content, while the solidus temperature is hardly affected by such content. The lattice parameter of the y and y' phases and the mismatch decreased with increasing Ni content, which caused the morphologic change of the γ' precipitates from cubes to spheres.

Biologically and Mechanically Biocompatible Titanium Alloys

Abstract: Nb, Ta, and Zr are the favorable nontoxic and allergy-free alloying elements suitable for use in titanium alloys for biomedical applications. Low-rigidity titanium alloys composed of nontoxic and allergy-free elements are receiving considerable attention. The advantage of low-rigidity titanium alloys in the healing of bone fracture and bone remodeling is successfully proven by using tibia of rabbit as a fracture model. Ni-free superelastic and shape memory titanium alloys for biomedical applications are being actively developed. The mechanical properties such as fatigue and fretting fatigue are important from the viewpoint of mechanical properties, which may be collectively referred to as mechanical biocompatibilities in the broad sense, in addition to the rigidity, i.e. Young's modulus. Bioactive surface modifications of titanium alloys for biomedical applications are very important for achieving further biocompatibility.

Interfacial Bonding Mechanism Using Silver Metallo-Organic Nanoparticles to Bulk Metals and Observation of Sintering Behavior

Abstract: We have proposed a novel bonding process using silver nanoparticles, which can be alternative to lead-rich high melting point solders. The bonding mechanism of silver metallo-organic nanoparticles to bulk materials (gold and copper) is discussed based on the observations of the bonded interface using Transmission Electron Microscope (TEM). At the interface of sintered silver and bulk gold, the crystal orientation of silver corresponded to that of gold. It is thought that the epitaxial layer of silver formed through silver nanoparticles being oriented in the direction of the gold crystal. At the interface of sintered silver and bulk copper, no epitaxial layer of silver on the copper crystal formed. Though the appearance of the crystal structure of silver/copper interface is different from that of the silver/gold interface, copper as well as gold are coherent with silver, and have been successfully bonded using the silver nanoparticles. [doi:10.2320/matertrans.MF200805]

Revisiting the Structure of Martensite in Iron-Carbon Steels

Abstract: A model is developed to describe the formation and crystal structure of martensite in quenched Fe-C steels based on the extensive published literature on the subject. Unique changes in the properties and structure of martensite are shown to occur at 0.6 mass% C, designated as the H-point. The concept of primary and secondary martensite is introduced in order to indicate that two different, sequential, martensites will form during quenching of Fe-C steels above 0.6 mass% C. Below 0.6 mass% C, only primary martensite is created through the two sequential steps FCC ! HCP followed by HCP ! BCC. Primary martensite has a lath structure and is described as BCC iron containing a C-rich phase that precipitates during quenching. The HCP transition phase is critical in interpreting the two martensite structures based on the premise that the maximum solubility of C in the HCP phase is 0.6 mass%. Primary martensite continues to form at compositions greater than 0.6 mass% C with the creation of a carbon-rich BCT phase. This is followed by the start of secondary martensite which forms at the MS (martensite start temperature) and creates the traditional BCT plates adjoining retained austenite. Both martensites are predicted to co-exist at the highest C contents. A quantitative model, based on the specific volume of the various phases obtained after quenching, has been used to calculate the composition of the precipitated C-rich phase for a 0.88 mass% C steel. It is predicted that the carbon-rich phase is either diamond or � (Fe2C) carbide. [doi:10.2320/matertrans.MRA2007338]

Significant Improvement in Mechanical Properties of Biomedical Co-Cr-Mo Alloys with Combination of N Addition and Cr-Enrichment

Abstract: An improvement in the mechanical properties of a biomedical Ni-free Co-Cr-Mo alloy under as-cast condition has been examined by means of tensile tests and microstructure observations. The solubility of N in Co-Cr-Mo alloys increases with increasing Cr content from 29 to 34 mass%. This results in a significant improvement in mechanical properties such as yield stress, tensile strength, and fracture elongation. The improvement in the mechanical properties results from the γ phase stabilization and inhibition of the a phase formation due to N addition. Increasing the Cr content also has contributed to the improved mechanical properties.

Origin of the Anomalous {1012} Twinning during Tensile Deformation of Mg Alloy Sheet

Abstract: In order to understand the origin of the anomalous twinning of the {10\\bar12} type, rolled sheets of AZ31 Mg alloy were deformed at room temperature in tension along the rolling direction. An excellent correlation was found between {10\\bar12} twinning tendency and basal dislocation slip activity. Calculation of strain tensor indicated that the diagonal strain components associated with the localized basal slip can be canceled completely by the {10\\bar12} twinning. The results led to the conclusion that anomalous {10\\bar12} twins were formed to accommodate the strain incompatibility caused by localized basal dislocation slip.

Microstructure and Mechanical Properties of Resistance Spot Welded Advanced High Strength Steels

Abstract: Integration of advanced high strength steels (AHSS) into the automotive architecture has brought renewed challenges for achieving acceptable welds. Resistance spot welding (RSW) is the primary method used in welding automotive structures, which has resulted in a demand to better understand RSW of AHSS. The varying alloy contents and processing techniques used in their production has further complicated this initiative. The current study examines resistance spot welding of AHSS including 590R, DP600, DP780 and TRIP780. HSLA material is also included to represent conventional high strength steels and benchmark AHSS performance. The mechanical properties and microstructure of these resistance welded steel alloys are detailed. Furthermore, a relationship between chemistries and fusion zone hardness is produced.

Microstructural and Mechanical Characteristics of AZ61 Magnesium Alloy Processed by High-Pressure Torsion

Abstract: Experiments were conducted on an AZ61 magnesium alloy to evaluate the microstructural characteristics and the mechanical properties after processing by High-Pressure Torsion (HPT). The results show that processing by HPT produces excellent grain refinement with average grain sizes of ?0.22 and ?0.11 ?m after processing at 423 K and room temperature, respectively. Tensile testing after HPT revealed the potential for achieving superplastic elongations with a maximum recorded elongation of 620% when testing at a temperature of 473 K. Using microhardness measurements, it is demonstrated that the the microstructure gradually evolves with increasing torsional straining in HPT so that ultimately there is a reasonably homogeneous structure across the disk.

Bonding Technique Using Micro-Scaled Silver-Oxide Particles for In-Situ Formation of Silver Nanoparticles

Abstract: We investigated a new bonding technique utilizing micro-scaled silver-oxide (Ag 2 O) particles. The results of our investigations revealed that bonding between electrodes using for semiconductor modules can be accomplished by adding myristyl alcohol to silver-oxide particles, followed by heating the mixture in air at 300°C under a pressure of 2.5 MPa. Since this bonding technique produces silver particles with a size of a few nanometers when the silver oxide is reduced by the presence of the alcohol, low-temperature sintering and bonding can be achieved.

Multi-Phase-Field Model to Simulate Microstructure Evolutions during Dynamic Recrystallization

Abstract: A numerical model to simulate microstructure evolution and macroscopic mechanical behavior during hot working was developed. In this model, we employed a multi-phase-field model to simulate the growth of dynamically recrystallized grains with high accuracy and the Kocks-Meching model to calculate the evolution of dislocation density due to plastic deformation and dynamic recovery. Furthermore, an efficient computational algorithm was introduced to perform the multi-phase-field simulation efficiently. The accuracy of the developed model was confirmed by comparing the migration rate of grain boundaries with the theoretical value. Also, the numerical results for a polycrystalline material are compared with those obtained from a cellular automaton simulation. Furthermore, the effects of the initial grain size, grain boundary mobility and nucleation rate on the dynamic recrystallization behavior were investigated using the developed model.

Dissimilar Welding of Al and Mg Alloys by FSW

Abstract: Microstructures and mechanical properties of dissimilar welding joint between Al alloy and Mg alloy by Friction Stir Welding (FSW) were investigated in comparison with laser welding of the same combination. Dissimilar joint of Al and Mg alloy by laser welding was very brittle because of building up Mg 17 Al 12 inter metallic compounds in fusion zone. On the other hand, FSW is anticipated to welding dissimilar alloys with enough joint strength because it is a solid-state process without melting. In this paper, FSW was carried out to make dissimilar butt joints of Al alloy and AZ31 magnesium alloy with various tool rotational speed and welding speed. These joints showed higher hardness in their stir zones than that of parent AZ31 alloy because of Mg-Al inter metallic compound formation. However, the hardness of stir zone was lower than that of fusion zone of laser welding, and was changed with the welding parameters of tool rotational speed and welding speed (i.e. heat input ratio of FSW). The optimum welding conditions of Mg and Al dissimilar FSW joint and the influence of inter metallic compound distribution with mixing of materials in stir zone were discussed.

Effect of Rare-Earth Elements Y and Dy on the Deformation Behavior of Mg Alloy Single Crystals

Abstract: Effect of rare-earth elements (Y and Dy) on the mechanical properties of Mg solid solution single crystal is investigated Comparing with the effect of other elements reported by previous studies, the solid solution strengthening by Y and Dy are much higher than that of other additives such as Zn for basal slip operation, while the isotropic strain by Zn atoms is higher than those of Y and Dy Strain-rate changing tests were conducted for a further understanding of the dislocation motion and it revealed that the activation volumes estimated for Mg alloys with Y and Dy are much smaller than that of Zn-added alloy, while the activation enthalpy is almost the same It was confirmed that the high strengthening effect by Dy addition is also found by Y addition, while the elastic interaction based on neither isotropic or anisotropic distortion are sufficient to explain the origin of the strengthening effect by Y and Dy addition

Active Hydroxyl Groups on Surface Oxide Film of Titanium, 316L Stainless Steel, and Cobalt-Chromium-Molybdenum Alloy and Its Effect on the Immobilization of Poly(Ethylene Glycol)

Abstract: The concentrations of hydroxyl groups located inside and on the surface oxide films of a commercially pure titanium, cp-Ti, a type 316L austenitic stainless steel, SS, and a cobalt-chromium-molybdenum alloy, Co-Cr-Mo, were evaluated using X-ray photoelectron spectroscopy, XPS, and a zinc-complex substitution technique. As a result, the concentrations of the hydroxyl groups detected by the zinc-complex substitution technique, defined as active hydroxyl groups, were much larger than those detected by other conventional techniques. The concentration of the active hydroxyl groups on Co-Cr-Mo was significantly larger than those on cp-Ti and SS. Poly(ethylene glycol), PEG, is a biofunctional molecule that inhibits the adsorption of proteins. The immobilization of PEG to metal surfaces by electrodeposition or immersion is an important technique to biofunctionalize the metals. The amounts of the PEG layer immobilized on the metals were governed by the concentrations of the active hydroxyl groups on each surface oxide in the case of electrodeposition; it was governed by the relative permittivity of the surface oxide in the case of immersion. The estimation of active hydroxyl groups on the surface oxide film with the zinc-complex substitution technique is useful for the elucidation of reactions between metal substrates and immobilized molecules. [doi:10.2320/matertrans.MRA2007317]

Forecasting of the Consumption of Metals up to 2050

Abstract: Forecasts up to 2050 are made of consumption of the following metals: Fe, Al, Cu, Mn, Zn, Cr, Pb, Ni, Si, Sn, rare earths, Mo, Li, Sb, W, Ag, Co, In, Au, Ga, Pt and Pd. The forecasts are based on the linear decoupling model of the relation between per capita metal consumption and per capita GDP. The models of each metal are applied to the economic development model of BRICs and G6 countries. According to these forecasts, the overall consumption of metals in 2050 will be five times greater than the current levels, and demand for metals, such as Au, Ag, Cu, Ni, Sn, Zn, Pb and Sb, is expected to be several times greater than the amount of their respective reserves. Demand for Fe and Pt, which is considered to be optimistic about the resource exhaustion, will also exceed the current reserves. Urgent measures are needed to find alternatives from common resources and to shift into sound materials circulation society.

The Origin of Midrib in Lenticular Martensite

Abstract: In the present paper, the origin of midrib in lenticular martensite is clarified by examining the similarity between midrib and thin plate martensite in detail and studying the stress-induced growth behavior of thin plate martensite at various temperatures. Although lenticular martensite, especially midrib, exhibits a zigzag array in general, some martensite plates which are branched or kinked were also observed as thin plate martensite. The substructure of midrib is completely twinned and the orientation relationship of midrib with respect to austenite is close to Greninger–Troiano relationship. These morphology, substructure and crystallographic features of midrib in lenticular martensite are quite similar to those of thin plate martensite. Furthermore, stress-induced growth behavior of thin plate martensite changes with deformation temperature. Thermally-transformed thin plate martensite grows keeping a thin plate shape when deformed at temperature close to the Ms temperature. However, it grows into a lenticular shape accompanying a substructure with a high density of dislocations after deformation at temperature much higher than Ms temperature. Therefore, it is concluded that midrib in lenticular martensite is thin plate martensite itself. The difference between lenticular martensite and thin plate martensite is only in their growth behaviors. [doi:10.2320/matertrans.MRA2007296]

Microstructure Evolutions of Rapidly-Solidified and Conventionally-Cast Mg97Zn1Y2 Alloys

Abstract: Microstructure evolutions of rapidly-solidified (RS) ribbon and conventionally cast bulk Mg-1 at%Zn-2 at%Y alloys have been studied by transmission electron microscopy (TEM), particularly focusing on formation process and phase stability of the long-period structures. It is found that there are significant differences in microstructural evolutions between the RS ribbon and the cast-bulk alloys, in terms of thermal stability of the long-period phases at temperatures higher than 673 K. For both the as-quench ribbon and the as-cast bulk specimens, 18R-type long-period phase is dominantly observed at grain boundaries. After annealing at temperatures higher than 673 K, the long-period phases at grain boundaries in the RS ribbon almost disappear to form Mg 24 Y 5 and Mg 3 Zn 3 Y 2 compounds within the grain interiors, while the long-period phases remained stable in the cast-bulk alloy even at temperatures higher than 673 K.

Effect of Strain Path in High-Pressure Torsion Process on Hardening in Commercial Purity Titanium

Abstract: The effect of strain path in high-pressure torsion (HPT) process on hardening was investigated in commercial purity titanium (Ti-0.03Fe-0.03O, mass%). After monotonic HPT (mHPT) straining up to N ¼ 10 turns at a rotation speed of 0.2rpm under a pressure of P ¼ 5GPa, theobtained Vickers microhardness, Hv, was around 3.5GPa and the microstructure consisted of equiaxed grains of 100 200nm with highdislocationdensity.ThisHvvaluewashardlyincreasedevenwithfurtherstrainandstraingradient(furtherrotation).Toinvestigatetheeffectofstrain path, cyclic (cHPT) and two-steps HPT (2sHPT) processes were carried out. The cHPT-straining performed by repetitive deformation ofN ¼ 1=2. In comparison with the mHPT process, the Hv was attained rapidly to the saturated value (Hv 3.5GPa). However, the maximum Hvvalue was similar to that obtained by mHPT-straining. In the 2sHPT process, first the disk of 20mm in diameter was deformed by HPT-straining. Secondly, the disk of 10mm was cut to contact with the circumference of the deformed disk, and then it was deformed. A higherhardness (Hv 3.8GPa) was obtained than that by monotonic or cyclic HPT-straining. These results indicate that multi-directional deformations(deformations with different strain paths) contribute to the hardening improvement. [doi:10.2320/matertrans.ME200714](Received September 3, 2007; Accepted November 13, 2007; Published December 12, 2007)Keywords: microstructure, hardening, strain path, titanium (Ti), heat generation, high-pressure torsion (HPT), severe plastic deformation(SPD).

Texture and Stretch Formability of Mg-1.5 mass%Zn-0.2 mass%Ce Alloy Rolled at Different Rolling Temperatures

Abstract: Texture and stretch formability of Mg-1.5 mass%Zn-0.2mass%Ce alloy rolled at different rolling temperatures were investigated. The Mg-Zn-Ce alloy rolled at 723 K and annealed at 623 K tended to produce a TD-split texture. The TD-split texture contributed to the low average r-value and high tensile elongation, resulting in the significant high stretch formability corresponding to the commercial Al alloys.

Characteristics of Zn-Al-Cu Alloys for High Temperature Solder Application

Abstract: Melting range, microstructure, mechanical properties and spreadabililty of Zn-(4� 6 mass%)Al-(1� 6 mass%)Cu alloys were investigated. Liquidus temperature was targeted between 655 and 675 K, and solidus temperature was targeted to 645 K. The liquidus temperature of the Zn-Al-Cu solders increased with Cu contents, but it decreased with Al contents. Microstructures of the Zn-Al-Cu solders consisted of primary "-phase (CuZn4), � -phase (Zn matrix), � -� eutectic phase (Zn-Al eutectic) and "-� eutectic phase (Zn-Cu eutectic), irrespective of the Al and Cu contents. Increasing the Al and Cu contents, hardness and tensile strength increased, but elongation decreased. The Al content played an important role in improving the spread ratio, the Cu content had no significant influence on the spread ratio. [doi:10.2320/matertrans.MF200809]

Precipitation of Solid Transmutation Elements in Irradiated Tungsten Alloys

Abstract: Tungsten-based model alloys were fabricated to simulate compositional changes by neutron irradiation, performed in the JOYO fast test reactor. The irradiation damage range was 0.17–1.54 dpa and irradiation temperatures were 400, 500 and 750 � C. After irradiation, microstructural observations and electrical resistivity measurements were carried out. A number of precipitates were observed after 1.54 dpa irradiation. Rhenium and osmium were precipitated by irradiation, which suppressed the formation of dislocation loops and voids. Structures induced by irradiation were not observed so much after 0.17 dpa irradiation. Electrical resistivity measurements showed that the effects of osmium on the electrical resistivity, related to impurity solution content, were larger than that of rhenium. Measurements of electrical resistivity of ternary alloys showed that the precipitation behavior was similar to that in binary alloys. [doi:10.2320/matertrans.MAW200821]

Nanostructuring of TiNi Alloy by SPD Processing for Advanced Properties

Abstract: Ultrafine-grained (UFG) alloy Ti49:4Ni50:6 possessing both nano- as well as submicrocrystalline structure has been successfully produced using two techniques of severe plastic deformation (SPD) processing: high pressure torsion and equal channel angular pressing. The features of microstructure, martensitic transformation and deformation behavior of the UFG alloy have been studied in details. The effects of grain size on the mechanical and functional properties of the alloy are discussed. (doi:10.2320/matertrans.ME200722) TiNi alloys are well-known thanks to their remarkable properties-enhanced strength, corrosion resistance, and especially superelasticity and shape-memory effect. Due to this, they are very promising for many structural and functional applications in engineering and medicine. 1-3) Superelasticity and shape-memory effect of TiNi alloys are associated with martensitic transformations (MT) of the austenite phase B2 into the martensite phase B19 0 . These two extraordinary properties have been the object of numerous fundamental investigations. At the same time, for various advanced applications superior properties of TiNi would be very desirable, since they are required for miniaturization of articles and enhancement of their functional characteristics. Recent investigations testify that an effective way to enhance the properties of various metals and alloys is their nano- structuring using severe plastic deformation (SPD) process- ing. 4-6) During last years in our laboratories a number of investigations have been performed, dealing with nano- structuring of TiNi alloys, 7-11) using two most popular SPD techniques-high-pressure torsion (HPT) and equal-channel angular pressing (ECAP), and with the effect of the formed nanostructure on the deformation behaviour of alloys and martensitic transformations. This paper reports the results of the investigations of mechanical and functional properties of the Ti49:4Ni50:6 alloy that has an ultrafine-grained structure in the nano- and submicrocrystalline ranges. 2. Experimental Procedure

Effect of CaO on Oxidation Resistance and Microstructure of Pure Mg

Abstract: This study was carried out to examine reduction mechanism of CaO and to investigate behaviors of CaO in pure Mg in terms of microstructure, oxidation resistance and phase formation. Pure Mg was used instead of Mg alloys to minimize the effects of other elements. With respect to CaO content, microstructures of the alloys showed prominent grain refinement. Mg2Ca phase was formed even in 0.07CaO added pure Mg by reduction, while Mg2Ca phase was formed over 1.35Ca added pure Mg. With respect to CaO content, the hardness of CaO added pure Mg was increased by grain refinement. From oxidation test by TGA, the oxidation behavior of CaO added Mg was similar to that of Ca added Mg. From AES result, there was the thin oxide layer mixed with MgO and CaO in CaO added Mg. [doi:10.2320/matertrans.MC200786]

Influence of High-Pressure Torsion Straining Conditions on Microstructure Evolution in Commercial Purity Aluminum

Abstract: The influence of heat generation during severe plastic deformation on microstructure evolution was investigated in commercial purity aluminum (Al 1050, CP-Al) by using high-pressure torsion (HPT) process. The microstructure was characterized by the observations of the torsion and the longitudinal planes. CP-Al disks were deformed by HPT-straining up to 20 turns (equivalent strain, "eq ,o f� 600) at 0.2 or 5 rpm at room temperature. To prevent the increase in specimen temperature, HPT-straining was also carried out in liquid nitrogen. In the all conditions, the value of Vicker’s microhardness, Hv, was saturated around 0.65 GPa and the microstructure consisted of the equiaxed grains of about 500 nm with quite low dislocation density. The microstructure in the early stage of HPT-straining showed the deformed (sub)structure, and then the equiaxed grain structure with high-angle boundaries formed by grain subdivision, recovery, continuous recrystallization and grain growth with increase in strain amounts and specimen temperature. [doi:10.2320/matertrans.ME200713]

Nanostructural Evolution of Cr-rich Precipitates in a Cu-Cr-Zr Alloy During Heat Treatment Studied by 3 Dimensional Atom Probe

Abstract: Nanostructural evolution of Cr (Cr-rich) precipitates in a Cu-0.78%Cr-0.13%Zr alloy has been studied after aging and overaging (reaging) by laser assisted local electrode 3 dimensional atom probe (Laser-LEAP). This material is a candidate for the first wall and divertor components of future fusion reactors. After prime aging at 460 C, Cr precipitates enriched with Zr were observed. Further reaging at 600 C caused the precipitates to grow to almost spherical Cr precipitates with 5 nm (1 h) in diameter and plate-like ones with 20 nm (4 h), respectively. Zr and impurities of Si and Fe were concentrated around the Cr precipitates, resulting in an almost pure Cr cores with interface regions enriched with Zr and the impurities. Probably, the strain induced by the incoherency of BCC Cr with matrix FCC Cu is relaxed by the formation of the enriched regions. [doi:10.2320/matertrans.MBW200736]

Effects of Welding Parameters on the Mechanical Performance of Laser Welded Nitinol

Abstract: The excellent pseudoelasticity, shape memory and biocompatibility of Nitinol has made it a leading candidate for various applications, including aerospace, micro-electronics and medical devices. Challenges associated with the welding Nitinol need to be resolved before its full potential in practical applications can be attained. The current study details the effects of process parameters on the mechanical and pseudoelastic properties of Ni-rich pulsed Nd:YAG laser welded Nitinol. The weld strength, pseudoelastic and cyclic loading properties for varying welding parameters are compared to those of the base metal. Furthermore, fracture surfaces have been analysed and detailed. Results show that process parameters greatly influence the mechanical performance and fracture mode of weldments.

Synthesis of W2C by Reactive Hot Pressing and Its Mechanical Properties

Abstract: Tungsten hemicarbide W 2 C with no or small amounts of W or WC was prepared by reaction-sintering from W and WC powders using a resistance-heated hot-pressing technique called spark plasma sintering. The product phases, density, microstructure, elastic moduli, hardness, and fracture toughness of the sintered bodies were determined. The stable region of the W 2 C phase had a narrow carbon content below 1860°C. W 2 C had a Poisson's ratio of 0.286, and its Young's modulus at zero porosity was determined to be 444GPa from the true density and bulk density dependence. These values suggest that W 2 C has elastic deformation behavior similar to that of W.

Mechanical Properties of Magnesium Alloy AZ31 after Severe Plastic Deformation

Abstract: Grain refinement of magnesium alloy AZ31 was studied in multidirectional forging (MDF) under decreasing temperature conditions. MDF was carried out up to large cumulative strains of 5.6 with changing the loading direction during decrease in temperature from pass to pass. MDF can accelerate the uniform development of very fine- grained structures and an increase of the plastic workability at low temperatures. New grain structures with the minimal grain size of 0.23 μm can be developed by continuous dynamic recrystallization at a final processing temperature of 403 K. As a result, the multidirectional- forged alloy showed excellent higher strength as well as moderate ductility at room temperature, and also a superplastic elongation of over 300% at 423 K. The mechanisms of strain-induced and fine-grained structure development and of the excellent plastic deformation are discussed in detail.

Removal of Lead from Contaminated Soils with Chelating Agents

Abstract: The biodegradable chelating agents [S,S]-ethylenediaminedisuccinic acid (EDDS), citric acid and the low biodegradable chelating agent ethylenediaminetetraacetic acid (EDTA) were investigated for their applicability for the removal of lead from soil by soil washing and electrokinetic processing. In the soil washing tests at 298 K, the removal efficiency of lead with EDDS and EDTA was high in the pH range from 7 to 10 and the ability of lead removal with EDDS in this pH region is comparable to that with EDTA. Meanwhile, the removal efficiency of lead with citric acid was approximately 50% at pH 4 and decreased with increasing pH. Therefore, citric acid was hardly useful. Acid contribution was predominant for the removal of lead with EDDS and citric acid at pH 4 and the complexation between these chelating agents and lead were negligible. In the electrokinetic tests at ambient temparature, EDTA was more effective than EDDS and citric acid for lead transport through the soil by electrokinetic processing.

Excellent Thermal Stability and Bulk Glass Forming Ability of Fe-B-Nb-Y Soft Magnetic Metallic Glass

Abstract: Effects of Y addition on the glass forming ability (GFA) of a Fe-B-Nb marginal glass former, and annealing effects on glassy/supercooled liquid phases as well as soft magnetic properties in the multicomponent Fe-B-Nb-Y alloy system were investigated. The origin of highly improved GFA in the multicomponent system is discussed with related to a characteristic exothermic phase transformation, chemical short range ordering, in the supercooled liquid region due to the positive heat of mixing between Nb-Y elements. The separating tendency between Nb and Y elements is considered to suppress precipitation of metastable Fe23B6 and � -Fe crystalline phases, thus to result in highly improving GFA and distinct high thermal stability against heat treatment of the alloy system. In addition, a glassy ring was fabricated by copper mold casting and magnetic properties were investigated before/after heat treatment. [doi:10.2320/matertrans.MBW200732]

Study on the Reduction of Molybdenum Dioxide by Hydrogen

Abstract: The reduction of MoO 2 powder by hydrogen is one of the most important steps for manufacturing ferromolybdenum alloy and molybdenum powder. The results of experiments on the kinetics of this reaction are presented in this paper. The experiments were carried out under nonisothermal condition in hydrogen atmosphere using TGA equipment. The nonisothermal experiments were carried out at various linear heating rates up to 1273 K. It was found that the reduction reaction is very fast under the whole heating rate until the reduction ratio of MoO 2 approaches to about 0.92. The reduction ratio of MoO 2 was about 0.98 after finishing the reduction reaction at a heating rate of 4 K/min. Kinetics of the reaction was analyzed from the dynamic TGA data by means of Coats and Redfern equation. The nucleation and growth model yielded a satisfactory fit to these experimental data.