Showing papers in "Materials Transactions in 2006"
TL;DR: In this article, the compositional dependence of mechanical properties and microstructural change of the extruded Mg-Zn-Y alloys has been investigated in the effort to develop a high strength Mg96Zn2Y2 alloy with long period ordered (LPO) structure.
Abstract: The compositional dependence of mechanical properties and microstructural change of the extruded Mg-Zn-Y alloys has been investigated in the effort to develop a high strength Mg-Zn-Y alloy with long period ordered (LPO) structure. The extruded alloy Mg96Zn2Y2 exhibited a high yield strength of 390 MPa and elongation of 5% at room temperature, and of more than 300 MPa even at the elevated temperature of 473 K. The heat-treated ingot metallurgy (I/M) Mg-Zn-Y alloys containing very small amounts of yttrium and zinc are characterized by a lamellar phase constructed of 2H-Mg and 14H-LPO structures. Extrusion of the Mg-Zn-Y I/M alloys with LPO structure led to refinement of � -Mg grains and high dispersion of a hard lamellar phase consisting of torn-off 2H-Mg and bent LPO structures with random grain boundaries, resulting in strengthening of the alloys.
266 citations
TL;DR: In this article, the microstructure, hardness and wear resistance of high-entropy Al0:5CoCrCuFeNiTix alloys are investigated using the well-developed arc-melting and casting method.
Abstract: High-entropy Al0:5CoCrCuFeNiTix alloys are synthesized using the well-developed arc-melting and casting method. The molar ratio (x )o f titanium is varied from 0 to 2.0. The microstructure, hardness and wear resistance of the alloys are investigated. The alloys exhibit simple FCC, BCC, CoCr-like and Ti2Ni-like phases. For a small addition of titanium, the alloys form a monolithic FCC solid-solution phase. Two phases of � 1 and � 2 based on BCC appear at the titanium content of x ¼ 0:4 and the � 1 phase becomes ordered at x ¼ 1:4. With the increase of titanium content, copper segregates to the interdendrite region in which nano-precipitates form. A CoCr-like phase forms when x ranges from 0.8 to 1.2. Ti2Ni-like phase forms when the titanium content exceeds x ¼ 1:0. The hardness value increases with titanium content. The alloys with lower titanium content exhibit similar wear resistance to Al0:5CoCrCuFeNi. The wear resistance is rapidly improved at titanium contents from 0.6 to 1.0, and reaches a maximum at x ¼ 1:0. This is followed by a gradual decrease with further increase of the titanium. The mechanisms behind the strengthening and wear resistance of the alloys are discussed. [doi:10.2320/matertrans.47.1395]
151 citations
TL;DR: The relationship between I D/I G ratio fitted from visible Raman spectra and sp 2 /sp 3 ratio done from XPS spectra of DLCH film shows a trend as discussed by the authors.
Abstract: The hydrogened diamond like carbon film (DLCH) with 1 μm thickness is made by hydrocarbon gas ion beam deposition method. The relationship between I D /I G ratio fitted from visible Raman spectra and sp 2 /sp 3 ratio done from XPS spectra of DLCH film shows a trend. The I D /I G ratio of deconvoluted visible Raman spectra shows a correlation with sp 2 /sp 3 ratio from XPS spectra as annealing temperature increases, the graphitization and the disorder increase. The I D /I G ratios fitted with two-curve Gaussian functions of Raman spectra tend to be proportional to sp 2 /sp 3 ratio fitted with three-curve with 100% Gaussian function of XPS spectra when post annealed treatment is below 400°C and without severe oxidation.
150 citations
TL;DR: In this article, the leaching of PGM from automotive catalyst residue was performed based on the formation of their chloro-complexes in various concentration of acidic solution, and the recovery of platinum, palladium and rhodium from the samples after hydrogen reduction pretreatments was examined in the leach process by using a mild solution mixture of NaClO-HCl and H2O2 at 65 � C for 3 h.
Abstract: Platinum-group metals (PGM) are important precious metals in many industrial fields However, their natural resource deposits are strictly limited Accordingly, their recycling process from wastes and/or secondary resources must be considered In this study, the leaching of PGM from automotive catalyst residue was performed based on the formation of their chloro-complexes in various concentration of acidic solution The recovery of platinum, palladium and rhodium from the samples after hydrogen reduction pretreatments was examined in the leaching process by using a mild solution mixture of NaClO–HCl and H2O2 at 65 � C for 3 h Effect of other solution mixtures on the extraction of the precious metals was also compared with NaClO–HCl–H2O2, such as HCl–H2O2 and NaClO–HCl The optimum condition to dissolve platinum,
141 citations
TL;DR: In this paper, the effects of zinc addition on microstructure evolution and mechanical properties of Mg-Gd-Y-(-Zr) based alloys are investigated in details using OM, TEM, Vickers hardness tests and tensile tests.
Abstract: The effects of zinc addition on microstructure evolution and mechanical properties of Mg-Gd-Y-(-Zr) based alloys are investigated in details using OM, TEM, Vickers hardness tests and tensile tests. Specific line-shaped structure is formed inside of matrix grain in the as-cast specimen. This structure is dissolved after a solution-treatment at 773 K. Instead of it, in the 0.3–1Zn alloy, the 14H LPSO structure is observed at grain boundaries of Mg matrix phases after the solution heat treatment. Metastable � 0 phase is formed during subsequent aging treatment at 498 K. The 14H LPSO structure is stable and remained even after the aging treatment. These structure and phase coexist at the peak-aged condition in the microstructure. In cast- specimens, 0.2% proof stress and tensile strength slightly decreases with an addition of zinc up to 0.75 mol% and rapidly decreases over 1 mol% zinc addition. On the contrary, in rolled-specimens, addition of 0.3–1 mol% zinc improves mechanical properties in both strength and ductility significantly. It is found that the UTSs reach more than 400 MPa in the 0.3–1Zn alloys. This characteristic effect is considered to be the contribution of LPSO structure and its specific orientation relationship with matrix phase.
131 citations
TL;DR: In this article, the formation, fundamental properties, workability and applications of late transition metal base bulk glassy alloys which have been developed after the first synthesis of Fe-based bulk glassys alloys by the copper mold casting method in 1995 are reviewed.
Abstract: We review our recent results of the formation, fundamental properties, workability and applications of late transition metal base bulk glassy alloys which have been developed after the first synthesis of Fe-based bulk glassy alloys by the copper mold casting method in 1995. The late metal transition base bulk glassy alloys were obtained in Fe–(Al,Ga)–(P,C,B,Si), Fe–(Cr,Mo)–(C,B), Fe–(Zr,Hf,Nb,Ta)–B, Fe–Ln–B(Ln=lanthanide metal), Fe–B–Si–Nb and Fe–Nd–Al for Fe-based alloys, Co–(Ta,Mo)–B and Co–B–Si–Nb for Co-based alloys, Ni–Nb–(Ti,Zr)–(Co,Ni) for Ni-based alloys, and Cu–Ti–(Zr,Hf), Cu–Al–(Zr,Hf), Cu–Ti–(Zr,Hf)–(Ni,Co) and Cu–Al–(Zr,Hf)–(Ag,Pd) for Cu-based alloys. These bulk glassy alloys exhibit useful engineering properties of high mechanical strength, large elastic elongation and high corrosion resistance. In addition, Fe- and Co-based bulk glassy alloys have good soft magnetic properties which cannot be obtained for conventional amorphous and crystalline type magnetic alloys. The Fe- and Ni-based bulk glassy alloys have already been used in some application fields. These late transition metal base bulk glassy alloys are promising as new metallic engineering materials.
121 citations
TL;DR: The β-Al5FeSi platelets have long been thought to be brittle and responsible for the inferior mechanical properties of Al-Si cast alloys as discussed by the authors, and two typical cracks, transverse and longitudinal, are commonly observed in β-al5Fe Si platelets, though some transverse cracks may be due to the brittleness.
Abstract: The β-Al5FeSi platelets have long been thought to be brittle and responsible for the inferior mechanical properties of Al-Si cast alloys. Two typical cracks, transverse and longitudinal, are commonly observed in β-Al5FeSi platelets. It is thought that the cracks are probably due to the presence of doubled-over oxide films (bifilm) though some transverse cracks may be due to the brittleness. The crack is actually the gap between the two dry sides of an entrained oxide film. Its wetted sides are the favoured substrates for the nucleation and growth of β-Fe platelets. This discovery of the formation of β-Fe platelets on folded films has answered many previously intractable questions encountered in β-Fe phase. For the future, one may speculate that if oxide films could be eliminated from Al melts, it may prove possible to create alloys with unusually high toughness, despite high Fe contents.
120 citations
TL;DR: In this paper, the influence of interfacial structure development at interface on the fracture mechanism and the bond strength of cold roll bonded Al/Cu bimetal plate was studied and no obvious Kirkendall effect of void formation was observed.
Abstract: The aim of this article is to study the influence of interfacial structure development at interface on the fracture mechanism and the bond strength of cold roll bonded Al/Cu bimetal plate. The Al/Cu bimetal plates are produced by cold roll bonding and then sintered at different conditions. The bond strength of the Al/Cu bimetal plate increases generally to maximum values and then decreases to low values with increasing sintering temperature and time. Interfacial structures develop with increasing sintering temperature and time. The main interfacial layers are Al 2 Cu, AlCu, Al 3 Cu 4 and Al 4 Cu 9 . The formation and thickening of those intermetallic compounds promotes cracks propagation and weakens the bond strength of the bimetal plates. The fracture mechanism transforms from ductile to brittle cleavage with the development of interfacial structures. While the bond strength of the material starts to decrease, no obvious Kirkendall effect of void formation is observed in the present study.
117 citations
TL;DR: In this article, the formation of characteristic interfacial oscillations with vortices at high energetic conditions was identified as FeTi and Fe2Ti intermetallics by X-ray diffraction and smooth wavy and flat topography was obtained for thin flyer plates due to less kinetic energy loss.
Abstract: Commercially pure titanium and 304 stainless steel were welded using explosive welding technique. The joints were evaluated using optical microscope, scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. The study indicates the formation of characteristic interfacial oscillations with vortices at high energetic conditions. The reacted products of the vortices have been identified as FeTi and Fe2Ti intermetallics by X-ray diffraction. Increase in the kinetic energy spent at the interface cause the volume of vortices to increase. Smooth wavy and flat topography has been obtained for thin flyer plates due to less kinetic energy loss. The results demonstrate a good welding interface for multi-layered welding using a thin stainless steel interlayer, as the kinetic energy dissipation at the interface was less. [doi:10.2320/matertrans.47.2049]
108 citations
TL;DR: In this paper, the β' phase precipitated in a 95 at%Mg-5 at%Gd (Mg 95 Gd 5 ) alloy aged in a peak hardness condition (at 200°C for 100 hrs) is studied by high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM).
Abstract: The β' phase precipitated in a 95 at%Mg-5 at%Gd (Mg 95 Gd 5 ) alloy aged in a peak hardness condition (at 200°C for 100 hrs) is studied by high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Atomic-scaled HAADF-STEM observations of the β' phase can propose a new structure model with an orthorhombic unit cell of a = 0.64 nm, b = 2.28 nm and c = 0.52 nm and a composition of Mg 7 Gd. The β' precipitates have a plate-shape with an about 40 nm width along the [001] m of the Mg-matrix and an about 100nm length along [210] m -typed directions, and joining of the plate-shaped precipitates establishes a two-dimensional cell structure parallel to the (001) m plane of the Mg-matrix.
108 citations
TL;DR: In this article, a novel energy-saving hydrometallurgical recovery process for copper from electronic scrap employing the Cu(I)-ammine complex has been presented on the basis of a thermodynamic consideration.
Abstract: A novel energy-saving hydrometallurgical recovery process for copper from electronic scrap employing the Cu(I)-ammine complex has been presented on the basis of a thermodynamic consideration. In order to experimentally explore the feasibility of the leaching stage in this process, the copper leaching behavior from a printed circuit board (PCB) in ammoniacal alkaline solutions has been investigated under a nitrogen atmosphere. Copper in PCB was oxidized by Cu(II) to form Cu(I)-ammine complex ions. The leaching reaction can be expressed as: Cu þ Cu(NH3)4 2þ ¼ 2Cu(NH3)2 þ . The Cu(II)-ammine complex significantly enhanced the leaching rate, while the Cu(I)-ammine complex slightly depressed it. Crushing of the PCB effectively enhanced the leaching rate, because the exposed metallic copper area is increased by the crushing. The effect of temperature on the leaching rate was insignificant. Consequently, the feasibility of the leaching stage in the proposed copper recovery process has been experimentally confirmed. [doi:10.2320/matertrans.47.1788]
TL;DR: In this paper, a first-principles calculation for UO2 in an antiferromagnetic structure with four types of point defects, uranium vacancy, oxygen vacancy, uranium interstitial and oxygen interstitial, has been performed by the projector-augmented-wave method with generalized gradient approximation combined with the Hubbard U correction.
Abstract: A first-principles calculation for uranium dioxide (UO2) in an antiferromagnetic structure with four types of point defects, uranium vacancy, oxygen vacancy, uranium interstitial, and oxygen interstitial, has been performed by the projector-augmented-wave method with generalized gradient approximation combined with the Hubbard U correction. Defect formation energies are estimated under lattice relaxation for supercells containing 1, 2, and 8 unit cells of UO2. The electronic structure, the atomic displacement and the stability of defected systems are obtained, and the effects of cell sizes on these properties are discussed. The results form a self-consistent dataset of formation energies and atomic distance variations of various point defects in UO2 with relatively high precision. We show that a supercell with 8 UO2 unit cells or larger is necessary to investigate the defect behavior with reliable precision, since point defects have a wide-ranging effect, not only on the first nearest neighbor atoms of the defect, but on the second neighbors and on more distant atoms. [doi:10.2320/matertrans.47.2651]
TL;DR: In this article, a single-mode applicator was used to investigate the heating behavior of various metal particles in a microwave environment, and the dependence of the heating rate of metal particles on their size was discussed in terms of the heat transfer rate.
Abstract: Microwave (MW) heating behavior of various metal particles was investigated using a single-mode applicator. Considering the distributions of the electromagnetic fields in the wave guide, specimens were placed at four specific positions with respect to the electric and the magnetic fields of MW. They were heated at conditions of constant power input. It was demonstrated that iron particles were heated well in the magnetic field, and that ferro-magnetic metal particles having the higher Curie point was heated the better. It was possible to heat iron bulk particles (� 3 mm) in a magnetic field without occurrence of electric discharge. In the range of nickel particle size between 45 and 150 mm, the particles with the smaller size were heated the better. Nickel oxide (NiO) was heated well only in the position of large electric field, which indicates that the heating was caused by the different (dielectric heating) mechanism from the metal particles. From these results, contribution of magnetic field to heating metal particles was discussed, considering the heating mechanisms of the magnetic loss and the eddy current loss. The dependence of the heating rate of metal particles on their size was discussed in terms of the heat transfer rate.
TL;DR: In this paper, the thermal desorption properties of metal-borohydrides M(BH4)n were investigated by gas-chromatography and mass-spectroscopy combined with thermogravimetry.
Abstract: Metal-borohydrides M(BH4)n (M ¼ Mg, Sc, Zr, Ti, and Zn; n ¼ 2{4) were synthesized by mechanical milling process according to the following reaction; MCln þ nLiBH4/nNaBH4 ! M(BH4)n þ nLiCl/nNaCl. Then the thermal desorption properties of M(BH4)n were investigated by gas-chromatography and mass-spectroscopy combined with thermogravimetry. The results indicate that the hydrogen desorption
TL;DR: In this paper, a study of the microstructural evolution during the whole manufacturing process reveals that the increase of the cooling rate during the hot rolling leads to a significant decrease of martensite banding in the microstructure of dual phase steels for sheets used in the automotive industry.
Abstract: The segregation of manganese during solidification from casting is responsible for banding problems of dual phase steels. Microstructural banding lasts during all the manufacture process, producing the deterioration of the material, so the final ductility and impact toughness of the sheets are decreased due to the high level of anisotropy. To avoid or reduce the problem of microstructural banding, it is proposed to modify the hot rolling parameters so the formation of ferrite-pearlite microstructures is avoided and thus the presence of banding. The study of the microstructural evolution during the whole manufacturing process reveals that the increase of the cooling rate during the hot rolling leads to a significant decrease of martensite banding in the microstructure of dual phase steels for sheets used in the automotive industry.
TL;DR: Friction stir welding was applied to ultra low-carbon interstitial free steels with mean grain sizes ranging from 0.7 μm, prepared by accumulative roll-bonding, to 27 μm as mentioned in this paper.
Abstract: Friction stir welding (FSW) was applied to ultra low-carbon interstitial free steels with mean grain sizes ranging from 0.7 μm, prepared by accumulative roll-bonding, to 27 μm. The steel with the intermediate grain size (1.8 μm) is most preferable for obtaining the highest hardness in the stir zone with the smallest grain size.
TL;DR: In this paper, the authors studied the evolution of the structure, substructure and functional properties of the equiatomic Ti-Ni alloy and obtained the maxima of the free recovery strain and constraint recovery stress after annealing in the 350-400 � C temperature range.
Abstract: The thermomechanical processing consisting in cold work (true strain e ¼ 0:3{1:9) followed by a post-deformation annealing (200–700 � C temperature range) is applied to the equiatomic Ti–Ni alloy. The evolution of the structure, substructure and functional properties of the material is studied. For all levels of cold work, the maxima of the free recovery strain and constraint recovery stress are obtained after annealing in the 350–400 � C temperature range. For a moderately cold-worked material (true strain e ¼ 0:3), this temperature range corresponds to polygonization; for a severely cold-worked material (e ¼ 1:9), it corresponds to the material nanocrystallization, while for a highly cold-worked material (e ¼ 0:88), the structure is mixed. An increase in the cold-work strain leads to an increase in the completely recoverable strain above 8% and in the maximum recovery stress up to 1450 MPa, as well as to the widening of the superelastic temperature range.
TL;DR: A new software GBstudio was developed for generating atomic coordinates in periodic grain boundary models composed two crystals, designed for modeling grain boundary structures in various geometries including coincident-site-lattice (CSL), tilt, and twist boundaries in easy and systematic ways.
Abstract: A new software GBstudio was developed for generating atomic coordinates in periodic grain boundary models composed two crystals. It was designed for modeling grain boundary structures in various geometries including coincident-site-lattice (CSL), tilt, and twist boundaries in easy and systematic ways. By this software, CSL boundaries of cubic crystals up to Σ99 can be constructed by selecting a few parameters in the candidate lists. Tilt and twist boundaries on representative rotation axes can also be generated in a similar way for cubic and non-cubic crystals. An editing menu is implemented to modify inappropriate atomic configuration at the boundary. The software is distributed via the Internet as a Java applet usable on web browsers.
TL;DR: In this paper, the impact of a metal particle on a metal substrate was analyzed using a dynamic finite element code (ABAQUS), and the effects of a substrate and a particle temperature on the critical velocity were numerically studied.
Abstract: Several thermal spray processes developed recently are characterized by relatively low temperature and higher velocity of sprayed particles. They include cold spray, high velocity oxy-fuel spray, and warm spray, in which majority or all the sprayed particles are in solid phase when impinging onto the substrate surface. Therefore, in order to understand the coating formation process of such processes, detailed knowledge concerning impact phenomena of a solid particle is essential. It is generally accepted that there exists a minimum velocity beyond which a particle adheres to the substrate and this velocity is called the ‘‘critical velocity’’. How the critical velocity depends on various materials and process variables is not fully understood yet. In this study, analysis of a metal particle impacting onto a metal substrate was carried out by using a dynamic finite element code (ABAQUS). Effects of a substrate and a particle temperature on the critical velocity were numerically studied. Also, effects of thermal conduction on the simulation results were discussed. It was found that critical velocity decreases with 1) higher stiffness of the substrate, 2) higher particles temperature, and 3) greater particle size. [doi:10.2320/matertrans.47.1697]
TL;DR: In this paper, the influence of carbon contents on the microstructures and mechanical properties of wrought Co-Cr-Mo alloys with C contents of 0.02, 0.09 and 0.18% were fabricated by hot-forging process.
Abstract: The wrought Co–Cr–Mo alloys with C contents of 0.02, 0.09 and 0.18% (mass%) were fabricated by hot-forging process to study the influence of carbon contents on the microstructures and mechanical properties. The microstructures of Co–29Cr–6Mo–0.02C and Co–29Cr– 6Mo–0.09C consist of equiaxed uniform grains which contain stacking faults, twins and " martensite bands. No carbide found at inter- and intragranular region. Co–29Cr–6Mo–0.18C consists of irregular grain sizes and carbide found at inter- and intra-granular region. The carbide in Co– 29Cr–6Mo–0.18C was identified as M23C6 type carbide from the XRD pattern analysis. It is found that the amount of stacking fault and " martensite are strongly dependent upon the C content. The density of stacking faults and " martensites observed in Co–29Cr–6Mo–0.09C
TL;DR: In this paper, a ternary compound titanium silicon carbide (Ti 3 SiC 2 ) was synthesized by using a pulse discharge sintering (PDS) process.
Abstract: Various powder mixtures from the starting powders of Ti/Si/C, Ti/SiC/C, Ti/Si/TiC, Ti/SiC/TiC and Ti/TiSi 2 /TiC were used for the synthesis of ternary compound titanium silicon carbide (Ti 3 SiC 2 ) by using a pulse discharge sintering (PDS) process. The Ti/Si/TiC powder was found to be the best among the five powder mixtures for Ti 3 SiC 2 synthesis. Phase purity of Ti 3 SiC 2 can be improved to ≈99 mass% at the sintering temperature of 1300°C for 15min. The relative density of all the synthesized samples is higher than 98-99% at the sintering temperature above 1275°C. The nearly single phase Ti 3 SiC 2 was found to show plastic deformation at room temperature and good machinability. Both electrical and thermal conductivity were found to be greater than two times of the values of a control pure Ti sample fabricated by the same sintering process. The thermopower of the synthesized Ti 3 SiC 2 was measured to be nearly zero in the testing temperature range, much lower than some common low thermopower substances such as gold or carbon. Their mechanical properties at ambient and elevated temperatures were also examined. The ternary compound Ti 3 SiC 2 is referred to as a "metallic ceramic" according to its physical and mechanical behavior representing both metals and ceramics.
TL;DR: In this paper, the effect of annealing temperature on microstructure and shape memory characteristics of Ti-22Nb-6Zr (at%) biomedical alloys was investigated by using tensiletests, XRDmeasurement,scanningelectronmicroscopy(SEM)andtransmissionelectron microscopy (TEM).
Abstract: Effect of annealing temperature on microstructure and shape memory characteristics of Ti–22Nb–6Zr(at%) biomedical alloys wasinvestigatedbyusingtensiletests,XRDmeasurement,scanningelectronmicroscopy(SEM)andtransmissionelectronmicroscopy(TEM).Afterseverecold-rolling,theplatewasannealedattemperaturesbetween773and1173K.The= transustemperatureinthisalloywasdeterminedtobe between 823 and 873K. The specimen annealed at 823K for 3.6ks exhibited a fine subgrain structure. A fully recrystallized structure wasobserved in the specimens annealed above 873K. The annealing temperature less affected the transformation temperature and recovery strain.However, the critical stress for slip decreased considerably with increasing annealing temperature, because the grain size increased. Allspecimens annealed above 823K exhibited stable superelastic behavior at room temperature.(Received November 4, 2005; Accepted December 21, 2005; Published March 15, 2006)Keywords: shape memory effect, superelasticity, biomaterials, titanium based alloy, titanium–niobium–zirconium, Hall–Petch relationship
TL;DR: The shape memory effect in an Fe-Mn-Si based SMA is governed by motion of Shockley partial dislocations which carry the fcc $ hcp phase transformations as discussed by the authors.
Abstract: The SME (shape memory effect) in an Fe–Mn–Si based SMA is governed by motion of Shockley partial dislocations which carry the fcc $ hcp phase transformations. The degree of SME is determined by preservation of the partial dislocations whereas the strength is determined by the internal stress opposing against the dislocation motion. The increase in the internal stress tends to induce dislocation reactions which ruin the preservation of the Shockley partials and hence to decrease the degree of SME. Nevertheless, usage of this SMA for construction of a large structural product has recently gained much attention even with sacrifice in the degree of SME. Upon application of this SMA in such a field, the optimum condition has to be searched both in the mechanical properties of the SMA itself and the type of the usage in the sense of deformation mode such as elongation, contraction, bending, twisting and so on. In this paper, the dislocation motion responsible for a good SME with high strength will be discussed on the ground of the basic knowledge of the dislocation generation, the motion and the reactions.
TL;DR: In this paper, a method to measure the geometrical tortuosity of a porous media for the two phases is presented, where the solid matrix is modeled as a network of linear connected segments and the thermal conductivity of metallic foams is determined by solving energy equation over the solid phase skeleton.
Abstract: Metallic foams are highly porous materials which present complex structure of three-dimensional open cells. The effective transport properties determination is essential for these widely used new materials. The aim of this work is to develop morphology analysis tools to study the impact of foams structure on physical transport properties. The reconstruction of the solid-pore interface allows the visualization of the 3D data and determination of specific surface and porosity. We present an original method to measure the geometrical tortuosity of a porous media for the two phases. A centerline extraction method allows us to model the solid matrix as a network of linear connected segments. The thermal conductivity of metallic foams is determined by solving energy equation over the solid phase skeleton. Results obtained on a set of nickel foams covering a wide range of pore size are discussed.
TL;DR: In this paper, a mathematical model for the reactive diffusion controlled by volume diffusion was used in order to analyze numerically the growth rate of the Fe2Al5 layer, and the interdiffusion coefficient was evaluated to be 5:93, 10 � 16, 1:18 � 10 � 14 and 2:92 � 10 ¼ 14 m 2 /s at T ¼ 823, 873 and 913 K, respectively.
Abstract: Using Al/Fe/Al diffusion couples prepared by a diffusion bonding technique, the reactive diffusion in the binary Fe–Al system was experimentally examined in a previous study. The diffusion couple was isothermally annealed at temperatures of T ¼ 823{913 K, and then a compound layer of Fe2Al5 was observed to form at the interface. The observation indicates that there exists the parabolic relationship between the mean thickness of the Fe2Al5 layer and the annealing time. The parabolic relationship means that the growth of the Fe2Al5 layer is controlled by volume diffusion. A mathematical model for the reactive diffusion controlled by volume diffusion was used in order to analyze numerically the growth rate of the Fe2Al5 layer. Through the analysis, the interdiffusion coefficient D of Fe2Al5 was evaluated to be 5:93 � 10 � 16 , 1:18 � 10 � 14 and 2:92 � 10 � 14 m 2 /s at T ¼ 823, 873 and 913 K, respectively. Expressing the temperature dependence of D as D ¼ D0 expð� Q=RTÞ, values of D0 ¼ 2:34 � 10 2 m 2 /s and Q ¼ 276 kJ/mol were obtained by the least-squares method. [doi:10.2320/matertrans.47.1480]
TL;DR: In this paper, a small amount of magnetovolume effect (MVE) was recovered by a small fraction of Ge in the Cu site, and the volume expansion becomes gradual (ΔT ∼ 100 K) and large negative thermal expansion is exhibited around room temperature.
Abstract: Metallic manganese nitrides Mn 3 AN (A = Zn, Ga, etc) are well-known for their large magnetovolume effect (MVE), i.e., a discontinuous volume expansion at the magnetic transition. However, MVE is exceptionally absent in Mn 3 CuN. We found that MVE is recovered by a small amount of Ge in the Cu site. This revival seems to coincide with recovery of the cubic structure. By further Ge doping, the volume expansion becomes gradual (ΔT ∼ 100 K) and large negative thermal expansion (NTE) is exhibited around room temperature [a = -12 x 10 -6 K -1 (a: coefficient of linear thermal expansion) for Mn 3 (Cu 0.5 Ge 0.5 )N]. Such a large, isotropic and non-hysteretic NTE is desirable for practical applications.
TL;DR: In this paper, the authors simulate grain boundary decohesion (embrittlement) in ferromagnetic bcc FeΣ3(111)[110] and fcc NiΣ5(012)[100] symmetrical tilt grain boundaries by progressively adding sulfur atoms to the boundaries.
Abstract: Using first-principles calculations, we simulate grain boundary decohesion (embrittlement) in ferromagnetic bcc FeΣ3(111)[110] and fcc NiΣ5(012)[100] symmetrical tilt grain boundaries by progressively adding sulfur atoms to the boundaries. We calculate the segregation energy of sulfur atom, tensile strength, and cohesive energy of the grain boundaries. We show that a certain amount of sulfur segregation (two atomic layers, 14.4 atom/nm 2 ) is energetically possible to realize considering the calculated segregation energies. At this concentration, the tensile strength and the cohesive energy of the grain boundaries reduce by one order of magnitude comparing with no segregation case.
TL;DR: A broad account of solute-centered atomic clusters in the structure and stability of metallic glasses has not been provided elsewhere as mentioned in this paper beyond a few simple cases, and detailed characteristics of a canonical collection of efficiently packed hard sphere clusters are presented as idealized structural elements in metallic glasses.
Abstract: A growing body of evidence supports the importance of solute-centered atomic clusters in the structure and stability of metallic glasses. Beyond a few simple cases, a broad account of these clusters has not been provided elsewhere. Detailed characteristics of a canonical collection of efficiently packed hard sphere clusters are presented here as idealized structural elements in metallic glasses. The nomenclature, topology, geometry and packing efficiency of these clusters are provided and their relevance to the structure of metallic glasses is discussed.
TL;DR: In this article, the shape memory alloys were used for concrete prestressing, and three-point bending tests were performed for the mechanical properties of the resulting concrete bricks, and it was found that prestressing increased the bending strength and cracking stress of the bricks.
Abstract: This article reports the mechanical properties of concrete prestressed by the Fe–Mn–Si-based shape memory alloys containing NbC that exhibit an excellent shape memory effect without the so-called ‘training’ treatment. A thermomechanically treated Fe–28Mn–6Si–5Cr–0.53Nb– 0.06C (mass%) alloy was used for this purpose. Four square bars of the alloy were embedded in mortar, and heated above their reverse martensitic transformation start temperature after hardening of the mortar matrix. Three-point bending tests were performed for the mechanical property characterization. It was found that prestressing by the shape memory alloys increased the bending strength and cracking stress of the mortar.
TL;DR: In this paper, the electronic structure of the full and half-Heusler alloys have been studied by ab-initio calculations using full potential augmented plane-wave method (FLAPW).
Abstract: The electronic structure of the full- and half-Heusler alloys have been studied by ab-initio calculations using full potential augmented plane-wave-method (FLAPW). It was shown that obtained equilibrium lattice parameters and magnetic moments agree well with available experimental data. The influence of vacancies on the electronic structure and magnetic properties of Ni 2-x MnGa and Co 2-x ZrSn is analyzed.