Activities of the constituents in an alloy proposed for the Pb-free solder, Sn–Mg–Zn, were studied experimentally using a mass spectrometer. The ion current ratios of Mg to Zn were measured in the temperature range 700–800 K . From the experimental results and the assessed thermodynamic properties of molten Sn–Mg, Sn–Zn, and Mg–Zn binary alloys, the excess Gibbs free energy of liquid Sn–Mg–Zn ternary alloy was determined. Also, phase diagram of Sn–Mg–Zn ternary system was determined.

View full abstract

The shear strength of the Cr/Cr–Cu/Cu UBM structure in both the high-melting solder bump and low-melting solder bump after aging were evaluated. SEM and TEM were examined in the intermetallic compounds and bump joint profiles at the interface between solder and UBM . The shear load concentrated on the bump was analyzed by finite element method. In 900-hour aging experiments, the maximum shear strength of Sn–97 mass%Pb and Sn–37 mass%Pb decreased by 25% and 20%, respectively. The growth of Cu₆Sn₅ and Cu₃Sn was ascertained by the aging treatment. The crack path changes from the interior of a solder to the intermetallic compound interface was evaluated. Compared with the Cu–Sn IMC, the amount of Ni–Sn IMC was small. The Ni layer is considered as the diffusion barrier.

View full abstract

The SiC/Si₃N₄ sintered materials were prepared by Spark Plasma Sintering at 2000°C. The crystal structure of sintered materials is cubic β-SiC type with relative density higher than 80%. All sintered materials show n-type conduction and the carrier concentration increases with increasing Si₃N₄ concentration. Seebeck coefficient α and electrical conductivity σ increased with increasing temperature indicating suitable for high temperature thermoelectric conversion. Thermoelectric properties are improved by addition of Si₃N₄ and the power factor α²σ takes a maximum value at SiC–7 mass%Si₃N₄.

View full abstract

This paper reports the color and the tarnishing behavior of CuMn15Zn15Al1 alloy in a synthetic sweat medium quantitatively. German silver BZn15–20–0.3 was selected for comparison. The results indicated that CuMn15Zn15Al1 has a silvery color similar to BZn15–20–0.3 but the tarnishing resistance of CuMn15Zn15Al1 in sweat is not as good as that of BZn15–20–0.3. For CuMn15Zn15Al1, tarnishing in sweat results in the decrease of L^∗ values and increase of a^∗ values, when both L^∗ and a^∗ are parameters in the CIE system to express the color. In other words, the color gets darker and redder after the sweat test. The corrosion layers were analyzed by means of Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The tarnishing products primarily consist of Cu₂O, ZnO and Mn oxides. Some chlorides and hydroxides are detected on the outmost surface.

View full abstract

Reddish cuprous oxide crystals can be readily formed by irradiating an aqueous alkaline Cu(II) solution containing suitable complexing agents with UV or sunlight in the presence of a photocatalyst such as TiO₂ or ZnO . Various factors, including the Cu(II) concentration, pH of the Cu(II) solution, amount of TiO₂ catalyst, method used to agitate the test suspension, concentration of potassium sodium tartarate, and intensity of UV radiation, affecting cuprous oxide preparations were investigated. Concentrations of Cu(II) and potassium sodium tartarate have no significant effect on reaction rates, while pH, and amount of TiO₂, play important roles in the reaction. The dispersion of TiO₂ in Cu(II) solution is another important factor. Cu(II) reduction rate is not affected as far as the amount of reduced Cu(II) plotted against the cumulative intensity of UV radiation is concerned. It is necessary to stop the cuprous oxide formation before the complete reduction of Cu(II), since metallic copper is formed on cuprous oxide.

View full abstract

The effects of Cr addition to Nb–22Si–5Mo alloy on phase equilibria, microstructures and mechanical properties are investigated by metallography, X-ray diffraction, scanning electron microscopy equipped with wavelength dispersive X-ray fluorescence spectroscopy and compression test at temperatures from room temperature to 1773 K . With increasing Cr content a duplex microstructure consisting of Nb₅Si₃ and Nb_ss (niobium solid solution) is changed to three-phase microstructure consisting of Nb₅Si₃, Nb_ss and NbCr₂. Chromium addition does not change the volume fraction of constituent phases in the two-phase alloys, whereas it increases the volume fraction of NbCr₂, C14 Laves phase, at the expense of mostly Nb_ss in the three-phase alloys. The c⁄a axis ratio of α-Nb₅Si₃ phase increases with increasing (Cr+Mo) content. It is found that Cr alloying in Nb_ss increases the room temperature strength due to atomic size misfit and decreases high temperature strength due to accelerated diffusion. The existence of C14 Laves phase increases high temperature strength, but degrades room temperature deformability. High temperature strength is found to be sensitive to the volume fraction and crystal structure of constituent phases as well as microstructure.

View full abstract

Fracture behaviors were investigated in the laminated alumina composite ceramics. To improve the mechanical properties of alumina ceramics, templated grain growth (TGG) technique of α-Al₂O₃ platelet and LaPO₄ as a second phase were introduced. Textured samples were made by the lamination of green tapes through the tape-casting method, while random samples were made through the conventional powder processing method. Green compacts were sintered at 1600°C for 2 h in air. Fracture toughness was tested using indentation strength bending (ISB) method. Indentation on the sample surface was produced by Vickers indent at various loads. From the bending test, enhanced fracture toughness was found in the textured composite, compared to the random composite.

View full abstract

Thermal behavior and mechanical properties of Pd-based glassy alloys with compositions of Pd_35+xCu₃₀Ni_15−xP₂₀ (x=0, 5, 7.5 at%, group-I) and Pd_40+xCu₂₀Ni_20−xP₂₀ (x=0, 5, 10 at%, group-II) have been studied. Group-I alloys lie in an invariant eutectic reaction region of the quaternary system. The invariant eutectic reaction of L→Cu₃Pd+Ni₂Pd₂P+Cu₃Pd₅P₂+quaternary phosphide exists at a composition of approximately Pd_42.5Cu₃₀Ni_7.5P₂₀ and at a temperature of about 800 K . Both group glasses possess a large supercooled liquid region of over 80 K before crystallization. The compressive strength, Young’s modulus and Vickers hardness in each group increase with increasing Ni content. The compressive fracture strength and Young’s modulus are in the range of 1610 to 1740 MPa and 100 to 110 GPa, respectively. Under a uniaxial compression mode, these glassy alloys deformed inhomogeneously and fractured adiabatically. No distinct plastic deformation was observed for group-I alloys, while group-II alloys exhibited serrated flow with a maximum plastic strain of about 1.3%.

View full abstract

Micro-dies with five steps were fabricated by machining with the focused ion beam (FIB) process using two types of WC–10%Co cemented carbide with a WC grain size of 5 \\micron and 0.5 \\micron. The surface roughness of the dies was investigated by atomic force microscopy (AFM). In the coarse-grained cemented carbide, the surfaces of the WC phase were very smooth. However, those of the Co phase were rough, particularly near the interface. In the fine-grained cemented carbide, the surfaces were smoother on the whole and the irregularities of roughness were smaller compared with the coarse-grained cemented carbide, but some voids of about 0.5 \\micron, almost the same size as the WC grain, were observed.

View full abstract