Kotaro Hanada

Phase Diagram of the (Na0.5K0.5)NbO3-ATiO3 Solid Solution

To elucidate mechanisms responsible for the enhanced piezoelectric properties in the potassium-sodium niobate-based solid solutions, phase diagram of the (1 − x) (Na0.5K0.5)NbO3-xATiO3 (A = Sr, Ba, and Pb) systems has been established according to the dielectric constant measurement and the crystal structure analysis results. A tetragonal/orthorhombic morphotropic phase boundary (MPB) is found around x∼ 0.05, where the piezoelectric properties were enhanced. Rietveld refinements show that the tetragonal/orthorhombic MPB is the same as that found in the lead zinc niobate-lead titanate system.

Fabrication of Mg alloy tubes for biodegradable stent application.

Though Mg alloys are promising candidates for biodegradable stents, it is very difficult to fabricate stent tubes with high dimensional accuracy using Mg alloys because of their low deformability. This study aimed to develop thin-walled, high-quality Mg alloy tubes with good performance in stent applications. Cold drawing with a fixed mandrel was carried out for extruded Mg-0.8%Ca and AZ61 alloy tubes using optimized drawing parameters and lubrication, and stent tubes with 1.5-1.8mm outer diameter and 150 μm thickness were fabricated. A dimensional evaluation showed that the tube dimensional errors were within 0.02-2.5%. Also, an immersion test of pure Mg with different crystal orientations showed that the crystal orientation affected the corrosion properties, results that are the same with other Mg alloys. The crystal orientation of the stent tube could be controlled by changing the deformation amount and direction in the drawing, showing that it is possible to further improve the biodegradability of stents by approaching their fabrication from a processing aspect.

Inside bead forming of aluminum tube by electro-magnetic forming

Abstract In this paper, the inside bead forming of aluminum tube (A6063TD) by electro-magnetic forming (EMF) is reported experimentally and numerically. The shape of the bead was affected by the change of the discharge voltage and the dimensions of a groove at a beading die which have a width and a shoulder radius. With the increase of the discharge voltage and the shoulder radius, the bead height increased due to the increasing of the bending moment. On the discharge voltage of over 4 kV (400 μF), the bead height rapidly increased so that the aluminum tube entered the groove at the beading die from both sides. Therefore the thickness strain at the top of the bead increased, the longitudinal strain of the aluminum tube saturated, and a necking appeared at the bead near the shoulder part of the beading die. Also, the simulation of the bead forming was carried out by using MARC and compared with the experimental results.

Consolidation of Cu-nDiamond Nanocomposites: Hot Extrusion vs Spark Plasma Sintering

Due to their interesting properties copper-based materials have been considered appropriate heat-sinks for first wall panels in nuclear fusion devices. The concept of property tailoring involved in the design of metal matrix composites has led to several attempts to use nanodiamond (nDiamond) as reinforcement. In particular, nDiamond produced by detonation has been used to reinforce copper. In the present study, powder mixtures of copper and nDiamond with 20 at. % C were mechanically alloyed (MA) and consolidated via hot extrusion or spark plasma sintering (SPS). The hardness evolutions as well as the structural characterization of as-milled nanocomposite powders and consolidated samples are reported. Density measurements indicate that the consolidation outcome varies significantly with the process used. Transmission electron microscopy (TEM) inspection of the extrusion consolidated sample revealed bonding at the interface between copper and nDiamond particles. The nDiamond size distribution was determined from TEM observations. The results obtained are discussed in terms of consolidation routes.

Effects of Vacancies on the Dielectric and Piezoelectric Properties of (Na0.5K0.5)NbO3-SrTiO3 Solid Solution

Vacancies have been introduced to the perovskite A- and B-site to study their effects on the dielectric and the piezoelectric properties of the (Na 0.5 K 0.5 )NbO 3 -SrTiO 3 solid solution. It is found that, rather different from in the case of PZT ceramics, both A- and B-site vacancies do not soften piezoelectric properties of (Na 0.5 K 0.5 )NbO 3 -SrTiO 3 solid solution.

Bulk Copper-Nanodiamond Nanocomposites; Processing and Properties

Copper has widespread use as engineering material, because of its structural and functional properties, notably high thermal and electrical conductivity. A major drawback of this base metal and its alloys is a relatively low hardness. This precludes its utilization in applications in which both high conductivity and high strength/hardness are needed, e.g. in injection moulds for plastics. Nanostructured metals and nanocomposites are ways to address the low hardness problem, provided the nanostructured material is thermally stable during processing and service. In the present research, composite powders, with 5 to 30 at % nanodiamond, were consolidated into bulk samples. The copper-nanodiamond composite powders were vacuum encapsulated and extruded at 600°C. A significant proportion of the initial hardness in the powders is retained after extrusion. Transmission electron microscopy (TEM) of the extruded material indicates good bonding between the nanodiamond particles and the copper matrix. Raman spectroscopy on the consolidated samples evidences the presence of graphite, possibly due to partial disintegration of ultradisperse nanodiamond agglomerates.

Development of Spherical Magnetic Abrasive Made by Plasma Spray

Magnetic abrasive used for the internal finishing of capillary tubes, which prevents accumulation of contamination and erratic flow of the conveyed fluid, is a composite particle, consisting of iron and Al 2 O 3 abrasive grains. The irregularity of the magnetic abrasive shape, due to the mechanical crushing process, causes nonuniform depth of cut of the abrasive and restricts the improvement of the finished surface quality. This has resulted in a narrow range of finishing performance. Moreover, the irregularity of the magnetic abrasive shape brings about difficulty in merely introducing it into capillary tubes. To break through these difficulties, this research proposes to develop a spherical iron-based magnetic abrasive, which carries Al 2 O 3 grains on the surface, made by plasma spray. First, this paper examines the feasibility of the plasma spray to make the existing magnetic abrasive more spherical, and suggests the conditions needed to produce the spherical magnetic abrasive. Second, it studies the development of the new spherical magnetic abrasive made of separate particles: iron particles and Al 2 O 3 abrasive grains, which carries the nonferrous abrasive on the outer surface alone. Their finishing performance, evaluated through the experiments using SUS304 stainless steel tubes, shows their applicability to magnetic abrasive finishing.

Piezoelectric (Na0.5K0.5)NbO3-SrTiO3 Ceramics in the Tetragonal-Orthorhombic Phase Boundary Studied by Raman Spectroscopy

Raman spectroscopy of lead-free piezoelectric (1-x)(Na 0.5 K 0.5 )NbO 3 −xSrTiO 3 ceramics and (Na 1 − y Ky)NbO 3 ones sintered by the Spark-Plasma-Sintering method have been performed to investigate the dynamical property in the intermediate phase of x = 0.05. From the comparison of Raman spectra between (1-x)(Na 0.5 K 0.5 )NbO 3 −xSrTiO 3 and (Na1 − yKy)NbO 3 at room temperature, the overdamped mode which became soften was found in the intermediate phase at x = 0.05. Although it is difficult to assign the mode because of using ceramics samples, this result has a possibility that the overdamped mode includes the soft mode observed in the orthorhombic phase.

Development of Spherical Iron-Based Composite Powder with Carried Alumina Abrasive Grains by Plasma Spray

This paper describes the development of spherical iron-based composite powder with carried alumina abrasive grains made by a plasma spray technique. Carbonyl iron powder (7.2 μm average size) and alumina abrasive grains (0.3 μm average size) are sprayed into the plasma flame from the respective nozzles simultaneously, or their mechanical mixture is directly plasma-sprayed. In case of the composite powder obtained by the direct spray method, the alumina abrasives are well carried on the carbonyl iron particles. However, a plasma current of more than 100 A causes melting and vaporizing of the alumina abrasives;, consequently the carbonyl iron and alumina abrasives are separated. The magnetic abrasive experiments with the composite powder developed are made for SUS304 stainless steel plate, and the result shows that the developed composite powder has high potential abrasive performance.

Investigation on Dielectric and Piezoelectric Properties of (1-x)(Na0.5K0.5)NbO3-xSrTiO3 Ceramics

Lead-free piezoelectric (1-x)(Na 0.5 K 0.5 )NbO 3 −xSrTiO 3 ((1-x)NKN- xST) solid solution has been fabricated around a morphotropic phase boundary (MPB) by Spark-Plasma-Sintering method. The phase diagram around MPB was studied by the dielectric measurement. The piezoelectric constant d 33 and electromechanical constant k p measurements shows that MPB is about at x = 0.05. Inverse dielectric constants are well fitted by the extended Curie-Weiss law above the Curie temperature and its fitting result shows that the fitting parameters, C and n values show the maxima for 0.95NKN-0.05ST. We suggest the existence of another phase boundary around x = 0.05. To confirm the another phase boundary, the Raman spectra of 0.975NKN-0.025ST and 0.9NKN-0.1ST samples at the tetragonal phases have been measured and comparison has been done.