The fluidity of Ti-6Al-4V-xB₄C composites is investigated by using a vacuum fluidity test. It is found that the solidification paths of Ti-6Al-4V are changed by B₄C additions. Differences in solidification processes dramatically affect the fluidity of Ti-6Al-4V-xB₄C composites. With the increase of B₄C additions, the fluidity of Ti-6Al-4V-xB₄C composites is not monotonically decreasing, it drops to a valley initially and then increases.

View full abstract

The influence of two-dimensional nano-structures on magnetic properties has been investigated in perpendicular antiferromagnetic coupled (AFC) Co₈₀Pt₂₀ stacked films. The AFC-samples consisted of [Co-Pt (10 nm)/Ru (0.46 nm)/Co-Pt (5 nm)] stacked layers, and the magnetization of the 5-nm-thick bottom Co-Pt layers was firstly reversed by AF-coupling. Hexagonal arrays of dots and holes were formed on both (top and bottom) Co-Pt layers and only on the top Co-Pt layer. The interlayer exchange coupling between the top and bottom Co-Pt layers across very thin Ru interlayer of 0.46 nm in thickness was kept even after the nanofabrication of about 100 nm in diameter. The coercivity of dot arrays markedly increased with a decrease in dot diameter, while the magnetic properties of hole arrays were less influenced by the nanoscale patterning. The magnetization rotation of AFC-samples with the patterned top layer changed from multiple to continuous reversal processes with decreasing in patterning size. For the top layer patterned sample, the minor loop shift of the 100-nm-dot arrays decreased from 240 to 140 kA/m, while the 100-nm-hole arrays showed almost the same strength of interlayer exchange coupling compared with that of continuous film prior to patterning.

View full abstract

Using conventional transmission electron microscopy (TEM) and aberration-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), compositional irregularity has been identified around long-period stacking order structures (LPSOs) in aged Mg₉₇Zn₁Y₂ alloys, which have coexistence of LPSO and α-Mg matrix. Elemental mappings show that compositional transition layers surround the growing LPSOs. The compositional transition layer includes solute atmosphere in the α-Mg matrix and transition layers of LPSOs with lower concentrations of solute elements. The Zn concentration in a transition layer of LPSO is higher than that of Y, which differs from the α-Mg matrix and LPSOs. The transition layer is an 18R-type stacking sequence. No transition layer was observed after the transformation from 18R-type to 14H-type LPSOs. These results indicate that the segregation of Zn is faster than that of Y, and that the transition layer is a non-stoichiometric 18R-type LPSO with Zn-rich lower concentration of the solute elements, which connects an 18R-type LPSO and an α-Mg matrix.

View full abstract

The applicability and effectiveness of the representative volume element (RVE) approach for predictions of creep properties in metal matrix composite materials were analyzed numerically in this paper. A special attention was paid to the sensitivity of numerical solutions with respect to the volume element size, in terms of short-term creep strength and secondary creep rate of the model. The numerical models were based on the microstructure of composite material which consisted of creeping matrix with randomly distributed non-creeping hard spherical particles. A modified random sequential adsorption algorithm was applied to reproduce volume elements of composite microstructures. Then, the elements were subjected to creep deformations with uniaxial stress boundary condition. Statistical analysis of numerical experiments for different volume element sizes showed that the effective creep properties can be determined for large volumes of the elements. In both cases of creep strength and secondary creep rate, the statistical fluctuations of the numerical solutions were decreased with increasing volume of element. Several test cases are also presented in order to validate the model against experimental results from literature, and the advantage and limitation of the RVE approach are discussed.

View full abstract

Grouting using calcium phosphate compound (CPC) has been used for countermeasure for liquefaction in geotechnical engineering applications and it is an economical and environmental friendly technique that develops to form calcium carbonate precipitation throughout the soil, leading to an increase in soil strength. In the paper, our aim was to improve strength by adding CPC with CaCO₃ (commercially found) and scallop shell (Naturally found) powder and exceed a maximum UCS of 100 kPa after 28 days of curing, which is the strength required as a countermeasure against soil liquefaction during earthquake. For that, initially Toyoura sand test pieces were cemented by CPC solutions only and cured up to 56 days and carried out unconfined compressive strength (UCS) test. Moreover, Toyoura sand test pieces were cemented by CPCs with CaCO₃ (CC) powder and CPCs with scallop shell powder and cured and these specimens also analyzed with UCS tests. The UCS of the sand test pieces cemented by CPC with scallop shell powder and CC powder was higher than that of the test pieces with no added powders. In addition, a series of laboratory experiments were conducted, including pH concentration, scanning electron microscope (SEM) in order to observe the microscopic structure, density before and after curing etc. The results indicate that the density and the pH concentration of the sand test pieces cemented by CPC with scallop shell powder and CC powder were higher than that of the test pieces with no added powders.

View full abstract

Indenter dependent indentation behaviors of the Zr-based bulk metallic glass, such as adhesion, serrated flows, shear bands, residual indent morphologies, were found and analyzed in this paper. An interesting phenomenon is presented that adhesion of the Zr-based bulk metallic glass appears during the indentation test using the cube-corner indenter but it’s not observed when using the Berkovich indenter. Corresponding to the adhesion behavior, “dirty” but new surfaces with the nano-scale dimple structure are formed by the cube-corner indenter while relatively smooth surfaces with few discrete shear bands are obtained by the Berkovich indenter. Indentation experiments indicate that the adhesion force between the cube-corner indenter and the Zr-based bulk metallic glass depends on the loading rate, the maximum penetration load and the cyclic loading number. These phenomena will enhance understanding of shear band formation, shear-induced softening, and adhesion of bulk metallic glasses.

View full abstract

As-cast and homogenization treated as-cast Al–Cu (3 mass% Cu) alloy samples were processed via high-pressure torsion (HPT) under an applied pressure of 8 GPa with 5 revolutions at room temperature. Microstructure, mechanical properties, and fracture surface morphology of the HPT-processed Al–Cu were investigated, demonstrating that the HPT process successfully resulted in distinct grain refinements in both samples. Significant improvements in the microhardness, tensile properties, and deformation homogeneity due to fine grains, high grain boundary misorientation angle, and homogeneous distribution of the θ phase were achieved after the HPT process of the homogenized sample. The homogenization treatment of the as-cast Al–Cu has a significant effect on the fracture surface morphology and fracture mode of the HPT-processed samples.

View full abstract

We developed open-cell copper foams with uniformly distributed nanopores by chemical dealloying of Al₂Cu samples that were synthesized by a powder process. High-energy ball-milling was utilized for mechanical alloying of aluminum and copper powders and either hot rolling or hot pressing was then employed to consolidate the ball-milled powders into sheets or pellets. Subsequent dealloying aluminum from the samples produced nanoporous copper foams. X-ray diffractometry and scanning electron microscopy confirmed the uniform formation of Al₂Cu and aluminum phases prior to dealloying, and the introduction of nanoporous structures after dealloying.

View full abstract

We propose a smelting reduction process for titanium that uses a flux without any added deoxidizer, such as metallic calcium. For the smelting flux, material from the CaO-Al₂O₃-ZrO₂ ternary system was utilized, and an arbitrary quantity of TiO₂ was added to the ternary flux. The mixed TiO₂-bearing quaternary flux was electrochemically treated in a reaction cell made of CaO-stabilized ZrO₂ solid electrolyte above the melting temperature of titanium. Small, lustrous particles were observed on the crushed flux surface after smelting and quenching, and these were analyzed by optical microscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy (EDX) during scanning electron microscopy, and wavelength-dispersive X-ray fluorescence spectroscopy. The formation of metallic titanium was confirmed by the X-ray diffraction data and elemental mapping by EDX, and was determined to be reasonable from thermodynamic investigations.

View full abstract

The effect of macro and micro porosity on properties of porous Ti-6Al-4V samples fabricated using a solid state space holder method is investigated. Sintering with mixing condition, with and without process control agents (PCA), and sintering conditions, pressure and temperature range of 30–60 MPa and 700–725°C were performed in order to get different macro pore morphology and micro pore quantity. It is found that macro-pore plays significant role to determine the properties of porous Ti-6Al-4V. Open porosity, Young’s modulus and strength are affected by the distribution of the pores. Randomly distributed pores will results in high value of open porosity yet higher Young’s modulus. Micro porosity only less affects on the mechanical properties of the porous product.

View full abstract

In this study, the effect of nickel powder addition to cold sprayed CoNiCrAlY coatings was investigated. In order to reduce production cost of cold spray and improve the deposition efficiency of CoNiCrAlY coatings, pure nickel (Ni) powder was added to the CoNiCrAlY and the resulting powder was cold sprayed using nitrogen (N₂) as the working gas. Deposition efficiency was increased as compared with a CoNiCrAlY coating without Ni under the same spray conditions. The microstructural characterization and phase analysis of the feedstock powders and the as-sprayed coatings were carried out by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). In the SEM images, the particle boundaries between Ni and CoNiCrAlY in the as-sprayed coating were clearly observed. Also, a significant amount of the CoNiCrAlY powder was encapsulated in the coating. To confirm the oxidation behavior of CoNiCrAlY with the Ni coating, heat treatment was carried out at 1000°C in ambient air. After heating, most of the boundaries between Ni and CoNiCrAlY disappeared and many pores were generally observed in the coating by interdiffusion of the powders. Over time, most of these pores disappeared by interdiffusion; thus, the number of pores decreased and the hardness of the coatings increased. In the EDX analysis of the coatings, movement of elements was definitely confirmed. Furthermore, the elements of thermally grown oxide (TGO) were analyzed to confirm the effect of CoNiCrAlY with Ni coatings, and a large quantity of NiO was observed on the coating layer. Because NiO can lead to faster delamination of thermal barrier coatings (TBCs), pretreatment in low oxygen partial pressure was carried out to prevent the formation of excess NiO. This pretreatment successfully prevented the growth of NiO TGO.

View full abstract

A smooth particle hydrodynamic (SPH)-based scratch model was proposed to study the influences of residual stress induced by the first cutting on subsequent scratch. In this paper, comparisons were made between the results of only scratching the specimen and those of subsequent scratching the specimen after cutting under different scratch depths. Chip formation, scratching forces and residual stress in scratching-induced subsurface were recorded on oxygen-free high-conductivity copper (OFHC) during the simulations. Simulation results indicated that the first cutting produced work hardening in the subsurface of the specimen and the increased hardness led to a thinner and more curled chip. Meanwhile, the minimum chip thickness also decreased because of residual stress induced by cutting. Moreover, it also resulted in high resistance during the subsequent scratch so that the scratched surface presented flat. However, the material on both the sides of the groove bulged in Scratch model. Therefore, scratch after cutting is beneficial to obtain scratched surface with high quality.  

View full abstract

Stress corrosion tests were performed for welded 308 stainless steel under proton irradiation at 473 K. The concentration of oxygen and hydrogen in the feed water was controlled to be below 5 and 10 ppb, respectively. The in-beam loading condition was 0 and 300 MPa in tension under an irradiation dose rate of 1.3 × 10⁻⁷ dpa/s. The electrochemical corrosion potential (ECP) was also measured during the tests. After the corrosion tests, the specimen surface at the fusion zone was examined by SEM for all specimens. Extensive electrochemical reactions on the specimen surface were implied by ECP measurement under the in-beam loading condition. The initiation of surface cracking followed by coalescence of numerous larger corrosion pits at the boundaries of ferrite phases in the austenitic matrix was detected for the in-beam specimens at 300 MPa. Thus, the initial process of stress corrosion cracking at weld metal would be accelerated under irradiation.

View full abstract

The (Ti_0.8Mo_0.2)C-xNi cermets (x = 10, 20, 30 and 40 mass%) were prepared by two milling processes; first, the (Ti_0.8Mo_0.2)C produced by mechanical alloying of Ti, Mo and C powders (Process I). Second, mechanical alloyed (Ti_0.8Mo_0.2)C and commercial Ni powders mixed by tumbling ball milling (Process II) for 72 h. On (Ti_0.8Mo_0.2)C-40Ni, the milling time of Process II was 96 h in addition of 72 h. The Vickers hardness with fracture toughness and the quantitative microstructural parameters were measured and analyzed. The relationship between fracture toughness and hardness for the cermets was on the fitted curve derived from the previous data for the cermets, except for the case of (Ti_0.8Mo_0.2)C-40Ni for 72 h, which is lower fracture toughness than that for the previous works and (Ti_0.8Mo_0.2)C-40Ni for 96 h. The contiguity of the samples tend to increase with increasing hard phase contents except for the case of (Ti_0.8Mo_0.2)C-40Ni for 72 h, which is higher than those of (Ti_0.8Mo_0.2)C-40Ni for 96 h. On the other hand, the coefficient of variation for hard phase of the both (Ti_0.8Mo_0.2)C-40Ni were almost same.

View full abstract

Spring applications require materials that possess a low Young’s modulus and high strength, in addition to having a lower alloying percentage for reduced costs. In this study, a new low-cost β-type titanium alloy with a lower alloying percentage than conventional β-type alloys was developed for spring applications using [Al]_eq and [Mo]_eq. The alloy is located in the near-β region and its β transus temperature is about 1023 K (750°C). This alloy could be cold rolled to a reduction ratio of 86.7% without any intermediate heat treatment. The solutionized alloy exhibits an ultimate strength of 925 MPa, a 0.2% proof stress of 910 MPa, an elongation of 18%, and a Young’s modulus of 78 GPa; the comprehensive characteristics are better than those of conventionally used alloys (Ti-15-3 and βC) for spring applications.

View full abstract

The diffusivity and solubility limit of Cu in A533B steel, which is used in reactor pressure vessels, were studied by atom probe tomography (APT). Cu-A533B steel diffusion couples were annealed at temperatures of 550, 600, and 700°C, and the resulting Cu concentration profiles were measured. For all annealing temperatures, the diffusivity of Cu in A533B steel were found to be 2–3 times higher than that in pure Fe, although the solubility limit of Cu was similar. APT was also used to study the effect of the grain boundary (GB) diffusion. The results indicated that no Cu segregation occurred at GB near the Cu/A533B steel interface, which may imply that GB diffusion of Cu was not effective in A533B steel.

View full abstract

Fatigue is an important factor of failure of structures such as bridges, buildings, etc. To prevent the failure, a sensing method of fatigue damage is desired. In previous studies, it was demonstrated that smart stress-memory patch is a suitable and effective method for fatigue monitoring, because it is possible to evaluate a number of fatigue cycles and stress amplitude of structure wirelessly. However, there are still some problems on the conductive property. For instance, using the conventional shape of conductive film, it was found out that the crack length could not be estimated accurately because sometimes the resistance of the conductive film was unstable and did not increase monotonically as the crack length increased. Moreover, effects of environment factors such as temperature and strain have not been figured out. The objective of this research is to clarify the effects of fabrication method, shape of conductive film and environment factors on conductive property of smart stress-memory patch and to improve the sensitivity on the crack length measurement. The sensitivity of the smart patch was evaluated by changing the fabrication procedure and the shape of conductive film under strain-controlled fatigue testing. It was shown that the effects of strain could be ignored under atmosphere environment and the effect of temperature could be ignored until around 65°C.

View full abstract

In this study, Fe–In (Fe–IIIB system) alloys of ferromagnetic thin films supersaturated with indium were prepared by a triode-type ion-plating process with dual vapor sources. The preparation of the supersaturated Fe–In thin films is discussed on the basis of the effect of excess energy on the nanostructure of thin films. The kinetic energy of ions and the ionization rate in evaporation particles were measured using a Langmuir probe and a Faraday cup, respectively. The excess energy of the ion-plating process increased with increasing applied bias voltage of a discharge electrode. X-ray diffraction analysis showed that crystal structures of the supersaturated film samples were α-Fe bcc structures of an iron solid solution alloy. The ion-plating process can control the solubility limit and nanostructure of iron alloy thin films.

View full abstract

Urchin structured nickel fine particles were successfully obtained by the hydrazine reduction of NiCl₂·6H₂O in ethanol. The particle structures, particularly the aspect ratios of the nickel nanoneedles on the surface, were controlled by changing the sequence of the addition of hydrazine and sodium hydroxide. These particles were not stabilized by organic compounds. In situ TEM observations at high temperatures revealed that the obtained fine particles began to deform at 350°C.

View full abstract

Tape length-dependence of voltage–current curve, critical current and n-value in a coated conductor with a local crack were studied by modeling analysis. In calculation, the specimen length was varied in the range of 1.5 to 18 cm where the influence of cracking of superconducting layer is sharply reflected in the voltage–current curve. The following results were obtained, which can be utilized for analysis and interpretation of the experimental results under applied tensile stress in laboratory scale of specimen length. The existence of a crack changed the critical current and n-value through the decrease in current-transportable cross-sectional area of the superconducting layer and the current shunting in the cracked cross-section for any specimen length and any crack size, while the extent of the change was dependent on specimen length and crack size. When the crack was large, critical current increased slightly and n-value decreased significantly with increasing specimen length due to the enhanced shunting current. On the other hand, when the crack was small, critical current increased slightly with specimen length due to the enhanced shunting current similarly to the case of large crack, but n-value decreased with increasing specimen length due to the enhanced shunting current but then it increased due to the enhanced voltage-development at higher voltage in the non-cracked part. Also, the features of the dependence of the relation of n-value to critical current on specimen length were revealed; the decrease in n-value with decreasing critical current became sharper for longer specimen.

View full abstract

Zeolite Na-X and Na-A were synthesized by mechanochemical activation of pyrophyllite and pyrophyllite-gibbsite mixture followed by hydrothermal reaction in NaOH solution at 75°C under atmospheric pressure. The formation of zeolite Na-X and Na-A was depended on the degree of activation caused by grinding; i.e., grinding accelerated the dissolution of loosely bonded Si substances rather than Al ones of the ground pyrophyllite particles leading the Si/Al molar ratio close to 1.2, which is favorable for the formation of zeolite Na-X. The mixed grinding of pyrophyllite and gibbsite enabled us to synthesize zeolite Na-A monophase. In the early stage of grinding within 60 min, the hydroxysodalite (HS) phase was detected, however, HS disappeared completely when the grinding time extended to 120 min. The highest crystallinity (I/I₀) of zeolite Na-A synthesized was estimated to 0.93 at the mixture with Si/Al molar ratio of 1.2.

View full abstract

The adsorption characteristics of Co(II) and Mn(II) ions on mesoporous silica SBA15 were investigated. SBA15 was synthesized from the silicate precursor tetraethyl-orthosilicate (TEOS), and it was functionalized with ethylene-diamine-tetra-acetic-acid (EDTA) and N,N-dimethyl-acetamide (DMAC), which consists of the amine functional groups. It was also characterized by nitrogen adsorption–desorption analysis, element analysis (EA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The adsorption capacities of EDTA functionalized SBA15 for Co(II) and DMAC functionalized SBA15 for Mn(II) in a single component system were found to be 10.12 mg/g and 6.8 mg/g, respectively. These values are about 10 times higher than that of as-synthesized SBA15. The adsorption isotherms and kinetics data were found to follow the Langmuir adsorption isotherm model and the Pseudo-second order kinetic model (r² > 0.99). After the 5 adsorption cycles, over 90% regeneration efficiency was achieved for the functionalized SBA15, which would be applied for recovery of the metals.

View full abstract

The internal structure of different types of graphite commonly found in the ductile cast iron were investigated by TEM technique for TEM samples prepared by FIB method to understand their nucleation and growth. Spheroidal and vermicular graphite were observed in the ductile cast iron with spheroidizing treatment. Flake graphite was observed in the same cast iron without the spheroidizing treatment. The spheroidal graphite had a three-fold internal structure, with an amorphous-like central region, annual rings of a layered intermediate region, and an outer region made up of large polygonal crystalline platelets in a mosaic-like structure. The vermicular and flake graphite had a similar to that of the outer region of the spheroidal graphite, in that it consisted of similar crystalline platelets.

View full abstract

Mg–Li system alloys with over 11 mass% Li have an excellent cold-workability in Mg alloys due to the bcc-structured crystal system. However this system alloys have poor corrosion resistance caused by Li solid-solution alloy. The corrosion resistance of conventional hcp-Mg alloys is influenced by the composition of impurity elements. Particularly, minute iron element deteriorates the corrosion resistance of Mg alloy and there is a threshold concentration on the corrosion rate in Mg alloys. In this study, the effect of iron element on the corrosion resistance of Mg–Li alloy was investigated by addition of iron. The corrosion resistance of Mg–Li with no Fe addition was higher than conventional Mg alloy. The corrosion rate of Mg–Li alloy increased with increasing iron concentration. However, there is no threshold iron concentration affected to the corrosion resistance on Mg–Li alloy.

View full abstract

For explaining about the quantized Barkhausen jump that is observed in iron nanowires system, we introduced the two type spin Josephson junction models. One type of these system are composed of the sandwich structure by FM (ferromagnet)/AM (anti ferromagnet)/FM junction, and its dual junction is consists of the sandwich structure by AF/FM/AF junction. In order to apply to spintronics technology these spin junction models, we constructed a dual control theory by pseudo-spin quantum Hall effect.

View full abstract

Each electrical resistivity of the ternary solder alloy of tin–copper–sulfur was compared to that of the binary solder alloy of tin–copper. A mixture of various tin, copper, and sulfur powder compositions was prepared by adding different amounts of sulfur into a eutectic composition of tin and copper. After each specimen axially compressed with 10 MPa was sintered at 250°C, tin sulfide was induced in the solder alloy because sulfur reacted with tin. Simultaneously, the oxide layers of the solder alloy were removed through a complicated combustion reaction between tin sulfide and tin oxide. As a result, the electrical resistivity of the ternary solder alloy (Sn-0.70Cu-0.32S) having 0.32 mass% of sulfur was reduced to at most 10.56 µΩ·cm, compared to 12.47 µΩ·cm of the binary solder alloy (Sn-0.70Cu) without sulfur.

View full abstract

The effect of Cu addition on the soft magnetic properties of Fe–Zr–Si amorphous alloy was investigated by X-ray analysis, TEM observation, and B-H curve tracer. As a melt-spun amorphous ribbon sample was annealed above the crystallization onset temperature, very fine α-Fe particles smaller than ∼15 nm were precipitated and uniformly distributed in an amorphous matrix. Cu addition to Fe–Zr–Si amorphous alloy annealed above the crystallization onset temperature resulted in decreased coercivity and increased saturation magnetization and permeability.

View full abstract