The role of the electrochemical reaction between solder and copper base metal in soldering flux was investigated in relation to wetting. The research includes the contact polarization between solder and base metal in soldering flux of RA type. The difference of electrode potential between solder and base metal in soldering flux plays an important role in removing the oxide film by contact polarization. It is concluded that the electrode potential of Sn-based lead-free solders should be significantly lower than copper to obtain good wettability, because the accelerated anodic dissolution of tin by contacting with the copper base metal enhances the wettability by the removal of tin oxide which is one of the stable oxide on base metal and solder. Sn–Pb has the adequate electrode potential to be effectively dissolved when contacted by copper. On the other hand, the electrode potential of Sn–3.5Ag is very close to copper: the condition gives extremely small contact current. The addition of less noble elements that can lower the electrode potential is effective to enhance the wettability of Sn–3.5Ag. Sn–Zn solder has extremely low electrode potential than a copper base metal; the situation excessively accelerates the preferential anodic dissolution of zinc resulting in the no dissolution of tin. The addition of lead to Sn–3.5Ag solder lowered the electrode potential, which increased the potential difference between solder and copper base metal, as a result the contact current between them was increased. The improved wettability is confirmed by adding lead to Sn–3.5Ag; all lead added solders showed a larger spread area, i.e., a smaller contact angle than Sn–3.5Ag after the spreading test. This work proposed the role of electrochemistry in wetting based on the potential difference between base metal and solder including the degree of contact corrosion current between them.

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Sn–3Ag–8Bi–5In solder (melting point, 461–477 K) was investigated as a lead(Pb)-free solder. In order to evaluate the solderability of the Sn–Ag–Bi–In alloy, the shear strength of soldered joint and inter-metallic compound (IMC) were investigated. As an experimental procedure, a 0.5 mm diameter solder was set on the Ni/Cu/Cr-pad of a Si-substrate. The solder ball on the pad was reflowed with Rosin Mildly Activated (RMA)-flux in air, and the reflow temperature was controlled between 483 K and 533 K. The shear strength and microstructure of the solder ball were evaluated with and without aging. The results show that the shear strength of the Sn–3Ag–8Bi–5In solder ball had the highest value of 1.69N by reflowing at 513 K for 10 s. The shear strength decreased from 1.69N to 0.95N as the IMC thickness was increased from 1.75 \\micron to 1.9 \\micron. Needle-shaped Ni₃Sn₄ and plate-like (Ni, Cu)₃Sn₄ formed on the interface between the solder and the Under Bump Metallization (UBM) that was bonded for 10 s at 513 K.

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The interfacial reaction and mechanical properties of Sn–Zn lead-free alloys/Cu joints were investigated under thermal exposure conditions. In the solder layer, Zn phases reacted with Cu and were transformed to Cu–Zn compounds with increasing exposure time. The microstructure change caused decreasing Vickers hardness of the solder layer. At the joint interface, although Cu–Zn compounds formed first, the formation of Cu–Sn compounds occurred with increasing exposure time. Simultaneously, the disappearance of Cu–Zn compounds and void formation occurred. The activation energy of the growth of Cu–Zn compounds at the joint interface was determined to be approximately 70 kJ/mol. That value is close to the activation energy of the diffusion of Zn in Sn crystal.

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Au–Ni plated Cu pads were reflow soldered by using lead free solder balls. The microstructure and strength of the as-reflowed solder joints were investigated. For solder joints using Cu-free Sn–Pb and Sn–Ag solder balls, a Ni₃Sn₄ reaction layer was formed on the boundary between solder and pads. On the other hand, a Cu–Sn based (Cu, Ni)₆Sn₅ reaction layer (η^′) was formed in solder joints using Cu-containing solder balls. The growth rate for an η^′ reaction layer during heat exposure at 423 K was much slower than that for a Ni₃Sn₄ reaction layer. This suppression of an η^′ reaction layer growth can be attributed to the fact that the Cu in solder balls was mostly removed during the formation of the η^′ layer. By ball shear test, cold bump pull and hot bump pull tests, mechanical properties of the obtained BGA joints were investigated. Fracture loads and crack propagation path changed by changing the mechanical tests, the BGA joints using Cu containing Sn–Ag–Cu solder or low P type Ni plating revealed better mechanical properties. We established the mismatch of the boundaries between reaction layers and the P-enriched Ni–P layer, which was caused by the chained voids formed due to the Kirkendall effect, led to low joint strength.

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This paper presents the mechanical properties and microstructure of Sn–Ag–Bi Pb-free solder. We evaluated the effects of Bi content on the mechanical properties of Sn–Ag–Bi solder such as tensile strength, elongation and deformation behavior at cross-head speeds of 0.1 mm/min and 500 mm/min. The experimental results show that at low cross-head speeds, the addition of Bi to Sn–Ag solder initially increases the tensile strength and decreases elongation due to solid-solution hardening of Sn-phase. As the Bi content is increased to 10 mass% and more, however, elongation increases to a maximum at Sn–Ag–Bi solder containing 57 mass%Bi. Deformation of Sn–Ag solder is governed by slip within the Sn phase, and for high-Bi solders (about 57 mass%Bi) deformation occurs due to slip at Sn–Bi grain boundaries. Intermediate-Bi solders, on the other hand, do not slip in either the Sn phase or at Sn–Bi grain boundaries. At high cross-head speeds, the elongation of both intermediate-Bi solders and high-Bi solders was low and almost constant, indicating slip at Sn–Bi grain boundaries becomes difficult. The impact resistance of these solders was investigated through charpy impact tests, and it is found that Bi has a marked effect on impact resistance. The impact absorption energy of Sn–Ag solder decreases rapidly with the addition of Bi.

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Wetting balance test is known to be the most versatile method to evaluate wettability during soldering process, because it provides quantitative information and time dependent wetting behavior. There are many other studies exist related with the wetting force, however, as to wetting time, there are few theoretical backgrounds and mathematical analysis. In this study, the wetting time is focused on a wettability index. The wetting curve, which shows time dependant wetting behavior, is predicted by using computer simulation and compared with oil experiment also, the mechanism of meniscus rise is analyzed. As a result, relationship of calculated and measured wetting curve can be obtained. It is found that the viscosity of a liquid is the major variable that determine the wetting time and wetting rate.

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The growth kinetics of intermetallic compound layers formed between eutectic Sn–58Bi solder and (Cu, electroless Ni–P/Cu) substrate were investigated at temperature between 70 and 120°C for 1 to 60 days. The layer growth of intermetallic compound in the couple of the Sn–58Bi/Cu and Sn–58Bi/electroless Ni–P system satisfied the parabolic law at given temperature range. As a whole, because the values of time exponent (n) have approximately 0.5, the layer growth of the intermetallic compound was mainly controlled by diffusion mechanism over the temperature range studied. The apparent activation energies of Cu₆Sn₅ and Ni₃Sn₄ intermetallic compound in the couple of the Sn–58Bi/Cu and Sn–58Bi/electroless Ni–P were 127.9 and 81.6 kJ/mol, respectively.

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This study included a comparison of the baseline Sn–3.5Ag eutectic to one near-eutectic ternary alloy, Sn–3.6Ag–1.0Cu and two quaternary alloys, Sn–3.6Ag–1.0Cu–0.15Co and Sn–3.6Ag–1.0Cu–0.45Co, to increase understanding of the effects of Co on Sn–Ag–Cu solder joints cooled at 1–3°C/s., typical of reflow assembly practice. The results revealed joint microstructure refinement due to Co-enhanced nucleation of the Cu₆Sn₅ phase in the solder matrix, as suggested by Auger elemental mapping and calorimetric measurements. The Co also reduced intermetallic interface faceting and improved the ability of the solder joint samples to maintain their shear strength after aging for 72 h at 150°C. Some recent additional results with Co and Fe additions are consistent with this catalysis effect, where a reduced total solute level was tested. The baseline Sn–3.5Ag joints exhibited significantly reduced strength retention and coarser microstructures.

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We fabricated Cu core Sn–Ag solder balls by plating pure Sn and Ag on Cu balls and clarified that Sn/Ag plating began to melt at a rather low temperature, the eutectic temperature of Sn–Ag–Cu. This early melting at the eutectic temperature was ascribed to the diffusion of Cu and Ag into the Sn plating during the heating process. We investigated the solderability of the BGA joint with the Ni/Au coated Cu pad to compare it with that of the commercial Sn–Ag and Sn–Ag–Cu balls. After reflow soldering, we observed a eutectic microstructure composed of β-Sn, Ag₃Sn, and Cu₆Sn₅ phases in the solder, and a η^′-(Au, Cu, Ni)₆Sn₅ reaction layer was formed at the interface between the solder and the Cu pad. The BGA joint using Cu core solder balls could prevent the degradation of joint strength during aging at 423 K because of the slower growth rate of the η^′-(Au, Cu, Ni)₆Sn₅ reaction layer formed at the solder-pad interface. Furthermore, we were able to fabricate Cu-cored, multicomponent Sn–Ag–Bi balls by sequentially coating binary Sn–Ag and Sn–Bi solders onto Cu balls. The coated balls also exhibited almost the same melting and soldering behaviors as those of the previously alloyed Sn–2Ag–0.75Cu–3Bi solders.

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One of the critical issues which needs to be solved in the packaging technology of high speed and high density semiconductor devices is the enhancement of micro-solder joint reliability and strength. The reliability and strength of the solder joints depend on the interfacial structures between metallization and lead free solder. Both the interfacial structures and the strengths of the solder joints between plated Ni–P alloy films with various P concentrations and various solder materials have been investigated. The places where intermetallic compounds crystallized were found to vary according to the P concentration in plated Ni–P alloy films and the composition of the solder. Pyramidal intermetallic compounds that formed on plated Ni–P alloy films had the following compositions: Sn–3.5 mass%Ag/Ni–2 mass%P, Sn–3.5Ag–0.7 mass%Cu/Ni–P(2, 8 mass%) and Sn–50 mass%Pb/Ni–P(2, 8 mass%). Whereas intermetallic compounds were crystallized in the solder of the Sn–3.5 mass%Ag/Ni–8 mass%P sample. A P-enriched layer was formed between the plated Ni–P alloy films and the intermetallic compounds. The thickness of the P-enriched layers of each sample increased with the reaction time. In experiments using the same solder material, the P-enriched layer of the solder/Ni–8 mass%P sample was much thicker than that of the solder/Ni–2 mass%P sample. In experiments with plated Ni–8 mass%P alloy films, the P-enriched layers became thicker in this order: Sn–50 mass%Pb/Ni–8 mass%P; Sn–3.5Ag–0.7Cu/Ni–8 mass%P; Sn–3.5 mass%Ag/Ni–8 mass%P . The strengths of the solder joints decreased with the P concentration in plated Ni–P alloy films for all solder materials. However, it was found that the strength degradation ratio varied with the solder materials and they increased in the following order: Sn–50 mass%Pb; Sn–3.5Ag–0.7 mass%Cu; Sn–3.5 mass%Ag. Therefore, it was found that the solder joint strength is very sensitive to the thickness of the P-enriched layer at the solder joint and the solder joint strength decreased with the thickness of the P-enriched layer independent of the solder materials.

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This paper discusses the creep behavior of example Sn-rich solders that have become candidates for use in Pb-free solder joints. The specific solders discussed are Sn–3.5Ag, Sn–3Ag–0.5Cu, Sn–0.7Cu and Sn–10In–3.1Ag, used in thin joints between Cu and Ni/Au metallized pads. The creep behavior of these joints was measured over the range 60–130°C. The four solders show the same general behavior. At all temperatures their steady-state creep rates are separated into two regimes with different stress exponents (n). The low-stress exponents range from ∼3–6, while the high-stress exponents are anomalously high (7–12). Strikingly, the high-stress exponent has a strong temperature dependence near room temperature, increasing significantly as the temperature drops from 95 to 60°C. The anomalous behavior of the solders appears to be due to the dominant Sn constituent. Joints of pure Sn have stress exponents, n, that change with stress and temperature almost exactly like those of the Sn-rich solder joints. Surprisingly, however, very similar behavior is found in Sn–10In–3.1Ag, whose primary constituent is γ-InSn. Research on creep in bulk samples of pure Sn suggests that the anomalous temperature dependence of the stress exponent is due to a change in the dominant mechanism of creep. Whatever its source, it has the consequence that conventional constitutive relations for steady-state creep must be used with caution in treating Sn-rich solder joints, and qualification tests that are intended to verify performance should be carefully designed.

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The tensile properties of Sn–3.5Ag and Sn–3.5Ag–0.75Cu lead-free solders were investigated. The effect of annealing at 100°C for 1 h before the tensile test on mechanical properties was small in both solders. The tensile strength decreased with decreasing strain rate, and with increasing test temperature. However, the ductility of each solder was relatively constant in the strain rate ranging from 1.67×10⁻⁴ s⁻¹ to 1.67×10⁻² s⁻¹ and in the test temperature ranging from −40 to 120°C. From the results of the strain-rate-change tests, the strain sensitivity for Sn–3.5Ag and Sn–3.5Ag–0.75Cu were found to be 0.077 and 0.078, respectively.

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The ball shear strength of BGA solder joints during isothermal aging was studied with Sn–3.5Ag–0.75Cu solder on three different pads (Cu, electroless Ni–P/Cu, immersion Au/Ni–P/Cu) at temperature between 70 and 170°C for times ranging from 1 to 100 days. The reliability of solder ball attachment was characterized by mechanical ball shear tests. As a whole, the shear strength of BGA joints decreased with increasing temperature and time. The shear strength for both the immersion Au/Ni–P/Cu and electroless Ni–P/Cu pads was consistently higher than that of the Cu pad for all isothermal aging conditions. The fracture surface showed various characteristics depending on aging temperature, time, and the types of BGA pad. The P-rich Ni layer formed at the interface between (Cu, Ni)₆Sn₅ and Ni–P deposits layer after aging, but fracture at this interface was not the dominant site for immersion Au/Ni–P/Cu and electroless Ni–P/Cu pad.

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Mechanical properties and ball shear strength of Sn–3.5Ag–Bi were investigated with Bi addition of 0–9 mass%. Solder characteristics of Sn–3.5Ag–Bi were improved with Bi addition to decrease the melting temperature, to promote wetting to Cu and Ni substrates, and to increase the tensile strength and fracture energy. Shear strength of Sn–3.5Ag–Bi solder bumps increased with Bi addition up to 5 mass%, and was kept almost unchanged with further increase of Bi addition. Shear strength exhibited a parabolic relationship with the tensile fracture energy of the solder alloys.

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Because of its potential to be used as a lead free solder material the thermodynamic properties of the liquid Al–Sn–Zn system were investigated. Using an appropriate galvanic cell, the partial free energies of Al were determined as a function of concentration and temperature. Thermodynamic properties were obtained for 30 alloys. Their composition was situated on three cross-sections with constant ratios of Sn:Zn=2:1, 1:1 and 1:2. The integral Gibbs energy and the integral enthalpy for the ternary system at 973 K were calculated by Gibbs-Duhem integration.

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High temperature solders that will not be affected in the subsequent thermal treatment are required in the step soldering process of multi-chip module (MCM) packaging. High-Pb solder alloys such as 95Pb–5Sn (numbers are all in mass% unless specified otherwise) are currently being used for this purpose. However, the development of the Pb-free solder alloy for high temperature applications is needed due to environmental issues. The solder alloys of Bi–Ag, Sn–Sb and Au–Sb–Sn systems are considered as candidates in this study. Aided by thermodynamic calculations, several specific compositions have been chosen and they were investigated in terms of melting behavior, electrical resistivity, wetting angle and hardness. The Bi–Ag alloy exhibited poor electro-conductivity while the Sn–Sb system had low melting temperatures. The ternary Au–Sn–Sb solder alloy shows prospects for high temperature applications in spite of poor wetting properties.

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A thermodynamic description of the Bi–In–Sb ternary system of lead-free solder alloys using the CALPHAD (Calculation of Phase Diagram) method is presented. Phase equilibria information such as vertical sections, liquidus projection and thermochemical quantities were calculated and compared with the experimental data. The calculated and experimental data are in excellent agreement in most cases.

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The interfacial structure and strength of solder joints between Sn–9 mass%Zn solder and plated Au/Ni–P alloy film on a Cu substrate have been investigated. Three reaction layers with 0.2 to 0.5 \\micron thickness were formed along the interface between the plated Ni–P alloy films and Sn–9 mass%Zn solder. The outermost layer contains a Ni–Sn intermetallic compound. The middle layer contains approximately 40 mass%Au, 35 mass%Zn, 20 mass%Ni and 5 mass%Sn. The thickness of the Au layer is 0.1 \\micron, so the Au layer does not dissolve. The innermost layer contains about 63 mass%Zn, 25 mass%Ni, 10 mass%Au and 2 mass%Sn. The strength of the Sn–9 mass%Zn solder joints take almost the same values independent of P concentration. The strength of Sn–Zn solder joints with Sn–Zn/Ni–2 mass%P, Sn–Zn/Ni–4 mass%P and Sn–Zn/Ni–8 mass%P joints were found to be almost constantly independent of reflow cycles. Therefore, Sn–9 mass%Zn solder is considered to be an excellent solder material for plated Ni–P alloy films.

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This paper deals with recent progress in stabilized supercooled liquid and the resulting bulk glassy alloys and focusing on the following factors; alloy composition, forming ability, formation mechanism, computed glass-forming ability, computed glass formation range, atomic configuration, production techniques, mechanical properties, corrosion resistance, soft magnetic properties, micro-forming ability, applications, significance to science and engineering, and future trends for bulk glassy alloys including supercooled liquid. As demonstrated in this review, the high stability of metallic supercooled liquid has already opened up new fields of investigation in basic science and yielded new engineering applications. There is every reason to expect that their importance will continue to increase.

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Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ bulk metallic glasses have been prepared by copper moulding. In order to obtain a fully amorphous sample, a careful control of the atmosphere conditions in the casting chamber was necessary. In particular, the presence of oxygen contamination promotes the nucleation of a fcc “big cube” phase, reducing glass formation. The crystallisation of bulk amorphous samples has been followed by DSC and values of about 4 kJ·mol⁻¹ have been obtained for the heat release at about 740 K. By high temperature DSC, a metastable-to-stable phase transformation has been evidenced at 938 K, which gives a heat evolution of 1.12 kJ·mol⁻¹. Melting and solidification of the alloy have been observed at 1070 K, giving an average value for the enthalpy change of about 8.2 kJ·mol⁻¹. The temperature dependence of the enthalpy difference between undercooled liquid and equilibrium crystal phases has been described on the basis of different models for the specific heat difference (ΔC_p) between the two phases. A best fitting of experimental data gives values of ΔC_p of about 21 J·mol⁻¹·K⁻¹ at the glass transition temperature (690 K), in good agreement with experimental values obtained from DSC measurements.

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The quantitative parameters such as supercooled liquid region or several reduced glass transition temperatures were applied for evaluating the glass-forming ability of Pd-based metallic glasses. A distinct proportional tendency was recognized between measured critical cooling rates and reduced glass transition temperature by liquidus temperature rather than eutectic temperature. Significance and physical meanings of the quantitative parameters for evaluating of glass-forming ability were also discussed. Furthermore, a new concept of a modified reduced glass transition temperature was proposed to evaluate the glass-forming ability. The modified reduced glass transition temperature as a function of critical cooling rate was found to exhibit a much clear linearity.

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The primary metastable phase in the Fe₇₀Nb₁₀B₂₀ amorphous alloy is the complex fcc Fe₂₃B₆ phase with a large lattice parameter. The atomic site of Nb atoms in this metastable phase was determined by the anomalous X-ray scattering (AXS) method. Nb atoms in the metastable phase located at the similar position expected in the local structural unit in the amorphous state. Thus, the precipitation of the metastable phase does not require long-distance diffusion of Nb atoms in the amorphous matrix.

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Time and temperature dependence of impurity diffusion is measured in detail for several ZrTiCuNiBe bulk glasses in a wide temperature range. We find that neither the quenched-in free volume nor a small volume fraction of crystals have a significant effect on the diffusivity. It is shown that the composition of these glasses has a much weaker effect on the diffusion coefficients than have structural changes of the glass. By long time relaxation the reversible metastable equilibrium of the glass structure could be reached at temperatures below the calorimetric glass transition. For this metastable equilibrium state a single set of diffusion parameters, activation enthalpy and pre-factor of the diffusion coefficient, is derived in the entire temperature range above and below the glass transition. This indicates that the usually observed non-linear Arrhenius behavior of diffusion coefficients in the ZrTiCuNiBe bulk glasses is caused by insufficient structural relaxation at temperatures below the calorimetric glass transition.

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The structural relaxation process in several Pd–Cu–Ni–P glasses was investigated by the electrical resistivity and the Mössbauer experiments. The change in the resistivity, ρ(300), and the corresponding slope, α(300)=(dρ⁄dT)₃₀₀, at room temperature was measured after a given heat treatment. The change in ρ(300) with isochronal annealing below the glass transition temperature (≈572 K), starting from room temperature, demonstrated that the ρ(300) increased with temperature and decreased beyond 550 K. The isothermal annealing at 570 K exhibited that the ρ(300) showed an increase, about 1%, during an initial annealing stage for 3.0×10² s and remained almost constant up to 6.0×10³ s, and hereafter monotonously decreased. The change in α(300) showed an opposite sign to that in ρ(300). The reversible change in ρ(300) due to isochronal annealing was observed in the heat treatment repeated between 350 and 550 K. The Mössbauer spectroscopy experiments were performed at room temperature to investigate the local structure change due to structural relaxation. The isomer shift and the quadrupole splitting for an annealed sample decreased in comparison with that of an as-quenched sample. Based on these results, the structural relaxation process and the structure change were discussed within the framework of the free volume model.

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We investigated the stability of the supercooled liquid in Zr-based glassy alloys by examination of their transformation behavior. The primary phase is an fcc Zr₂Ni phase in a Zr₆₅Al_7.5Ni₁₀Cu_17.5 glassy alloy with high glass-forming ability (GFA). By substitution of Ag, Pd, Au or Pt for only 1 at%Cu, an icosahedral quasicrystalline phase (I-phase) precipitates with the fcc Zr₂Ni phase. The primary phase changes to the single I-phase at higher noble metal contents. It is further found that the I-phase precipitates by a small amount of substitution for Cu with other elements as well as the noble metals, which have a weak or positive chemical affinity with one of the constitutional elements in the Zr–Al–Ni–Cu glassy alloy. Thus, the slight deviation from the three component rules for high GFA is effective for the I-phase formation. The I-phase is also formed as a primary phase in the Zr_65+yAl_7.5Ni₁₀Cu_17.5−y (y=1–7) glassy alloys. A slight change in the composition has the similar effect as the addition of element such as noble metals and so on. An icosahedron is contained as a structure unit in the fcc Zr₂Ni and I-phases and hence the glassy structure is correlated with the local icosahedral atomic configuration. The high-resolution transmission electron microscopy image of the Zr₇₀Al_7.5Ni₁₀Cu_12.5 glassy alloy reveals a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short- or medium-range order exists in the supercooled liquid as well as in the glassy phase and it stabilizes the supercooled liquid state in the Zr-based alloys. An I-phase also precipitates as a primary phase by substituting Pd, Au or Pt for only 1 at%Cu in the Zr₇₀Cu₃₀ glassy alloy. From these results, the appearance of the supercooled liquid region is attributed to the existence of the icosahedral atomic configuration consisting of Zr and Cu.

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The structural behavior of the Zr₅₂Ti₅Cu₁₈Ni₁₅Al₁₀ bulk glass has been investigated in situ by means of high-temperature X-ray synchrotron diffraction. The crystallization starts with the formation of an extremely fine nanostructure followed by the transformation into tetragonal NiZr₂-type crystals plus an unknown phase. Both phases are metastable and transform at about 1123 K into the stable equilibrium phases. The temperature dependence of the scattering curve I(q) of the glass can be well described within the framework of the Debye theory. At the glass transition the first derivative dI(q)⁄dT changes. A Debye temperature θ=412 K was estimated for the glassy, and θ=162 K for the liquid state of the Zr₅₂Ti₅Cu₁₈Ni₁₅Al₁₀ alloy. The short-range order of the glass, of the supercooled liquid state, and of the equilibrium melt at T=1193 K is found to be quite similar. The results point to the formation of complex chemically ordered clusters already in the melt.

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Bulk glassy Ni-based alloys with high fracture strength exceeding 2700 MPa were prepared in Ni₆₀Nb_40−x−yTi_xZr_y system by copper mold casting. The glassy alloys with distinct glass transition were obtained in the wide composition range from 0 to 35%Ti and 0 to 30%Zr and the largest supercooled liquid region before crystallization was 76 K for Ni₆₀Nb₁₅Ti₁₀Zr₁₅. The maximum diameter was 2 mm for Ni₆₀Nb₂₀Ti₁₅Zr₅ and the glass transition temperature (T_g), crystallization temperature (T_x) and reduced glass transition temperature (T_g⁄T_l) of the bulk glassy alloy were 841 K, 898 K and 0.61, respectively. The Young’s modulus (E), compressive fracture strength (σ_c,f) and compressive fracture elongation (ε_c,f) were 156 GPa, 2770 MPa and 2.4%, respectively, for the bulk alloy. There is a tendency for fracture strength to increase with increasing E, T_g and liquidus temperature (T_l). It is therefore interpreted that the high strength is due to strong bonding nature among the constituent elements.

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It is known that an anelastic deformation occurs more remarkably for amorphous ribbon alloys than for crystalline metallic alloys by the tensile test. In addition, the result of the molecular dynamics simulation on tensile and shearing tests for Cu single component amorphous metal has indicated that the anelastic deformation occurs more remarkably under the shearing stress rather than under the tensile stress. In this report, tensile and torsional tests were actually performed for bulk metallic glasses to examine the difference in the anelastic behavior under shearing and tensile stresses. Single-phase bulk metallic glasses, La₆₀Al₂₀Ni₁₀Cu₅Co₅, Pd₄₀Cu₃₀Ni₁₀P₂₀ and Zr₅₅Cu₃₀Ni₅Al₁₀ (at%), were chosen together with a steel, JIS SGD 400-D, as a representative of metallic crystals. The test specimens were a round bar shape and the diameters of a parallel gage section were 4 to 10 mm. No anelastic behavior was observed for the steel under tensile and shearing stresses. Although the metallic glasses did not exhibit distinct anelastic deformation under the tensile stress, the shearing stress mode leads to a significant anelastic deformation even at low stress level. The amount of the anelastic deformation increases with an increase in the shearing stress level.

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With the aim of developing a large size bulk glassy Fe-based alloy with good soft magnetic properties by the powder metallurgy technique, we have applied the spark-plasma sintering technique to a Fe₆₅Co₁₀Ga₅P₁₂C₄B₄ glassy alloy powder with a large supercooled liquid region of 50 K before crystallization. The existence of the supercooled liquid region enabled us to form a large size bulk glassy alloy of 20 mm in diameter and 5 mm in thickness with a high relative density of 99%. The resulting bulk glassy alloy exhibits good soft magnetic properties, i.e., 1.20 T for saturation magnetization, 14 A/m for coercive force and 6000 for maximum permeability. The good soft magnetic properties for the multicomponent Fe-based bulk alloy are attributed to the combination of the high relative density and the maintenance of the single glassy structure. The success of forming the large size bulk glassy alloy with good soft magnetic properties by the powder metallurgy techniques is promising for future use as practical soft magnetic materials.

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Bulk amorphous Fe_65.5Cr₄Mo₄Ga₄P₁₂C₅B_5.5 rods with diameters of 1.5–3 mm were prepared by copper mold casting. Besides casting, bulk amorphous Fe₇₇Al_2.14Ga_0.86P_8.4C₅B₄Si_2.6 samples in the shape of discs (diameter of 10 mm and thickness of 3 mm) were prepared from melt-spun ribbons by high-energy ball milling and subsequent compaction of the resulting powders in the supercooled liquid region. The as-cast amorphous FeCrMoGaPCB samples exhibit a low coercivity, below 10 A·m⁻¹. In the case of the FeAlGaPCBSi alloy, the milling-induced stress causes significant differences in coercivity between the ribbons and the powders. The relatively low coercivity of about 5–10 A·m⁻¹ characteristic for the melt-spun ribbons increases after 1 hour of ball milling to a value of about 2200 A·m⁻¹. Subsequent annealing of the ball-milled powders leads to a decrease of H_c by a factor of 10 to about 220–250 A·m⁻¹. The bulk samples prepared by hot pressing of the crushed ribbons show a coercivity of about 120–140 A·m⁻¹. For both alloys, thermal stability measurements show a distinct glass transition, followed by a supercooled liquid region of 60 K for Fe_65.5Cr₄Mo₄Ga₄P₁₂C₅B_5.5 and of 30 K for Fe₇₇Al_2.14Ga_0.86P_8.4C₅B₄Si_2.6. For the Fe_65.5Cr₄Mo₄Ga₄P₁₂C₅B_5.5 alloy, crystallization of the amorphous phase as observed by in-situ X-ray diffraction measurements in transmission configuration occurs via the formation of a metastable intermediate phase. The phases observed in the crystalline state obtained by heating do not correspond to those occurring after slow cooling.

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Fe-based glassy alloys with high boron concentrations in (Fe, Co)–(Nd, Dy)–B system were found to exhibit a large supercooled liquid region (ΔT_x) and good soft magnetic properties. The Fe₆₂Co_9.5Nd₃Dy_0.5B₂₅ glassy alloy with ΔT_x of 56 K exhibits high saturation magnetization (I_s) of 1.41 T, low coercive force (H_c) of 2.6 A/m and large permeability (μ_e) at 1 kHz of 12000. The Fe₆₂Co_9.5Nd₃Dy_0.5B₂₅ glassy alloy rods were produced in the diameter range up to 0.75 mm by copper mold casting. The substitution of 2 at% elements TM (TM=Nb, Ta, Mo and W) for Fe and Co, remarkably increases the ΔT_x and T_g⁄T_l, leading to an increase in the glass-formation ability (GFA) for Fe_60.3Co_9.2Nd₃Dy_0.5B₂₅TM₂. The ΔT_x and T_g⁄T_l increase from 56 to 87 K and 0.56 to 0.57, respectively, and the glassy alloy rods were produced in the diameter range up to 1.2 mm. The saturation magnetization I_s decreases slightly, while the coercive force H_c remains almost unchanged by the addition of 2 at% TM elements.

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Magnesium-based glass matrix composites containing oxide particles were produced by mechanical alloying of Mg₅₅Cu₃₀Y₁₅ elemental powder mixtures with the addition of MgO, CeO₂, Cr₂O₃ or Y₂O₃ oxide particles. The formation of the glassy phase was characterized by X-ray-diffraction and transmission electron microscopy methods and was found to proceed almost unaffected by the presence of the oxides. Differential-scanning-calorimetry-analysis revealed, that the amorphous matrix features a wide supercooled liquid region with an extension of about 40–50 K. Differences in the thermal stability of the composites depending on the oxide addition are discussed. Viscosity measurements proved the existence of a characteristic minimum of viscosity in this temperature range which was used to consolidate the powders into bulk samples by uniaxial hot pressing. The deformation behaviour under compression at room temperature as well as at elevated temperature of 423 K yielded excellent properties compared to conventionally produced magnesium-based alloys.

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Bulk Nd₆₀Fe₃₀Al_10−xB_x (x=0, 2.5, 5, 7.5 and 10 at%) alloys with hard magnetic properties were prepared by an arc melting method. The bulk alloys have weights of 10 and 100 mg with button shapes of 1 and 6 mm in thickness, respectively. The X-ray diffraction and TEM observation data reveal that the Nd₆₀Fe₃₀Al₁₀ bulk alloy exhibits an amorphous phase while the other alloys consist of partial crystalline and amorphous phases. The bulk Nd₆₀Fe₃₀Al₁₀ amorphous alloy of 1 mm in thickness exhibits crystallization temperature (T_x) of 802 K, eutectic temperature (T_e) of 925 K, and reduced crystallization temperature (T_x⁄T_e) of 0.87. The alloy exhibits hard magnetic properties at 298 K, i.e., saturation magnetization of 0.13 T, remanance of 0.09 T, and intrinsic coercive filed of 275 kA/m under an applied field of 1242 kA/m. These thermal and magnetic properties are nearly the same as those for the corresponding bulk amorphous cylinders of 1 to 12 mm in diameter prepared by copper mold casting. The replacement of Al with B in Nd–Fe–Al amorphous alloy causes a decrease in amorphous-forming ability (AFA), although their hard magnetic properties remain almost unchanged. The reason for the decrease in AFA was analyzed using mixing enthalpy (ΔH_mix) and mismatch entropy (S_σ) corresponding the empirical criteria for the achievement of high AFA. Furthermore, amorphous-forming composition regions (AFCRs) were calculated by giving a limitation for formation of an amorphous phase to ΔH_mix and S_σ values, which arises from the statistics for 6500 amorphous alloys listed in a database. The calculated AFCR of the Nd–Fe–Al and Nd–Fe–B alloy systems agrees with the experimental data reported previously. The decrease in AFA by the replacement of Al with B in the Nd₆₀Fe₃₀Al_10−xB_x alloys is interpreted from the result that Nd₆₀Fe₃₀B₁₀ is located near the edge of the AFCR in Nd–Fe–B system.

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Rapidly and slowly quenched Nd_90−xFe_xAl₁₀ glassy alloys with thicknesses up to 3 mm were investigated comparatively by structural and magnetic measurements in the temperature range 5–800 K and external fields up to 9 T . The glass-forming ability decreases increasing Fe content. Room temperature coercivities of over 0.6 T are observed, depending on composition and external field. The huge increase of the coercive field up to 5.5 T at low temperatures as well as the dependence on the cooling rate are supposed to result from the non-collinear magnetic structures developed in these amorphous alloys. From DC and AC magnetic measurements combined with neutron diffraction results we conclude that the structure, which is quenching conditions dependent, consists of a packing of nanometer-sized clusters. The topological and magnetic structures of Nd_90−xFe_xAl₁₀ melt-spun ribbons and cast rods in a wide range of temperatures and for different x values are modelled using the reverse Monte Carlo method (RMC). The hypotheses of a cluster model, in which exchange interactions, local random anisotropies and thermal effects are competing, are proposed.

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High temperature inductor applications require improved magnet performance, including simultaneous high magnetization and low core losses at ever higher operation frequencies. Conventional polycrystalline soft magnet alloys are mature technologies with little room for meaningful improvement. Recently, nanocrystalline soft magnetic materials possessing reduced hysteretic losses and offering higher operation frequencies than conventional alloys have been introduced. These nanocrystalline soft magnets with compositions Fe–Co–Zr–B–(Cu) have been offered as alternatives to the conventional alloys. This paper describes the processing, structure, and magnetic properties of these materials.

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The stabilization of supercooled metallic liquid occurs for a number of alloys where the constituent elements have the following three rules, i.e., multi-component of more than three elements, significant mismatches of atomic size above 12% among the main three elements, and negative heats of mixing among their main elements. The use of the stabilized supercooled liquid has enabled us to synthesize a number of novel advanced metallic materials. In this review, we present the alloy components, fabrication processings, structures, mechanical properties and applications of high-strength Al- and Mg-based alloys with glassy, nanocrystalline or nanoquasicrystalline phase which were developed on the basis of the concept of the utilization of stabilized supercooled liquid for the last one decade.

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Nanocomposite Al-based alloys can be obtained with a combination of amorphous, crystalline and quasicrystalline phases. In order to understand the correlation between the nanostructure and the mechanical behaviour, four nanocomposite alloys with different characteristics were studied: two alloys from the Al–Fe–Cr–Ti system consisting of a spherical nanoquasicrystalline phase in an α-Al matrix; one alloy from the Al–Fe–V–Ti system consisting of a mixture of amorphous and α-Al phases; and one alloy from the Al–Mn–Cr–Cu system consisting of nanocrystalline particles embedded in an α-Al matrix. Melt-spun samples were prepared and the structure was characterised by means of X-ray diffraction and transmission electron microscopy. Differential scanning calorimetry was used to study the thermal stability and the transformation processes. Tensile tests, fractographic analysis and Vickers microhardness at room temperature were performed in order to evaluate the mechanical behaviour. A combination of solid solution, particle dispersion and grain refinement strengthening was responsible for the high strength of the alloys. The microstructure of the alloy Al₉₃Fe₃Cr₂Ti₂ (at%) remained acceptably stable up to 703 K, due to the slow coarsening rate of the icosahedral phase.

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Devitrified Al-based and Zr-based amorphous alloy nanocomposites with nanoscale precipitates of element, compound or quasicrystalline particles are regarded as new prospective structural materials with good mechanical properties. In order to analyse the strengthening behaviour of the partially devitrified amorphous nanocomposites, a phase mixture model is presented, in which the partially crystallised Al-based or the Zr-based amorphous alloys is regarded as a nanocomposite of nanoscale particles and the remaining amorphous matrix. Most attention is paid to the change of solute concentration in the matrix. The element, compound or quasicrystalline particles are treated as perfect materials. The matrices are treated as amorphous materials, in which the solute concentrations change depending on the solute concentration and volume fraction of precipitate particles. Investigating the solute concentration changes associated with overall mechanical properties could prove that the phase mixture model can successfully describe the strengthening mechanism in the devitrified Al-based and Zr-based amorphous nanocomposites.

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Aluminium-based Al–Fe alloys with Fe content of 2, 4, 5, 8 and 11 mass% were examined using X-ray diffraction and Mössbauer spectroscopy. The alloys were prepared by various techniques: remelting, accelerated cooling by centrifugal casting, rapid quenching from the melt at a rate of 10⁶ K/s, and mechanical alloying of pure elements in high-energy planetary ball mill. It is shown that the crystalline structure refinement and the composed phases of the alloys essentially depend on the techniques used for the sample preparation. Phase transformations by severe plastic torsion deformation of the alloys prepared by various techniques were studied. The highest supersaturation of Fe in the aluminium-based solid solution can be reached using two subsequent techniques of alloy treatment: rapid quenching and high-pressure torsion.

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Ti–(37.5−X) at%Si–X at%Fe (X=0–10) powder mixtures have been mechanically alloyed in a planetary ball mill under an argon atmosphere for 180 ks. The milled alloy powders become amorphous and crystallization temperature is 843 K for X=5, being 90 K higher than that for X=0. Milled powders have been consolidated using a pulse current sintering process under 1.5 GPa. The porosity of an amorphous compact solid consolidated at 813 K is estimated to be 7.5% for X=5, being much lower than 24% for X=0. Fe addition to Ti–37.5 at%Si powder mixtures in mechanical alloying improves the stability of an amorphous phase and forming-ability of compact solid powders.

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A nanocrystalline layer was fabricated in bond area of 0Cr16Ni22Mo2Ti steel using flash welding. The average grain size near bond line is about 30 nm and the farther the distance from the bond line, the larger the size of the nanocrystallites. The thickness of the nanocrystalline layer is about 80 \\micron. The formation mechanism of the nanocrystallites may be that the metal in liquid state in the bond area is solidified under both high undercooling and high density d.c. electric current that can refine the microstructure of metal solidification.

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We have investigated the glass-transition kinetics of nine Ge_xSe_1−x glasses by differential scanning calorimetry. Relation between the drive (heating-rate q) and response (heatflow shift ΔH at T_g) is seen to be strictly linear only for GeSe₄, known to signify the bulk-rigidity threshold for this series. From an Arrhenius analysis the activation energies for glassy relaxation are estimated, and point to the existence of different thermokinetic phases below and above the threshold composition. Series behaviour of the kinetic activation is conciled to a concurring one seen in the size of cooperatively diffusing regions. The anomalies are attributed to structural crossovers with Ge doping; first from the parent uniform Se-chains to that of backbones out-branching at corner-shared Ge(Se_1⁄2)₄ tetrahedral clusters, and subsequently interconnecting by edge-shared configurations to realize a random pearl-necklace 3-D covalent network.

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Microstructures in martensites and effects of uniaxial stress, magnetic field and hydrostatic pressure on martensitic transformations, which were investigated by the author, are briefly summarized. Unsolved problems related to this investigation are pointed out and some ideas are proposed to solve the problems. Interactions between lattices and electrons should be clarified in order to establish the cause of martensitic transformation. In particular, the exact electronic band structure at Brillouin zone boundaries should be delineated, and whether martensitic nuclei are indeed grown from precursory strained regions in matrix phases should be clarified. How the precursory strained region is related to the lattice invariant strain considered in the phenomenological crystallographic theory for martensitic transformations and actually observed by TEM should also be clarified. Some other future research subjects, such as the effects of uniaxial stress, magnetic field and hydrostatic pressure on martensitic transformations, and various related functions, such as shape memory effect and superelasticity, are further pointed out.

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Effects of annealing temperature (T_a) on the structure of hydrogenated amorphous silicon carbide (a-SiC:H) films prepared by RF plasma chemical vapor deposition (CVD) method are investigated by using Fourier Transform-Infrared Spectrometry (FT-IR), X-ray Photoelectron Spectroscopy (XPS) and UV-VIS spectrophotometer techniques. It is found that an annealing process results in structural rearrangement and evacuation of hydrogen atoms from CH_n and SiH_n bonds. The emission of hydrogen bonded to silicon and carbon responsible for the decrease of optical band gap (E_opt) by 0.70 eV in the range of T_a from 573 to 873 K . This hydrogen loss is interpreted in terms of hydrogen molecule formation and outerdiffusion. In addition, the surface morphology of films was investigated by atomic force microscopy (AFM).

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This paper describes tensile properties of a peak-aged Mg–4Y–3RE alloy at room temperature to 823 K with 10⁻⁵–10⁻¹ s⁻¹. The Mg alloy exhibited high strength (> 250 MPa) at room temperature to 473 K . However, the strength rapidly decreased at 573 K . It is suggested that a large decrease in strength at 573 K is attributed to grain boundary sliding. Also, elongation increased rapidly at 723–823 K . This is likely to arise from the relatively high strain rate sensitivity of about 0.3 due to the glide-controlled dislocation creep.

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Solvent extraction experiments for separation of impurities from Ni-rich solution were carried out for manufacturing of high purity Ni compounds from acid leaching solution of spent Ni–Cd secondary battery. Artificial and leaching solutions were used as aqueous phases and PC88A saponified by sodium in kerosene were used as organic phase. The extraction order is Zn>Mn>Co>Ni and extraction percentage of metal ions was increased with increase of the concentration of extractant, initial pH of aqueous phase and ratio of O/A . The separation of cobalt, zinc and manganese from nickel was effectively accomplished at the condition of extraction stage=1, O/A=1 and initial pH 5.0 with 1.0 mol/dm³ PC88A saponified to 50% with NaOH.

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Nano-structured Ag layers with the thickness in a range of d_Ag=0.9–24 nm sandwiched between MgO layers are formed by rf sputtering. The morphology of nano-structured Ag is observed by the transmission electron microscope. Then the optical property is measured in a range of wavelength of 0.24–2.6 \\micron, which covers the solar energy spectrum. Several characteristics are recognized. For example, the nano-structured Ag layer having the intermediate morphology between the nano-particle and the continuous film shows the effective optical property in absorbing solar spectrum, such as large absorptance not only at visible region but also at near-infrared region. Moreover, it is found that the nano-structured Ag layers with d_Ag≤5.4 nm and with d_Ag≥24 nm are thermally stable at 673 K, but those with d_Ag=6.3–13.5 nm are thermally unstable. In order to utilize the advantageous characteristics of the nano-structured Ag layers for the solar absorber coating, the optical constant of each layer is experimentally evaluated. Then the selective solar absorber coating with functional graded structure made of all nano-structured Ag layers is designed. The fabricated coating shows the high-performance such as the photo-thermal conversion efficiency of 0.72 for air mass 1.5 at an operating temperature of 373 K, the thermal stability as well.

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An electronically mediated reaction (EMR) has been explored to produce tantalum powder semi-continuously by the calciothermic reduction of tantalum chloride (TaCl₅). TaCl₅ feedstock and reductant calcium alloy were charged into electronically isolated locations in a molten CaCl₂ bath at 1123 K . The feed was freshly recharged three times, but the bath was reused without replenishment during four repeated reduction experiments. The current flow through an external path between the feed (cathode) and reductant (anode) locations was monitored. A current between 0.2 and 0.9 amps was measured during the reaction in the external circuit connecting cathode and anode. Tantalum powder was readily obtained after each experiment, but its purity decreased from 95% to 87%Ta as the run number increased. Tantalum powder obtained from EMR was fine compared with that of metal powder metallothermic reduction. Tantalum powder with low aluminum and nickel content was obtained although liquid Ca–Al–Ni alloy was used as the reductant. The results demonstrate the possibility of semi-continuous production of tantalum powder by the EMR without the direct physical contact between the feed and reductant. The mechanism of the calciothermic reduction of TaCl₅ in the molten salt was discussed, using an isothermal chemical potential diagram.

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Carbon fibers produced from PAN (polyacrylonitrile) as a precursor are generally subjected to the three heat treatment processes of stabilization and carbonization followed by graphitization. Stabilized fibers and high-temperature heat-treated fibers were carbonized in a high magnetic field imposed parallel to the fiber axis under a temperature of 1773 K and a tension of 8N per 12000 pieces of fibers. The carbon fibers produced from the stabilized fibers in a magnetic field of 5 T showed higher tensile strength than those done in no magnetic field, and the high-temperature heat-treated fibers processed in the magnetic field resulted in reverse. It is found that the fibers processed in the magnetic field have a larger crystallite size than those treated in no magnetic field. The mechanism of increase in the crystallite size due to the imposition of a high magnetic field has been discussed on the basis of an intermolecular cross-linking reaction model, in which the radical pair theory is modified by taking account of magnetic field.

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A protective carbon film, prepared by electron-cyclotron-resonance (ECR) plasma sputtering, has attracted considerable interest because the film can possess both the high wear durability and the high conductivity without doping. Such properties can be obtained, for example, when a negative bias voltage V_B (−40≤V_B≤−140 V) is applied to a substrate made of silicon. Little is known, however, about the atomic structure and bonding state of the ECR films for such a bias region, so that the physical origins of the macroscopic properties are not fully understood. In the present study, electron energy-loss spectroscopy (EELS) in a transmission electron microscope has been applied to investigate such ECR films that were deposited on a sodium chloride substrate for three different bias voltages: 0 V, −75 V and −120 V . The physical density of each ECR film was found to be lower than that of graphitized carbon and that of amorphous carbon. For each of the ECR films, the fraction of sp² bonding was estimated to be more than 90%. The carbon clusters with sp² bonding were considered to be more ordered for V_B=−75 V and −120 V than for V_B=0 V . The averaged density of valence electrons did not change much for each film, but the band structure is considered to vary depending on a local area. For the film prepared by the ECR technique, the macroscopic properties of the film such as electronic and mechanical ones may be controlled by controlling the ordering of sp² clusters.

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