The thermal stability and hydrogen permeability of Ni₄₂Zr₃₀Nb_28−xTa_x (x=0,7,14,21,28) amorphous alloys have been studied in the present work. The substitution of Nb by Ta was found to be effective in improving the thermal stability of the Ni₄₂Zr₃₀Nb₂₈ amorphous alloy. The onset crystallization temperature of the Ni₄₂Zr₃₀Nb_28−xTa_x amorphous alloys was increased by 58 K from 807 K for Ta-free composition to 865 K for Ni₄₂Zr₃₀Ta₂₈ due to the Ta addition. The hydrogen permeability of the Pd-coated Ni₄₂Zr₃₀Ta₂₈ amorphous membrane was measured to be about 0.86×10⁻⁸ mol·m⁻¹·s⁻¹·Pa^−1⁄2 at 673 K, which is slightly lower than that of the Pd-coated Ni₄₂Zr₃₀Nb₂₈ amorphous membrane. The hydrogen permeability of the Ni₄₂Zr₃₀Ta₂₈ amorphous membrane was revealed to be more temperature dependent in comparison to that of the reference membrane. The higher thermal stability combined with good hydrogen permeability give rise to the possibility of the practical use for Ni₄₂Zr₃₀Ta₂₈ amorphous alloy as a dense metal membrane operating at higher temperatures.

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We have evaluated the predictive ability of a simple method combing the efficient cluster packing model of metallic glasses proposed by Miracle, chemical mixing enthalpy and the normalized configurational entropy S_config⁄R in rapidly locating the bulk metallic glass (BMG)-forming composition region, in four multicomponent alloy systems. It is shown that the BMG-forming regions are similar in the topologically and chemically equivalent La-Al-Co and Ce-Al-Co alloy systems. However, in the topologically equivalent Zr-Ti-Cu-Ni and Zr-Ti-Al-Cu-Ni alloy systems, the BMG-forming regions are quite different due to the difference in chemical bonding between constituents. BMG formation is most probably a compromise between topological and chemical effects. This method could be a new approach to rapidly locate BMG-forming composition region in multicomponent alloy systems, in which eutectic compositions are difficult to be measured in experiments.

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A small amount of boron was added to Ni₆₀Pd₂₀P₂₀ and Ni₆₅Pd₁₅P₂₀ alloys. The alloys containing 3 at% boron showed improved thermal stability and glass-forming ability. The supercooled liquid region of as-spun ribbons was enlarged by about 10 K for both Ni₆₀Pd₂₀P₁₇B₃ and Ni₆₅Pd₁₅P₁₇B₃ alloys. The critical diameters for glass formation were increased up to 15 mm for Ni₆₀Pd₂₀P₁₇B₃ and 10 mm for Ni₆₅Pd₁₅P₁₇B₃, respectively. The reason of the minor B addition leading to the significant improvements of thermal stability and glass-forming ability was investigated.

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The heat capacity of a Ni₃₆Nb₂₄Zr₄₀ glassy alloy was measured by adiabatic calorimetry from 13 to 300 K. The smoothed values of molar heat capacity were calculated from the data using a least-squares method. The standard enthalpy, entropy, and Gibbs energy were calculated from the smoothed heat capacity values. Assuming H(0)=0 and S(0)=0 at 0 K, the heat capacity, enthalpy, entropy, and Gibbs energy at 298.15 K are 24.91 J·K⁻¹·mol⁻¹, 5.252 kJ·mol⁻¹, 36.45 J·K⁻¹·mol⁻¹, and −5.615 kJ·mol⁻¹, respectively.

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Fine-grained tungsten carbide copper (WC-Cu) cemented carbide was sintered via spark plasma sintering at 1773 K using a fine WC powder with a mean particle size of 0.11 μm. The mechanical properties were compared with tungsten carbide cobalt (WC-Co) cemented carbide and a binderless WC-sintered material. The Vickers hardness and fracture toughness obtained by the indentation fracture method for WC-10 mass% Cu cemented carbide were ∼1600 and ∼10 MPa·m^0.5, respectively, which were in no way inferior to the values for WC-Co cemented carbide. Increasing the amount of copper improved the toughness and degraded the hardness. WC-Cu cemented carbide exhibited much higher creep resistance than WC-Co cemented carbide, and was the same as the binderless WC-sintered body up to 1273 K.

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The dealloying behavior of Cu₆₀Zr₃₀Ti₁₀ metallic glass was investigated under free corrosion conditions using hydrofluoric acid (HF) solutions at room temperature. After immersing in HF solutions with various concentrations (0.05, 0.1, 0.5 and 1 M) for 300 s, color of all samples changed to be pinkish or peachy, which was ascribed to Cu based on the XRD patterns. According to the SEM-EDS study, HF immersion selectively leached the Zr and Ti elements, leaving Cu behind. Increasing the HF concentration increased the dealloying rate. Moreover, the HF concentration strongly influenced the surface morphology of the resulting Cu.

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Resistance welding of Zr₅₅Cu₃₀Al₁₀Ni₅ metallic glass sheets was investigated at 723 K in a supercooled liquid region. The welding time was changed from 5 s to 20 s at 723 K. The joint interface of the metallic glass was no defect and no crack. X-ray diffraction technique of the bonding interface of specimens was performed. The specimens showed halo patterns showing existence of only glassy phase, when the welding time was 5 s and 10 s. X-ray diffraction patterns of specimen bonded for 20 s showed crystalline peaks with halo patterns for the welding for 20 s. The crystalline phase at the bonding interface was small. Transmission electron micrograph at the bonding interface showed nanostructures of NiZr₂ and Al₅Ni₃Zr₂.

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The interfacial microstructure and thermal stability of Zr₅₅Cu₃₀Ni₅Al₁₀ metallic glass joints formed by ultrasonic bonding were investigated. The analysis of interfacial microstructure by scanning electron microscopy and transmission electron microscopy has proven the successful formation of a considerably broad adhered area free of devitrification by ultrasonic bonding without external heating. The thermal analysis of the as-prepared Zr₅₅Cu₃₀Ni₅Al₁₀ metallic glass by differential scanning calorimetry has revealed the change in the devitrification temperature of Zr₅₅Cu₃₀Ni₅Al₁₀ metallic glass depending on the heating rate. The direct measurement of the temperature at the interface during ultrasonic bonding has clarified the thermal history at the interface. The temperature exceeds barely the glass-transition temperature (T_g) and the total time exceeding T_g is very short. It is also suggested that the temperature starts to decrease while the ultrasonic vibration is being applied due to the suppression of frictional sliding by adhesion. As a result, the thermal stability of the metallic glass is not deteriorated by ultrasonic bonding.

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A tube consisted of chitin/chitosan nanofibers is one of the candidates to support nerve regeneration. However, chitin/chitosan would cause inflammation when implanted in human body. This study indicates that chitosan nanofibers (degree of deacetylation; 78% and 93%) could be modified by alternate soaking in calcium and phosphate solutions, resulting in the improvement of their biocompatibility in terms of both in vitro cell culture experiment and in vivo animal test. Deacetylation of the chitosan nanofibers appeared to have little effect on in vitro and in vivo behaviors after 3 days. However, the alternate soaking process clearly improved in vitro and in vivo responses against the chitosan nanofibers. During the process, the surface morphology of the chitosan nanofiber was not changed, i.e. no hydroxyapatite was deposited due to the limited number of soaking. Thus, the surface chemical and physical states of the modified chitosan nanofiber such as surface charge, surface free-energy, and wettability was found to influence both the cell attachment and inflammation.

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Gas-atomized Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 metallic glassy alloy powders were consolidated by a spark plasma sintering (SPS) process. The densification behavior during the SPS process as well as the structure, thermal stability and mechanical properties of the sintered specimens were investigated. The glassy alloy powders were densified rapidly when the temperature exceeded about 740 K. The density of the sintered specimens increased with an increase in sintering temperature. The specimens with full densification and no crystallization were obtained by the SPS process at a sintering temperature of 773 K with a loading pressure of 600 MPa. The sintered specimens exhibit high-strength and can meet large-size requirement.

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Magnetic pulse welding was applied to the lap joining of crystalline pure aluminum and metallic glass (Zr₄₈Cu₃₆Al₈Ag₈ and Cu₅₀Zr_42.5Al_7.5) and interfacial microstructure was examined. The metallic glass fractured in brittle manner in conventional plate layout. However, Al/metallic glass joints were successfully obtained without fragmentation of brittle metallic glass by setting a soft aluminum plate as a shock absorber behind the metallic glass. The welding interface exhibited characteristic wavy morphology as well as that of metal/metal joints. Thin layer with medium chemical composition of the metallic glass and Al was also produced at the welding interface. No chemical composition change took place in the area of 2 μm and more away from each matrix/intermediate layer interface. Also, no hardness change of Al matrix was detected in the area of 2 μm and more away from Al/intermediate layer interface. Hardness of metallic glass matrix close to the welding interface was not constant, however, TEM observation revealed that the metallic glass matrix retained the amorphous structure after the welding. These obtained results are considered to indicate that the metallic glass did not crystallize after the magnetic pulse welding.

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Fe-based bulk glassy alloys (BGAs) are known to have great potential for structural applications because of their high strength and relatively low material cost. However, their brittle nature hinders further applications. We have recently developed a new ductile (Fe_0.76Si_0.096B_0.084P_0.06)_99.9Cu_0.1 BGA with a strength of 3.3 GPa and a large plastic strain of about 4% in compression. A well developed vein pattern on the fracture surface and highly-dense multiple shear bands on the surface of the specimen were observed. A large number of α-Fe like clusters (<10 nm) are found to disperse in the matrix glass. These clusters possibly act as nucleation sites for the α-Fe nanocrystallization in slipping shear bands dynamically. This results in development of the multiple shear bands causing highly improved plasticity in the (Fe_0.76Si_0.096B_0.084P_0.06)_99.9Cu_0.1 BGA.

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Au₄₀Si_17-20Cu_28-30Ag_5-7Pd₅ glassy alloys showed a wide supercooled liquid region of 42–53 K and a large reduced glass transition temperature of 0.568–0.605, indicating high stabilization of supercooled liquid and high glass-forming ability (GFA). The best GFA was obtained from Au₄₀Si₂₀Cu₂₈Ag₇Pd₅ alloy, and a fully glassy sample with a diameter of 6 mm could be fabricated by copper mold casting. The bulk glassy alloys exhibited very low T_g of 400–424 K, high fracture strength of over 1100 MPa, and corrosion resistance superior to SUS316L in 1 N H₂SO₄ solution.

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Dissimilar laser brazing of boron nitride ceramics and cemented carbide has been investigated by using silver-copper-titanium braze alloys with different titanium contents of up to 2.80 mass%; efficient bond strength was achieved using brazes with more than 1.25 mass% of titanium. The contact angle between hexagonal boron nitride ceramics and the molten braze, which was measured by the sessile drop method at 1123 K, decreased to less than 30° when the Ti content was over 0.41 mass%. The difference in the wetting property determined by laser brazing method and that by sessile drop method is attributed to the difference in the heating process of the two methods. Structural analysis of the interface between the boron nitride ceramics and the braze was carried out by electron probe micro-analysis (EPMA).

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A Zr₅₅Cu₃₀Ni₅Al₁₀ bulk metallic glass plate was successfully welded below its crystallization temperature by friction stir welding. The flash formation and heat concentration at the shoulder edge was minimized using a wider tool with the shoulder surface recessed by an angle of 3°. To evaluate the crystallization of the weld, the microstructure and mechanical properties were analyzed using DSC, XRD, TEM, and micro-hardness. As a result, it was found that the amorphous structure and original mechanical properties were maintained throughout the entire joint.

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The Ni₅₇Nb₁₉Zr₁₉Ta₅ glassy alloy possesses high corrosion resistance in severe environments, i.e. boiling 6 N HNO₃ and 6 N HNO₃ + 5 g/l Cr⁶⁺ solutions. In both solutions, the corrosion resistance of the Ni₅₇Nb₁₉Zr₁₉Ta₅ alloy is much better than that of NAR-310Nb stainless steel which is developed as nitric acid corrosion resistant stainless steel. XPS analysis reveals that the high corrosion resistance of the Ni-based glassy alloys is due to the formation of the highly protective passive film composed exclusively of Nb⁵⁺ and Ta⁵⁺ cations after immersion in the solution without Cr⁶⁺ ions, and Nb⁵⁺, Ta⁵⁺ and Cr³⁺ cations after immersion in the solution with Cr⁶⁺ ions.

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The authors successfully formed a bond between bioactive hydroxyapatite (HA) ceramics and titanium (Ti)-based bulk metallic glasses (Ti₄₀Zr₁₀Cu₃₆Pd₁₄: BMG) through a growing integrated layer (GIL) to develop a new type of biomaterial. The GILs were formed on the BMG surfaces by hydrothermal-electrochemical (HE) techniques. The BMG substrates were treated in a 5 mol/L NaOH solution at 90°C for 600, 2400 and 7200 seconds while a constant electric current of 50 mA/mm² was maintained between the electrodes. Then the BMG disks with the GIL and a powder mixture of calcium phosphate di-hydrate (CaHPO₄·2H₂O) and calcium hydroxide (Ca(OH)₂) were simultaneously treated with an autoclave for hydrothermal hot-pressing (HHP) (150°C, 40 MPa, 7.2 ks). Direct bonding between the HA ceramics and the BMG disks could be achieved through the above processing method. Scanning electron microscopy observations was conducted around the interface between BMG and HA. The bonding model of the bonding BMG and HA was suggested. The bonding was achieved through the amorphous nano-meshed layer consumption during the HHP processing. Sufficient thickness of GIL derived from hydrothermal-electrochemical treatment for over 2.4 ks is needed for the bonding.

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In this study, the microstructure and electrochemical properties of PVD TiN and (Ti, Al) N coatings on Ti₄₀Zr₁₀Cu₃₆Pd₁₄ bulk metallic glass were investigated. The microstructure of TiN or (Ti, Al) N coatings, the BMG substrate and the interface was investigated by high-resolution transmission electron microscopy. The electrochemical behavior of PVD coatings on the Ti-based BMG was studied by measuring potentiodynamic polarization curves in Hanks’ solution. HREM observation revealed that the sputtering TiN ((Ti, Al) N) coating consisted of cubic TiN ((Ti, Al) N) phase with a lattice parameter of 0.426 (0.422) nm in nanoscale. The polarization curves showed that the open circuit potential shifted to a more positive potential and the passive current density decreased due to the protective TiN or (Ti, Al) N coating.

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This study is concerned with the characterization of oxide layers formed on Ni-free stainless-steel and the immobilization of a silane coupling agent, i.e. γ-aminopropyltriethoxysilane (APS). The Ni-free stainless-steel was oxidized at three different temperatures, 800 K, 1000 K and 1200 K in air, and then the APS molecules were immobilized on the surface at room temperature. The surface of the samples was characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The composition of surface oxides formed through the oxidizing treatment was identified to be two types of oxide, namely Fe₂O₃ and Cr₂O₃. The atomic ratio of Cr to Fe+Cr increased with an increase in the oxidizing temperature. The amounts of APS immobilized on each surface followed the sequence of 1200 K < 1000 K < 800 K of the oxidizing temperature. It was found that the surface oxide formed at 800 K is the best carrier of APS under these conditions. It is apparent that Fe₂O₃ is more easily fixed by APS than Cr₂O₃.

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In order to improve the mechanical properties of Zr₅₅Al₁₀Ni₅Cu₃₀ metallic glass, tungsten-reinforced Zr₅₅Al₁₀Ni₅Cu₃₀ was developed. Tungsten particles with a diameter φ=100 μm were uniformly distributed into the matrix, exhibiting good wettability with the Zr₅₅Al₁₀Ni₅Cu₃₀ metallic glass matrix. Due to the extremely high melting temperature of tungsten, the tungsten particles coexisted with amorphous Zr₅₅Al₁₀Ni₅Cu₃₀, although a reaction layer of ZrW₂ and a crystallized matrix formed to a certain extent depending on the sample. Nevertheless, the total amount of crystallization in both the matrix and the reaction phases remained small. As the volume fraction of W was increased from 0 to 8.7%, the plastic strain increased from 0 to 1.3%, and the fracture strength increased from 1480 to 1870 MPa. The coefficient of thermal expansion of monolithic Zr₅₅Al₁₀Ni₅Cu₃₀ decreased from 10.4×10⁻⁶ K⁻¹ to 8.2×10⁻⁶ K⁻¹ in the case of the composite containing 30% W powder.

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A feasibility study has been conducted to determine whether the low temperature joining process such as soldering process and wire bonding process can be applied to join a bulk metallic glass (BMG) to a BMG and a BMG to a crystalline metal. Therefore, in order to evaluate the solderability of BMGs, the spread test of the solder was basically performed for three kind of BMGs in this study. As a result, Pd-based BMG exhibited a good wetting behavior of the solder at 503 K and 523 K. On the other hand, concerning Cu-based and Zr-based BMGs, there was no wetting of the solder on the surface of BMGs regardless of the peak temperature. Then the ultrasonic soldering process was tested to establish the joint process for BMGs. It was clear that the application of ultrasonic is effective to the soldering process.

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Magnetic properties are perhaps the most remarkable and unique properties of Fe-based amorphous alloys. To obtain high saturation magnetization, high Fe content is preferred. However, there is a strict upper limit of Fe content for the formation of a single amorphous structure with good magnetic softness. Fe-based amorphous alloys with high Fe content over the limit have an as-quenched structure consisting of coarse α-Fe grains in an amorphous matrix, which inevitably results in inferior magnetic softness. We have studied the effect of P and/or Cu additions on the microstructure of Fe-based amorphous alloys with high Fe content. The α-Fe grain size and the coercivity (H_c) decrease by the simultaneously adding P and Cu. The Fe-rich FeSiBPCu alloys with the optimized composition have an extremely small α-Fe-like phase of about 3 nm or smaller in a diameter, exhibits the higher J_s of about 1.67 T than that of the typical Fe-based amorphous alloy and show the low coercivity (H_c) of about 4 Am⁻¹ in an as-quenched state.

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Bulk metallic glass composed of Ti₄₀Zr₁₀Cu₃₆Pd₁₄ (Ti-Cu BMG) has superior mechanical properties compared to titanium metal, which makes it promising for new orthopedic implant applications. We studied improvement of the surface properties of Ti-Cu BMG, focusing on enhancing corrosion resistance and adding bioactivity with a methylsiloxane (MS) coating. The MS was prepared by hydrolysis polymerization of methyltriethoxysilane, and was coated onto Ti-Cu BMG by dipping and drying at 80 °C. The ability of the MS coating to reduce Cu ion elution from the Ti-Cu BMG was investigated by autoclaving coated disks at 121 °C for one hour in a hydrochloric acid solution controlled at pH 0.4 to 4. Cu ion elution from MS-coated Ti-Cu BMG was very low (less than 1000 ppb); this value was less than half that from uncoated Ti-Cu BMG. The MS coating retained sufficient adhesion to the Ti-Cu BMG even after the autoclave tests. The mechanism of Cu ion elution through the MS coating film appeared to be via steady-state diffusion, and the degree of reduction in ion elution was dependent on the coating thickness. Bioactivity was added by coating the Ti-Cu BMG with a calcium-containing methylsiloxane (MS-Ca) layer. The coating formed a double-layered structure of bone-like apatite after soaking in a simulated body fluid for 3 days. A series of tests indicated that MS-Ca and MS coatings were useful for improving corrosion resistance and for adding bioactivity. MS coated Ti-Cu BMG is therefore a promising material for biomedical applications.

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We have investigated the origin of significantly high thermal stability of Zr₅₀Cu₄₀Al₁₀ metallic glass and its crystallization behavior as compared to Zr₇₀Cu₂₀Al₁₀ and Zr₇₀Cu₃₀ glassy alloys, by differential scanning calorimetry (DSC), x-ray diffraction (XRD) and resonant ultrasound spectroscopy (RUS) techniques. It was found from XRD and DSC analyses that (i) constituent atoms in Zr₅₀Cu₄₀Al₁₀ are highly close-packed in a glassy state and (ii) Zr₅₀Cu₄₀Al₁₀ glass shows a complicated crystallization process when it is heated at conventional heating rates, but when it is rapidly heated, the ordered B2-type ZrCu is dominantly formed. The high thermal stability and its crystallization behavior are discussed in terms of the long-range-diffusion of atoms and elastic strain energy.

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Transfer thermal plasma of Ar was deposited on the surface of Na₂O-SiO₂ molten slag at about 1200 to 1350°C using a hybrid plasma furnace composed of transfer- and non-transfer plasma. The dependence of the transferred-type thermal plasma current on oxygen potential of the glass has been studied using an oxygen sensor made of solid electrolyte. During application of the transfer plasma with current less than 0.4 A, the oxygen partial pressure at the slag surface increased to 1×10⁻³ from 1×10⁻¹⁶ atm and that in the out gas of Ar was decreased from 1×10⁻⁴ to 1×10⁻¹² or 1×10⁻¹⁴ atm. This paper describes a physical model aimed at studying the most dominant parameter for sheath forming from the above mentioned.

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Different morphologies of α-Fe₂O₃ films including particles, porous, granular and nanosheets have been prepared by directly oxidizing the as-deposited Fe films in air. The effects of the heating temperature, duration time and the rate of heating have been systematically studied. By adjusting the rapidly oxidation conditions, one can easily control the morphology of α-Fe₂O₃ films from clusters of particles to porous films, and finally to granular films. In addition, through the oxidation process at the low heating rate, α-Fe₂O₃ nanosheets can be easily fabricated on the Si substrate.

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Static tensile tests, dynamic mechanical analysis as well as electron microscopy were used to characterize the macromechanical properties of MWNT-filled polycarbonate composites. Meanwhile the behavior of the nanotube/polymer interfaces was examined by changing nanotube contents and measuring electrical conductivity and dielectric spectroscopy. When the interface achieved the state of percolation (2 mass% MWNT), strain of fracture of MWNT-filled polycarbonate composites reached a peak of 9.3%, elastic modulus increased 30% comparing to pure polycarbonate and damping ratio bottomed out.

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The authors previously reported that even a trace level of copper (0.01% Cu) acts as a sulfide-former to form copper sulfide (Cu-S) in non-Ti-added steel in which Mn has been thought to be the only sulfide-former so far. A new concept of copper-related sulfide precipitation is now extended to Ti-added steel. In addition, the total sulfide precipitation in Ti-added steel is reconfigured with the new knowledge of Cu-S. The new concept is shown in three consecutive papers. This first paper focuses on the sulfide precipitation in austenite-heat-treated Ti-added steel.
Through TEM observation and quantitative chemical analysis, it is reported that the sulfide precipitation in austenite-heat-treated Ti-added steel reflects not only the precipitation in the austenite region but also the inevitable precipitation behavior during the cooling process from austenite to ferrite region, especially trace-level-Cu-induced Cu-S precipitation in ferrite region during rapid cooling. The mechanism of the inevitable sulfide precipitation during the cooling process is mainly based upon TiS-decomposition-induced morphological change and the re-precipitation of sulfur which remains solute over precipitatable limit during the heat-treatment in austenite region, and is precisely discussed in relation with Cu-S precipitation.

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This report is the second paper in three consecutive papers to know the whole sulfide precipitation in Ti-added steel by adding a new knowledge that even a trace level of copper (0.01%Cu) acts as a sulfide-former to form copper sulfide (Cu-S). The second paper focuses on the sulfide precipitation in ferrite region in Ti-added steel, especially in real-produced hot-rolled and annealed steel sheets.
Although it has been believed that the sulfide precipitation is completed only in austenite region except for a few limited papers, Ti₄C₂S₂, MnS and Cu-S are really formed in ferrite region. When as-hot-rolled Ti-added steel is annealed, the sulfide precipitation transforms morphologically and compositionally. The phenomenon can be explained through the same mechanism in the first paper that TiS-decomposition-induced re-solute sulfur is re-precipitated. When annealed in ferrite region, already-precipitated TiS is changed into Ti₄C₂S₂ and re-solute sulfur comes out along the estimated reaction “4TiS+2[C]→Ti₄C₂S₂+2[S]”, and it is re-precipitated in ferrite region as other precipitates (Ti₄C₂S₂, MnS and Cu-S). The precipitation of Cu-S is estimated to occur at the lowest temperature among re-precipitated sulfides, and therefore is affected by the precedent sulfide precipitation phenomena.

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This report corresponds to the third paper in three consecutive papers to know the whole sulfide precipitation in Ti-added steel by adding a new knowledge that even a trace level of copper (0.01%Cu) acts as a sulfide-former. The authors show the strange phenomenon of copper sulfide in Ti-added steel in long-time-annealing in ferrite region. When annealed for short time (ex. 90 s), much of Cu-S is precipitated, but the amount of Cu-S is small at longer-time-annealing, while TiS reduces and Ti₄C₂S₂ increases monotonically. This phenomenon does not mean that Cu-S is initially formed and then dissolved away, but the Cu-S precipitation should be interpreted as causal evidence of “(re-)solute sulfur and its re-precipitation” along the same concept in the first and the second papers. Long-time-annealing means that our proposed reaction “4TiS + 2[C] → Ti₄C₂S₂ + 2[S]” proceeds rightward and the re-solute sulfur is re-precipitated as Ti₄C₂S₂ (and MnS). Consequently, the amount of Cu-S is small. In contrast, short-time-annealing is not long enough to stabilize re-solute sulfur as Ti₄C₂S₂ (and MnS) and much of sulfur still remains solute. Therefore the amount of Cu-S is increased.
Furthermore, the phenomena in three consecutive papers is organized into an integrated concept to understand the whole sulfide precipitation in Ti-added steel in both austenite and ferrite region.

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We investigated the effects of austempering and subzero treatment on the damping capacity in austempered ductile cast iron. The damping capacity of austempered ductile cast iron was rapidly increased by the austempering treatment, although it was not affected by the austempering temperature or time. After subjecting the austempered ductile cast iron to subzero treatment, the austenite was transformed into martensite, and the volume fraction of the martensite increased as the subzero treatment temperature decreased. The subzero treatment sharply increased the damping capacity of the austempered ductile cast iron. However, the damping capacity gradually increased as the subzero treatment temperature decreased. By increasing the subzero treatment time, the damping capacity rapidly increased until the subzero treatment time reached 30 min, after which it increased gradually. By increasing the volume fraction of the martensite, the damping capacity was rapidly increased until the volume fraction was 5%, beyond which it increased gradually.

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This study commences by performing an experimental investigation to measure the temperature distribution within a casting system comprising a cylindrical aluminum casting and a green-sand mold. The experimental temperature measurements are then used to compute the effective heat transfer coefficient at the mold/metal interface using four different formulae. In the temperature measurement, a symmetric arrangement of thermocouples is proposed and proven to be feasible, which can reduce the influence of heat-transfer and solidification characteristics in a casting experiment due to the close-spaced thermocouples. As an important role in the calculation of the effective heat transfer coefficient, the metal temperature at the mold/metal interface is calculated using an extrapolation technique and an inverse scheme. A lump capacity method is also utilized to estimate the average values of the effective heat transfer coefficients, which are consistent with those of the previous effective heat transfer coefficients. The numerical results obtained for the temperature curves in the green-sand mold are found to agree well with the experimental profiles. Finally, with the effective heat transfer coefficients obtained above, a finite element simulation is performed using FIDAP software to model the evolution of the temperature distribution within the casting during the solidification process. The predicted solidification time is found to be in reasonable agreement with that observed in the experimental casting process.

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Mg alloys containing Mg₂Si and Mg₂Sn phases are promising inexpensive heat-resistant magnesium alloys for automobile engine applications. This study examined the microstructure and creep properties of Mg-6Sn-5Al-2Si alloys. The microstructures of these alloys were characterized by the presence of thermally stable Mg₂Si and Mg₂Sn and thermally unstable Mg₁₇Al₁₂ precipitates. Creep tests were performed at 30, 50 and 70 MPa at 150, 180 and 200°C. Trace amounts of Sr and Zn were added to these alloys to improve the mechanical properties by modifying the precipitates in the matrix. The influence of the combined addition of Sr and Zn on the microstructure and mechanical properties was also studied. Analyses of the mechanical properties indicated that Sr and Zn addition improved the tensile strength but decreased the creep resistance.

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TiB and TiC reinforced titanium matrix composite was in situ synthesized by consumable vacuum arc remelting and hot-forging based on reaction between titanium, B₄C powder and graphite powder. The phases were analyzed through X-ray diffraction. The microstructure was examined by means of optical microscopy (OM) and scanning electron microscopy (SEM). Creep behavior was tested at three temperatures: 600°C, 650°C and 700°C respectively within a stress range 100∼350 MPa. Class I solution behavior was observed and true stress exponent n=3.5 was obtained for the composite. Threshold stress, load transfer and micro-structural strengthening are considered for reasonably explaining the creep behaviour. It is concluded that strengthening mechanism can be owed to co-effect of all the three factors. True activation energy equal to 343 kJ/mol was obtained after compensation by threshold stress.

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Though closed cell Al foams have extremely low density and high energy absorption performance, they are expected to improve the compressive strength and to clear the dynamic compression characteristics for much more practical application.
In this research, the effects of density, test piece size and alloying (Al-10.0 mass%Zn-0.3 mass%Mg) on the uniaxial static and dynamic compressive strength was examined. Dynamic compressive strength were examined by the Split Hopkinson Pressure Bar (SHPB) method and the drop weight impact test device.
As a result, the dynamic plateau stress of pure Al foams was about 1.3 times larger than the static one, and there was a scale effect of test pieces.
The dynamic plateau stress of Al alloy foams was about 1.1 times larger than the static one, and there was less scale effect of test pieces for plateau stress because the cell walls of Al alloy foams tend to collapse owing to brittleness by alloying.
The effect of the inner gas enclosed in cells on the dynamic response of pure Al foams by SHPB is also discussed. When providing inner gas vent holes, dynamic plateau stress decreased close to the static one. With Al foams, the increasing in dynamic plateau stress may be caused by the inner gas pressure rising under dynamic compressive conditions as well as influence of the strength and ductility of the cell wall.

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During thixomolding^® of Mg alloys, fine grains (size of ∼10 μm) and continuous eutectic compounds are formed along grain boundaries. These compounds are partly responsible for the superior creep strength of Mg alloys. In this study, we investigate the effects of eutectic compounds formed along grain boundaries in thixomolded^® Mg₉₆Zn₂Y₂ on creep deformation at 573 K. By performing microstructure analyses, we find that two types of continuous eutectic compounds—Mg₃Y₂Zn₃ and Mg₁₂YZn—are formed in the alloy. The strain rate of Mg₉₆Zn₂Y₂ is about two orders of magnitude lower than that of a heat-resistant alloy Mg₉₃Al₅Ca₂ (Mg-6 mass%Al-3 mass%Ca) at 573 K. The stress exponent n at 573 K is approximately 7, and it is considered that creep deformation is controlled by dislocation motion. All scribe lines produced on a specimen of Mg₉₆Zn₂Y₂ are curved. Furthermore, in the case of a specimen with a creep strain of 7%, no abrupt steps are observed at grain boundaries and interfaces between the α-Mg matrix and eutectic compounds. Our results indicate that eutectic compounds formed along grain boundaries are effective in suppressing grain boundary sliding.

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It was found that aluminum alkoxide reaction of aluminum alloy 6063 occurs in ethyl alcohol containing aluminum chloride. The reaction is explained by the superimposition of Al/Al³⁺ reaction as the anodic reaction and ethanol/ethlate reaction as the cathodic reaction. In an environment containing chloride ions, an Al/AlCl₃ reaction participates in anodic reaction above and then becomes dominant anodic reaction. Rate of aluminum dissolution by the Al/AlCl₃ anodic reaction in ethyl alcohol is accelerated due to the fast system which has low polarization resistance. It is shown that aluminum alkoxide (aluminumtriethoxide) as corrosion product will produce hydrogen peroxide on the way of chain process of productions of ethyl chloride, diethyether and ethyether peroxide. It is also pointed out that the hydrogen peroxide will play a strong cathodic role in further pitting corrosion process.

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Corrosion behaviors of DP-type and TRIP-type cold rolled steel sheet have been investigated using cathodic Tafel extrapolation test and immersion test, measuring nano-scale hardness of various phases and the volume fraction of various phases, and analyzing inclusion and nitride. Based upon nano-scale hardness of various phases before and after potentiodynamic anodic polarization test in deaerated 5 mass% NaCl at 35°C, the phase with the most inferior corrosion resistance in DP-type steel is martensite (α′) and that in TRIP-type steel is bainite (α_B). The reasons why corrosion rate of TRIP-type steel is lower than that of DP-type steel are first, the volume fraction (39.8 vol%) of bainite (α_B) in TRIP-type steel is higher than that (15.9 vol%) of martensite (α′) in DP-type steel and second, the corrosion resistance of oxide and nitride formed in TRIP-type steel is more than that of sulfide formed in DP-type steel.

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The effects of basicity (the ratio between CaO and SiO₂) and FeO content on softening and melting temperatures of direct reduced iron (DRI) residual, otherwise known as slag, were investigated.
Sample slag pellets were prepared for two target compositions, CaO-SiO₂-10%MgO-5%Al₂O₃ and CaO-SiO₂-5%MgO-10%Al₂O₃. Two sets of experiments were conducted on the pellets: one varied basicity values between 1.83 and 0.55, and the other varied the FeO contents between 10% and 50% at constant basicity. The softening and melting process under elevated temperature was recorded using an optical softening-melting temperature measuring device and the temperature points were recorded at the four distinct shape changes of the sample pellets: initial deformation, sphere and hemisphere formation, and complete melting.
The lowest softening and melting temperatures of the CaO-SiO₂-5%MgO-10%Al₂O₃ samples occurred at a basicity of 0.55 while for the CaO-SiO2-10%MgO-5%Al₂O₃ samples it occurred at 0.70. This corresponds to the liquidus temperatures on the CaO-SiO₂-MgO-Al₂O₃ quaternary phase diagram. At constant basicity, the deformation temperature of CaO-SiO₂-10%MgO-5%Al₂O₃ samples was found to be higher than that of CaO-SiO₂-5%MgO-10%Al₂O₃ samples. Lastly, the addition of FeO below 20% to the CaO-SiO₂-MgO-Al₂O₃ system significantly decreased the softening and melting temperatures of the slag samples. However, further addition of FeO beyond 20% produced inconclusive results.

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The equilibration of a Ag-Pb-based melt with PbO-NaO_0.5 and PbO-CaO melts at 1273 K was investigated. A chemical equilibrium technique was used to carry out measurements. The oxygen partial pressure was measured by an electromotive force (EMF) method. The activity coefficient of AgO_0.5 in the PbO-NaO_0.5 and PbO-CaO melts and that of PbO in the PbO-NaO_0.5 melt was derived. The addition of NaO_0.5 to the PbO-based melt resulted in a slight decrease in the activity coefficient of AgO_0.5. However, the activity coefficient of PbO decreased remarkably with an increase in the concentration of NaO_0.5 in the PbO-based melt. Therefore, improved phase separation of Ag from the PbO-based melt was achieved by the addition NaO_0.5. The addition of CaO in the PbO-based melt did not cause any change in the activity coefficient of AgO_0.5.

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The authors attempted to use steel can pellets after removing the Al-Mg alloy of can’s cap part using differences in the melting point of steel and Al, for melt-casting spheroidal graphite cast iron in a high-frequency furnace. Then, they examined differences in the mechanical properties such as tensile strength and hardness and the microstructure of cast test specimens. Although tensile strength and hardness increased with an increase in the blending ratio of steel can pellets as an iron source, the specimen made by melting only steel can pellets as an iron source showed a remarkable drop in elongation. However, since abnormality in the microstructure was not recognized in all tested specimens, it was judged that material properties were not deteriorated when iron scrap was replaced with steel can pellets within the blending ratio of up to 60%. Judging from these test results, it is suggested that steel can pellets used in this experiment can be utilized as a raw material for spheroidal graphite cast iron in the blending ratio up to 60%.

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An alternating current (AC) was imposed upon the hypereutectic Mg-Si melt during solidification to modify the primary Mg₂Si crystals in the fixed temperature range between 700 and 630°C. The effects of current intensity and frequency have been investigated in the present study. For every sample, 200 primary Mg₂Si crystals were measured and 200 data were then statistically analyzed. The average size and standard deviation were used to evaluate the modification effect, including the refinement and uniformity of sizes of the modified primary Mg₂Si crystals. The results show that both frequency and current intensity were significant to determine the modification effect. When the current intensity was fixed at 60 A, the average size increased and uniformity of sizes of the primary Mg₂Si crystals improved with the increase in the frequency to 2 kHz. However, in the case that the frequency was fixed at 1 kHz, the statistical average size increased and uniformity of sizes improved with the increase in the current intensity to 60 A. With the further increase in the current intensity to 90 A, the statistical average size and uniformity of sizes had no obvious changes. The average size drastically decreased and uniformity of sizes remarkably improved with the increase in the estimated electromagnetic force to a critical value of about 126 Nm⁻³, corresponding to the current intensity of 60 A and frequency of 1 kHz. However, the average size was constant if the electromagnetic force exceeded the critical value.

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Lotus-type porous aluminum with cylindrical pores oriented in one direction was fabricated by a casting method utilizing the decomposition of moisture in a vacuum. Hydrogen decomposed from moisture is utilized for cylindrical pores to grow during unidirectional solidification. However, pores are not formed in the case of a casting in hydrogen or argon atmosphere, because hydrogen or argon gas pressure suppresses the pore growth. The porosity of lotus aluminum does not depend on the moisture amount, which indicates that the moisture amount is almost saturated within the amount used in this study. The average pore diameter does not depend on the moisture amount, because the pore diameter depends mainly on ambient pressure and solidification rate. The distribution of pores becomes homogeneous by decreasing melting temperature, because the rate of the reaction of moisture possibly becomes low (more suitable for pore growth) by decreasing the melting temperature.

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To improve the deposition efficiency of copper fine particles mean diameter around 5 μm onto metallic substrate surface in cold spray process, optimization in nozzle design was performed by numerical simulation. Particles velocity reached up to 585 m/s under the optimum conditions with originally designed nozzle based on the simulation results. In the spraying of copper particles onto normal steel substrate, lamellar-like microstructure was formed near the interface in the steel substrate. Correspondingly, remarkable hardness increase in this lamellar-like region of the steel substrate was recognized due to the higher velocity of the particles attained. Moreover, to reduce the bow shock effect especially for fine particles on the substrate surface in cold spray process, special nozzle was newly designed. The deposition efficiency, Vickers hardness and coating adhesion strength increased significantly especially in case of fine particles, as well as at higher pressure level of the working gas, while nominal particle velocity decreased with the special nozzle. Numerical simulation indicated that the pressure levels on the substrate surface decreased effectively in the newly designed special nozzle. In the observation of sprayed individual particles onto the substrate, extended metal jet was recognized at the splat’s periphery when the particle was sprayed with the special nozzle. The results indicate that the decrease of particles velocity due to bow shock was suppressed effectively in the special nozzle as compared to the conventional one.

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Glass formation was achieved by mechanical milling of crystalline Ni₅₉Ti₁₆Zr₂₀Sn₅ pre-alloyed powders. Compared to the glassy alloy ribbon of the same composition obtained by melting-spinning method, the alloy powders milled for 24 h exhibited a lower crystallization temperature and do not have a distinct glass-transition characteristic. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicated that a small fraction of the powder exists in nanocrystalline state within the glassy matrix. The obtained Ni₅₉Ti₁₆Zr₂₀Sn₅ powdered specimen was heated rapidly by microwave radiation and the bulk porous sample was obtained under a low applied pressure of 5 MPa.

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We imposed an alternating current on a commercially used aluminum alloy to control its solidified structure. It was applied in the initial stage of the solidification in a static system and during pouring from the tundish to the mold in a flowing system. In the static system, the solidified structure around the electrodes changed from a dendritic structure to an equi-axed one by imposing the current. However, equi-axed structure was not observed at the bottom of the vessel because the primary solid particles in the liquid phase remelted by the sedimentation to a relatively high temperature region. In the flowing system, the solidified structure was also modified from a dendritic structure to an equi-axed structure by imposing the alternating current except for the finally solidified region. The reason why the dendritic structure was obtained at the finally solidified region is that the current did not flow in the metal because of the discontinuous melt dripping in the pipe between the tundish and the mold in the last stage of the pouring. Therefore, it has been confirmed that imposition of the alternating current on the aluminum alloy during its solidification is a useful tool for modification of the structure from dendritic to equi-axed structures.

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The residual stresses and work hardening relaxations of the shot peened layer on the TiB₂/6351Al composite during thermal exposure were investigated. The results showed that the residual stresses were relaxed in the whole deformation layers especially under higher temperatures. The relaxation processes during isothermal annealing can be described using a Zener-Wert-Avrami function. The thermal stability of work hardening is higher than that of residual stresses. And both the activation enthalpies of the residual stresses and work hardening relaxations are higher than the enthalpy of aluminum self diffusion. For residual stresses relaxation, the enthalpy increment was caused by the hindrance effects of reinforcements. While for the work hardening relaxation, the increment was caused by the combination of hindrance effects of the reinforcements and the precipitates.

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In order to increase the productivity, the gas bottom blowing technique has been widely applied to mix molten iron/slag inside the ironmaking smelter. The main function of the technique is to increase the interface area between slag and iron, then to enhance the rate of the smelting reduction. In this study, the simulated experiments of the ironmaking smelter using water model were conducted to investigate the mixing degree of molten iron/slag under different gas bottom blowing conditions. In the experiments, the major parameters of the gas bottom blowing were the inside diameter of tuyere (6.0 to 15.0 mm), the total gas flow rate (320 to 480 normal liter/min), the placement of the bottom blowing tuyeres, and the stirring energy. In the water model, water and spindle oil were selected to be the substitute of liquid iron and molten slag, respectively, inside the smelter. Additionally, thymol was used as the tracer of mass transfer between the water phase and the oil phase. Based on the mass transfer rate equation with the analyzed data of thymol concentration during experiments, the mixing degree could be distinguished for different blowing conditions.
In this study, it was found that the mixing degree of water and oil in the case of 10.0 mm inner diameter tuyere was higher than those of other size tuyeres under the same gas flow rate via 4 tuyeres. Also, the mixing degree increased with increasing the total gas flow rate. Additionally, the mixing degree in the case of 4 tuyeres in the square-corner placement was higher than that in the triangle-corner-center placement at the same tuyere size and total gas flow rate. If considering both mixing efficiency and the gas consumption, the best choice of blowing condition would be four tuyeres of 10.0 mm diameter in the square-corner placement under the total gas flow rate of 320 normal liter/min.

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Vapor grown carbon fiber reinforced pure aluminum matrix composites were fabricated by the hot-pressing method below the melting temperature of pure aluminum. The surface structures of the vapor grown carbon fibers and the interfacial structures between the fibers and the matrix in the composite were observed. The precipitation mechanism of crystalline aluminum carbide was also investigated. An interlayer with an amorphous-like structure formed at the interface between the carbon surface structure and the aluminum matrix. This interlayer between the wave or irregular carbon structure and the matrix grew more rapidly than that formed between the linear carbon surface structure and the matrix. The thickness of the interlayer increased with the increased fabrication temperature of the composite. Crystalline aluminum carbide could not easily be precipitated in the composite fabricated below 933 K owing to the thicker interlayer separating the vapor grown carbon fibers and aluminum. By either extending the heat-treatment time to 18 ks or increasing the fabrication temperature to 933 K, we could promote the precipitation of crystalline aluminum carbide in the composite. After heat-treating the composite produced at 933 K, aluminum carbide crystals precipitated from the stacked carbon lamellae at the interface between the fibers and the matrix.

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An effect of homogeneous irradiation of electron beam with low potential (HIEBL) on the micro-fracture resistance of borosilicate glass was studied by using indentation of hardness test. 0.04 MGy-HIEBL increased the critical resistant energy (E_f) of micro plastic deformation to generate the crack and tremendously decreased their experimental errors. Furthermore, the high values of the midpoints (E_f^mid) of E_f values were obtained from 0.04 to 0.22 MGy of irradiation dose. If HIEBL annihilated the spontaneous crack origins, the minimum E_f value (E_f^min) before irradiation was the critical resistant energy of micro-plastic deformation to propagate the crack (E_f^p). Since HIEBL of less than 0.43 MGy didn’t affect the fracture toughness (K_IC) estimated by fracture toughness to propagate the crack using standard indentation fracture method, the E_f^p value of the borosilicate glass didn’t depend on the irradiation dose. On the other hand, the critical resistant energy of micro-plastic deformation to generate the crack (E_fⁿ; E_fⁿ=E_f−E_f^p) was defined. Thus, HIEBL increased the E_f values because of increasing E_fⁿ values. Based on the increasing the height of electron spin resonance (ESR) spectra, HIEBL formed dangling bonds in silica glassy network structure, as well as reformed the crack tip from sharp to dull. Thus, they probably relaxed the residual strain. If the partial relaxation of the residual strain mainly occurred around these dangling bonds of the silicon-oxygen pairs in the network structure, the increased E_f value was mainly due to the relaxation of the network structure, as well as the annihilation of crack origin. Therefore, HIEBL prevented the crack generation.

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