Masahisa Otsuka

Indentation creep of β-Sn and Sn-Pb eutectic alloy

Abstract This study has been conducted to determine whether or not the indentation creep test provides results equivalent to those of the conventional uniaxial creep tests in the dislocation creep regime. When a conical indenter is pressed into the test surface, the plastic region beneath the indenter extends while maintaining its geometrical self-similarity as indentation proceeds. The occurrence of self-similar indentation leads to a constitutive equation from which the power-law creep exponent, n , and the activation energy for creep, Q , can be derived. The values of Q and n so obtained are in approximate agreement with the conventional uniaxial creep test results, drawn from some sources. The results indicate that two independent rate-controlling processes take place during the creep deformation of β-Sn and fine-grained Sn–Pb eutectic alloy (grain size: ∼10 μm) regardless of the temperature employed.

Nucleation of new grains during discontinuous dynamic recrystallization of 99.998 mass% Aluminum at 453 K

The dynamic recrystallization process of a 〈111〉 oriented aluminum single crystal of 99.998 mass% purity has been investigated in the temperature range between 373 and 693 K. The orientation imaging microscopy observation at 453 K revealed that continuous dynamic recrystallization works as a nucleation process for the discontinuous dynamic recrystallization.

Experimental and computational creep characterization of Al–Mg solid-solution alloy through instrumented indentation

Carefully designed indentation creep experiments and detailed finite-element computations were carried out in order to establish a robust and systematic method to extract creep properties accurately during indentation creep tests. Samples made from an Al–5.3 mol% Mg solid-solution alloy were tested at temperatures ranging from 573 to 773 K. Finite-element simulations confirmed that, for a power-law creep material, the indentation creep strain field is indeed self-similar in a constant-load indentation creep test, except during short transient periods at the initial loading stage and when there is a deformation mechanism change. Self-similar indentation creep leads to a constitutive equation from which the power-law creep exponent n, the activation energy Q c for creep, the back or internal stress and so on can be evaluated robustly. The creep stress exponent n was found to change distinctively from 4.8 to 3.2 below a critical stress level, while this critical stress decreases rapidly with increasing temperature. The activation energy for creep in the stress range of n = 3.2 was evaluated to be 123 kJ mol−1, close to the activation energy for mutual diffusion of this alloy, 130 kJ mol−1. Experimental results suggest that, within the n = 3.2 regime, the creep is rate controlled by viscous glide of dislocations which drag solute atmosphere and the back or internal stress is proportional to the average applied stress. These results are in good agreement with those obtained from conventional uniaxial creep tests in the dislocation creep regime. It is thus confirmed that indentation creep tests of Al–5.3 mol% Mg solid-solution alloy at temperatures ranging from 573 to 773 K can be effectively used to extract material parameters equivalent to those obtained from conventional uniaxial creep tests in the dislocation creep regime.

Effect of high-temperature heat-treatment on the pinning properties of melt-textured Nd123

Abstract We have investigated the effect of high-temperature annealing on the superconducting transition and the flux pinning properties of Nd123 melt-textured in 1% O 2 Ar. After the high-temperature annealing, a decrease in J c was observed in most samples even though no appreciable change was observed in T c . TEM observations and EDX analysis show that the spatial variation of the Nd/Ba ratio almost disappears after high-temperature annealing. Therefore, the observed change in J c - B properties can be understood by a reduction in the field-induced pinning due to homogenization of Nd/Ba substitution regions. These results strongly support the idea that the secondary peak effect and high pinning performance in Nd123 can be ascribed to the presence of Nd/Ba spatial variation.

Superconducting properties of Gd123 superconductor fabricated in air

Single-grain bulk Gd-Ba-Cu-O superconductors 32 mm in diameter have successfully been grown by melt-processing in air. In contrast to Sm123 and Nd123, the superconducting properties of Gd123 bulk superconductors were not degraded even when they were fabricated in air, which is attributed to the small range of Gd-Ba solid solution. The sample with the chemical composition of Ba-rich Gd123 (Gd0.95Ba2.05Cu3Oy) was also fabricated in air and exhibited superconducting properties superior to those of the sample with the stoichiometric ratio.

Mechanical properties of porous carbon material: Woodceramics

The mechanical properties of Woodceramics which were made from medium-density fiberboard have been investigated with special reference to the effect of burning temperature on their bending Youngs modulus and bending strength. Woodceramics made from beech wood have also been tested to clarify the compressive strength anisotropy, and the role of phenol resin impregnation in strengthening the beech based charcoal.The bending Youngs modulus hardly varies for burning temperatures between 300 and 500°C, but it improves remarkably for burning temperatures between 500 and 800°C. The bending strength degrades with temperature for burning temperatures between 300 and 500°C, but it improves remarkably with increasing temperature of burning between 500 and 800°C. The bending Youngs modulus and bending strength gradually degrade with temperature for burning temperatures at and above 2000°C.The compressive strength of beech wood burned at 800°C in the longitudinal direction is greater than that in the radial direction, which in turn is greater than that in the tangential direction; this reflects the anisotropy of wood. Woodceramics made from beech wood have a compressive strength superior to beech charcoal in any of the following three directions: 4.5 times in the longitudinal direction, 3.4 times in the radial direction, and 2.0 times in the tangential direction. Both for beech charcoal and beech Woodceramics, brittle fracture is brought about by the buckling of cell wall in compression along the longitudinal direction but by the bending of cell wall in the compression along radial and tangential direction.

Influence of Laser Beam Irradiation Conditions on the Machinability of Medium Density Fiberboard Impregnated with Phenolic Resin

The applicability of CO2 laser beam machining (cutting) to resin impregnated woody products has been investigated with special reference to the effect of laser beam machining parameters such as laser power, feed speed of workpiece, pulse duty, frequency, assist gas pressure and defocus distance. The optimum laser beam machining conditions are as follows: Laser power: 1500 W; output wave form: pulse oscillation wave (pulse duty: 40%); frequency: optional (0 to 1000 Hz); feed speed of workpiece: 900 mm/min; assist gas: nitrogen gas; assist gas pressure: optional (0.1 to 0.5 MPa); and defocus distance: (0 to 1 mm).A carbonized layer of 1 to 2 mm thickness is always formed near the cut surface. In other words, materials not thermoformed after impregnation with phenol resin are influenced by heat to some extent while being machined by the laser beam.

Cold seeded melt growth of RE-Ba-Cu-O superconductor (RE = Gd, Y)

Abstract For the cold seeded melt growth of RE–Ba–Cu–O, it is important to decompose the precursor completely without melting the Nd–Ba–Cu–O seed crystal. We have studied the variation of growth mode with the maximum holding temperature ( T max ) and the holding time for Y and Gd systems. Growth modes were changed by T max and classified into four groups. In the case of Gd system, the temperature window for single-domain growth was narrow compared with Y system. This is ascribed to the fact that the decomposition temperature of Gd system is close to that of Nd123 seed crystal.

Phase relations in the Nd-Ba-Cu-O system in reduced oxygen atmospheres

We have studied the quasi-binary phase diagrams along the line connecting NdBa2Cu3Oy and BaCuO2+w in reduced oxygen atmospheres: p(O2) = 10-3 and 10-2 atm. The nucleation and melt of NdBa2Cu3Oy (Nd123) in Ba-rich solvent were observed in situ using a laser scanning microscope in 1% O2 + Ar and 0.1% O2 + Ar. The liquidus and solidus lines of nearly stoichiometric Nd123 have been constructed. We have found that phase relations are quite different between 1% O2 + Ar and 0.1% O2 + Ar. In a 0.1% O2 + Ar environment BaCuO2+w undergoes incongruent melting (BaCuO2+w→Ba2CuO3+z + L→BaO + L) and Nd422 decomposes into the Nd2O3 phase.

Isothermal shear fatigue life of Sn-xAg-0.5Cu flip chip interconnects

The mechanical shear fatigue test has been performed to look for the effect of silver content on the fatigue properties of Sn-xAg-0.5Cu (x = 1, 2, 3 and 4) flip chip interconnections. As the strength of the solder alloy increases with increasing silver content, the increase in silver content results in preventing a shear plastic deformation of solder bump. Therefore, the flip chip joints made using higher silver content solder such as 3 and 4Ag exhibit longer fatigue life, if the same levels of displacement is applied. The fatigue ductility of the solder decreases with increasing the silver content. Therefore, the fatigue endurance of the 1Ag solder itself is superior to other solders in high plastic strain regime, even though the strength of the solder is the lowest in the solders tested. Based on this study, the 3Ag solder might exhibit good fatigue performance for all condition, and the 1Ag solder is optimum for severe strain condition.Copyright